Idle Cell-IMA

Idle Cell -IMA

Idle Cell

An ATM cell used for cell stuffing where rate adaption is required. As Physical Layer cells, idle cells are required and cannot, therefore, be replaced by assigned cells during the process of cell multiplexing; this is unlike Unassigned Cells , which are not necessary at a network level and which can be replaced, therefore. See also ATM Reference Model, Physical Layer, Rate Adaption and Unassigned Cell.

Idle Channel Code

A repetitive pattern (code) that identifies an idle channel.

Idle Channel Noise

Noise which exists in a communications channel when no signals are present.

Idle Line Termination

An electronic network which is switch controlled to maintain a desired impedance at a trunk or line terminal when that terminal is in an idle state.

Idling Signal

Any signal that indicates no data is being sent.

IDN

Integrated Digital Network.

IDNX

1. International Data Exchange Network.

2. Integrated Digital Network eXchange.

IDP

InterDigital Pause.

IDR

Intermediate Data Rate.

IDS

1. Internal Data Services.

2. Intrusion Detection Service.

IDSL

A xDSL variant that uses ISDN BRI (Basic Rate Interface) technology to deliver transmission speeds of 128 Kbps on copper loops as long as 18,000 feet. IDSL is symmetric, i.e., equal bandwidth is provided in both directions. IDSL is a dedicated service for data communications applications, only. In that respect, IDSL differs from ISDN, which fundamentally is a circuit-switched service technology for voice, data, video and multimedia applications. IDSL terminates at the user premise on a standard ISDN TA (Terminal Adapter). At the LEC CO, the loop terminates in collocated ISP electronics in the form of either an IDSL access switch or a IDSL modem bank connected to a router. The connection is then made to the ISP POP via a high-bandwidth dedicated circuit. IDSL is used by LECs to deliver relatively low speed DSL services in geographic areas where ISDN technology is in place, but ADSL technology is not. See also xDSL, ADSL, BRI, ISDN, HDSL, RADSL, SDSL, Terminal Adapter, and VDSL.

IDT

1. Inter-DXC Trunk.

2. Inter-Machine Digital Trunk.

IDTS

Integrated Data Test System. A software package that allows the user to test Analog, Digital, Fractional T-1, and T-1 Circuits, remotely, at the various MCI terminal locations.

IDTV

Improved Definition TeleVision. See Improved Definition Television.

IDU

1. Interface Data Unit: The unit of information transferred to/from the upper layer in a single interaction across the SAP. Each IDU contains interface control information and may also contain the whole or part of the SDU.

2. Indefeasible Right of Use. A right to use something, which right cannot be taken away from you, i.e. voided or undone. A term that generally applies, in contemporary terms, to the purchase of an optical fiber within a sheath of fibers owned by another company. Companies that lay optical fiber generally lay much more than they need. They do so because so much of the cost is associated with securing the right-of-way, trenching, burying conduit, etc. So they "lay a lot of pipe," much of which initially is left "dark" (i.e., inactive). They then are in a position to either lease or sell the extra fibers, and the bandwidth they represent. If you buy, rather than lease, a fiber, you have an IRU.

IE

Incoming Exclusion.

IEC

1. InterExchange Carrier. Also called an IXC (as in IntereXchange Carrier). In practice, an IEC or IXC is any common carrier authorized by the FCC to carry customer transmissions between LATAs. In practice this means anyone and his brother who print up stationery, rent a few lines and proclaim themselves to be in the long distance phone business. Except for AT&T, regulation of long distance carriers by the FCC is perfunctory. It is less perfunctory by the local state authorities, some of whom still think competition in telecommunications is a mild form of insanity.

2. International Electrotechnical Commission. The international standards and conformity assessment body for all fields of electrotechnology, including electricity and electronics. The IEC publishes a number of international standards and technical reports on a wide variety of subjects including telecommunications (LANs, MANs and WANs), video cameras , electrical cables, communications protocols (e.g., HDLC), Open Systems Interconnection (OSI), optical fiber cables and connectors, and diagnostic X-ray imaging equipment. www.iec.ch.

