I
.info (information) - Pronounced dot info.The Internet generic Top Level Domain (gTLD) intended for, although not restricted to, informational sites.This is an unsponsored domain. See also gTLD, Internet, and unsponsored domain.
.int (international) - Pronounced dot i-n-t. The Internet generic Top Level Domain (gTLD) reserved
exclusively for organizations formed under international treaties between governments.This is an unsponsored domain. See also gTLD, Internet, and unsponsored domain.
I series - The series of ITU-T Recommendations specifying protocols and interfaces relating to integrated service digital network (ISDN).
| Recommendation | Description |
|---|---|
| I.113 | B-ISDN Vocabulary |
| I.120 | Integrated services digital networks (ISDNs) |
| I.121 | Broadband aspects of ISDN |
| I.122 | Framework for frame mode bearer services |
| I.150 | B-ISDN ATM Functional Characteristics |
| I.211 | B-ISDN service aspects |
| I.233.1 | ISDN frame relaying bearer service |
| I.233.2 | ISDN frame switching bearer service |
| I.311 | B-ISDN General Network Aspects |
| I.313 | B-ISDN network requirements |
| I.320 | ISDN protocol reference model |
| I.321 | B-ISDN protocol reference model |
| I.324 | ISDN network architecture |
| I.327 | B-ISDN Functional Architecture Aspects |
| I.354 | Network performance objectives for packet-mode communication |
| I.355 | ISDN 64 kbit/s connection type availability performance |
| I.356 | B-ISDN ATM layer cell transfer performance |
| I.361 | B-ISDN ATM Layer Specification |
| I.362 | B-ISDN ATM Adaptation Layer Functional Description |
| I.363 | B-ISDN ATM Adaptation Layer (AAL) Specification |
| I.363.1 | B-ISDN AAL Type 1 |
| I.363.2 | B-ISDN AAL Type 2 |
| I.363.3 | B-ISDN AAL Type 3/4 |
| I.363.5 | B-ISDN AAL Type 5 |
| I.1413 | B-ISDN User-Network Interface |
| I.420 | Basic user-network interface (BRI) |
| I.421 | Primary rate user-network interface (PRI) |
| I.430 | Basic user-network interface: Layer 1 |
| I.431 | Primary rate user-network interface: Layer 1 |
| I.432 | B-ISDN User-Network Interface-Physical Layer |
| I.530 | Network interworking between an ISDN and a PSTN |
| I.555 | ATM and Frame Relay interworking |
| I.570 | Public/private ISDN interworking |
| I.610 | B-ISDN Operations and Maintenance Principles and Functions |
| I.761 | Inverse multiplexing for ATM (IMA) |
| I.762 | ATM over fractional physical links |
I-series Recommendations
I-hold - See hold.
i-Mode (Internet Mode) - A microbrowser technology that supports text, graphics, audio, and video
for Web access over the Japanese cellular network. In consideration of the inherently limited bandwidth of
the cellular network, i-Mode employs Compact HTML (C-HTML), a simplified version of HTML similar to Wireless Markup Language (WML) used in WAP networks. Transmission between the handhelds
and the i-Mode-enabled cell sites is via packet mode, using packets of 128 octets, at rates up to 9.6 kbps.
i-Mode is a proprietary service developed by NTT DoCoMo, initially for the Japanese market. See also
browser, cellular radio, octet, packet, WAP, and WML.
i.e. (id est) - Translates literally from Latin as that is [to say], meaning in other words.
I - The symbol for current intensity, measured in amperes. See also current.
I/F (Inter/Face) - See interface.
I/O (Input/Output) - The computer component that receives data from or transmits data to a system
or device, such as a buffer, peripheral, storage unit, or another computer across a network.
IA (Implementation Agreement) - See Implementation Agreement.
IAB (Internet Architecture Board) - Originally known as the Internet Activities Board.A technical advisory group of the Internet Society (ISOC) that provides oversight for the architecture for the protocols and
procedures used by the Internet. The IAB supervises the activities the Internet Engineering Task Force
(IETF) and the Internet Research Task Force (IRTF). In combination, those organizations set policy and
direction.The IAB comprises 13 expert individuals who use the resources of their sponsoring companies to
further the interests of the Internet. See also architecture, IETF, Internet, IRTF, ISOC, and protocol.
IAD (Integrated Access Device) - A device installed at the customer premises that enables multiple
services to share a single circuit. For example, an IAD might support simultaneous PSTN voice, packet
voice or data, and video to share a single local loop.An IAD typically is installed by the telco or other service provider, and may run a combination of PSTN, Ethernet, IP, and frame relay or ATM protocols. See
also ATM, Ethernet, frame relay, IP, local loop, protocol, and PSTN.
IANA (Internet Assigned Numbers Authority) - Originally managed a group of functions performed by the Information Sciences Institute under contract with the United States Department of
Defense Advanced Research Project Agency on the ARPANET.Those functions included the assignment
of parameters for Internet protocols, management of the Internet Protocol (IP) address space, assignment
of domain names, and management of root server functions. Internet protocol parameters managed by
IANA include the assignment of Transmission Control Protocol (TCP) ports, which are logical points of
connection. In fact, IANA initially was the responsibility of Jon Postel, who performed those functions
until his death in 1998. At that time, Internet Corporation for Assigned Names and Numbers (ICANN),
an independent not-for-profit organization, assumed the responsibility for managing IANA. See also
ARPANET; ICANN; Internet; IP; logical; port; Postel, Jon; protocol; root server; and TCP.
ICANN (Internet Corporation for Assigned Names and Numbers) - A not-for-profit organization formed in 1999 to assume the responsibilities for management of the Internet Assigned Numbers
Authority (IANA). See also domain name, IANA, Internet, IP, logical, port, protocol, root server, and TCP
ICASA (Independent Communications Authority of South Africa) - The regulatory authority in
South Africa responsible for broadcasting and telecommunications services.
ICE (In Case of Emergency) - The directory name for an emergency contact number that users should
enter into their cell phones. If you were to be clobbered by a train or otherwise hurt badly, others could
quickly find and call an ICE number to alert friends or relatives.
ICEA (Insulated Cable Engineers Association) - A professional organization dedicated to developing cable standards for the electric power, control, and telecommunications industries. ICEA has the objective of ensuring safe, economical, and efficient cable systems utilizing proven state-of-the-art materials and
concepts. See Appendix A for contact information.
icky-pic (icky–plastic insulated cable) - A type of outside telephone cable that comprises some number of twisted pair copper conductors protected from moisture by an unpleasantly sticky and gooey (i.e.,
icky) water-blocking gel, and surrounded by a plastic sheath. (Almost as icky is the citrus-based solvent
that seems to be required to wash off the gel.) Icky-pic can be used in aerial and direct bury construction.
See also aerial cable and direct bury cable.
ICMP (Internet Control Message Protocol) - An extension to the original Internet Protocol (IP) that
reports errors that may have occurred in the processing of datagrams. For example, a datagram may be
undeliverable or an incorrect route may have been chosen. ICMP supports the testing of a path to a distant host computer through an echo function known as the ping utility. ICMP also supports the requesting of a subnet mask. ICMP is integral to IP and must be implemented in both hosts and routers. See also
datagram, echo, host, IP, ping, and utility.
ICST (Information and Communication Science and Technology) - An international term used to
describe a blend of information services (IS) and telecommunications science and technology. See also IS.
ID - 1. Inside Diameter. 2. Identification.
IDDD (International Direct Distance Dialing) - A feature of the public switched telephone network
(PSTN) that enables a subscriber to dial an international long-distance telephone number directly, i.e.,
without the intervention of an operator. Domestic DDD was introduced by the Bell System in 1951. DDD
and IDDD are virtually ubiquitous today, although they are not available in some developing countries.
See also appointment call, long distance, and PSTN.
IDF (Intermediate Distribution Frame) - A distribution frame that serves as an intermediate point of
inside cable and wire interconnection between the main distribution frame (MDF) and the terminal blocks
or terminal outlets. See also MDF.
IDSL (ISDN Digital Subscriber Line) - A DSL variant that employs ISDN BRI (Basic Rate Interface) technology to deliver symmetric transmission rates of 128 kbps or 144 kbps on unshielded twisted
pair (UTP) local loops as long as 18,000 feet. IDSL bonds the two 64-kbps bearer (B) channels to provide
a 128-kbps channel, and bonds the 16-kbps data (D) channel to bring the total to 144 kbps. Unlike ISDN,
which is a circuit-switched network service for voice, data, fax, video, and multimedia, IDSL operates only
at the local loop level to provide always-on Internet access. IDSL is virtually non-existent in the United
States, where ISDN never enjoyed any significant success. As IDSL compares so unfavorably with asymmetric digital subscriber line (ADSL) and other DSL variants with respect to bandwidth, the very low
IDSL penetration rates will only decrease. See also ADSL, always on, bandwidth, bonding, BRI, circuit switch,
Internet, ISDN, local loop, symmetric, transmission rate, UTP, and xDSL.
IDU (Interface Data Unit) - In asynchronous transfer mode (ATM), referring to a frame of data presented to an ATM interface for switching.ATM Adaptation Layer 3/4 (AAL3/4) supports message mode
service, in which only one IDU is passed.AAL3/4 also supports streaming mode service, in which multiple interface data units (IDUs) are passed in a data stream.An IDU can be up to 65,535 octets in length,
with a cyclic redundancy check (CRC) added as part of the trailer. See also AAL3/4, ATM, CRC, frame,
IDU, message mode service, octet, streaming mode service, and trailer.
IE (Internet Explorer) - See Internet Explorer.
IEC - 1. International Electrotechnical Commission.The IEC was formed in 1904 with the objective of
standardizing the nomenclature and ratings of electrical apparatus and machinery. Among its accomplishments are the development of the International Electrotechnical Vocabulary and the Système international
d’unités (SI). See Appendix A for contact information. See also SI. 2. InterExchange Carrier. See IXC.
IEEE (Institute of Electrical and Electronics Engineers) - A worldwide not-for-profit professional
association for the advancement of technology.The IEEE establishes standards and otherwise serves as a leading technical authority in areas including aerospace systems, computers and telecommunications to biomedical engineering, electric power, and consumer electronics. In telecommunications, the IEEE is most notable
for its 802 Working Group, which set local and metropolitan area network (LAN and MAN) standards.The IEEE formed in 1963, with the merger of the American Institute of Electrical Engineers (AIEE), formed in
1884, and the Institute of Radio Engineers (IRE), formed in 1912. See also LAN and MAN.
IESG (Internet Engineering Steering Group) - The group responsible for the day-to-day management of the activities of the Internet Engineering Task Force (IETF), including management of the standards process.The IESG provides the final technical review of standards submitted by the IETF. See also
IETF and standard.
IETF (Internet Engineering Task Force) - The group of the Internet Society (ISOC) that identifies,
prioritizes, and addresses short-term Internet issues and problems, including protocols, architecture, and
operations. The IETF publishes proposed Internet standards in the form of Requests for Comment
(RFCs). Once the final draft of a standard is prepared, it is submitted to the Internet Engineering Steering Group (IESG) for approval. The IETF operates under the supervision of the Internet Architecture
Board (IAB). See also architecture, IESC, IAB, Internet, ISOC, protocol, RFC, and standard.
IFP (Internet Fax Protocol) - See T.38.
IGF (International Gateway Facility) - A point of interconnection between an international carrier
and a national carrier.An IGF commonly serves not only as a physical gate between the international and
national networks, but also as a point-of-protocol conversion, perhaps interfacing an international E-carrier
circuit to a domestic T-carrier circuit.The gateway also may serve as a point of media conversion, perhaps serving to interconnect a submarine fiber optic cable or satellite link to a microwave or copper wire
circuit. See also carrier, media converter, network, and protocol converter.
IGP (Interior Gateway Protocol) - An interior protocol for routing within an Autonomous System
(AS), i.e., a group of routers within a given administrative domain. IGP was described in IETF RFC 1074
(1988). Common IGPs include the Routing Information Protocol (RIP) and the Open Shortest Path First
(OSPF) protocol. See also AS, domain, exterior protocol, IETF, interior protocol, OSPF, protocol, RIP, router, and
routing.
