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 out-of-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.

• United States Independent Telephone Association (USITA)
• United States Telecom Association (USTA)
• United States Time Division Multiple Access (US TDMA)
• UNI (User Network Interface)
• universal ADSL (universal Asymmetric Digital Subscriber Line Lite)
• Universal Character Set (UCS)
• Universal Code (Unicode)
• Universal Coordinated Time (UTC)
• Universal International Freephone Number (UIFN)
• Universal Mobile Telecommunications System (UMTS)
• Universal Plug and Play (UPnP)
• universal serial bus (USB)
• universal service
• Universal Service Administrative Company (USAC)
• Universal Service Fund (USF)
• University Corporation for Advanced Internet Development (UCAID)
• UNIX
• Unlicensed Mobile Access (UMA)
• Unlicensed National Information Infrastructure (U-NII)
• unshielded twisted pair (UTP)
• unsolicited grant service (UGS)
• unspecified bit rate (UBR)
• unsponsored domain
• UN (United Nations)
• update