IEEE

Institute of Electrical and Electronics Engineers , Inc. IEEE, founded in 1884, says it's the world's largest technical professional society, consisting of over 320,000 members in 147 countries . The IEEE's technical objectives "focus on advancing the theory and practice of electrical, electronics and computer engineering and computer science." The IEEE sponsors technical symposia, conferences and local meetings, and publishes technical papers. It also is a significant standards-making body responsible for many telecom and computing standards, including those standards used in LANs ” e.g. the 802 series. www.ieee.org.

IEEE 1394

Also called Firewire. An IEEE data transport bus that supports up to 63 nodes per bus, and up to 1023 buses. The bus can be tree, daisy chained or any combination. It supports both asynchronous and isochronous data. 1394 is a complementary technology with higher bandwidth (and associated cost) than Universal Serial Bus. For a bigger explanation, see 1394 and USB.

IEEE 488

IEEE 488 is the most widely-used international standard for computer-to-electronic instrument communication. It is also known as GPIB and HPIB.

IEEE 802

The main IEEE standard for local area networking (LAN) and metropolitan area networking (MAN), including an overview of networking architecture. It was approved in 1990. See 802.

IEEE 802.1

This IEEE committee defines the LAN Management and bridging standards.

IEEE 802.1d

An algorithm, the original version of which was invented by Digital Equipment Corporation, that is used to prevent bridging loops by creating a spanning tree. The algorithm is now documented in the IEEE 802.1d specification, although the Digital algorithm and the IEEE 802.2 handles errors, framing, flow control, and the Layer 3 service interface.

IEEE 802.11

See 802.11b.

IEEE 802.2

A data link layer standard used with the IEEE 802.3, 802.4 and 802.5 standards. 802.2 is the more modern form of 802.3. Novell recommends that it be used on its NetWare networks in preference to the 802.3 (which will still work). Most Ethernet networks support both 802.2 and 802.3. For more on the 802 series, see the numbers definitions at the front of this dictionary.

IEEE 802.3

A Local Area Network protocol suite commonly known as Ethernet. Ethernet has either a 10 Mbps or 100 Mbps throughput and uses Carrier Sense Multiple Access bus with Collision Detection CSMA/CD. This method allows users to share the network cable. However, only one station can use the cable at a time. A variety of physical medium dependent protocols are supported. This is the most common local area network specification. For a much fuller explanation, see Ethernet.

IEEE 802.3 1Base5

IEEE standard for baseband Ethernet at 1 Mbps over twisted pair wire to a maximum distance of 500 meters . Also called Starlan.

IEEE 802.3 10Base-5

IEEE standard for baseband Ethernet at 10 Mbps over coaxial cable to a maximum distance of 500 meters.

IEEE 802.3 10Base-T

Also called 802.3i. 10Base-T is an IEEE standard for operating Ethernet local area networks (LANs) on twisted-pair cabling using the home run method of wiring (exactly the same as a phone system uses) and a wiring hub that contains electronics performing similar functions to a central telephone switch. The full name for the standard is IEEE 802.3 10Base-T. The 10Base-T standard, issued in the fall of 1990, defined the requirements for sending information at 10 million bits per second on ordinary unshielded twisted-pair cabling. The 10Base-T standard defines various aspects of running Ethernet on twisted-pair cabling such as:

• Connector types (typically eight-pin RJ-45),

• Pin connections (1 and 2 for transmit, 3 and 6 for receive),

• Voltage levels (2.2 volts to 2.8 volts peak), and

• Noise immunity requirements to filter outside interference from telephone lines or other electronic equipment.