III (International Information Infrastructure) - Synonymous with Global Information Infrastructure
(GII).The international version of the National Information Infrastructure (NII), or Information Superhighway. See also Information Superhighway and NII.
ILEC (Incumbent Local Exchange Carrier) - A company providing local telephone service prior to
the introduction of local competition, which introduced one or more competitive LECs (CLECs). In the
United States, an ILEC is a company that as of February 8, 1996 provided telephone exchange services to
the area in which it was authorized to provide service and was permitted to participate as a member of the
National Exchange Carrier Association (NECA). See also carrier, IXC, and NECA.
ILF (InfraLow Frequency) - ILF radio is in the frequency range of 300–3000 Hz (3 kHz) and has a
wavelength of 1,000–100 km. ILF radio has no contemporary telecommunications applications. See also
electromagnetic spectrum, frequency, Hz, and wavelength.
IM (Instant Messaging) - A client/server messaging technology that is much like e-mail, but operates
in near real time. Instant messaging originated in the 1970s on PLATO, a private online instructional system
for schools and universities in the United States, and was popularized in 1996 by ICQ, an Israel-based
company later acquired by AOL. (Note: Instant Message is a Service Mark (
SM
) of AOL.) There are now
a number of public Web-based IM services and enterprise systems, all of which are proprietary, i.e., non-standard. IM users create, by mutual consent, closed user groups (CUGs), commonly known as buddy
lists, of correspondents.As IM occurs in near real time, it is necessary that both correspondents in a given
message session be online at the same time.Therefore, IM systems include a presence mechanism to advertise all users of the status (e.g., available or unavailable) of all other users. Some IM systems now support
one-way messaging if the recipient is not online. In this mode, the recipient can access the message at a
later time, much like an e-mail communication. IM features typically include presence, privacy, contact lists
(buddy lists), attachments, and message history. Some systems also include text, voice, and video and conferencing, and even whiteboarding. See also client/server, CUG, e-mail, near-realtime, presence, proprietary, standard, and whiteboarding.
IMA (Inverse Multiplexing over ATM) - An inverse multiplexing technique that fans out an Asynchronous Transfer Mode (ATM) cell stream across multiple circuits between the user premises and the edge
of the carrier network. In such a circumstance, multiple physical T1 circuits, for example, can be used as a
single, logical ATM pipe.The IMA-compliant ATM concentrator at the user premises spreads the ATM
cells across the T1 circuits in a round-robin fashion, and the ATM switch at the edge of the carrier network scans the T1 circuits in the same fashion in order to reconstitute the cell stream. See also ATM, carrier, concentrator, multiplexing, network, switch, and T1.
image decimation - Also known as filtering. See filtering.
image - A still photograph or other still visual representation of a person, place, or thing.Video comprises
a series of still images presented in rapid succession.
IMAP (Internet Message Access Protocol) - An IETF standard (RFC 2193) protocol for accessing
e-mail. IMAP enables the client to manage mail much more effectively than POP3, an earlier standard that
is widely deployed. IMAP enables the user to view the header of each mail message before deciding whether
to download it, delete it, or take other action. IMAP also enables the user to create, manipulate, and delete
individual mail folders and mailboxes on the server. However, IMAP requires that the connection be maintained between client and server continuously while working with mail, whereas POP3 enables the user to
work with mail offline.Also, security is an issue with IMAP, as the remote client takes on the appearance of
a remote virtual server. See also client, e-mail, IETF, POP3, RFC, server, and virtual server.
IMP (Instant Messaging and Presence) - See IMPP and SIMPLE.
impedance (Z) - The total passive opposition offered by a circuit to the flow of an alternating electric
current (AC), impedance is a combination of resistance, inductive reactance, and capacitive reactance. See
also AC, capacitance, inductance, and resistance.
Imperial Standard Wire Gauge - Synonymous with British Standard Gauge (BSG).The measure of the
diameter, or thickness, of a conductor in England. See also gauge.
Implementation Agreement (IA) - Consensus agreements, developed and promoted by the Frame
Relay Forum (FRF), that address manufacturer interoperability issues. (Note: The Frame Relay Forum
merged with the ATM Forum and MPLS Forum to form the MFA Forum.)
See also frame relay and MFA Forum.
| Implementation Agreement | Description |
|---|---|
| FRF.1.2 | User-to-Network (UNI) (April 2000) |
| FRF.2.1 | Network-to-Network Interface (NNI) (July 1995) |
| FRF.3.2 | Multiprotocol Encapsulation (MEI) (April 2000) |
| FRF.4.1 | SVC User-to-Network Interface (UNI) (January 2000) |
| FRF.5 | Frame Relay/ATM PVC Network Interworking (December 1994) |
| FRF.6.1 | Customer Network Management (MIB) (September 2002) |
| FRF.7 | PVC Multicast Service and Protocol Description (October 1994) |
| FRF.8.2 | Frame Relay/ATM PVC Service Interworking (February 2004) |
| FRF.9 | Data Compression (January 1996) |
| FRF.10.1 | Network-to-Network SVC (September 1996) |
| FRF.11.1 | Voice over Frame Relay (May 1997, Annex J added March 1999) |
| FRF.12 | Fragmentation (December 1997) |
| FRF.13 | Service Level Definitions (August 1998) |
| FRF.14 | Physical Layer Interface (December 1998) |
| FRF.15 | End-to-End Multilink Frame Relay (August 1999) |
| FRF.16.1 | Multilink Frame Relay UNI/NNI (May 2002) |
| FRF.17 | Privacy (January 2000) |
| FRF.18 | Network-to-Network FR/ATM SVC Service Interworking (April 2000) |
| FRF.19 | Operations, Administration and Maintenance (March 2001) |
| FRF.20 | IP Header Compression (June 2001) |
Frame Relay Implementation Agreements
Implicit Congestion Notification - In frame relay, inference by user equipment that congestion has
occurred in the network.The inference is triggered by realization of the receiving frame relay access device
(FRAD) of transmission delays. Based on block, frame or packet sequence numbers, another protocol may
recognize that one or more frames have been lost in transit. Control mechanisms at the upper protocol
layers of the end devices then deal with frame loss by requesting retransmissions. See also block, Explicit
Congestion Notification (ECN), FRAD, frame, packet, and protocol.
IMPP (Instant Messaging and Presence Protocol) - A group of specifications proposed by the Internet Engineering Task Force (IETF) and intended to define the protocols necessary to build an IM system
that will scale to Internet size.The RFCs define presence requirements, and common semantics and data
formats to facilitate the development of gateways between services. See also gateway, IETF, IM, Internet,
presence, protocol, RFC, and SIMPLE.
Improved Mobile Telephone Service (IMTS) - Also known as specialized mobile radio (SMR) and trunk
mobile radio (TMR). See SMR.
impulse noise - Noise on a circuit that can be caused by voltage spikes in equipment, voltage changes
on adjacent pairs in a copper cable, tones generated for network signaling, maintenance and test procedures, lightening flashes during thunderstorms, and a wide variety of other phenomena.As impulse noise
is short in duration (
1
⁄100 of a second, or so); it has little effect on voice communications, but can cause bit
errors in a data transmission. See also noise.
IMS (IP Multimedia Subsystem) - An architectural concept built around a packet core and providing
an environment in which a user can access a wide range of multimedia services using any device and any
type of network connection. IMS supports Internet Protocol (IP) sessions between devices over any type
of connection and protocol, whether wireline or wireless in nature. IMS will support sessions between
devices in the PSTN, Internet, WLAN, and cellular domains, recognizing the limitations of each and
adjusting as required, even as a terminal device roams amongst them. IMS manages internetwork handoffs,
bandwidth negotiation and quality of service (QoS), while it keeps peers engaged in the session advised
via the Session Initiation Protocol (SIP) as to the level of multimedia presence. IMS originated in the 3rd
Generation Partnership Project (3GPP), which was seeking a common means by which GSM cellular
operators could deliver data services. IMS subsequently transcended the cellular domain, and is now being
embraced by both wireless and wireline service providers. Industry groups such as the Multiservice
Switching Forum (MSF), European Telecommunications Standards Institute (ETSI), and Alliance for
Telecommunications Industry Solutions (ATIS) have adopted IMS as the foundation for their next-generation
infrastructure strategies. See also 3GPP, architecture, ATIS, cellular radio, ETSI, Internet, IP, multimedia,
packet, protocol, PSTN, QoS, session, SIP, wireless, wireline, and WLAN.
IMT (InterMachine Trunk) - A high-capacity, multichannel circuit that interconnects circuit switches
in the core of a carrier network.
IMT-2000 (International Mobile Telecommunications-2000) - An initiative of the ITU-R for a
twenty-first century wireless network architecture that replaced Future Public Land Mobile Telecommunications System (FPLMTS) as that organizations vision for a single global standard for digital wireless networks. Specifications call for operation on the 2 GHz (2000 MHz) band and include high-mobility
applications at 128/144 kbps, pedestrian speed applications at 384 kbps, and fixed wireless applications such
as wireless local loop (WLL) and in-building applications such as wireless LANs (WLANs) at 2.048 Mbps.
Technologies and standards falling under the IMT-2000 umbrella include 2.5G and 3G such as Enhanced
Data rates for GSM Evolution (EDGE), General Packet Radio Service (GPRS), High-Speed Circuit
Switched Data (HSCSD), and Universal Mobile Telecommunications System (UMTS). See also 2.5G, 3G,
cellular radio, digital, EDGE, GPRS, HSCSD, UMTS, wireless, WLAN, and WLL.
IMTC (International Multimedia Telecommunications Consortium) - A not-for-profit organization with the stated mission of promoting, encouraging, and facilitating the development and implementation of interoperable multimedia teleconferencing and telecommunications solutions through open
standards. IMTC focus is on the T.120 and H.320 standards suites for data conferencing and video telephony, respectively. See Appendix A for contact information.
IMTS (Improved Mobile Telephone Service) - Also known as specialized mobile radio (SMR) and trunk
mobile radio (TMR). See SMR.
IN (Intelligent Network) - A public switched telephone network (PSTN) that, at a minimum, provides
for the switches to consult centralized, service- and customer-specific databases for routing instructions
and authorization code verification. Intelligent Network Version 1 (IN/1) was conceived at Bell Labs and
unveiled in 1976 with the introduction of INWATS (800) services and the first common channel signaling (CCS) system. IN/1 services included INWATS, calling card verification, and voice virtual private networks (VPNs). IN is dependent on the service creation element (SCE), a set of modular programming
tools permitting services to be developed independently of the switch, thereby divorcing the servicespecific programmed logic from the switch logic.This enables the service to be developed independently and be made available to all switches in the network. IN/1 was succeeded by the advanced intelligent network
(AIN), developed by Bell Labs in the early 1980s. See also AIN, Bell Labs, CCS, database, PSTN, routing,
SCE, switch, and VPN.
in the clear Referring to radio frequency (RF) - transmission with no encryption or scrambling mechanism for security purposes. See also encryption, RF, scramble, and security.
in the wild - Referring to an application in the real world, rather than a laboratory experiment or
demonstration or an unproven concept.
in-band signaling and control - Signaling and control that takes places over the same physical path (i.e.,
through the same switches and across the same circuit) and either occupies the same frequencies or competes for the same time slots as the user payload. In-band signaling is intrusive, or disruptive, in nature.As
examples, touch-tone signals can disrupt a voice conversation and call-waiting alerts can terminate a
modem connection.T-carrier signaling clearly is in-band rather than out-of-band, as it involves bit robbing, which periodically replaces payload bits with signaling bits. E-carrier signaling and control occurs
exclusively in time slots reserved for that purpose. See also frequency, out-of-band signaling and control, payload, signaling and control, and time slot.
