PDF of this tutorialACF (Admission Confirmation)
The confirmation message in response to an H.323 ARQ.
ARQ (Admission Request)
An H.323 message from an H.323 endpoint to an H.323 gatekeeper, requesting the IP address of a remote device.
DNS (Domain Name System)
System used in the Internet for translating names of network nodes into addresses.
DTMF (Dual Tone Multifrequency)
Use of two simultaneous voice-band tones for dialing (such as touch tone.)
H.248
An ITU recommendation that defines “gateway control protocol.” H.248 is the result of a joint collaboration between the ITU and the IETF. It is also referred to as IETF RFC 2885 (MEGACO), which defines a centralized architecture for creating multimedia applications, including VoIP. In many ways, H.248 builds on and extends MGCP.
H.323
H.323: An ITU recommendation that defines “packet-based multimedia communications systems.” In other words, H.323 defines a distributed architecture for creating multimedia applications, including VoIP. H.323 is an extension of the ITU–T standard H.320 that enables videoconferencing over LANs and other packet-switched networks, as well as video over the Internet.
IETF (Internet Engineering Task Force)
A community of engineers that seeks to determine how the Internet and Internet protocols work, as well as to define the prominent standards. This task force consists of more than 80 work groups and operates under the auspices of ISOC (Internet Society, an international nonprofit organization, founded in 1992, that coordinates the evolution and use of the Internet. They are headquartered in Reston, Virginia, United States).
IMT (Inter-Machine Trunk)
The bearer channels associated with SS7 links.
IP (Internet Protocol)
Network layer protocol in the TCP/IP stack offering a connectionless internetworking service. IP provides features for addressing, type-of-service specification, fragmentation and reassembly, and security.
ISDN (Integrated Services Digital Network)
Communication protocol, offered by telephone companies, that permits telephone networks to carry data, voice, and other source traffic.
ITU (International Telecommunication Union)
An international organization within the United Nations System (http://www.unsystem.org) where governments and the private sector coordinate global telecom networks and services (a function formerly performed by the CCITT, Consultative Committee for International Telegraph and Telephone).
LCF (Location Confirmation)
The confirmation message in response to an H.323 LRQ.
LRQ (Location Request)
A request message between two H.323 gatekeepers to find the address of an H.323 endpoint.
MEGACO
Also known as IETF RFC 2885 and ITU Recommendation H.248, defines a centralized architecture for creating multimedia applications, including VoIP.
MGCP (Media Gateway Control Protocol)
Also known as IETF RFC 2705, defines a centralized architecture for creating multimedia applications, including VoIP.
PRI (Primary Rate Interface)
ISDN interface to primary rate access. Primary rate access consists of a single 64-Kbps D channel plus 23 (T1) or 30 (E1) B channels for voice or data. Compare with BRI (Basic Rate Interface), ISDN interface composed of two B channels and one D channel for circuit-switched communication of voice, video, and data.
Protocol translation
In this model, a company uses IP–based protocol translators to interconnect two or more VoIP protocol domains. IP translators allow a company to retain the flexibility of using multiple VoIP protocols, do not introduce the delay problems that additional TDM interconnections do, and do not require a wholesale replacement or swap of existing equipment.
PSTN (Public Switched Telephone Network)
General term referring to the variety of telephone networks and services in place worldwide. Sometimes called POTS.
RAS (Registration, Admission, and Status Protocol)
The suite of messages between H.323 endpoints and H.323 gatekeepers. The messages are made up of Requests (xRQ), Confirmations (xCF), and Rejections (xRJ). The “x” letter denotes the type of messages, including Admission, Registration, Bandwidth, and Disconnect.
RCF (Registration Confirmation)
The confirmation response from the H.323 gatekeeper to an H.323 endpoint.
RRQ (Registration Request)
The Registration request from an H.323 endpoint to an H.323 gatekeeper.
RTP (Real-Time Transport Protocol)
Also known as IETF RFC 1889, defines a transport protocol for real-time applications. 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 services such as payload type identification, sequence numbering, timestamping, and delivery monitoring to real-time applications. RTP is used by all the VoIP signaling protocols.
SDP (Session Definition Protocol)
RFC 2327. The media negotiation signaling used by SIP and MGCP.
Single Protocol Architecture
In this model, a company moves all of its VoIP devices and services to a single protocol, simplifying the network as a whole. The downside to this approach is that it might not be possible to migrate existing equipment to support the new protocol, a situation that can limit the company’s ability to take advantage of some existing services. In addition, it limits the potential connectivity to other networks that are using other VoIP signaling protocols.
SIP (Session Initiation Protocol)
Also known as IETF RFC 2543, defines a distributed architecture for creating multimedia applications, including VoIP.
SS7 (Signaling System 7)
Standard CCS system used with B–ISDN and ISDN. Developed by Bellcore. CCS (Common Channel Signaling) is a signaling system used in telephone networks that separates signaling information from user data. A specified channel is exclusively designated to carry signaling information for all other channels in the system.
TDM (Translation through Time Division Multiplexing)
Technique in which information from multiple channels can be allocated bandwidth on a single wire based on pre-assigned time slots. Bandwidth is allocated to each channel regardless of whether the station has data to transmit.
TRIP (Telephony Routing over IP)
RFC 3219. A protocol for distributing E.164 numbering plans between VoIP devices, similar to how BGP or OSPF distribute IP routes between routers.
VoIP (Voice over IP)
The ability to carry telephony-style voice over an IP–based network with POTS–like functionality, reliability, and voice quality. VoIP enables an IP network to carry voice traffic (for example, telephone calls and faxes). VoIP occurs because the TDM voice is packetized by a DSP, which resides in a VoIP gateway, of the VoIP phone. Once the voice is packetized, it can then be routed over an IP network. VoIP separates the signaling over voice calls from the bearer portion of voice calls (the audio). The signaling is handled by H.248, H.323, MGCP, or SIP. The bearer is carried by RTP.
