SIP skills are key to internet telephony

Salaries for networking and telecoms specialists with SIP skills are high

Salaries for networking and telecoms specialists with SIP skills are high

What is it?

The key to soft telephony, instant messaging and much else, Session Initiation Protocol (SIP) is used for setting up communications sessions between devices on the internet.

SIP is a lightweight client easily embedded in end-user devices, including PCs, personal digital assistants and 3G phones, enabling them to communicate with and provide services to other SIP-enabled devices.

Early adopters concentrated on internet telephony - voice over IP - but quality and reliability were poor and traditional telecoms companies, seeing their infrastructure investment threatened, were resistant.

Now telecoms companies such as Siemens and Nortel are in the vanguard, along with Cisco, Microsoft and a host of start-up companies. Issues such as quality of service and security are being tackled and applications are becoming more sophisticated.

Where did it originate?

SIP was developed in the mid-1990s with a structure based on SMTP e-mail. It was taken over and standardised by the Internet Engineering Task Force in 1999.

What is it for?

SIP telephony applications include conferencing and combined voice, video and graphics. SIP Instant Messaging and Presence Leveraging Extensions (Simple) defines how SIP should be used for instant messaging, enabling different suppliers' implementations to communicate with one another.

Much current research is into "presence" applications, using an event monitoring and notification mechanism which alerts people when a user is at their desk, re-routes calls to their mobile phone when they are out, or begins a conference automatically when all participants are available.

What makes it special?

SIP is a potentially universal standard which is simple to work with and easily extensible to accommodate new applications and communications media. It is not dependent on the infrastructure and exchange services used by traditional telephony. Instead, SIP-enabled devices communicate directly with each other, making use of any available path, and relying on the web's domain name service to find any device by its unique IP address.

SIP components can be easily commoditised and distributed. Analyst firm Gartner said, "Enterprises that adopt SIP in their architectures should be able to be more selective with communications applications from different suppliers." However, this depends on suppliers sticking strictly to the standards and commercial developments rapidly outstrip the standards-setting working groups.

How difficult is it to master?

SIP is a simple protocol but its applications can be complex. People already working in networking or telephony can learn the essentials of SIP in two days.

Where is it used?

Most applications are within organisations, although telcos that see their traditional voice markets threatened are developing IP telephony services. Much work needs to be done on privacy, security and related issues before presence-based commercial services are rolled out, if these are not to become intrusive and disruptive.

What systems does it run on?

SIP is being built into Windows XP and Messenger and Cisco's gateways and servers. Phone manufacturers such as Nokia offer downloadable SIP development kits.

What is coming up?

Work is being done on SIP security and reliability, but there is a long way to go before the 99.999% uptime expected from conventional telephony.


Training is available from major manufacturers and their partners and independent IP telephony specialists

Rates of pay

Roles requiring SIP include voice over IP engineers, digital communications software developers, network support and contact centre staff. Salaries in this fast-moving sector are high.

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