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Glossary of VOIP Terms - Page 3 |
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Gateway3 A gateway is an H.323 device that converts one form of media into another form, for example, PSTN voice into VoIP,
has a fair amount of intelligence, and can function on its own in a point-to-point situation. |
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H.248 The ITU-T protocol recommendation for the control of media gateways by media gateway controllers. See Megaco. |
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H.323 An ITU-T standard for handling video, data and voice call information. This standard was originally proposed for the
PictureTel system, which allowed video/voice calls, but has been enlarged to encompass many types of media devices.
This “protocol” is actually a umbrella for multiple protocols, each responsible for different items such as packet format
and transmission, video codecs, voice codecs, call signaling, conferencing, etc. Version 1 was formally approved in
1996 and the latest, version 4, was approved in November 2000. |
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Header The addressing and routing information contained at the beginning of a data packet. An IP packet header contains the
IP address of the source and destination systems along with hop counts, packet type, data bytes count, etc. An Ethernet
packet header contains the MAC (Media Access Control) addresses of the sending and receiving computers on the
Ethernet LAN along with a packet type and a count of the number of data bytes in the packet. |
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IETF The Internet Engineering Task Force is the organization responsible for defining standards that affect or use the IP
network. |
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In-band Signaling The use of tones to convey addressing information (ANI, destination number and information integer digits) in
conjunction with changes in the state of the circuit (T1 “A” and “B” bits, E&M E-lead and M-lead, etc.) Tones may be
MF or DTMF. |
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ILEC An Incumbent Local Exchange Carrier is the local telephone company originally granted a monopoly by the
government. See CLEC. |
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Interoperability Interoperability refers to the ability of a piece of equipment to interoperate with other equipment from different
vendors. For example, some VoIP gateways cannot interoperate with other vendors’ gateways even though they all
purpose to use the same signaling and transport protocols. This is often due to incomplete specifications or poor design
and implementation. Many gateways do not interoperate because the existing VoIP protocols were more concerned
with the basic issue of voice transport and do not consider higher-level issues such as call control and/or applications. |
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IP Internet Protocol is the base protocol upon which the Internet packet-based network operates. TCP, UDP, RTP and
SCTP all operate on top of IP and use it as their transport protocol. The IP protocol is not a reliable protocol, meaning
it does not guarantee delivery and receipt of a packet, which is what makes the public Internet IP network unreliabl |
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IP Network An Internet Protocol network is a packet-oriented network designed to transport packets of data between systems.
Systems are assigned IP addresses that identify them to the IP network. This network is not designed to reliably
transport packets between systems, i.e., it does not guarantee packets transmitted by one system will arrive at the
intended recipient system. It is left to higher-level protocols such as TCP to guarantee correct and reliable delivery. IP
packets are not related as far as the IP network is concerned. |
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ISC The International Softswitch Consortium is an organization of companies and other organizations that work on a set of
open standards for voice call control by softswitches. NACT is a member of this organization. |
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ISDN Integrated Services Digital Network is a point-to-point signaling protocol designed to interface PBX equipment with
central office switches. It uses out-of-band signaling on a data link that is carried with the bearer circuits. A U.S.
based ISDN PRI circuit is sometimes referred to as a 23B+D circuit, which means it is a T1 circuit that has 23 Bearer
circuits (DS0 channels) used for voice transport plus one Data circuit used to transport the ISDN signaling protocol
message data packets. |
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ISUP ISDN User Part is the network signaling protocol that sets up and tears down calls in the PSTN network using
messages transmitted between switches over the SS7 data network. The ISUP protocol is a connection-oriented or
circuit-oriented protocol, meaning that ISUP messages between systems are about connections or circuits between
them. ISUP messages do not stand on their own, meaning multiple messages will be sent and received concerning the
same connection or circuit in a specific order, each time the circuit is used for a call. ISUP messages are transported
over the SS7 network by the MTP3 or M3UA transport protocol layers. |
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ITU International Telecommunications Union—the international standards organization for all types of radio and telephony
telecommunications. |
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ITU-T International Telecommunications Union—Telecommunications sector. The part of the ITU responsible for both
circuit-switched and packet-switched telecommunications. |
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IXC An Interexchange Carrier is normally a long distance telephone company in the United States. It interconnects ILEC,
CLEC and other IXC switches to form the PSTN. |
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LAN A Local Area Network is a network within a small geographic area to which various devices such as computers and
printers are attached. Examples of LAN technologies are Ethernet, Arcnet, and IBM Token-ring.
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