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Like many large enterprises, Cisco makes a lot of phone calls.  Cisco previously used a lot of TDM trunks from multiple carriers to carry thousands of voice calls from our North American Cisco offices to the PSTN. The problem is, we had over 100 TDM trunks we were paying for every month, to carry our voice calls for these sites.  Four years ago we started looking around for a more cost-effective and manageable way to support all these calls.  After a good deal of searching, screening vendors and testing, we finally found it, using Session Initiation Protocol (SIP) trunking technology.

For the Cisco campuses in San Jose and Research Triangle Park (RTP), we will replace over a hundred PRI (23 channel) TDM trunks, used for long-distance voice calls for all of our North American sites, with SIP trunks.  The new San Jose link is a 250 Mbps SIP trunk carved out of a 10 Gigabit Ethernet WAN access line, while the RTP link is a 20 Mbps SIP trunk carved out of a 45 Mbps DS3 WAN access line. Together, these SIP trunks give us the capacity to carry over 2400 concurrent calls and a total voice call volume of 2 million minutes per month.
In each location, the SIP trunks are connected to the Cisco Advanced Services Routers (ASR) acting as Session Border Controllers connected to a local Cisco Catalyst 6506 MPLS router.


Both SIP trunks handle long-distance voice calls placed by employees, as well as outbound calls for local contact centers and long-distance calls placed by the Cisco Single Number Reach feature. This use of SIP trunks gives us three types of cost savings:

  1. Lower expenses for voice trunks and associated equipment, as well as reduced toll charges.
  2. Lower operational costs because of fewer voice trunks to manage.
  3. Consolidated communications, with the ability to send video and data over the same SIP trunk with VoIP traffic.

Since SIP trunking is a relatively new technology, Cisco conducted a proof-of-concept project for about a year before selecting a carrier. This project allowed Cisco to address potential issues such as correct call routing, compatibility with new Cisco Unified Communications Manager versions, and each carrier’s performance against Cisco’s required SLAs.

With SIP trunks now successfully deployed for North America, Cisco is considering SIP trunks for other Cisco locations, especially in Europe and Asia.

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