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Glossary of VOIP Terms - Page 5 |
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SCCP - SCCP is the Signaling Connection Control Part protocol used to deliver transaction messages that do not perform call
setup and teardown, which is the responsibility of the ISUP protocol. It is connection-less, meaning each message
stands on its own and does not depend on any messages sent before or after it. |
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SCTP - SCTP is the Stream Control Transmission Protocol created for transmitting SS7 messages over the IP network. Since
the IP network does not guarantee the delivery of messages through the network, nor provides for redundant physical
paths through the network, the SCTP protocol performs these functions. |
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Signaling Gateway - A signaling gateway (SG) is an IETF and ISC concept. It is a device or computer that interfaces a softswitch with a
signaling system such as SS7. |
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SIP - Session Initiation Protocol is a protocol designed to allow personal computers to place telephone calls on the Internet.
It is often used by devices on the Internet and is currently used for telephone calls, most often “SIP-enabled”
telephones. It is proposed as a protocol for gateways, and especially for softswitches. Currently there are gateways
that interface with SIP-enabled telephones, but the SIP protocol really is not well-suited for control of a gateway by a
softswitch, which currently is a source of raucous debate within the VoIP community. |
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Softswitch - A softswitch is an IETF and ISC concept and a device or computer that controls the setup and teardown of calls in
media gateways. A softswitch has no network interface cards and call control software that tracks and controls calls in
other computers such as media gateways or media gateway controllers. |
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SS7 - Signaling System 7 is the international data network and signaling protocols that control the PSTN voice circuits and
calls. These protocols have country-by-country variations. ITU SS7 is the base on which the national variants are
based. ANSI SS7 is the North American SS7 variant. |
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SS7 Network - The Signaling System 7 network is a data network that transmits messages between switches and other computers used
in the PSTN. More than one message-based protocol can use the SS7 data network for transport of messages between
switches and computers. Examples of message-based protocols that use the SS7 data network are ISUP and TCAP.
SS7 messages are typically transmitted over redundant data links, often over dual point-to-point telephone lines using
modems (A-link) or through a DS0 channel on two T1 or E1 digital spans (F-link). |
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SS7 Point Code - The SS7 data network uses “point codes” to identify switches and computers connected to the SS7 data network. |
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Subscribers - The customers of a telephone company that are signed up for service. |
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Tandem Switch - A tandem switch interconnects with other PSTN switches. It is often called a “class 4” switch, a reference to the
original AT&T hierarchal network structure. |
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TCAP - Transaction Capabilities is a message-based protocol that is used to perform non-call services, such as Local Number
Portability database lookups, portable 800-number translation, etc. It transports its messages over the SCCP
connectionless-oriented protocol. |
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TCP - The Transmission Control Protocol is the IP protocol that guarantees delivery of a data packet from the sender to the
receiver. This is a “reliable” protocol that guarantees delivery and order of packets, but which has a lot of overhead
and can take a long time guaranteeing packet transmission. It is the protocol used on the public Internet with web
browser software. It is highly unsuitable for the transport of real-time data such as voice and video. |
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TDM - Time Division Multiplexing is the technique by which circuit-switched networks (PSTN) carry multiple voice calls
over a single physical circuit. This is accomplished by transmitting individual PCM samples from multiple calls in a
serial fashion 8,000 times per second for 24 calls on a T1 circuit and for 30 or 31 calls on an E1 circuit. |
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UDP - The User Datagram Protocol is the IP protocol that delivers data in the same manner in which it was sent (i.e., if the
sender transmits 20 bytes in a packet, they are delivered to the receiver as 20 bytes together). This is an “unreliable”
protocol that does not guarantee delivery or order of delivered packets, but which has little overhead. |
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Vocoder - Vocoder is an acronym for voice coder/decoder. A synonym is software codec. This is the term given to the process
of encoding and decoding voice using an algorithm implemented in software and/or hardware. The process is often
referred to as voice compression and decompression. Common vocoder algorithms are G.711 (PCM), G.723.1 (used
by Microsoft’s NetMeeting), G.726 (ADPCM, used by the NACT STX switch/IPAX gateway for voice message
playback), G.728 and G.729. This function is usually performed by hardware or DSP software. |
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VoIP - Voice over the IP network is a general term that refers to any means of converting voice calls into voice data packets
that are transmitted over an IP network, either public or private. |
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WAN - A Wide Area Network is a network that covers a large geographic area and interconnects many devices such as
computers, telephones, etc. A WAN often cannot use the same technologies as a LAN due to electrical or other
physical limitations. The two most well-known circuit-switched and packet-switched WANs are the PSTN and
Internet, respectively. |
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WAN Interface - A WAN interface is the hardware and software that converts data packets on a LAN to data packets on a WAN. This is
most often found in routers that convert from Ethernet LAN technology to T1/E1/OC3/OC12 technology.
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