Telecom decoder ring: What is SIP?
Wednesday, April 15th, 2009 at 10:54 am by Sam Schneider

SIP powers virtually all VoIP traffic today. Have you ever wondered what it means? Session Initiation Protocol (SIP) is a text-based protocol, like HTTP or SMTP, used in multimedia (voice-over-IP, video, instant messaging) applications to initiate, modify or terminate an interactive user session. SIP was originally designed by Henning Schulzrinne at Columbia University.

SIP builds on prior Internet protocols: SMTP, which defines the format for e-mail messages; and HTTP, which defines the format for Web-based communication. Additionally, SIP uses functions from RTP/RTCP and touches on other Internet protocols like H.323, TCP, UDP, and IP. It is widely used as signaling protocol for these technologies.

Source: Mark Miller’s VoIP Tutorial Part I

Similar to HTTP, SIP is text-based and allows all types of equipment to communicate with each other, regardless of make, model or geographic location. By utilizing two elements, clients and servers, SIP allows individuals to communicate in real time.

In Practical Terms for Businesses

SIP enables the next generation of communications - it’s a major part of the transition from analog to digital. The SIP protocol enables your IP phone to tell the carrier that you have picked up the phone to make a call, and the carrier should send dial tone. SIP sets up and tears down communication, but does not actually carry your voice/text/video; it works with a variety of other protocols like RTP to send that information.

Many telecom companies, most visibly Vonage and AT&T are using SIP to connect their Voice over Internet Protocol (VoIP) users. A new wave of telephony providers, called Internet Telephony Service Providers, or ITSPs for short, have grown up around the SIP protocol and offer services built on SIP.

Industry Terminology You Should Know

Like many businesses, the telecom world is full of acronyms and jargon terms that originate in engineering but have little meaning for the end user (that’s you!). Here are a few of the most common terms to help you make sense of all the jargon:

SIP Trunk(ing)
A bundle of telephony services built on SIP protocol signaling and RTP audio streams. Generally includes essential features like e911, 411, long distance calling and more.

Asterisk
The most popular SIP phone system, built on an open source platform.

PBX (Private Branch Exchange)
A type of phone system widely used in business. Can power anything from a five person office to a multi-national firm’s calling needs.

    Essential SIP Information & Resources

    For the latest and greatest in SIP and general Internet Telephony, take a look at Andy Abramson’s VoIP Watch Blog, or head over to TMCnet’s web portal which maintains a massive amount of VoIP articles, whitepapers and webinars. For more in-depth links, check out these resources:

    Mark Miller’s “Understanding SIP” series

    Part I: History and Architecture
    Part II: Protocol Capabilities
    Part III: Message Formats
    Part IV: Describing the SIP Session
    Part V: SIP Signaling
    Part VI: Testing SIP Interoperability

    Other Prominent SIP Resources

    Wikipedia’s Session Initiation Protocol Entry
    SIP Center - SIP News & More
    The VoIP Info Wiki
    SIP Trunk.org - SIP Resources
    VoIP News - Insightful articles and the latest news

    Did we miss an important aspect of SIP? Did we get it all wrong? Have you discovered an up-and-coming new SIP portal we should know about? Leave a comment.

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    • Pspanoudis
      hallo

      We have a cisco call manneger Ver 6.1
      we wand to connect as a ship trunk through sip Firewall.
      30 Euros is the maximum per month or we can by more credit for every month?


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