If you are evangelizing the cost savings and convergence capabilities of SIP, but have customers that need more security and reliability, SIP over MPLS may be the answer.

SIP over MPLS provides an alternative to SIP over dedicated Internet access or SIP trunking the more typical deployment approaches. The benefits of running SIP over MPLS, experts say, include improved call quality with low latency, less jitter, better capacity control and end-to-end quality of service. And, when it comes to security, MPLS avoids exposure to the public Internet, making SIP over MPLS more secure than over other transport options.

You can choose how big your lines going to be and then you can control what goes across those lines,” said Jim Schmidt, director of sales engineering for US Signal, in a recent webinar hosted by the Technology Channel Association. So in contrast to an Internet circuit where you may get a denial-of-service attack that could adversely impact your voice traffic, on an MPLS network, thats not going to happen.”

Within an IP network, SIP, or session initiation protocol, is used for establishing sessions, which could be as simple as a phone call or as complex as a collaborative multimedia conference. 

MPLS, or multiprotocol label switching, transports any protocol, including SIP, through a wide area network by using tags or labels that define not only its destination but the class of service it should receive. It also creates a virtual private network for a customers traffic in this case converged voice and data services within the carrier cloud.

Circumventing the public Internet is key. Chris Connor, director of product management for Level 3 Communications Inc., said in the TCA webinar, that not only is security improved but so is traffic management and performance with the ability to prioritize voice or video traffic, for example. In addition, Connor says many carriers run classes of service across their networks, creating voice or video queues in their networks. Typically the SLAs and performance characteristics of those voice/video queues within carrier MPLS networks are a lot better, so you are going to get much better performance for voice services than you would over a best-efforts public Internet service,” he said.

In certain multilocation environments running SIP over MPLS also can result in additional cost savings from centralizing SIP trunking. Centralized SIP trunking routes all VoIP traffic, including branch office traffic, through a central site over WAN links (in this case MPLS). In contrast, distributed SIP trunking requires a local SIP trunk at the branch site over which VoIP traffic is routed directly to the service provider.

In addition to eliminating local voice trunks, centralizing SIP trunking has the added benefit of eliminating local phone systems and the costs of long-distance calling between networked sites. In addition, voice calling capacity can be shared across the entire enterprise.

Nena Dodson, principal network services engineer for XO Communications Inc., said in the TCA webinar that SIP trunking centralization over MPLS works best for organizations with 15 or more locations; any fewer and she said it becomes difficult to justify the cost of the equipment required to secure and centralize the network.

In addition to a large number of locations, customers that might benefit from SIP over MPLS include those with:

Khali Henderson contributed to this article.