In-house BPL (In-house Broadband over Power Line) - A data communications transmission technology that allows a device to connect to a local area network (LAN) directly through the low voltage
(LV) electric grid inside the premises.The LV grid runs at 110 volts at 50–60 Hz in North America, and
220 volts at 50 Hz in Europe and most of the rest of the world. HomePlug 1.0 standards support up to 16
nodes sharing theoretical bandwidth of up to 14 Mbps over a LAN based loosely on Ethernet standards. HomePlug uses of a version of orthogonal frequency division multiplexing (OFDM) specially tailored for
powerline environments. HomePlug 1.0 specifies 84 equally spaced subcarriers, within each of which several differential modulation techniques are employed. Security is through the 56-bit Data Encryption Standard (DES). See also Access BPL, bandwidth, BPL, broadband, DES, HomePlug, LAN, node, OFDM, PLC, and
voltage.
in-house broadband over power line (In-house BPL) - See In-house BPL.
incident angle - See angle of incidence.
incremental redundancy (IR) - See IR.
incumbent local exchange carrier (ILEC) - See ILEC.
Independent Communications Authority of South Africa (ICASA) - See ICASA.
independent telephone company - Referring to United States telephone companies that are not part
of the Bell System, i.e., are not owned by AT&T.The term was obsoleted when AT&T divested the operating telephone companies in 1984 as a result of the Modified Final Judgement (MFJ), also known as the
Divestiture Decree.The term is now doubly obsolete as the AT&T of the twenty-first century bears no
resemblance to that of the nineteenth and twentieth centuries. Nonetheless, more than 1,000 telephone
companies continue to refer to themselves as independent. See also MFJ.
index of refraction (IOR) - See IOR.
index-matching gel - A gelatinous substance with an index of refraction (IOR) that closely matches that
of the core of an optical fiber. Mechanical splices and connectors are filled with index-matching gel to
reduce Fresnel reflections from a fiber end face. See also connector, core, Fresnel reflection,IOR,mechanical splice,
and optical fiber.
inductance (L) - The property of an electric circuit or device by virtue of which a varying current
induces an electromotive force (emf), i.e., voltage (V), in that circuit or device, or in an adjacent circuit or
device. See also circuit, current, emf, and voltage.
inductive reactance (XL) - The opposition to the flow of alternating electric current (AC) in an inductor. Inductive reactance is an inertial reaction to changes in the electromagnetic field created when an
alternating voltage is applied. When AC passes through a component that contains reactance, energy is
alternately stored in and released from a magnetic field or electric field. In the case of magnetic energy, the
reactance is inductive.The greater the amount of inductance, the greater the inertial opposition.The faster
the reversal of current, the greater the inertial opposition. Inductive reactance is measured in Ohms (Ω).
See also capacitive reactance, inductance, and reactance.
inductor - A device comprising one or more windings of a conductive material, around a core of air or
a ferromagnetic material, for introducing inductance into an electric circuit.An inductor opposes changes in
current, whereas a capacitor opposes changes in voltage. See also capacitor, inductance, and inductive reactance.
Industrial/Scientific/Medical (ISM) - See ISM.
InfiniBand - An architecture and specification for data flows between processors and high performance
I/O devices such as servers in a storage area network (SAN), InfiniBand is a high-performance switched
fabric interconnect standard.The baseline 1X InfiniBand specification supports a signaling rate of 2.5 Gbps using 8B10B coding, which yields a data rate of 2 Gbps.The more capable 4X specification quadruples
the signaling rate to 10 Gbps and the data rate to 8 Gbps by spreading a datastream over four bonded links.
The 12X specification supports a signaling rate of 30 Gbps and a data rate of 24 Gbps. Double-rate and
quad-rate options effectively double and quadruple each of these theoretical speeds. See also 8B10B, architecture, bonding, and SAN.
InFLEXion - See FLEX.
infobahn - A play on the terms information superhighway and the German autobahn, an expressway
known for its high speed limits.Actually, posted speed limits on the autobahn are more along the lines of
suggestions. See information superhighway.
Information and Communication Science and Technology (ICST) - See ICST.
information service - As defined in the U.S.Telecommunications Act of 1996, the offering of a capability for generating, acquiring, storing, transforming, processing, retrieving, utilizing, or making available
information via telecommunications, and includes electronic publishing, but does not include any use of
any such capability for the management, control, or operation of a telecommunications system or the management of a telecommunications service. As interpreted by the Federal Communications Commission
(FCC), broadband wireline services such as digital subscriber line (DSL) and cable modem service are
information services, rather than telecommunications services. See also broadband, cable modem, DSL, FCC,
Telecommunications Act of 1996, telecommunications service, and wireline.
Information Superhighway - Also known as the infobahn.The Internet and its physical infrastructure,
including access and transport circuits, switching and routing systems, public and private networks, and
online services, with emphasis on high-speed and broadband capabilities.The term was popularized in the
United States during the Clinton-Gore administration (1993–2001), and is generally associated with Vice
President Al Gore.The Clinton-Gore administration is no longer in power and the term is now considered obsolete.The National Information Infrastructure (NII) is a similar concept promoted by the United
States government. See also access circuit, Internet, network, NII, router, service, switch, system, and transport circuit.
information technology (IT) - See IT.
infralow frequency (ILF) - See ILF.
infrared (IR) - See IR.
infrastructure mesh - In wireless local area networks (WLANs), a node mesh, that is, a mesh by which
the majority of access points (APs) interconnect on a peer-to-peer basis through wireless RF links, with
only those at the logical edge of the mesh connecting back to the wired LAN domain. An infrastructure
mesh eliminates the requirement for cabling from the APs or wireless routers to wired ports on switches,
or for cabling between APs. See also AP, mesh topology, pure mesh, RF, and WLAN.
infrastructure mode - In wireless local area networks (WLANs), a manner of operation that involves a
centralized hub, or access point (AP), through which computers and peripherals interconnect and intercommunicate. See also ad hoc mode and WLAN.
initialism - An unpronounceable abbreviation comprising the initial letters of a term and commonly used
in place of that term. Each letter of an initialism is pronounced independently. Fox example, SDH is the initialism for Synchronous Digital Hierarchy.An acronym is a pronounceable word formed from the initials or
other parts of several words that comprise a term. SONET, for example, is the acronym for Synchronous
Optical NETwork, the North American standard for fiber optic transmission systems that later became internationalized as SDH.Acronyms and initialisms generally comprise all uppercase letters, although they sometimes are all lower case, or a mixture of upper and lower case. Examples include SONET, SDH, bit (binary
digit), bps (bits per second), QoS (Quality of Service), and Sesame (Secure European Systems for Applications in a Multivendor Environment). See also abbreviation, acronym, and contraction.
injection fiber - See launch cable.
input/output (I/O) - See I/O.
INRIA (National de Recherche en Informatique et en Automatique) - Translates from French as
the National Institute for Research in Computer Science and Control. The French National Institute for
Research in Computer Science and Control operates under the dual authority of the Ministry of Research and
the Ministry of Industry, and dedicated to fundamental and applied research in information and communication science and technology (ICST).
insertion gain - The gain, or increase in signal power, resulting from the insertion of a component, such
as an amplifier or repeater, in a circuit. Insertion loss is measured as a comparison of signal power at the
point the incident energy strikes the component and the signal power at the point it exits the component.
Insertion gain typically is measured in decibels (dB), although it also may be expressed as a coefficient or
a fraction.A negative gain is a loss. See also attenuation, dB, and insertion loss.
insertion loss - 1. The attenuation, or loss in signal power, resulting from the insertion of a component,
such as a connector or splice, in a circuit. Insertion loss is measured as a comparison of signal power at the
point the incident energy strikes the component and the signal power at the point it exits the component.
Insertion loss typically is measured in decibels (dB), although it also may be expressed as a coefficient or a
fraction.A negative loss is a gain. See also attenuation, dB, and insertion gain. 2. In a fiber optic transmission
system (FOTS), insertion loss is a measure of loss across a circuit due to all factors, including absorption,
bending loss from both macrobends and microbends, diffusion, dispersion, Fresnel reflection, and leaky
modes. See absorption, bending loss, macrobend, microbend, diffusion, dispersion, Fresnel reflection, insertion gain, and
leaky mode.
inside plant (ISP) - See ISP.
inside vapor deposition (IVD) - See IVD.
inside wire - and cable Referring to wire and cable systems inside a customer premises, often owned
by the end user. See also ISP and OSP.
instant messaging (IM) - See IM.
Instant Messaging and Presence (IMP) - See IMPP and SIMPLE.
Instant Messaging and Presence Protocol (IMPP) - See IMPP.
Institute of Electronic and Electrical Engineers (IEEE) - See IEEE.
Insulated Cable Engineers Association (ICEA) - See ICEA.
insulation - The dielectric material that surrounds a metal conductor and prevents it from touching
another conductor or the ground and, thereby, shorting the circuit. Insulation typically is made of some
sort of plastic material. Inside wire and cable standards vary according to the applications, but generally
favor insulation that is characterized as low flame-spread, low-smoke, and low-toxicity.
insulator - 1. A material that does not conduct electricity, heat, light, etc. 2. In the context of telecommunications, an insulator is a material that does not conduct electricity, i.e., a dielectric. See also conductor
and dielectric.
insure - 1. To obtain an insurance policy on something. 2. Used in error to mean to make certain of
something of something by taking necessary precautions. I vote for #1, exclusively. It makes me crazy
when people talk about how some process or some such thing insures some result. I think that the only
thing that insures something is an insurance policy, and even that only insures that somebody gets paid
when the barn burns down or some such thing and even that assumes that the insurance company will
actually live up to the terms of the policy and pay up. Oh, well, maybe it’s just me utilizing my editorial
privilege and ranting on and on and on in unnecessarily complex sentences. See also ensure and utilize.
integrated access device (IAD) - See IAD.
integrated circuit - Synonymous with microcircuit and semiconductor chip. In computer hardware, a
miniaturized electronic circuit comprising many individual circuit elements, such as transistors, diodes,
resistors, capacitors, and inductors, etched on a tiny wafer of semiconducting material such as silicon. See
also capacitor, circuit, diode, electronics, inductor, resistor, and transistor.
integrated messaging - Synonymous with multimedia messaging and unified messaging. See unified
messaging.
integrated services digital network (ISDN) - See ISDN.
Integrated Services LAN (ISLAN) - Specified by the IEEE as 802.9 and also known variously as
IsoEthernet and IsoEnet. ISLAN is considered obsolete. See also 802.9, IEEE, and IsoEthernet.
intellectual property - Property derived from the work of human intellect. Intellectual property laws
cover a wide range of property created by artists, authors, inventors, and musician, and protect copyrights,
patents, trademarks, and trade secrets. See also copyright, patent, and trademark.
intelligent network (IN) - See IN.
intelligent peripheral (IP) - See IP.
Interactive Video and Data Services (IVDS) - See 218-219 MHz Service.
interactive voice response (IVR) - See IVR.
intercom - An abbreviation of intercommunication, an intercom system is a closed (i.e., not networked)
system that allows members of a group to converse with each other. An intercom system can be standalone, although Centrex systems, key telephone systems (KTSs), and PBXs commonly feature intercom
capabilities. See also Centrex, KTS, and PBX.
interexchange carrier (IEC or IXC) - See IXC.
interface data unit (IDU) - See IDU.
interface - 1. The common physical point, boundary, surface, or plane where two things touch, meet, or
come together.The interface between the core and cladding in a glass optical fiber (GOF) is an example
of such a physical interface. See also cladding, core, and GOF. 2. The device or component that serves to
physically and logically interconnect two other devices or systems and that enables their interoperation.
Such an interface may comprise a combination of hardware and firmware.A trunk interface that connects
a trunk and a switch or router is an example of such an interface. See also hardware and firmware. 3. Software that logically interconnects two computers or a computer and another device and allows them to
interoperate. Such software generally is characterized as performing a gateway function. A gateway that
accomplishes protocol conversion between X.25 and frame relay is an example. See also gateway, protocol,
and software. 4. Software that enables a user to work with a computer program perhaps in an intuitive way.
Examples include a command-line interface and a graphical user interface (GUI). See also program and software. 5. Software that enables a computer to work with another program, or with the computer hardware.
Such software enables the computer to function as a whole. See also API, hardware, program, and software.
interference - 1. In general, spurious or extraneous energy that appears in the circuitry of a system or
component and impedes the reception of desired signals. 2. In radio communications, the negative impact
of undesired energy by emission, radiation, or induction on the reception of desired signals.
interferometer - See etalon.
interframe compression - A step in video compression that considers and eliminates redundant information in successive video frames.The background of a movie scene, for example, might not change, even
though the actors move around the set. See also compression, frame, and video.
