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Dip into SIP

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SIP trunking has long been on the technology watch list, but as SIP trunking services have matured, the time is now to jump in with both feet. Many of your peers have already made the leap. SIP trunking service revenue jumped 128% in 2011 from the previous year, according to the market research firm Infonetics.

Why SIP?
SIP essentially brings the dial tone for your phone system over the network. Organizations traditionally have used ISDN Primary Rate ISDN (PRI) circuits to connect their phone systems to the public telephone network, but with the widespread adoption of IP applications and networks, IP-based circuits are becoming more popular and have many advantages.

First and foremost, you can save money by leveraging centralized SIP trunking to connect your IP phone system across your different locations. Using SIP allows you to reduce the number of local access circuits and trunks to your branch offices. For many organizations, centralized trunk designs can result in a 30 percent to 50 percent reduction in trunks.

Using SIP gives you more flexibility in purchasing bandwidth as well. With traditional circuits, you have to buy in blocks of 23 trunks in North America. Or buy in blocks of 30 in Europe and other regions. If you need 26 trunks, you end up paying for 46. With networking over an IP network, you pay for the number of trunks you use. And you get more flexibility to handle spikes with bursting services. A bursting service lets you use more trunks then your basic subscription when needed and simply pay as you go.

SIP, being IP-based, also means easier integration with unified communications applications, such as presence, instant messaging, videoconferencing and collaboration.

SIP trunking also provides businesses with regional or international operations more flexibility and the ability to reduce their cost through leveraging the IP networks broad connectivity. SIP service providers can build their network to interconnect to the PSTN at various points. The subscriber then sends the call to the service provider who, via their IP network, routes it to the right region where it jumps back to the PSTN. Customers can also choose to leverage the IP network to reach multiple services providers in different regions. In each case, the IP network is leveraged for as much of the route as possible to save costs.

With this configuration comes another important benefit. Because SIP allows business to connect to multiple points on the traditional network, they can have local phone numbers anywhere. They are no longer restricted to the number block assigned to their nearby central office.

Improved voice survivability is another key benefit of SIP. Using SIP can add to the survivability of PSTN access by combining SIP trunking with the provisioning of traditional PSTN connections as a failover or a call capacity contingency measure. Additionally, by leveraging connections to the IP network at multiple locations, business can protect their voice services from last mile interruptions. Their trunk calls will no longer be dependent on that wire to the central office. Instead they will simply need to find a path for packets over one of the multiple links to the network.

Consider Security
With SIP trunking, your phone system is essentially connected to the Internet, which means you need to establish a separation between your corporate network and the service provider’s network. Establishing that separation will help you address the potential security issues, including denial-of-service (DoS) attacks that may come in over the Internet.

A best practice for protecting against these risks is to add a SIP-compliant firewall or a session border controller (SBC) to protect your corporate network against malicious attacks and traffic and to ensure that only approved traffic passes into the heart of your business. These solutions both hide your internal network and your user IP addresses from the outside world as well as monitor the traffic in and out to block improper communications.

Interoperability
Interoperability is a key issue in the evolution of SIP. When choosing a SIP service provider, ensure that the service is certified to work with your IP PBX. The best way to do this is to check with your provider. In most cases you will find they run an inter-operability program where they test and confirm the system and the service provider work together. The testing program will also typically provide you any necessary information you need to order the right services and configure your system.