Integrating SIP Trunks in Enterprise Networks for Next-Generation Unified Communications
By Cisco Systems
Published August 2007; Posted December 2007


The far-reaching benefits of Unified Communications can truly be realized with “pervasive Unified Communications” networks. Pervasive Unified Communications require the transition from TDM to IP-based solutions of enterprise-to-service provider and inter-service-provider interconnect trunks. Trunking solutions based on Session Initiation Protocol (SIP) are emerging as the most versatile solution for this transition to next-generation, pervasive Unified Communications networks.

However, wholesale transition of TDM trunks to Unified Communications SIP trunks is not a trivial undertaking. TDM trunking, and the voice gateways that tie the trunks into the IP-based Unified Communications world, are a widely deployed, time-proven and trusted solution. Despite limitations in accommodating next-generation Unified Communications services, TDM’s proven resiliency and rich feature set in the areas of security, privacy, diagnostics, billing, demarcation, and traffic shaping and policing still set the standard against which new solutions are measured. New Unified Communications trunking solutions must offer similar service-level assurances for enterprises and service providers to consider them as a viable alternative. Enterprises thus need a way to maintain all of the benefits associated with TDM interfaces while exploiting the efficiencies of extending Unified Communications beyond the enterprise.

To enable new pervasive Unified Communications services while minimizing risk, enterprises require an evolutionary and cost-effective approach to Unified Communications SIP trunk adoption. Proposed solutions should not require a complete replacement of existing equipment, but should instead allow for the incremental adoption of Unified Communications SIP trunks. Moreover, solutions must also allow the Unified Communications SIP trunks to coexist with TDM voice gateway trunks. As service provider offerings and enterprise confidence increase, such solutions allow organizations to gracefully migrate services from TDM trunks to Unified Communications trunks as needed, thereby minimizing risk. This is a similar approach to the one taken by enterprises during the migration of TDM telephony to IP telephony through the use of toll bypass, coexistence of both systems, and eventual replacement of TDM equipment – all done at the pace dictated by the business needs of the enterprise.

This paper briefly describes the business advantages and challenges of Unified Communications trunking and the network considerations for adoption. The paper introduces the Cisco® Unified Border Element, highlighting the features that make it a compelling solution for this far-reaching communications transformation. The paper concludes with recommendations for possible starting points for enterprises embarking on this evolution.


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