Interim Standard 136 (IS-136) - See IS-136.
Interim Standard 2000-A (IS-2000-A) - See IS-2000-A.
Interim Standard 54 (IS-54) - See IS-54.
Interim Standard 856 (IS-856) - See IS-856.
Interior Gateway Protocol (IGP) - See IGP.
interior protocol - A protocol concerned with routing within a network. Interior Gateway Protocol
(IGP) is an interior protocol. See also exterior protocol, IGP, protocol, and routing.
interlaced scanning - The process of refreshing a video screen that is used with most analog TV systems.
Interlaced scanning involves two fields. Odd lines (field 1) are refreshed in one scan, and even lines (field 2)
in the next. Each set of odd and even lines refreshed constitutes a frame refreshed. See also progressive scanning and scanning.
interLATA - Referring to a long distance call between Local Access and Transport Areas (LATAs). In the
United States, LATA boundaries were defined in the Modified Final Judgement (MFJ) that broke up the
AT&T Bell System on January 1, 1984. The Regional Bell Operating Companies (RBOCs) and their
component Bell Operating Companies (BOCs) initially were prevented from offering interLATA toll
services. See also BOC, LATA, MFJ, and RBOC.
interleaving - See byte interleaving.
intermachine trunk (IMT) - See IMT.
intermediate distribution frame (IDF) - See IDF.
intermodulation noise - Noise that is the result of modulation, demodulation, and any nonlinear characteristics of the transmission medium or transmission system components. See also modulation and noise.
internal reflection - See total internal reflection.
International Direct Distance Dialing (IDDD) - See IDDD.
International Electrotechnical Commission (IEC) - See IEC.
international gateway facility (IGF) - See IGF.
International Information Infrastructure (III) - Synonymous with Global Information Infrastructure
(GII).The international version of the National Information Infrastructure (NII), or Information Superhighway. See also Information Superhighway and NII.
International Mobile Telecommunications-2000 (IMT-2000) - See IMT-2000.
international Morse code - See Morse code.
International Multimedia Telecommunications Consortium (IMTC) - See IMTC.
International Organization for Standardization (ISO) - See ISO.
International Record Carrier (IRC) - See IRC.
International Telecommunication Union (ITU) - See ITU.
International Telecommunication Union-Radiocommunication Sector (ITU-R) - See ITU-R.
International Telecommunication Union-Telecommunication Standardization Sector (ITU-T
or ITU-TSS) - See ITU-T.
International Telegraph Alphabet #2 (ITA #2) - See Baudot code.
Internet Activities Board The original name for the Internet Architecture Board (IAB) - See IAB.
Internet Architecture Board (IAB) - See IAB.
Internet Control Message Protocol (ICMP) - See ICMP.
Internet Corporation for Assigned Names and Numbers (ICANN) - See ICANN.
Internet Engineering Steering Group (IESG) - See IESG.
Internet Engineering Task Force (IETF) - See IETF.
Internet Exchange (IX) - See IX.
Internet Explorer (IE) - A highly capable Web browser developed by Microsoft (1995) and packaged
with Microsofts Windows suite of software. See also browser and WWW.
Internet Fax Protocol (IFP) - See T.38.
Internet Protocol (IP) - See IP.
Internet Protocol next generation (IPng) - The working name for what became Internet Protocol
version 6 (IPv6). See IPv6.
Internet protocol suite - See TCP/IP protocol suite.
Internet Protocol television (IPTV) - See IPTV.
Internet Protocol version 4 (IPv4) - See IPv4.
Internet Protocol version 6 (IPv6) - See IPv6.
Internet Research Task Force (IRTF) - See IRTF.
Internet Small Computer System Interface (iSCSI) - See iSCSI.
Internet Society (ISOC) - See ISOC.
Internet - A massive, global network of packet data networks based on the Internet Protocol (IP) suite.The
Internet is grounded in the U.S. Department of Defense ARPANET (Advanced Research Projects Agency
NETwork), which began in 1969 as a means of linking personnel and systems involved in various computer
science and military research projects. The Internet since has grown to comprise more than 400 million
hosts connected to more than 60,000 academic, business, and governmental networks in more than 150
countries. The Internet also has evolved to support not only data, but also voice, image, video, facsimile,
audio, and multimedia communications. Fundamental to the Internet is the Internal Protocol (IP) suite,
which, in the context of the OSI Reference Model, includes the Internet Protocol (IP) at the Network
Layer and Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) at the Transport Layer.
At the Application Layer are File Transfer Protocol (FTP), Simple Mail Transfer Protocol (SMTP), Simple
Network Management Protocol (SNMP), and Telecommunications Network (TELNET). The physical
infrastructure has evolved into one that is largely broadband in nature, comprising extremely high speed
transmission systems and routers.The physical topology is organized in a hierarchical manner, as follows:
Level 1: Network Access Points (NAPs) and MAEs serve as points of interconnection where national and regional carriers exchange traffic
Level 2: National backbones comprising facilities-based, long haul carriers
Level 3: Regional carriers comprising facilities-based, long haul carriers operating in a single state or province
Level 4: Internet Service Providers (ISPs)
Level 5: End users
See also ARPANET, backbone, broadband, carrier, computer, data, end user, FTP, host, Internet2, ISP, IP, long haul circuit, MAE, NAP, network, Network Layer, OSI Reference Model, packet, router, SMTP, SNMP, system, TCP, TELNET, transmission system, Transport Layer, and UDP.
internet - An interconnection of networks that is so seamless as to appear to the user as one network.The
networks can include local area networks (LANs), metropolitan area networks (MANs), and wide area networks (WANs). See also Internet, LAN, MAN, network, seamless, and WAN.
Internet2 - A private Internet for the benefit of its member organizations, which include the U.S.
National Science Foundation (NSF), the U.S. Department of Energy, more than 200 U.S. research universities, and over 60 private companies formed into a not-for-profit consortium. Internet2 is not a separate
physical network, and it does connect to the present Internet, as required. Internet2 is a project of the University Corporation for Advanced Internet Development (UCAID), a not-for-profit entity created specifically to develop and manage the network.The Internet2 and its members are in the process of developing
and testing technologies such as IPv6, multicasting, and quality of service (QoS) mechanisms in support
of what they characterize as revolutionary Internet applications such as digital libraries, virtual laboratories, distance-independent learning, and tele-immersion. The Internet2 initiative is parallel and complementary to the Next Generation Internet (NGI) initiative funded by the United States federal government. The physical transmission infrastructure initially (1995) was in the form of the very-highspeed Backbone Network Service (vBNS), which was replaced by the Abilene Project. Géant2 is a similar European backbone project. See also Abilene Project, Géant2, IPv6, multicast, NFS, NGI, QoS,
tele-immersion, UCAID, and vBNS.
Internetwork Packet Exchange (IPX) - See IPX.
Internetwork Packet Exchange/Sequenced Packet Exchange (IPX/SPX) - See IPX/SPX.
intersymbol interference (ISI) - See ISI.
intraLATA - Referring to a local long distance call within the boundaries of a Local Access and Transport Area (LATA). In the United States, LATA boundaries were defined in the Modified Final Judgement
(MFJ) that broke up the AT&T Bell System on January 1, 1984.The Regional Bell Operating Companies
(RBOCs) and their component Bell Operating Companies (BOCs) initially were prevented from offering interLATA toll services, but they and other local exchange carriers (LECs) had the exclusive right to
offer local exchange service and intraLATA toll service. See also BOC, LATA, LEC, MFJ, and RBOC.
intranet - A private network based on the TCP/IP protocol suite and designed to provide access to information resources within a company, university, or other organization. Designed to look much like a site
on a private World Wide Web (WWW) and based on the same protocols, an intranet supports familiar
client/server software such as browsers and e-mail. Intranets can be used for communications to and
between employees to advise them of company policies, job postings, company events, product literature,
press releases, and so on. On a password-protected basis, privileged users can access sensitive internal company information, including customer billing records and network usage data. Intranets support the transmission of images, video clips, and sound clips, as well as textual information. Hypertext links can be
included to hot link to other sites and databases.An intranet can be confined to a campus environment or
can extend across the wide area to link together multiple, geographically dispersed locations. Access from
an intranet to the wider public Internet is possible through a security firewall. Extranets are intranets
opened to select groups of users outside the company. See also browser, database, e-mail, extranet, firewall,
hypertext, Internet, protocol, protocol suite, TCP/IP, and WWW.
intrinsic loss - In fiber optics transmission, signal attenuation due to absorption and scattering resulting
from internal forces or inherent characteristics of the optical fiber. See also absorption, attenuation, extrinsic
loss, optical fiber, scattering, and signal.
inverse multiplexer - A device that performs inverse multiplexing. See inverse multiplexer.
inverse multiplexing over ATM (IMA) - See IMA.
inverse multiplexing - A technique that is the inverse, or opposite, of multiplexing.Traditional multiplexing folds together multiple low-speed channels onto a high-speed circuit. Inverse multiplexing spreads
a high-speed channel across multiple low-speed circuits. Inverse multiplexing is used where an appropriately high-speed circuit is not available.A 6-Mbps data stream, for example, might be inverse multiplexed
across four (4) T1 circuits, each running at 1.544 Mbps. Inverse multiplexing over ATM (IMA) fans out an
ATM cell stream across multiple circuits between the user premises and the edge of the carrier network.
In such a circumstance, multiple physical T1 circuits can be used as a single, logical ATM pipe.The IMAcompliant ATM concentrator at the user premises spreads the ATM cells across the T1 circuits in a round
robin fashion, and the ATM switch at the edge of the carrier network scans the T1 circuits in the same
fashion in order to reconstitute the cell stream.There is a similar implementation agreement (IA) for Frame
Relay. Multilink point-to-point protocol (PPP) serves much the same purpose in the Internet domain.
inverter - 1. A device that converts electrical energy from direct current (DC), typically 12 or 48 volts,
to alternating current (AC), typically 120 volts. See also AC and DC. 2. In digital systems, a logic gate that
inverts the polarity of an electrical pulse from positive (+) to negative (–) or from negative (–) to positive
(+). See also digital, polarity, and pulse.
INWATS (INward Wide Area Telecommunications Service) - WATS service for incoming calls,
only, INWATS was a discounted bulk long distance plan in the United States and Canada that reversed
the charges to the called party, rather than the calling party.Although INWATS service, as such, has been
obsoleted, toll-free services are common throughout the world. Such services are toll free only to the
caller, of course. See also toll free service and WATS.
ion - An atom or group of atoms that has acquired a positive (+) or negative (–) electric charge by gaining (+) or losing (–) one or more electrons through a chemical reaction or by the action of certain forms
of radiant energy.The movement of electrons and ions constitutes electric current. See also current, electron,
hydroxyl, and ionosphere.
ionosphere - Four regions of the Earth’s outer atmosphere, beginning at an altitude of approximately 55
kilometers (34 miles), ionized by solar radiation.The ionosphere contains high concentrations of ions and
free electrons, and can serve to reflect certain radio signals back to Earth, depending on their frequency
and angle of incidence. Long-range radio communications depend on this skywave propagation, or atmospheric skip. See also angle of incidence, frequency, and skywave.