Ethernet is the most popular LAN in the world. Ethernet running on loop coaxial cable ” typically called thin Ethernet or thinnet ” is the most popular way of running Ethernet local area networks. Loop networks suffer from the major problem that one cut in the cable can destroy the complete network. 10Base-T is a much more reliable ” though more expensive ” way of connecting LANs, since it requires electronics at the center of the home run. As I write this, the most common form of 10Base-T electronics is a small box joining about 12 workstations together. To get more on the LAN, you simply daisy chain the boxes together. The boxes are unbelievably reliable. They're easy to install and they often come with LAN management software, which gives you statistics on who's using the network, for how long, what the performance is, and what potential problems might crop up, etc. The cable 10Base-T networks use to connect between their central electronics and their attached workstations is typically standard twisted pair phone wiring, which is a lot easier to install than coaxial cable. 10Base-T networks are now becoming most popular and are being installed at faster rate than old-style loop coaxial wired LANs. For a fuller explanation see Ethernet.

IEEE 802.3 10Broad36

This IEEE standard describes a long-distance type of Ethernet cabling with a 10-megabit-per-second signaling rate, a broadband signaling technique, and a maximum cable-segment distance of 3,600 meters.

IEEE 802.3b

IEEE standard for 10Broad36. Approved in 1985, it is the standard for broadband Ethernet at 10 Mbps over coaxial cable to a maximum distance of 3600 meters. It was incorporated into ISO/IEC 8802-3.

IEEE 802.3c

IEEE standard for 10 Mbps baseband repeaters. The standard was approved in 1985, and is incorporated into ISO/IEC 8802-3.

IEEE 802.3d

IEEE standard for media attachment devices and baseband media over fiber optic repeater links. Approved in 1987, it has been incorporated into ISO/IEC 8802- 3.

IEEE 802.3e

IEEE standard for 1Base-5, baseband Ethernet at 1 Mbps over twisted pair wire to a maximum distance of 500 meters. Also called Starlan. The standard addresses physical media, physical signaling and media attachment. Approved in 1987, it is incorporated into ISO/IEC 8802-3.

IEEE 802.3h

Standard for layer management in CSMA/CD networks. Approved in 1990, it has been incorporated into ISO/IEC 8802-3.

IEEE 802.3i

The IEEE standard addressing multisegment 10 Mbps networks, and twisted-pair media for 10Base-T networks. 10Base-T is an IEEE standard for operating Ethernet local area networks (LANs) on twisted-pair cabling using the home run method of wiring (exactly the same as a phone system uses) and a wiring hub that contains electronics performing similar functions to a central telephone switch. The full name for the standard is IEEE 802.3 10Base-T. The 10Base-T standard, issued in the fall of 1990, defined the requirements for sending information at 10 million bits per second on ordinary unshielded twisted-pair cabling; the standard has been incorporated into ISO/IEC 8802-3. The 10Base-T standard defines various aspects of running Ethernet on twisted-pair cabling such as:

• Connector types (typically eight-pin RJ-45),

• Pin connections (1 and 2 for transmit, 3 and 6 for receive),

• Voltage levels (2.2 volts to 2.8 volts peak), and

• Noise immunity requirements to filter outside interference from telephone lines or other electronic equipment.

Ethernet is the most popular LAN in the world. Ethernet running on loop coaxial cable ” typically called thin Ethernet or thinnet ” is the most popular way of running Ethernet local area networks. Loop networks suffer from the major problem that one cut in the cable can destroy the complete network. 10Base-T is a much more reliable ” though more expensive ” way of connecting LANs, since it requires electronics at the center of the home run. As I write this, the most common form of 10Base-T electronics is a small box joining about 12 workstations together. To get more on the LAN, you simply daisy chain the boxes together. The boxes are unbelievably reliably. They're easy to install and they often come with LAN management software, which gives you statistics on who's using the network, for how long, what the performance is, and what potential problems might crop up, etc. The cable 10Base-T networks use to connect between their central electronics and their attached workstations is typically standard twisted pair phone wiring, which is a lot easier to install than coaxial cable. 10Base-T networks are now becoming most popular and are being installed at faster rate than old-style loop coaxial wired LANs. For a fuller explanation see Ethernet.

