SUBSCRIBE TO TMCnet
TMCnet - World's Largest Communications and Technology Community

CHANNEL BY TOPICS


QUICK LINKS




 

A Note on SIP

By: Richard “Zippy” Grigonis

SIP (the Session Initiation Protocol (News - Alert)) is a multimedia call control protocol, perhaps the most successful and popular protocols after IP itself. SIP, a text protocol, competes with its binary code predecessor, H.323, which is actually a suite of protocols that define the framework of such elements as terminals, gateways, gatekeepers, MCUs (Multipoint Control Units) and feature servers. H.323 is thus an “umbrella” technology that even specifies all subsidiary media codecs and how they are transported as packets encapsulated in RTP (Real-time Protocol) or RTCP (Real-Time Control Protocol). H.323 calls upon Q.931 for call setup, H.225 for call signaling, and H.245 for exchanging terminal capabilities and the creation of media channels. SIP, however, is a much simpler protocol.

SIP deals with other protocols on a sort of “need-to-know” basis: For example, like H.323, SIP can work with RTP, but does not mandate its use. As its name implies SIP deals in conferencing “sessions” between two or more participants, with control over creating, modifying and terminating or “tearing down” those communications sessions. In that respect SIP also takes the place of what Q.931 and H.225 do in the H.323 suite. Unlike H.323, SIP is independent from its underlying protocols (UDP (News - Alert) or TCP) and is even independent of the underlying network in terms of high availability.

Various companies have devised SIP stacks for SIP-enable devices. GAO Research, for example, offers integrated solutions suitable for any IP Communications application. They offer both H.323 and SIP Voice/Video-over-IP stacks, and their all-in-one packaged solutions include associated audio and video codecs, and telephony modules.

In particular, GAO’s SIP protocol stack implementation complies with IETF RFC2543 (March 1999), and is modified as per the latest updates of the standard to correctly manage the fundamental connection between the call-originating and call-terminating parties. Moreover, GAO’s interesting, multi-layered API makes it easy to build simple applications as well as complex implementations.




Interestingly, GAO offers three Voice/Vide-over-IP Integrated Solutions (News - Alert): H.323-only, SIP-only, and the H.323 + SIP solution. The modular platform based on the SIP protocol stack provides an integrated solution which uses SIP call control and management, a set of media codecs, and additional telephony services including T.38 fax relay capabilities. The SIP solution does not specify the use of RTP/RTCP as required for H.323 protocol. However, in the case of using both the H.323 and SIP stack, an integrated solution can use either H.323 or SIP for call control and management. When requiring H.323-only or SIP-only applications, the H.323 or SIP call control modules that aren’t used can be removed to reduce the memory footprint. SIP advanced services can be used in parallel with both SIP or H.323 audio/video conferencing.

As for actual applications that rely on SIP, we encountered one just as this issue was going to press: Avaya (News - Alert) just announced (March 30, 2009) the launch of their Avaya Aura, a new architecture that integrates communications across multi-vendor, multi-location and multi-modal businesses. Avaya Aura radically simplifies complex communications networks, reduces infrastructure costs and quickly delivers voice, video, messaging, presence, web applications and more, to employees anywhere. Avaya Aura will be available globally in May 2009.

This new architecture is propelled by the SIP-based Aura Session Manager, which centralizes communications control and application integration. Avaya’s Aura Session Manager coordinates various communications applications and systems by decoupling the apps from the network. Services can therefore now be deployed to users depending on what they need rather than by where they work or the capabilities of the system to which they are connected. Session Manager thus reduces complexity and paves the way for the implementation of broader unified communications strategies.

In terms of multi-vendor use, SIP helps integrates multichannel communications across multiple locations and other suppliers’ solutions. The Avaya Intelligent Customer Routing is an application that transfers customers and their essential information to the right agent or expert using the quickest and most efficient route possible.

In case your technical people somehow are flummoxed by all of this, both the Avaya Aura and the Avaya Intelligent Customer Routing tap into Avaya’s Avaya new Strategic Communications Consulting practice, which is adept at helping enterprises develop their communications using the Avaya’s most advanced expertise, tools and capabilities. In short, Avaya’s total approach can solve business issues by maximizing technologies, such as unified SIP-based architectures.

To be specific, Avaya Aura offers the ability to create new applications and quickly extend them to users anywhere; map applications to individual employee profiles, making the appropriate features globally available regardless of the location, system or device to which they are connected; reduce costs through centrally managed, enterprise-wide dial plans and on-net calling, global least-cost routing and PSTN access from the most cost-effective location; eliminate local application servers and optimize software licensing across the full breadth of the enterprise rather than for a single location; and massively scale to 250,000 business users and 25,000 locations.

Avaya’s Communication Manager, their flagship voice and video telephony software, becomes a business feature server in this scenario, allowing Avaya’s PBX (News - Alert) platform to be exposed as SIP features and services coordinated from Session Manager. (Additionally, Presence Services, formerly known as Intelligent Presence Services, takes a more central role within the communications platform, expanding the ability to federate presence from multiple sources and vendors for a more accurate view of an employee or work group availability.)

For companies with branch locations, Avaya Aura Branch Edition provides the capabilities of Avaya Aura as a SIP-based replacement for key systems in small locations. This enables companies to go from standalone stores and branches (or small contact centers) to a full, SIP-connected enterprise. In turn, Avaya Aura delivers boosts productivity in terms of providing the ability to create new applications and quickly extend them to workers anywhere. It can map applications to individual employee profiles, making the appropriate features globally available regardless of the location, system or device to which employees are connected. There are also some cost savings to boot, since the system is based on centrally managed, enterprise-wide dial plans and on-net calling, global least cost routing, and PSTN access from the most cost-effective location. It also eliminates local application servers and optimizes software licensing across the enterprise, rather than for a single location.

Any way you look at it, SIP is here to stay. It’s becoming the fundamental call control/signaling protocol that facilitates interoperability between SIP phones, IP PBXs, etc. and is even serves as the underlying protocol to the upcoming IP Multimedia Subsystem (News - Alert), a worldwide common service architecture for both wireline and wireless communications networks. IT

 

The following companies were mentioned in this article:

Avaya Lucent – (www.avaya.com)

GAO Research – (www.gaoresearch.com)

» Internet Telephony Magazine Table of Contents



Today @ TMC
Upcoming Events
ITEXPO West 2012
October 2- 5, 2012
The Austin Convention Center
Austin, Texas
MSPWorld
The World's Premier Managed Services and Cloud Computing Event
Click for Dates and Locations
Mobility Tech Conference & Expo
October 3- 5, 2012
The Austin Convention Center
Austin, Texas
Cloud Communications Summit
October 3- 5, 2012
The Austin Convention Center
Austin, Texas