IOR (Index Of Refraction) - The ratio between the velocity of light in a vacuum to the velocity of
light in a transmission medium, such as a given type of glass. Refraction refers to the phenomenon by
which light changes velocity and changes direction (i.e., bends or refracts) as it exits one medium and
enters another of different density.The IOR is mathematically expressed as
n = c ÷ v
where c is the velocity of light in a vacuum, and v is the speed of light in the given medium. So, IOR is the
mathematical inverse of velocity of propagation (Vp). IOR is a convenient means for expressing the differences between the speed of light in different types of optical fiber, as well as between the core and cladding
of a glass optical fiber (GOF).
| Medium | Signal Velocity (km/s) | Velocity of Propagation (Vp) | Index of Refraction (IOR) |
|---|---|---|---|
| Vacuum | 300,000 | 100.00 | 1.0000 |
| Air | 299,890 | 99.97 | 1.0003 |
| Water | 226,000 | 75.33 | 1.3275 |
| Optical Fiber | 203,910–209,910 | 67.57–68.97 | 1.4500–1.4800 |
Index of Refraction (IOR)
Not all glass is created equal, by the way.The raw material for all glass is quartz sand, a very pure sand
comprising nearly 100 percent crystalline quartz silica. During the manufacturing process, the glass is purified to reduce the slight amount of iron oxide that might be present, various dopants (i.e., impurities) are
added to alter brittleness and other characteristics, and heat treatments can be applied to produce tempered
glass. Glass optical fiber is typically doped with some amount of germanium oxide (GeO2) or other compounds, which increase the IOR and variously impact other operating characteristics of the fiber at certain wavelengths. Erbium-doped fiber amplifiers (EDFAs) are used extensively in long haul fiber optic
transmission systems (FOTS) in place of more traditional optical repeaters. It is extremely important to know the IOR of a given cable in order to calculate latency, i.e., the delay
imposed on the signal, from end-to-end, by the medium. Latency has significant impact on the synchronization of transmitters, repeaters, multiplexers, and other active devices in a digital transmission system,
and particularly in a high speed system such as a FOTS that runs at signaling speeds up to 40 Gbps.
The IOR also has considerable impact on the physical construction of a glass optical fiber, which consists of an inner core surrounded by one or more layers of cladding.The optical signal is intended to travel
through the inner core, and the cladding serves in various ways to ensure that happens. Step-index fiber is
characterized by a sharp decrease in the IOR between the core and cladding, i.e., the cladding is sharply
lower in IOR than the core material. This sharp step of approximately one percent in IOR at the
core/cladding interface causes any errant light rays to reflect back into the core in a phenomenon known
as total internal reflection. Graded-index fiber is characterized by a gradual decrease in the refractive index
of the cladding through a great many layers of glass.The approach causes the errant light rays to gradually
gain in velocity and bend back towards the core. Step-index construction is used largely in single-mode
fiber (SMF) and graded-index in multimode fiber (MMF). See also core, cladding, graded-index fiber, latency,
MMF, SMF, step-index fiber, and Vp.
IP (Intelligent Peripheral) - In the advanced intelligent network (AIN) architecture, a separate computing device that enhances the delivery of certain services by offloading processing demands from a service control point (SCP) and providing a basic set of services to the SCP. The role of the IP typically
includes collection of digits, collection and playing of voice prompts, collection of voice responses and
their conversion to digits, menu services, and database lookups. As examples, voice processing and voice
recognition can be implemented on an IP in support of the processing of collect calls. Because the abbreviation IP is used so extensively to identify the Internet Protocol, the term special resource function (SRF)
often is used to describe these peripherals and the functions they perform. See also AIN and SCP.
IP (Internet Protocol) - In the context of the OSI Reference Model, a Network Layer (Layer 3) connectionless protocol for the routing of datagrams through gateways connecting networks and subnetworks,
IPv4, the first version to be deployed, is defined in IETF RFC 791 and is the basic block of the Internet.
IP can be characterized as datagram-oriented because each IP packet works its way through the network
independently, with no thought of an individual packet belonging to a larger stream of packets. IP also can
be characterized as a best effort protocol, as it offers no guarantees of delivery, no sequencing, and no error
detection and correction mechanism. IP provides for packet segmentation and reassembly and provides
specific addressing conventions in the form of dotted decimal notation. IP supports routing control, as well
as status translation and communications.Although IP has no concept of the specific content of the packet
or of its service requirements, it supports multiple service types, including low-delay, high-bandwidth, and
high-reliability paths. Dial-up IP access protocols include Ethernet over Point-to-Point Protocol (Enet
over PPP) Serial Line Internet Protocol (SLIP), and Point-to-Point Protocol (PPP).There are two versions
of IP. The legacy version is IPv4, which is widely deployed. The most current version is IPv6, which is
deployed sparingly, largely due to the fact that it is not compatible with older routers.Although IP can be
used on a standalone basis, it more typically is used in conjunction with higher layer protocols in the
TCP/IP protocol suite. See also bandwidth, best effort, connectionless, datagram, dial-up access, dotted decimal notation, IETF, IPv4, IPv6, gateway, Internet, network, Network Layer, OSI Reference Model, packet, PPP, protocol,
router, segmentation, SLIP, and TCP/IP protocol suite.
IP address (Internet Protocol address) - A binary number that uniquely identifies a host computer
connected to the Internet.The IP packet header provides an originating address field so that a host can
identify itself as the originator of a packet.The IP packet header also provides a destination address field
so that an originating host can identity the target host for which a packet is intended. Based on that information, the Internet routers can act to deliver the packet to the target host, which can respond to the originating host, as appropriate. All IP addresses are written in dotted decimal notation. An IPv4 address, for
example, comprises 4 fields separated by dots and expressed as xxx.xxx.xxx.xxx, with each field given a value in decimal notation of 0–255, the range expressed by a single octet in binary notation. See also binary,
binary notation, computer, dotted decimal notation, header, host, Internet, IPv4 address, IPv6 address,octet, and packet.
IP Captioned Telephone Service - A hybrid Telecommunications Relay Service (TRS) that involves a
special telephone with a text display. Rather than using TTY or computer technology for text entry, the
called partys speech is re-voiced by the communications assistant (CA), converted into text by a voice
recognition system, and transmitted directly to the hearing-impaired callers display telephone over the
Internet.The CA can simultaneously listen to one party and read the text of the other party. See also Internet, TRS, TTY, and voice recognition.
IP Centrex - Synonymous with hosted PBX and virtual Centrex. Centrex service provided from a network-based carrier-class IPBX platform to which the user organization connects over the public Internet
or a private IP network as though it were a remote Centrex central office (CO). See also carrier-class, Centrex, Internet, and IPBX.
IP Multimedia Subsystem (IMS) - See IMS.
IP PBX Synonymous with IPBX - See IPBX.
IP Relay A text-based Telecommunications Relay Service (TRS) that uses the Internet Protocol (IP) based
Internet rather than a traditional public switched telephone service (PSTN) connection to communicate.A
speech- or hearing-disabled person initiating an IP Relay TRS call uses a computer or other text input device
to call the TRS relay center over an Internet connection and give the communications assistant (CA) the destination telephone number, which the CA uses to place a traditional telephone call.The CA then serves as a
translator, relaying the text of the calling party in voice to the called party, and converting the voice of the
called party into text for the benefit of the caller. See also Internet, IP, PSTN, and TRS.
IP security (IPsec) - See IPsec.
IP-enabled Frame Relay - Also known as Private IP.A frame relay variant that employs virtual routers
to route frames at the Network Layer of the OSI Reference Model. IP-enabled Frame Relay typically
makes use of MultiProtocol Label Switching (MPLS) to speed frame processing and support quality of
service (QoS). See also frame relay, IP, MPLS, Network Layer, OSI Reference Model, QoS, and router.
IP-enabled PBX (Internet Protocol-enabled Private Branch eXchange) - A PBX that couples
VoIP (Voice over Internet Protocol) onto a conventional PBX based on time division multiplexing
(TDM). The intelligent IP phones can take the form of either hardphones or softphones that connect
either over a switched Ethernet LAN. The LAN-attached data terminals interconnect as usual. The IP
phones connect to the PBX through an Ethernet port on a line card that includes an IP gateway that
resolves the interface issues between the TDM bus and the switched Ethernet LAN that supports VoIP.
Calls between the LAN-attached IP phones are conducted on a peer-to-peer basis using their LAN addresses, and are confined to the LAN. Calls between TDM phones also are on a peer-to-peer basis
through the TDM switching matrix. Calls between a LAN-attached IP phone and a PBX-attached TDM
phone go through the gateway, where protocol issues are resolved, including address translation between
PBX extension numbers and Ethernet LAN addresses. See also LAN, IPBX and PBX.
IPBX (Internet Protocol Private Branch eXchange) - Synonymous with IP PBX. A pure IPBX is
based on a client/server architecture that generally is implemented on a switched Ethernet LAN platform
running at 100 Mbps or more in support of VoIP. Client software residing on intelligent IP hardphones
and softphones runs against one or more servers that can be distributed across an enterprise, perhaps in
geographically diverse locations connected over the public Internet or, preferably, a private IP-based network. One or more telephony servers are responsible for all call control functions (e.g., call setup and teardown), telephony applications (e.g., feature content and class of service (CoS) assignments), and associated
databases (e.g., IP and station numbering schemes and assignments, and directory information). Although
the switched Ethernet LAN infrastructure is shared between voice and data, and perhaps video, each IP
phone has a dedicated physical port on an Ethernet switch in order to minimize any issues of congestion
at the port level. Further,VoIP generally runs in a logical virtual LAN (VLAN) partition to maintain an
acceptable level of quality of service (QoS). A digital signal processor (DSP) embedded in each IP phone
digitizes the analog voice signals in pulse code modulation (PCM) format and may compress the resulting
voice data. Application software then forms VoIP packets, which are then inserted into Ethernet frames,
and presented to the switch.
There are several hybrid IPBX approaches that allow a user organization variously to maximize the
embedded investment in conventional TDM-based PBX equipment and ease into a pure IPBX mode.An
IP-enabled PBX is a conventional TDM PBX circuit switch platform with a VoIP module. A hybrid
TDM/IP PBX has both TDM and IP components co-existing, side by side.The TDM component comprises TDM line and trunk cards and ports and a TDM bus.The IP component comprises Ethernet ports,
an Ethernet switch, a router, and IP trunk ports. A gateway interconnects the TDM and IP components,
both of which are under the control of a telephony server running a commercial operating system (OS).
See also client/server, CoS, DSP, Ethernet,gateway, IP, IP Centrex, IP-enabled PBX, LAN, PCM, QoS, VLAN,
and VoIP.
IPng (Internet Protocol next generation) - The working name for what became Internet Protocol
version 6 (IPv6). See Ipv6.
IPsec (Internet Protocol security) - A standards-based security suite that operates transparently and
may eliminate the need for proprietary firewall mechanisms in some applications. IPsec also provides for
encapsulation of the secured IPv6 packets inside IPv4 datagrams, in consideration of both the increasing
need for security and the long-term transition process to IPv6. IPsec is described in IETF RFC 2401 and,
in the context of the OSI Reference Model, runs at the Network Layer (Layer 4). See also datagram, encapsulate,, firewall, IETF, IPv4, IPv6, Network Layer, OSI Reference Model, and packet.
IPTV (Internet Protocol TeleVision) - Referring to distribution of television programming over a
network running the IP protocol.This approach delivers each TV channel only to the subscriber premises
that select to view it, rather than broadcasting it to all stations on the network.The primary focus on IPTV
is from telephone companies offering voice, Internet access, and TV programming over broadband fiber
optic local loops conforming to passive optical network (PON) standards. See also broadband, broadcast, channel, fiber optics, IP, local loop, PON, and TV.
IPv4 (Internet Protocol version 4) - The legacy version of IP, IPv4 is the widely deployed foundation
protocol on which the Internet is built. Developed in the 1970s and documented in IETF RFC 791
(1981), IPv4 is a Network Layer (Layer 3) connectionless protocol for the routing of datagrams through
gateways connecting networks and subnetworks. IPv4 also can be characterized as a best effort protocol,
as it offers no guarantees of delivery, no sequencing, and no error detection and correction mechanism.
IPv4 provides for packet segmentation and reassembly and provides specific addressing conventions in the
form of dotted decimal notation. IPv4 supports routing control, as well as status translation and communications.While IPv4 has no concept of the specific content of the packet or of its service requirements,
it also supports multiple service types, including low-delay, high-bandwidth, and high-reliability paths. In
the 30+ years since IPv4 was introduced, the Internet (and the world, in general) has become a much more
complicated, more intense, more populated, and less secure place. In a contemporary context, IPv4 is criticized for its inadequate address space and lack of inherent security mechanisms. IPv6, the current version
resolves those issues, but is incompatible with older routers and other legacy Internet infrastructure. So,
IPv4 remains the dominant protocol of the Internet. Although IPv4 can be used on a standalone basis, it
more typically is used in conjunction with higher layer protocols in the TCP/IP protocol suite. The total size of the IPv4 datagram, including the header, can be up to 65,535
octets in length.At a minimum, all networks must support a packet of at least 576 octets.As illustrated in Figure I-1, the minimum size of the IP header is 20 octets.The IPv4 datagram contains the following fields:
• VERS (VERSion): 4 bits identifying the IP version number.The version number is 4.