IEEE 802.3j

IEEE standard for 10Base-F, which provides for fiber optics links connecting 10 Mbps active and passive starbased baseband networks. The standard was approved in 1993 and is incorporated into ISO/IEC 8802-3.

IEEE 802.3k

IEEE standard for layer management for repeaters in 10 Mbps baseband networks. It was approved in 1992 and is incorporated into ISO/IEC 8802-3.

IEEE 802.3l

A conformance statement for the media attachment unit protocol for 10Base-T networks. The statement was approved in 1992 and is incorporated into ISO/IEC 8802-3.

IEEE 802.3p

IEEE standard for media attachment unit layer management for 10 Mbps baseband networks. The standard was approved in 1992 and is incorporated into ISO/IEC 8802-3.

IEEE 802.3q

Provides guidelines for the development of managed objects. Approved in 1993, it was incorporated into ISO/IEC 8802-3.

IEEE 802.3r

IEEE standard for CSMA/CD and physical media specifications for 10Base-5, which is baseband Ethernet at 10 Mbps over fat coaxial cable to a maximum distance of 500 meters. This version of the original Ethernet standard was updated in 1996.

IEEE 802.3t

Standard for 120-ohm cables in 10Base-T simplex links. Approved in 1995, it was incorporated into ISO/IEC 8802-3.

IEEE 802.3u

A supplement to 802.3 that governs Carrier Sense Multiple Access/Collision Detection (CSMA/CD) for 100 Mbps networks, i.e., 100Base-T, commonly known as Fast Ethernet. Approved in 1995, this supplement covers the specification's MAC parameters, the physical layer, and repeaters for 100Base-T4, TX, and FX.

IEEE 802.3v

IEEE standard for 150-ohm cables in 10Base-T link segments. Approved in 1995, it was incorporated into ISO/IEC 8802-3.

IEEE 802.3z

Gigabit Ethernet over fiber standard, ratified on June 29, 1998. See Gigabit Ethernet.

IEEE 802.4

A physical layer standard specifying a LAN with a token-passing access method on a bus topology. Used with Manufacturing Automation Protocol (MAP) LANs. Arcnet can work this way. Typical transmission speed is 10 megabits per second.

IEEE 802.5

A physical layer standard specifying a LAN with a token-passing access method on a ring topology. Used by IBM's Token Ring hardware. Typical transmission speed is 4 or 16 megabits per second. Typical topology is star.

IEEE 802.6

This IEEE standard for metropolitan area networks (MANs) describes what is called a Distributed Queue Dual Bus (DQDB). The DQDB topology includes two parallel runs of cable ” typically fiber-optic cable ” linking each node (typically a router for a LAN segment) using signaling rates in the range of 100 megabits per second.

IEEE 802.9

This IEEE committee deals with integrated voice and data LANs, i.e. Isochronous Ethernet.

IEEE 802.10

This committee deals with LAN security.

IEEE-SA

The IEEE Standards Association (IEEE-SA), an internationally recognized standards-setting body, develops consensus standards through an open process that brings diverse parts of an industry together. It has a portfolio of more than 870 completed standards and more than 400 in development. IEEE-SA promotes the engineering process by creating, developing, integrating, sharing and applying knowledge about information technologies and sciences for the benefit of humanity and the profession. www.standards.ieee.org.

IEN

Internet Experimental Note. A standards document similar to an RFC, and is available from the Network Information Center (NIC). IENs contain suggestions and proposals for Internet implementations or specifications.

IEPG

Internet Engineering Planning Group. A group primarily composed of Internet service operators. Its goal is to promote a globally coordinated Internet operating environment. Membership is open to all.

