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April 2009 | Volume 12 / Number 4
Ask the SIP Trunk Expert

The Importance of One Converged Network

Enterprises can connect to SIP trunks in a variety of ways, thanks to an increasing array of options now available from Internet Telephony (News - Alert) Service Providers (ITSPs). Two common methods are connecting via a managed service and directly over the Internet.

The full potential of SIP trunks – in both scenarios – can only be achieved when the voice and data networks are truly converged. Only then can SIP trunks support an array of beneficial features such as supporting soft clients, connecting remote workers and allowing users to manage their account on the PBX (News - Alert) or application server.

With a managed service, service providers connect enterprises to SIP trunks over a managed line, where the ITSP hosts the SIP trunk service separate from access to the public Internet. The SIP trunk service provider connects the enterprise into a LAN created in its service cloud. In this scenario the voice and data networks are separated, and certain features that are enabled with SIP are not possible, such as support for remote workers and the use of soft clients from PCs that have no access to the separate voice network. Here a border element can be utilized to merge the two networks, so that the Quality of Service (QoS) benefits of the managed connection are maintained, but the promise of converged communications can be supported.

Carriers can also connect enterprises to SIP trunks directly via the Internet, through the enterprise firewall and directly to the data LAN. The enterprise must enable NAT traversal to permit the SIP signaling to enter the network. The enterprise must also maintain its security defenses, permitting SIP traffic to enter the network while preventing unauthorized access or use of the servers on the LAN or the telephony system. In this case the border element provides the necessary functionality to resolve these issues and enable more advanced SIP capabilities.

SIP trunking is a service that offers great benefits to the enterprise. With a high quality edge device, service providers and enterprises can be assured of high quality voice without concern for losing control of the converged network.

Steven Johnson (News - Alert) is President of Ingate® Systems (

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