• IHL (Internet Header Length): 4 bits indicating the length of the header, which has a minimum value of five 32-bit words, or 20 octets.The IHL also provides a measurement of where the TCP header, or other higher-layer, header begins.
• Type of Service (ToS): 8 bits indicating the quality of service (QoS) requested for the datagram. Although TCP/IP networks currently do not provide guaranteed QoS, the networks will attempt to honor QoS requests in terms of parameters that include packet precedence (i.e., priority), low delay, high throughput, and high reliability.
• Total Length: 16 bits describing the total length of the datagram, including the IP header.The maximum size is 65,535 octets (2 16 –1, with 0 not considered as it has no value).All network hosts must be able to handle a datagram of at least 576 octets.
• Identification: 16 bits that are used in fragmentation control. In the event that the receiving network cannot accommodate a datagram of the specified total length, that datagram must be fragmented. Each fragment must contain a copy of the identification field and certain other fields in the IP header so they can be reassociated and the datagram can be reconstituted.
• Flags: 3 bits that define the manner in which the fragmentation occurs.The first bit always is set at 0.The second bit defines whether fragmentation is permitted.The third bit is used to identify the last fragment in a series of fragments.
• Fragment Offset: 13 bits that identify where the fragment fits in the complete set of fragments that comprise the original datagram.This field is used to sequence the fragments correctly, as they may arrive at the destination device out of sequence.
• Time To Live (TTL): 8 bits that specify the length of time in seconds that the datagram can live in the Internet system.The maximum length of time is 255 seconds (2 8 –1, with 0 not considered, as it is the official time of death), or 4.25 minutes. From the instant the IP datagram enters the Internet, each gateway and host that acts on the datagram decrements the TTL by at least one second.When the TTL reaches 0, the datagram is declared dead and is discarded.The TTL mechanism prevents packets from wandering the Internet for eternity, at which point they would have no value, and would only contribute to overall network congestion. Over time, the TTL field has been redefined to indicate, as an option, the number of hops, that is the number of routers through which the packet travels.The default TTL is 64.
• Protocol: 8 bits identifying the higher-layer protocol that created the message contained in the Data field. Examples include Transmission Control Protocol (TCP) and User Datagram Protocol (UDP).
• Header Checksum: 16 bits used for error control in the header.The process is that of a cyclic redundancy check (CRC).
• Source IP Address: 32 bits containing the IP address of the source host.
• Destination IP Address: 32 bits containing the IP address of the destination host.
• IP Options, If Any: An optional, variable-length field used by gateways to control fragmentation and routing options.
• Padding:A variable-length field used only when necessary to ensure that the IP header extends to an exact multiple of 32 bits.
• Data: A variable-length field that contains the actual data content, or payload. See also bandwidth, best effort, connectionless, CRC, datagram, dial-up, dotted decimal notation, error control, IETF,IPv4,IPv4 address,IPv6,gateway, header, host,Internet, network,Network Layer,octet,OSI Reference Model, packet, payload, PPP, protocol, QoS, router, segmentation, SLIP, TCP, TCP/IP protocol suite, and UDP.
IPv4 address (Internet Protocol version 4 address) - A binary number that uniquely identifies a host
connected to the Internet and running the IPv4 protocol suite.The IP packet header provides an originating address field so that a host can identify itself as the originator of a packet.The IP packet header also
provides a destination address field so that an originating host can identity the target host for which a
packet is intended. Based on that information, the Internet routers can act to deliver the packet to the target host, which can respond to the originating host, as appropriate.The IPv4 address field size is 32 bits,
which yields the theoretical potential for 2
32
or 4,294,967,296 unique addresses.All IP addresses are written in dotted decimal notation, which also is known as dotted quad format in the case of IPv4. Each IPv4
address field is divided into four fields separated by dots and expressed as
xxx.xxx.xxx.xxx
with each field given a value in decimal notation of 0–255, the range expressed by a single octet in binary
notation (2
8
= 256, or 0–255). (Note: Leading zeros are suppressed.) The addressing architecture defines five
address formats, each of which begins with one, two, three, or four bits that identify the class of the network (Class A, B, C, D, or E).The Network ID space identifies the specific network, and the Host ID space
identifies the specific host computers on the network. Classes A, B, and C are each associated with a range
of IP addresses that supports a limited number of networks per class and a limited number of hosts per
network. Class D addresses are reserved for multicast purposes and Class E addresses
are reserved for future use.
| Class | Address Range | Networks per Class | Hosts per Network |
|---|---|---|---|
| A | 1.0.0.1 to 126.255.255.254 | 126 | 16,777,214 |
| B | 128.0.0.1 to 191.255.255.254 | 16,384 | 65,534 |
| C | 192.0.0.1 to 223.255.255.254 | 2,097,152 | 254 |
| D | Reserved for multicast purposes | ||
| E | Reserved for experimental use |
IPv4 Address Classes
The Internet Corporation for Assigned Names and Numbers (ICANN) assigns public IP addresses to organizations desiring to place computers on the Internet.Theoretically speaking, the size of the user organization determines the IP Class and, therefore, the number of available host addresses, although no more Class A addresses are being assigned and virtually all Class B addresses have already been assigned.The user organization assigns the host address numbers internally and can reassign them on the basis of either static or dynamic addressing. Static addresses are permanently or semi-permanently associated with a specific host. Dynamic addresses are assigned each time a connection is established.There are both public and private IP address spaces. Computers on private LANs running the TCP/IP protocol suite do not require public addresses, at least not for internal use within the LAN domain. Private IP addresses are set aside for such purposes and will never be used publicly.The Internet Protocol version 6 (IPv6) addressing scheme is quite different. See also binary, binary notation, Class A, Class B, Class C, Class D, Class E, computer, decimal notation, dynamic address, header, host, ICANN, Internet, IPv6 address, multicast, packet, and static address.
IPv6 (Internet Protocol version 6) - The IPv6 specification grew out of the efforts of the IPng (IP
next generation) Working Group to define a successor protocol to IPv4. Specified originally in IETF RFC 1883 (1995), since replaced by RFC 2460 (1998), IPv6 overcomes many of the limitations of IPv4, most
notably with respect to address space, integration of application level protocols, quality of service (QoS),
and security.The total size of the IPv6 datagram, including the header, is increased beyond the IPv4 limit
of 65,535 octets to support jumbo payloads. At a minimum, all network links must support a maximum
transmission unit (MTU) of at least 1,280 octets. The IPv6 header is 40 octets, compared to the IPv4 header of 20 octets, and
can be extended as necessary through optional headers associated with higher layer protocols such as Transmission Control Protocol (TCP) and User Datagram Protocol (UDP). In a departure from IPv4, the IP
header and any extension headers associated with the datagram are in addition to the payload length.The
IPv6 datagram contains the following fields:
• VERS (VERSion): 4 bits identifying the IP version number.The version number is 6.
• Class: 8 bits used by originating nodes and/or forwarding routers to identify and distinguish between different packet classes or priorities, as set by upper-layer protocols.This field replaces the IPv4 Type of Service (ToS) field.
• Flow Label: 20 bits used by a source host indicating any special handling requested for a flow, or sequence, of datagrams. Real-time voice, audio, or video communications exemplify applications that require special flow treatment.
• Payload Length: 16 bits describing the total length of the datagram.This field is much like the Total Length field in IPv4, although the Payload Length field does not include the IP header. IPv6 supports jumbo payloads larger than the traditional 65,535 octets.At a minimum, all network links must support a maximum transmission unit (MTU) of at least 1280 octets.The IPv6 payload length includes any IPv6 header extensions,TCP or UDP headers, and any Application Layer headers that might be associated with the datagram.
• Next Header: 8 bits identifying the header immediately following the IPv6 header. Examples include TCP, UDP, Fragment, and Authentication.
• Hop Limit: 8 bits that specify the number of hops through which the packet can travel. Each router along the path decrements the field value by one until the value reaches zero, at which point the packet is discarded.This field is similar to the IPv4 TTL (Time To Live) field, with the exception that the seconds parameter has been eliminated and only the hops parameter is supported.
• Source Address: 128 bits (hexadecimal) containing the IP address of the source host.
• Destination Address: 128 bits (hexadecimal) containing the IP address of the destination host. IPv6 supports multiple extension headers. RFC 1883 recommends that they be placed in the following order:
• Hop-by-Hop Options: Optional information that must be examined by every node along a path taken by a packet.This header carries information such as the type of extension header immediately following, and specific instructions as to what should be done if the processing node does not recognize the Option Type, and whether or not the option data may change en route.This header also identifies the length of the Hop-by-Hop header, and contains padding options.
• Destinations Options: Optional information that must be examined by the destination host.This header carries information such as the type of header immediately following, the length of the Destination header, and padding options.
• Routing: This IPv6 source node uses this header to list one or more intermediate modes to be visited along the path the packet takes to its destination.
• Fragment: The IPv6 source node uses this header to send a packet larger than the path MTU will accommodate.All fragmentation occurs at the source node.
• Authentication: As defined in RFC 2402, this header contains a mechanism for ensuring the connectionless integrity and data origin authentication of IP datagrams, as well as an anti-replay option. This header might also include a non-repudiation mechanism, which provides the origination node with confirmation of packet receipt. Included in this header may be the authentication algorithm and keys, the encryption algorithm and keys, and other security-related parameters.
• Encapsulating Security Payload: As defined in RFC 2406, this header provides confidentiality through encryption, and limited confidentiality of the traffic flow. It also may provide connectionless integrity and data origin authentication of IP datagrams, as well as an anti-replay option. IPsec (IP security) is a standards-based security suite that operates transparently and may eliminate the need for proprietary firewall mechanisms in some applications. IPsec also provides for encapsulation of the secured IPv6 packets inside IPv4 datagrams, in consideration of both the increasing need for security and the long-term transition process to IPv6.
IPv6 addressing is considerably enhanced, in comparison to IPv4. Not only is the address space increased to 128 bits, but IPv6 also supports multiple address types, including anycast, multicast, and unicast. IPv6 offers highly flexible address assignment through two approaches. Stateful autoconfiguration dynamically assigns unique addresses to devices as they require them, drawing from a pool of such addresses. Stateless autoconfiguration employs two IP addresses, and is particularly advantageous in mobile applications. One address is assigned permanently to the mobile device, and another address is used to route data to the network to which the mobile device is connected at the time. See also algorithm, anycast, Application Layer, authentication, datagram, encryption, firewall, flow, hop, IETF, IPng, IPsec, IPv4, IPv6 address, jumbo payload, key, MTU, multicast, node, non-repudiation, payload, protocol, QoS, real-time, stateful autoconfiguration, stateless autoconfiguration, TCP, TTL, UDP, and unicast.
IPv6 address (Internet Protocol version 6 address) A binary number that uniquely identifies a host
computer connected to the Internet and running the IPv6 protocol suite.The IP packet header provides an
originating address field so that a host can identify itself as the originator of a packet.The IP packet header
also provides a destination address field so that an originating host can identity the target host for which a
packet is intended. Based on that information, the Internet routers can act to deliver the packet to the target
host, which can respond to the originating host, as appropriate.The IPv6 address field size is 128 bits, which
yields the theoretical potential for 2
128
or 340,282,366,920,938,463,463,374,607,431,768,211,456 unique
addresses.At this level, the dotted decimal notation convention employed in IPv4 becomes cumbersome, so
an IPv6 address comprises 8 sections separated by colons and expressed as
x:x:x:x:x:x:x:x
where each x represents 16 bits defined in hexadecimal notation. Following are example IPv6 addresses:
FEDC:BA98:7654:3210:FEDC:BA98:7654:3210
1080:0000:0000:0000:0008:0800:200C:417A
with each field given a value in decimal notation of 0–65,535, the range expressed by two octets in binary
notation (2
16
= 65,536, or 0–65,535). Leading zeros can be suppressed, which simplifies the latter above
address to the following:
1080:0:0:0:8:800:200C:417A
If one or more groups (sections) of 16 zeros appear in an address, they can be compressed through the
use of a :: (double colon) code.This compresses the above address to the following:
1080::8:800:200C:417A
Technically speaking, IPv6 addresses are assigned to interfaces, rather than nodes.The IPv6 addressing
architecture provides for unicast, multicast, and anycast addresses.