IES

1. Inter-Enterprise Systems is EDI (Electronic Data Interchange) and inter-company electronic mail, fax, electronic funds transfer, videotex/online databases and the exchange of CAD/CAM graphics. See also EDI.

2. Information Exchange Services.

IESS

INTELSAT Earth Station Standard.

IETF

Internet Engineering Task Force. Formed in 1986 when the Internet was evolving from a Defense Department experiment into an academic network, the IETF is one of two technical working bodies of the Internet Activities Board. Comprised entirely of volunteers, the IETF meets three times a year to set the technical standards that run the Internet. The actual technical work is done by IETF working groups, which are grouped into areas of interest such as routing, transport, and security. The working groups seek the advice of the Internet community through draft RFCs (Requests For Comment), and then submit their recommendations to the IETF for final approval. The final standards are then published as standard RFCs. Of late, the IETF has been the forum where engineers and programmers have cooperated to solve the succession of crises caused by the Internet's phenomenal growth. Examples of IETF standards include DHCP (Dynamic Host Configuration Protocol), IPv6 (Internet Protocol version 6), LDAP (Lightweight Directory Access Protocol), and MPLS (MultiProtocol Label Service).

The IETF working groups are grouped into areas, and managed by Area Directors, or ADs. The ADs are members of the Internet Engineering Steering Group (IESG). Providing architectural oversight is the Internet Architecture Board, (IAB). The IAB also adjudicates appeals when someone complains that the IESG has failed. The IAB and IESG are chartered by the Internet Society (ISOC) for these purposes. The General Area Director also serves as the chair of the IESG and of the IETF, and is an ex-officio member of the IAB. The Internet Assigned Numbers Authority (IANA) is the central coordinator for the assignment of unique parameter values for Internet protocols. The IANA is chartered by the Internet Society (ISOC) to act as the clearinghouse to assign and coordinate the use of numerous Internet protocol parameters. First-time attendees might find it helpful to read The Tao of the IETF. www.ietf.org.

IF

See Intermediate Frequency.

IFC

Information From Controller.

IFCC

Internet Fraud Complaint Center. A partnership of the FBI and the NW3C, the National White Collar Crime Center. IFCC's mission is to address fraud committed over the Internet. For victims of Internet fraud, IFCC provides a convenient and easy-to-use reporting mechanism that alerts authorities of a suspected criminal or civil violation. For law enforcement and regulatory agencies at all levels, IFCC offers a central repository for complaints related to Internet fraud, works to quantify fraud patterns, and provides timely statistical data of current fraud trends. www.ifccfbi.gov.

IFFT

Inverse Fast Fourier Transform. See Fast Fourier Transform.

IFG

The minimum idle time between the end of one frame transmission and the beginning of another. On Ethernet 802.3 LANs the minimum interframe gap is 9.6 micro-seconds.

IFIP

International Federation for Information Processing. A research organization that performs substantive pre-standardization work for OSI. IFIP is noted for having formalized the original Message Handling System (MHS) model. www.dit.upm.es/~cdk/lflp.html.

IFITL

Integrated Fiber in the Loop.

IFP

Internet Fax Protocol is specified in ITU-T recommendation T.38 as the method for supporting facsimile transmissions over IP (Internet Protocol) networks. See also T.37 and T.38.

IFRB

International Frequency Registration Board.

IFS

International Freephone Service. See Freephone and IFTS.

IG

Isolated Ground. In AC electricity, an isolated ground is a type of outlet characterized by the following features and uses:

• It may be orange and must have a Greek "delta" on the front of the outlet. (A delta looks like a triangle.)

• It must be grounded by an insulated green wire.

• It must have insulation between the ground terminal and the mounting bracket .

• It is used primarily to power electronic equipment because it reduces the incidence of electrical "noise" on the ground path .

