Implementation Considerations when Enhancing Enterprise Communications Solutions with SIP Trunks
Communications Transformations
By Cisco Systems
Published June 2007; Posted December 2007

Abstract:

Increasingly, service providers are starting to offer an IP method of connecting branches and enterprise communications systems to the PSTN. These systems are generally referred to as "SIP trunk services" because the Session Initial Protocol (SIP) is used as the signaling method between the service provider and the enterprise communications systems. SIP trunk access is being provided for both local and long-distance PSTN access. These SIP trunks allow for unified communications IP access to the PSTN from the enterprise as well as the promise of new applications and services with end-to-end unified communications IP calling between enterprise users and external users.

Most enterprises add unified communications SIP trunk access to their networks in addition to the traditional TDM connectivity already in place. Cisco solutions offer enterprises the unique capability of upgrading their existing equipment that provides TDM connectivity to also support IP connectivity to the service provider. This connectivity provides access to new services for their users while at the same time minimizing reconfiguration in the network by keeping existing call patterns in place as well as providing backup access for emergency calling and redundancy.

When deciding whether, or when, to add a unified communications SIP trunk entry point to your network, be sure to consider more than the cost and services of the offering. This decision also has implications for call routing, high availability, Call Admission Control (CAC), security, and various other aspects of network design. This paper discusses the technical considerations of this integration.