• Unicast: A unicast address is associated with a single interface that is associated with a single node, and can, in effect, identify the node. A unicast address can be of several types and here are also specialpurpose unicast subtypes, including IPv6 addresses with embedded IPv4 addresses.A global unicast address is a conventional, publicly routable address that can be used in the Internet or any public domain.A link-local address is similar to an IPv4 private IP address, as it is not meant to be routed, but confined to a single segment.A site–local address is used by an organization that has not yet connected to the Internet.A loopback address is used when a host needs to send a packet back to itself.
• Multicast: A multicast address identifies a group of nodes, each of which can belong to multiple groups.A packet sent to a multicast group is delivered to every interface in the group. Multicast addresses begin with the binary prefix 11111111.A multicast address essentially is a targeted version of an IPv4 broadcast address.
• Anycast: An anycast address is assigned to multiple interfaces, typically on multiple nodes.A packet with an anycast address is delivered to the closest interface with that address, as determined by the routing protocols measure of distance.Anycast addresses are allocated from the unicast address space.
IPv6 address types are defined in RFC 3513.The Internet Protocol version 4 (IPv4) addressing scheme is quite different. See also anycast address, binary, binary notation, broadcast, compression, computer, dotted decimal notation, hexadecimal notation, global unicast address, header, hexadecimal notation, host, interface, Internet, IPv4 address, link-local address, loopback address,multicast address, node, packet, protocol suite, router, site–local address, suppression, and unicast address.
IPX (Internetwork Packet eXchange) - The Network Layer (Layer 3) protocol in Novell NetWare
for exchanging packets between LANs. IPX is similar to the Internet Protocol (IP), but is not industry
standard and has been overwhelmed by IP. Sequenced Packet Exchange (SPX) is the associated Transport
Layer (Layer 4) protocol. See also IP, IPX/SPX, LAN, Network Layer, protocol, and SPX.
IPX/SPX (Internetwork Packet eXchange/Sequenced Packet eXchange) - The Network Layer
(Layer 3) and Transport Layer (Layer 4) protocols in Novell NetWare. IPX/SPX is similar to TCP/IP, but
is not industry standard and has been overwhelmed by the TCP/IP protocol suite. Novell currently supports the TCP/IP protocol suite. See also Network Layer, protocol, protocol suite, and TCP/IP.
Ir (Iridium) - A silver-white metallic element, iridium has 77 electrons around its nucleus and, therefore, is number 77 in the Periodic Table of Elements. (We used to refer to iridium as having an atomic
weight of 77, but that characterization is only relative and not absolute; the term, therefore, is obsolete.)
The name is from the Greek iridis, translating as rainbow, due to the fact that when iridium is dissolved in
hydrochloric acid, its salts are of various colors of the rainbow. Iridium is a component of extremely hard,
corrosion-resistant alloys used in pen nibs, jewelry, surgical instruments, watch and compass pivot bearings,
electrodes, and chemical crucibles.At one time, the official measurement of the meter was recorded as the
distance between two fine lines engraved on a platinum-iridium bar kept at the International Bureau of
Weights and Measures in Paris. See also Iridium.
IR - 1. InfraRed. Infrared light is in the frequency range of 300 GHz–400 THz and has a wavelength of
1 mm–0.75 mm (750 nm). EHF radio has applications in fiber optics and free space optics (FSO) transmission systems. Infrared light is at the very lower limit of the radio spectrum, just above extremely high
frequency (EHF) radio. See also EHF, electromagnetic spectrum, fiber optics, frequency, FSO, Hz, and wavelength.
2. Incremental Redundancy.Also known as Hybrid ARQ II.An enhanced automatic repeat request (ARQ)
technique employed in EGPRS (Enhanced General Packet Radio System), the packet-switched mode of
Enhanced Data rates for GSM Evolution (EDGE) cellular radio networks.As transmission begins, IR initially transmits packets with little forward error correction (FEC) overhead in an attempt to maximize
throughput. If the initial transmission cannot be successfully decoded by the receiver, IR ratchets up the
FEC overhead until it finds a level at which the receiver can successfully decode the transmission. See also
ARQ, cellular radio, EDGE, EGPRS, FEC, overhead, and throughput.
IRC (International Record Carrier) - A carrier that offers record communications services, which are
services that are designed or used primarily to transfer information that originates or terminates in written or graphic form. Examples of record communications services include telex and TWX. See also record
communications services, telex, and TWX.
iridium (Ir) - The silver-white metallic element with an atomic number of 77, Iridium is represented by
the symbol Ir. See also Ir.
Iridium - The first mobile satellite system (MSS) operating in low-Earth orbit (LEO). According to legend, the wife of a Motorola executive was vacationing in the Bahamas during 1987 and was irritated
by her inability to place a cellular telephone call. As the story goes, she complained to her husband, and
captured his imagination, so to speak. Motorola engineers subsequently determined that a constellation
of 77 communications satellites in non-geosynchronous low-altitude orbits would be sufficient to provide cellular-like service to essentially all dry land on the Earth’s surface. Motorola named its proposed 77-
satellite constellation Iridium, after the element iridium (Ir), which has 77 electrons whizzing around its
nucleus. Subsequently, the proposal was pared down to 66 operational satellites, although the name Iridium
stuck. After all, Iridium seems to roll off the tongue better than dysprosium (Dy), the rare earth element
with an atomic weight of 66. Dysprosium, by the way is from the Greek dysprositos, meaning hard to get
at, which is hardly a good name for a communications technology.The Iridium constellation is now fully
launched and is fully operational, with 11 operational satellites, and 1 spare, placed in each of the 6 orbital
planes, at altitudes of 421.5 nautical miles. Connectivity between each satellite and the Earth is established via 48 highly focused spot beams, each of which has a footprint of approximately 30 miles (50 km) in
diameter.Assuming line of sight (LOS) is available, the end user can connect directly from a satellite phone
to a satellite using the L-band, at frequencies of 1.616–1.6265 GHz. Alternatively the user can connect
from a landline through a local terrestrial gateway at Ka-band frequencies of 29.1–29.3 GHz on the uplink
and 19.4–19.4 GHz on the downlink.When connected to the satellite, the inter-satellite links operate in
the Ka-band, at frequencies of 23.18–23.38 GHz. Iridium is essentially a cellular telephone network in
reverse.The satellites are much like cellular base station transceivers that whiz around the Earth whereas
the user terminal device remains relatively stationary. Iridium applications go well beyond cellular telephony and currently include aviation and maritime applications such as aircraft and ship tracking and enroute voice, fax, and data communications between crews and terrestrial operations centers. See also base
station, cellular radio, downlink, footprint, GEO, Ka-band, L-band, LEO, LOS, MSS, spot beam, transceiver, and
uplink.
IRTF (Internet Research Task Force) - The group of the Internet Society (ISOC) that deals with longterm issues.The work of the IRTF is accomplished in small, focused research groups that work on topics
related to Internet protocols, applications, architecture, and technology. See also application, architecture,Internet, ISOC, protocol, and technology.
IS (Information Services) - The formal term for a data processing department, also known as Management Information Systems or Management Information Services (MIS). An IS department typically is responsible for all computer, network, and storage systems and technologies, from design through implementation
and support.The traditional term was Information Technology (IT).
IS-136 (Interim Standard 136) - An improvement to the IS-54 standard that added a digital control channel (DCCH) for residential and in-building coverage, increased battery standby time, text messaging, overthe-air activation, and circuit switched data (CSD) capabilities. See also CSD, DCCH, IS-54, and texting.
IS-2000-A (Interim Standard 2000-A) - In cellular radio systems, also known as 3x.An enhancement
to CDMA2000 that uses three cdmaOne carriers for total bandwidth of 3.75 MHz. See also bandwidth,
carrier, cellular radio, CDMA2000, and cdmaOne.
IS-54 (Interim Standard 54) - A 2G digital cellular radio standard from the Electronics Industry
Alliance (EIA) and Telecommunications Industry Association (TIA) and later approved by the American
National Standards Institute (ANSI) to officially become ANSI/TIA/EIA-567. IS-54 is an extension of
the analog Advanced Mobile Phone System (AMPS) and is commonly known as Digital AMPS (DAMPS) and United States Digital Cellular (USDC). IS-54 evolved into IS-136.The two standards jointly
specified the time division multiple access (TDMA) method and are often referred to as TDMA. See also
2G, ANSI, cellular radio, D-AMPS, EIA, IS-136, TIA, and TDMA.
IS-856 (Interim Standard 856) - A 3G digital cellular radio standard from the Electronics Industry
Alliance (EIA) and Telecommunications Industry Association (TIA) for what is more commonly known as
CDMA2000 (Code Division Multiple Access 2000). See also 3G, CDMA2000, cellular radio, EIA, and TIA.
iSCSI (internet Small Computer System Interface) - A network protocol specified by the Internet
Engineering Task Force (IETF) in RFC 3347 (July 2002) for the use of the Small Computer System Interface (SCSI) protocol over TCP/IP networks.As data exits the computer, headed toward the storage device,
a host bus adapter (HBA) converts the data to a SCSI format, enclosed in an Internet Protocol (IP) packet,
and transmitted over an Ethernet network.An advantage of iSCSI is that it is transparent, as the server software sees what looks to be a SCSI controller and the network sees only IP traffic.The protocols employed
at Layers 2, 3, and 4 are Ethernet, IP, and Transmission Control Protocol (TCP). Further, iSCSI is intended
to run at speeds up to 10 Gbps over 10 Gigabit Ethernet (10GigE), over IP wide area networks (WANs),
and at lower cost than Fibre Channel. See also 10 Gigabit Ethernet, IETF, IP, OSI Reference Model, protocol,
SCSI, TCP, Transport Layer, and WAN.
ISDN (Integrated Services Digital Network) - A set of ITU-T Recommendations describing a set
of interfaces for access to a digital public switched telephone network (PSTN) intended to provide ubiquitous access to a wide range of services, including voice, data, video, and multimedia.The I series ISDN
Recommendations map into the OSI Reference Model at the bottom three layers:
• Network Layer: The Q.931 specifications include user-to-user and network-to-network call control messages for both circuit-switched and packet-switched networking.
• Data Link Layer: ISDN specifies the Link Access Procedure, D Channel (LAPD). Issues of packetization, error control, and flow control are addressed.
• Physical Layer: Mechanical and electrical issues including connectors, signaling rates, line coding, and synchronization. ISDN Recommendations describe three types of channels:
• Bearer (B): Channels that bear the end user data, or payload.
• Data (D): Also known as Delta channels. Channels set aside for out-of-band signaling and control functions. D channels also can support low-speed end user packet data and telemetry applications.
• High-speed (H): Aggregations of B Channels (2 to 30) to accommodate bandwidth-intensive applications such as video.
The User Network Interface (UNI) is defined differently at two levels. Basic rate interface (BRI) for low-speed access at rates up to 128 kbps. Primary rate interface (PRI) is defined for high-speed access in North America at 1.544 Mbps. Primary rate access (PRA) is defined for high-speed access in European and other countries at 2.048 Mbps. Common Channel Signaling System #7 (SS7), which supports outof-band signaling and control, is a fundamental requirement of ISDN. Broadband ISDN (B-ISDN) is set of specifications from the ITU-T for an ISDN requiring transmission channels capable of supporting rates greater than the primary rate. See also bandwidth, B channel, B-ISDN, BRI, channel, circuit switch, Data Link Layer, D channel, H channel, I series, ITU-T, LAPD, Network Layer, OSI Reference Model, out-of-band signaling and control, packet switching, payload, Physical Layer, PRA, PRI, PSTN, SS7, and UNI.