IGMP

Internet Group Management Protocol. A protocol used by IP hosts and gateways to report their multicast group memberships. When used in concert with a multicast protocol, the IP-based network can support multicasting. See Multicast.

Ignition Key

A rod arranged to strike the arc in an arc generator of high frequency currents.

IGP

1. Interior Gateway Protocol. The protocol used to exchange routing information between collaborating routers in the Internet. RIP and OSPF are examples of IGPs.

2. Integrated Graphics Processor.

IGRP

Interior Gateway Routing Protocol. A distance-vector routing protocol developed by Cisco Systems for use in large, heterogeneous networks. It learns the best routes through a LAN or the Internet.

IGT

Ispettorato Generale delle Telcomunicazioni (General Inspectorate of Telecommunications, Italy).

IGW

International Gateway Switch.

III

Information Industry Index.

IILC

Information Industry Liaison Committee (part of ATIS). See Exchange Carriers Standards Association.

IINREN

Interagency Interim National Research and Education Network. Evolving operating network system. Near term research and development activities will provide for the smooth evolution of this networking infrastructure into the future gigabit NREN. See NREN.

IIR

Interactive Information Response.

IIS

Microsoft Windows NT's Internet Information Server, which is similar to Netscape's Webserver. IIS lets you set up a web site and control and manage it remotely though the Internet, assuming you have a necessary privileges and a Web browser.

IISP

1. The Information Infrastructure Standards Panel formed by ANSI in July 1994 to accelerate the development and acceptance of standards critical to the establishment and deployment of the information superhighway. See ANSI.

2. Interim Interface Signaling Protocol. A call routing scheme used in STM networks. Formerly known as PNNI Phase 0. IISP is an interim technology meant to be used pending completion of PNNI Phase 1. IISP uses static routing tables established by the network administrator to route connections around link failures.

IITF

Information Infrastructure Task Force. This task force of high level representatives from federal agencies was formed by the Clinton Administration to identify and address the issues of creating a National Information Infrastructure. The Task Force relies on the members of the Industry Advisory Council as it assesses the requirements of individuals and businesses that will shape future networks. See also National Information Infrastructure.

IIW

The ISDN Implementors Workshop, a group within the North American ISDN Users Forum.

IKE

Internet Key Exchange. IKE is an IPsec (Internet Protocol security) mechanism that is used to create SAs (Security Associations) between two entities in an IP-based VPN (Virtual Private Network) application. IKE sets up a secure tunnel between the entities, authenticating their identities, negotiating the SAs, and exchanging shared key material between them in order that data can be encrypted and decrypted by those with privileged data access. As a dynamic key exchange mechanism, IKE relieves the users from the drudgery of manually configuring the SAs, which process is difficult and labor- intensive . See also Authentication, IPsec, Tunneling, and VPN.

IKP

Internet Keyed Payments Protocol. An architecture for secure payments over the Internet in the general context of Electronic Commerce. iKP is a public-key cryptography which defines transactions of a credit card nature, where a buyer and seller interact with a third party, such as a credit card company, in order to authorize transactions on a secure basis. SEPP (Secure Electronic Payment Protocol) is a standard implementation of iKP. iKP specifies RSA as the public-key encryption and signature algorithm. See also Electronic Commerce, RSA and SEPP.

ILA

Intermediate Light Amplification. Several backbone telecommunications carriers use this term to refer to "repeater" points along their fiber network; points from which shunts to other networks can easily be derived.

ILAN

A protocol independent router for token ring and Ethernet networks from CrossComm Corporation, Marlboro, MA.

ILCR

International Least Cost Route.

ILD

Injection Laser Diode.

ILEC

An Incumbent Local Exchange Carrier is the dominant phone carrier within a geographic area as determined by the FCC. Section 252 of the Telecommunications Act 1996 defines Incumbent Local Exchange Carrier as a carrier that, as of the date of enactment of the Act, provided local exchange service to a specific area. The Act provided that the Commission may treat "comparable carriers as incumbents" if they either "occupy a position in the market for telephone exchange service within an area that is comparable to the position occupied by the ILEC or such a "carrier that has substantially replaced an ILEC...." or if "such treatment is consistent with the public interest..." See also CLEC, Colocation and ELEC.

