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SIP Trunking – What is it and Why Should You Care?

Strategically Speaking
May 29, 2013

James Key Author: James Key,

Anyone who has been involved with IP telephony and Unified Communications in recent years has without a doubt come across the phrase "SIP trunking".  For those of you not yet familiar with SIP, let’s start by giving a brief overview.

SIP stands for Session Initiation Protocol and is an application layer control protocol (signaling) used for creating, modifying, and terminating media sessions with one or more participants.  These media sessions typically involve Voice over IP calls (VoIP), but can also include instant messaging, presence, and video conferencing.  SIP is similar to other widely used protocols such as HTTP and SMTP in that it provides a flexible, open standard that can be leveraged efficiently with a variety of different Unified Communications systems and technologies. 

SIP trunking is the technology that is expected to eventually replace traditional circuits and ultimately be the primary transport mechanism for voice traffic between an enterprise and the PSTN (Public Switched Telephone Network).   Traditionally, enterprises would procure voice services separately from the data services.  These voice services where delivered as bundles of physical wires from a telephone company and came in the form of a PRI (Primary Rate Interface), BRI (Basic Rate Interface) and/or POTS (Plain Old Telephone System) lines.  With SIP trunking, an enterprise can potentially eliminate the need for these fixed PSTN lines and "funnel" all voice traffic over the existing data network to the service provider who then in turn routes it to the PSTN.

SIP trunking can provide many benefits over traditional circuits. Although all the benefits are far too numerous to list, the three more frequently discussed are as follows:

1.  Cost reduction

Although cost reduction benefits can be argued and can greatly vary, there is the potential for reduction for multisite enterprises by centralizing SIP trunks, and eliminating the need for maintaining traditional circuits at each site.  There is also the possibility of leveraging the already existing data network for voice.  Technologies such as Metro Ethernet and MPLS, allow an enterprise to save money by making optimal use of current data network resources.

2. Disaster recovery/Business Continuity

SIP trunking gives the ability to easily redirect individual Direct Inward Dial (DID) numbers from one SIP trunk to another.  An example would be a SIP trunk coming into the headquarters, and a SIP trunk coming into the DR facility. These trunks can be utilized to load balance inbound calls, and should either trunk become unavailable, the service provider can easily route all calls to the other trunk(s).   With traditional circuits, these individual DIDs are typically confined to single sites PRI and must be forwarded by the telephone company to a designated number in the event of an emergency. The key point here is that with SIP trunking, inbound phone numbers are not confined to any single location.

3. Geographic number portability

DIDs are no longer confined to the local Exchange Carrier (LEC). If an office relocates to an area with a different LEC, those numbers can be re-presented across the new network. 

In Summary:

SIP has been increasingly representing the underlying technology forming the foundation for Unified Communications solutions in today's modern enterprise. SIP has the potential to provide flexibility, significant costs savings, and increase network resiliency if properly tested and implemented.  As with any new implementation, there may be some "bumps in the road", but these can be kept to a minimum and easily resolved with an experienced and well prepared technical team. 

Do you have experience with SIP technology?  We’d love to hear your story!


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