VOIP Glossary of Terms Page 4 Q.931 ISDN connection control protocol, roughly comparable to TCP in the Internet protocol stack. Q.931 doesn't provide flow control or perform retransmission, because the underlying layers are assumed to be reliable and the circuit-oriented nature of ISDN allocates bandwidth in fixed increments of 64 kbps. Q.931 does manage connection setup and breakdown. In H.323 scenario, this protocol is encapsulated in TCP and sent to port 1720. Quality of Service A subjective rating of telephone communications quality in which listeners judge transmissions by qualifiers, such as excellent, good, fair, poor, or unsatisfactory. RBOC Regional Bell operating company (RBOC) is a term describing one of the U.S. regional telephone companies (or their successors) that were created as a result of the breakup of American Telephone and Telegraph Company (AT&T, known also as the Bell System or "Ma Bell") by a U.S. Federal Court consent decree on December 31, 1983. The seven original regional Bell operating companies were Ameritech, Bell Atlantic, BellSouth, NYNEX, Pacific Bell, Southwestern Bell, and US WEST. Each of these companies owned at least two Bell operating companies (Bell operating company). The BOCs were given the right to provide local phone service while AT&T was allowed to retain its long-distance service. The RBOCs and their constituent BOCs are part of the class of local exchange carriers (LECs). In addition to the RBOCs, there are more than 100 other franchised local telephone companies classed as local exchange carriers. Competitive local exchange carriers (CLECs) are additional companies allowed to compete with the LECs. These include AT&T in some localities and power companies. An interexchange carrier (IXC) is a long-distance carrier that carries traffic between LECs. Under the Telecommunications Act of 1996, RBOCs and LECs are allowed to compete for long-distance telephone traffic under certain circumstances. RBOCs are generally in competition for digital data and Internet traffic with wireless service providers and cable TV companies. RBOCs are gradually making available new telephone carrier technologies such as ISDN and DSL. Router A hardware and software system that directs data packets entering the router toward their intended destinations. Routers have various physical interfaces such as 100baseT Ethernet, T1, E1, DS3, OC-3, etc. Routing is based upon the destination address contained within the header of the IP data packet. RSVP Resource Reservation Protocol. Protocol that supports the reservation of resources across an IP network. Applications running on IP end systems can use RSVP to indicate to other nodes the nature (bandwidth, jitter, maximum burst, and so on) of the packet streams they want to receive. RSVP depends on IPv6. Also known as Resource Reservation Setup Protocol. RTP Real-Time Transport Protocol. Commonly used with IP networks. RTP is designed to provide end-to-end network transport functions for applications transmitting real-time data, such as audio, video, or simulation data, over multicast or unicast network services. RTP provides such services as payload type identification, sequence numbering, timestamping, and delivery monitoring to real-time applications. Session border controller (SBC) A new category of network equipment that enables interactive communications across IP network borders. SBCs closely integrate signaling and media control and serve as a transit point for all signaling and media streams going through the service provider's network. The ability to traverse firewalls and network address translators ensures ubiquity of network reach, whilst advanced routing and interworking capabilities maintain mission-critical quality of service. Session Initiation Protocol (SIP) 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. Signaling System 7 (SS7) The international data network and signaling protocols that control the PSTN voice circuits and calls, ensuring that calls are set up securely and efficiently. Although SS7 is an international telecommunications standard, it has country-by-country variations. Softswitch (Also referred to as media gateway controller or call agent). The generic name for a new approach to telephony switching that has evolved to enable transporting voice traffic over packet-switched networks. At the most basic level, a softswitch is defined as media gateway controller software that provides call control and resource management for a media gateway. Call control relates to the setup and termination of calls, including call routing. A softswitch also provides call authentication and authorization, and accounting services by accessing information available in an existing Signaling System 7 (SS7) network. TAPI Telephony API A programming interface that allows Windows client applications to access voice services on a server. T1 A 1.544 Mbps point-to-point dedicated, digital circuit provided by the telephone companies. The monthly cost is typically based on distance. T1 lines are widely used for private networks as well as interconnections between an organization's PBX or LAN and the telco. The first T1 line was tariffed by AT&T in January 1983. However, starting in the early 1960s, T1 was deployed in intercity trunks by AT&T to improve signal quality and make more efficient use of the network. A T1 line uses two wire pairs (one for transmit, one for receive) and time division multiplexing (TDM) to interleave 24 64-Kbps voice or data channels. The standard T1 frame is 193 bits long, which holds 24 8-bit voice samples and one synchronization bit with 8,000 frames transmitted per second. T1 is not restricted to digital voice or to 64 Kbps data streams. Channels may be combined and the total 1.544 Mbps capacity can be broken up as required. See DS, T-carrier, bipolar transmission, D4 and ESF. Time Division Multiplexing (TDM) The technique by which circuit-switched networks (PSTN) carry multiple voice calls over a single physical circuit. Trunk A communications channel between two points, typically referring to large-bandwidth telephone channels between switching centers that handle many simultaneous voice and data signals. Trunking Trunking means that several connections in a network may be established simultaneously, and that setup of connections proceeds automatically using the channels available at the time in question. In this way many users may share a few connections, and if the number of connections is increased, the capacity of the network is increased more than proportionally. This means that an optimal trunking effect is obtained in very large networks. UA User Agent. A SIP UA is a device that transmits SIP packets over IP. VoIP VoIP (voice over IP - that is, voice delivered using the Internet Protocol) is a term used in IP telephony for a set of facilities for managing the delivery of voice information using the Internet Protocol (IP). In general, this means sending voice information in digital form in discrete packets rather than in the traditional circuit-committed protocols of the public switched telephone network (PSTN). A major advantage of VoIP and Internet telephony is that it avoids the tolls charged by ordinary telephone service. In addition to IP, VoIP uses the real-time protocol (RTP) to help ensure that packets get delivered in a timely way. Using public networks, it is currently difficult to guarantee Quality of Service (QoS). Better service is possible with private networks managed by an enterprise or by an Internet telephony service provider (ITSP). VoIP Trunking Service providers can use this application to connect enterprise and call center customers directly to their VoIP network. By bypassing local operators and toll charges, the VoIP Trunking application enables service providers to offer attractive termination rates for both domestic and international long distance calling. This application connects seamlessly to the enterprise/call center's PBX, allowing employees to make off-net calls at reduced rates.         <Prev Next>