ILLP

Inter Link-to-Link Protocol.

ILMI

Interim Link Management Interface: An ATM Forum-defined interim specification for network management functions between an end user and a public or private network and between a public network and a private network. ILMI is based on a limited subset of SNMP capabilities.

ILNP

Interim Line Number Portability.

ILS

1. Input buffer Limiting Scheme. A flow control scheme used in data communications that blocks overload by limiting the number of blocks arriving at a buffer.

2. Instrument Landing System.

3. Internet Locator Service. In a September 1997 White Paper on "IP Telephony," Microsoft wrote, "User-to-IP mapping information is stored and continually refreshed using the Internet Locator Service (ILS) Dynamic Directory, a real-time server component of the Active Directory, which is part of Windows NT."

ILSR

IPX Link State Router. Novell's improvement on its RIP distance vector-based routing protocol.

ILT

Idle Line Termination.

IM

Instant Messaging.

IMA

1. Interactive Multimedia Association. Formed in 1991 (rooted in IVIA, Interactive Video Industry Association), an industry association chartered with creating and maintaining standard specifications for multimedia systems. www.ima.org.

2. Inverse Multiplexing over ATM. You have a high speed data stream. But not a high speed transmission link. You have several low speed links. Inverse multiplexing lets you join several slow speed links together and pretend that they're one high speed link. Here's a formal definition. IMA is an access specification approved in 1997 by the ATM Forum. This User Network Interface (UNI) standard allows a single ATM cell stream to be split across multiple access circuits from the user site to the edge of the carrier's ATM network. In an ATM LAN application, for instance, the ATM switch deployed in the enterprise backbone typically operates at 155 million bits per second or 622 Mbps. In this example, ATM traffic from the enterprise to the public ATM carrier-based network, requires 6 Mbps ” well more than the 1.544 million bits per second provided by a T-1, but less than a full T- 3 (which is 45 million bits per second). Rather than subscribing to a T-3, which requires a fiber optic access circuit and is very expensive, IMA is used. Thereby, the ATM data stream is split across four T-1 circuits by an access concentrator which possesses IMA capability. The IMA process works in a round- robin fashion, with cell number 1 traveling over T-1 number 1, cell #2 traveling over T-1 #2, and so on. Each of the four T-1 circuits is relatively inexpensive, can be provisioned over twisted-pair, and is readily available. At the edge of the carrier network, the ATM switch receives each of the four separate data streams, and reverses the IMA process to put the original datastream back together, which is then switched and transported through the network to the far edge. At that far edge, the IMA process may take place again, from the edge of the carrier network, over four T-1s, and to the IMA-capable ATM concentrator on the user premises. IMA is specified in the ATM forum specification AF-PHY-0086.000 Inverse Multiplexing for ATM Specification Version 1.0 and dated July 1997. Go to ftp://ftp.atmforum.com/pub/approved- specs /af-phy-0086.000.pdf to read and download a copy of the 140-page document. The definition of IMA is not easy. One reader, Rosario Brinquis of Madrid Spain, has contributed the following definition, which he thinks really captivates the essence of IMA: A methodology is described which provides a modular bandwidth for user access to ATM networks and for connection between ATM network elements at rates between the traditional order multiplex levels, for instance, between the DS1/E1 and DS3/E3 levels in the asynchronous digital hierarchies. DS3/E3 links are not necessarily readily available throughout a given network and therefore the introduction of ATM Inverse Multiplexers provides an effective method of combining the transport bandwidths of multiple links (e.g., DS1/E1 links) grouped to collectively provide higher intermediate rates.

   See also ATM, Inverse Multiplexer and TDM.