Learning guide: VoIP protocols and standards

The Israelis are credited with placing the first computer-to-computer call in 1995. Though the audio quality was poor and likened to the "voice sounds" that were transmitted during the first historical call made in 1875 by Alexander Graham Bell, this call would prove to be the geniuses of a new communication platform, a shift to an epoch of unprecedented mobility and services that is redefining enterprise telephony.

The Israelis are credited with placing the first computer-to-computer call in 1995. Though the audio quality was poor and likened to the "voice sounds" that were transmitted during the first historical call made in 1875 by Alexander Graham Bell, this call would prove to be the genesis of a new communication platform, a shift to an epoch of unprecedented mobility and services that is redefining enterprise telephony.

Since 1995, VoIP's call quality and reliability has steadily improved, and now rivals the quality and dependability of traditional TDM (time-division multiplexing) calls while also offering users unprecedented mobility, call features and services and marked cost savings.

Setting the standard

The rapid evolution of VoIP was made possible in part by the use of protocols and standards, or special sets of rules that end points in a telecommunication connection use when they communicate. Standard bodies are responsible for writing the rules that keep the lines of communication wide open. The goals of standards organizations are centered primarily on developing, amending, revising and updating standards to foster the ubiquity of a technology. In the case of VoIP, vendors, architects and developers, researchers, telecom providers, and users rely on their comprehensive expertise and experience to bring about successful and secure VoIP adoptions. See below for list of standard bodies and forums.

The foundation: TCP/IP

TCP/IP (Transmission Control Protocol/Internet Protocol) is the basic communication language or protocol of the Internet. It can also be used as a communications protocol in a private network (either an intranet or an extranet). When you are set up with direct access to the Internet, your computer is provided with a copy of the TCP/IP program just as every other computer that you may send messages to or get information from also has a copy of TCP/IP. Two protocols are also necessary for VoIP service: a signaling protocol and a speech transmission protocol. Read on for a more detailed explanation of TCP/IP.

Signaling protocols

Call signaling is used in Voice over IP (VoIP ) systems to establish connections between endpoints, or between an endpoint and a gatekeeper. The most commonly used VoIP signaling protocols are as follows:

SIP (Session Initiation Protocol)
H.323 
MGCP (Media Gateway Control Protocol) 
MEGACO (a contraction of Media Gateway Controller) or H.248 
SS7 (Signaling System 7) 
ISDN (Integrated Services Digital Network)
Q signaling

Speech transmission protocols

UDP (User datagram protocol)
RTP (Real-Time Transport Protocol)
TCP (Transmission Control Protocol)

Standards and protocols for VoIP management

DHCP (Dynamic Host Configuration Protocol)
ENUM
RSVP (Resource Reservation Protocol)
BGP (Border Gateway Control)
COPS (Common Open Policy Service Protocol)

Standard bodies and forums

CableLabs
ETSI (European Telecommunications Standards Institute)
H.323 Forum
IDPR.com (Internet Protocol Detail Record)
IETF (Internet Engineering Task Force) 
IMTC (International Multimedia Telecommunications Consortium)
IPTEL.org
ITU (International Telecommunications Union)
MFA Forum
MSF (Multiservice Forum)
OpenH323
SIP Center
SIP Forum
W3C (World Wide Web Consortium)

Additional resources

Learning guide: SIP
In this learning guide, you'll find out what SIP is, how it works, which applications are SIP friendly, what compatibility and interoperability issues surround SIP and more.

Editor's picks: Standards and protocols
Without standards and protocols, having a telephone conversation over the Internet or a dedicated Internet Protocol (IP) network instead of dedicated voice transmission lines would not be possible. In this collection of editor-selected resources, you'll find articles, news, expert advice, webcasts, white papers and more covering H.323, SIP and the inherent challenges of interoperability.

SIP school: A to Z on SIP 
In this complete guide to SIP, you'll learn how this signaling protocol's modularity and openness simplifies communications, improves productivity and sets the stage for multimedia networks. School is in session!

What are media gateways and how do H.323, SIP, MGCP and other support protocols work?

Securing SIP 
In this complete guide to SIP, you'll learn how this signaling protocol's modularity and openness simplifies communications, improves productivity and sets the stage for multimedia networks. School is in session!

SIP and the Future of VoIP - Expert Webcast 
Gartner predicts that 90 percent of all new corporate telephone networks will be IP-enabled and based on SIP protocols by 2008. It's only a matter of time before VoIP becomes a mission critical communication system. Still, concerns remain around the security of VoIP and the underlying SIP protocol, fearing that they are susceptible to similar types of threats and exploits that plague the Web and email. In part one of this three-part Webcast, Andrew Graydon, Chair of the Security Requirements Committee, VoIPSA, identifies the security issues associated with SIP and what you can do to mitigate them.

For a glossary of all terms, view this VoIP protocol listing.

This was first published in October 2006

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