ISDN Digital Subscriber Line (IDSL) - See IDSL.
ISDN modem - Synonymous with, and more correctly known as, Terminal Adapter (TA). See TA.
ISI (InterSymbol Interference) - Signal distortion caused by the overlap of symbols (i.e., the smallest
units transmitted) in a digital transmission system. Intersymbol interference includes the overlap of bits in
a purely digital transmission system, such as a fiber optic transmission system (FOTS), or sinusoidal waveforms in a digital system involving the modulation of a carrier waveform, such as a T-carrier or E-carrier
system. See also pulse dispersion.
ISLAN (Integrated Services Local Area Network) - Specified by the IEEE as 802.9 and also known
as IsoEthernet and IsoEnet. ISLAN is now considered obsolete. See also 802.9, IEEE, and IsoEthernet.
ISM (Industrial/Scientific/Medical) - Radio frequency (RF) bands in the 902–928 MHz, 2.4–2.5
GHz, and 5.8–5.9 GHz ranges. In the United States and most countries, these bands require no licensing.
As signal propagation characteristics are excellent at these relatively low frequencies (particularly in the
lower of the two bands), they are employed extensively in a wide variety of applications, including Wireless Local Area Networks (WLANs). See also propagation, RF, and WLAN.
ISO (International Organization for Standardization) - A network of the standards institutes of 157
countries. ISO is not an acronym. Rather, it is derived from the Greek isos, meaning equal, suggesting that
all members of the organization have an equal voice. ISO is a non-governmental organization intended to
serve as a bridge not only between countries, but between the governmental and private sectors. In the
context of telecommunications, ISO is perhaps best known for the development of the OSI Reference
Model. See Appendix A for contact information. See also OSI Reference Model.
ISO/IEC 11801 - An international standard from the International Organization for Standardization
(ISO) and the International Electrotechnical Commission (IEC), specifying general-purpose telecommunications structured cabling systems. The standards include both copper wire and optical fiber inside
cabling systems.The standard specifies classes of twisted pair copper performance, as follows:
Class A: # 100 kHz
Class B: # 1 MHz
Class C: # 16 MHz
Class D: # 100 MHz
Class E: # 250 MHz
Class F: # 600 MHz
ISOC (Internet Society) - A voluntary organization that lends formal structure to the administration of
the Internet. ISOC is the organizational home of the Internet Engineering Task Force (IETF), Internet
Architecture Board (IAB), Internet Engineering Steering Group (IESG), and Internet Research Task Force
(IRTF).The ISOC is active in such areas as censorship and freedom of expression, taxation, governance,
and intellectual property. ISOC has granted the IESG formal authority to make decisions on standards. See
also IAB, IESG, IETF, Internet, IRTF, and standards.
isochronous - From the Greek isos, meaning equal or uniform, and chronos, meaning time. 1. Equal in frequency, or periodicity. Uniform in time, having equal duration, or occurring at precise intervals. Isochronous communications, such as real-time audio and video, are stream-oriented, flowing at a constant and
regular pace, with each audio and video element being of equal importance.Therefore, each element (e.g.,
instant of audio or pixel of color) must be delivered to the receiver in exactly the sequence in which it
was presented to the transmitter and with no significant level of either latency (i.e., delay), or jitter (i.e.,
variation in delay). See also jitter, latency, near-realtime, and store-and-forward. 2. A type of digital circuit in
which the device on one end sets the bit rate for its own transmission and the receiving device copies that
bit rate when responding, but there is no clock signal on the circuit interface
IsoEnet (IsoEthernet) - See IsoEthernet.
IsoEthernet (Isochronous Ethernet) - Also known as IsoEnet and Integrated Services LAN (ISLAN).
Specified by the IEEE as 802.9 (1995), IsoEthernet was intended to support isochronous traffic such as
voice and videoconferencing over the same twisted pair as Ethernet.To traditional Ethernet at 10 Mbps,
IsoEthernet added 96 ISDN B channels and a single D channel, all of which are 64 kbps channels and all
of which share a cable using the 20 MHz signaling rate of 10BaseT Ethernet. The added B channels
increased the theoretical Ethernet transmission rate by 6.144 Mbps, bringing the aggregate nominal rate
to 16 Mbps.The individual B channels could be used for voice, or could be bonded for high speed videoconferencing. ISLAN is considered obsolete, having been overwhelmed by switched Ethernet at 100
Mbps, 1 Gbps, and even 10 Gbps. See also 10BaseT, 802.9, B channel, bonding, D channel, Ethernet, IEEE,
ISDN, and isochronous.
isotropic - 1. Having physical properties (e.g., conductivity, elasticity, and power density) that are the same
in any direction of measurement. 2. In telecommunications, an antenna, light source, or sound source that
theoretically radiates a signal with equal power density in all directions.A purely isotropic source does not
exist, except in theory. In telecommunications, as in all things natural and unnatural, perfection is purely
theoretical.
ISP - 1. InSide Plant.All of the telecommunications apparatus, equipment, wiring, and systems housed in
buildings. ISP includes the main distribution frame (MDF), intermediate distribution frames (IDFs), inside
wire and cable systems, switches and routers, multiplexers, storage batteries, backup power generators, and
related equipment. See also outside plant. 2. Internet Service Provider. A company that provides Internet
access services to end users.An ISP can be local, regional, national, or international in nature and can provide a wide range of access alternatives, including dial-up and ADSL. See also ADSL and dial-up.
IT (Information Technology) - The traditional, formal term for a data processing department. The
contemporary term is Information Services (IS).
ITA #2 (International Telegraph Alphabet #2) - See Baudot code.
ITU (International Telecommunication Union) - Chartered by the United Nations (UN), the ITUT primarily is responsible for setting recommendations intended to ensure the interconnectivity of
national telecommunications networks.Those recommendations are treated as standards in most countries.
The original predecessor organization was the International Telegraph Union (ITU), which was formed
in 1865 to ensure the interconnectivity of national telegraph networks.The ITU formed the International
Telephone Consultative Committee (CCIF) in 1924, the International Telegraph Consultative Committee (CCIR) in 1925, and the International Radio Consultative Committee (CCIR) in 1927. The ITU
changed its name in 1934 to the International Telecommunication Union and in 1956 the CCIT and
CCIF merged to form the International Telephone and Telegraph Consultative Committee (CCITT). In
1992, the ITU formed into three sectors, the ITU-Telecommunication (ITU-T), Radiocommunication
(ITU-R), and Telecommunication Development (ITU-D). See Appendix A for contact information. See
also ITU-D, ITU-R, and ITU-T.
ITU-D (International Telecommunication Union-Development Sector) - The sector of the ITU
that works to further telecommunications development around the world, especially in developing countries. See Appendix A for contact information. See also ITU.
ITU-R (International Telecommunication Union-Radiocommunication) - The sector of the
ITU that studies technical questions relating to radio communications and manages international radio frequency (RF) spectrum and satellite orbits.The ITU-R originally (1925) was the Comité consultatif international des Radiocommunications (CCIR), which translates from French as the International Radio
Consultative Committee. See Appendix A for contact information. See also ITU and RF.
ITU-T (International Telecommunication Union-Telecommunication Standardization Sector) -
The sector of the ITU that studies technical questions relating to telegraph and telephone communications
and establishes international telecommunications standards to ensure the interconnectivity of national networks.The ITU-T previously (1956) was known as the Comité consultatif international télégraphique et
téléphonique (CCITT), which translates from French as the International Telegraph and Telephone Consultative Committee.
| Series | Description |
|---|---|
| A | Organization of the work of ITU-T |
| B | Means of expression: definitions, symbols, classification |
| C | General telecommunication statistics |
| D | General tariff principles |
| E | Overall network operation, telephone service, service operation and human factors |
| F | Non-telephone telecommunication services |
| G | Transmission systems and media, digital systems and networks |
| H | Audiovisual and multimedia systems |
| I | Integrated services digital network (ISDN) |
| J | Cable networks and transmission of television, sound program and other multimedia signals |
| K | Protection against interference |
| L | Construction, installation and protection of cables and other elements of outside plant |
| M | Telecommunication management, including TMN and network maintenance |
| N | Maintenance: international sound programme and television transmission circuits |
| O | Specifications of measuring equipment |
| P | Telephone transmission quality, telephone installations, local line networks |
| Q | Switching and signaling |
| R | Telegraph transmission |
| S | Telegraph services terminal equipment |
| T | Terminals for telematic services |
| U | Telegraph switching |
| V | Data communication over the telephone network |
| X | Data networks, open system communications and security |
| Y | Global information infrastructure, Internet protocol aspects and next-generation networks |
| Z | Languages and general software aspects for telecommunication systems |
ITU-T Series Recommendations
IVD (Inside Vapor Deposition) - A commonly used technique for the mass production of glass optical fiber, IVD begins with heating silica and germanium dopant to the point of vaporization.As the glass
vapor cools, it is deposited as layers of soot on the inside of a rotating hollow glass cylinder, which typically remains as the outside cladding of the end product.The first layers deposited are cladding of relatively
pure silica.The final layer is germanium-doped silica, which forms the core. If the end product is to be a
step-index fiber, there is an abrupt change in the chemical composition between the core and cladding. If
the end product is to be a graded-index fiber, there will be many graded layers of silica of slightly different chemical compositions deposited on the cylinder wall to yield slightly and successively less pure layers
of cladding surrounding the fiber axis.The composition of the glass layers in a graded-index fiber is much
like the arrangement of the annular rings of a tree. Once the deposition process is complete, the entire
glass cylinder is sintered and collapsed into a preform cylinder, which is cooled and stored.The tip of the preform cylinder is reheated to a temperature of 2,500 degrees in a drawing tower.The resulting gob of
molten glass is carefully drawn by gravity, in a process known as broomsticking, into a fiber as long as 20
kilometers.As the fibers cool, an acrylate coating is applied to protect the raw glass from physical damage.
As is the case with all of these techniques, OVD takes place in a vacuum environment, as it is the exposure to oxygen that makes glass so brittle. Outside vapor deposition (IVD) is a similar process, with the
soot deposited on the outside of a rotating ceramic bait rod that is slipped out of the glass cylinder prior
to the formation of the preform cylinder. See also cladding, core, dopant,graded-index fiber, IVD, sintering, and
step-index fiber.
IVDS (Interactive Video and Data Services) - See 218–219 MHz Service.
IVR (Interactive Voice Response) - Interaction between a human and a computer in which the human
caller inputs commands and requests to the computer, which responds in either pre-recorded or synthesized speech form.The human input can be the form of spoken words or as tones sent via the telephone
keypad. If the input is speech, IVR is much like having a frustrating conversation with a dimwitted and
highly inflexible human call center agent. In a database access application, a voice processing system with
IVR capability is positioned as a front end to a general-purpose computer and multiple databases.Through
speech recognition technology, and text-to-speech (TTS) capability, and perhaps voice print matching for
security, a complete transaction can be accomplished on a voice basis without human involvement&except
for the caller, of course. Reservations centers and financial institutions make heavy use of such capabilities in support of routine transactions, thereby reducing staffing levels and providing customer service on
a 24 × 7 basis.Telephone companies increasingly use voice recognition technology to provide automated
access to directory databases.
IX (Internet eXchange) - An official Network Access Point (NAP) at which an Internet service
provider (ISP) can access the Internet backbone and exchange traffic with other ISPs. Some NAPs are
known as NAPs, some as Internet Exchanges (IXs), and some as MAEs.Tier 1 IXs are located in Amsterdam, The Netherlands (AMS-IX); London, England (LINX); Sophia-Antipolis, France (SFINX); Cape
Town and Johannesburg, South Africa (CINX and JINX); Hong Kong, Peoples Republic of China
(HKIX); and Tokyo, Japan (JPIX). See also Internet, ISP, MAE, and NAP.
IXC (IntereXchange Carrier, or IEC) - A company providing long haul telephone service between
local exchange carriers (LECs), that is, local telephony companies (telcos) or other providers of local telephone service. See also carrier, LATA, LEC, and long haul circuit.
l’Institut National de Recherche en Informatique et en Automatique (INRIA) - See INRIA.
