SIP Trunking

Is it right for you?

SIP (Session Initiated Protocol) trunking is getting a lot of press recently and many vendors are now recommending SIP trunking with their Voice over Internet Protocol (VoIP) phone systems. Do you need or want SIP? The answer depends on many factors, but let's first start by looking at what SIP trunking is and the benefits of SIP trunking. We will also look at some of the pitfalls that need to be considered.


SIP is a protocol that covers more than just VoIP packets and how to handle set up and features. What are the advantages of SIP with regards to voice services and what needs to be considered before you order your first SIP trunk?


To have a SIP trunk connect directly to a PBX, the system needs to be "SIP capable." This allows your PBX or VoIP phone system to connect directly to an ITSP (Internet Telephone Service Provider). The ITSP may be the traditional local exchange provider, like AT&T, or a provider dedicated to SIP traffic.

A few of the benefits:

  • Generally, since the traffic is bypassing the PSTN, the cost of a long    distance (LD) call is greatly reduced with VoIP. AT&T, for example, charges only .02 per minute for Domestic LD calls when using VoIP.
  • Since the connection is via an Ethernet connection in the VOIP system, there is no need to purchase PRI cards for your PBX. These cards can cost up to $2500 each.
  • SIP trunks can be added to existing IP connections; you do not have to purchase full PRI's with 23 channels when you may only need a few voice channels.
  • Most carriers offer "free calling" between enterprise locations that have SIP trunks.
  • SIP trunks can work on traditional IP connections, so you may be able to purchase SIP trunks on existing Internet connections.
  • You may be able to get "Virtual Numbers". If your office is in San Francisco and you want a local New York number to ring in San Francisco, SIP Trunks may be the product you want.

Looking at the benefits, you can see why many Customers and Vendors are pushing SIP trunks.


Some issues with SIP trunks and a few things that you should watch out for:

  • SIP trunk specifications vary by ITSP. While the basic features may work with a given PBX, there may be many that will not work between every ITSP and every VoIP PBX. However, standards are developing for "SIP-Connect Specifications" that many vendors are starting follow. Be careful; SIP trunks may not be approved for your VoIP system by all carriers.
  • SIP trunks are delivered by IP. This may be over the public Internet or over a private MPLS connection. Depending on how you receive your SIP trunks, you may have to upgrade your Firewall to be SIP capable. In addition, if you are using NAT (Network Address Translation) you need to be sure that the firewall is capable of NAT traversal so that SIP packages arrive correctly.
  • You need to consider how your LAN (Local Area Network) is designed. Do you have enough bandwidth?
  • Is your Vendor "Certified" to enable SIP on your VoIP system? There is much more to setting up SIP trunks than just "turning on" SIP features. There maybe additional settings such as jitter buffers and echo cancellation that need to be set, depending on the ITSP. Your vendor should be very familiar with these settings and be willing to work with the carrier to adjust your system after making several test calls and measuring the quality of calls.
  • Security needs to be considered since many times the SIP trunks are coming in from the Public Internet. Many businesses are utilizing SIP trunks through their MPLS networks to minimize threats to their systems.
  • You must be certain that your selected carrier is certified for compatability for your brand of VoIP equipment.

SIP trunks are entering the market quickly and will probably be very common in the next year. SIP trunks can save you money and make maximum utilization of your bandwidth, but implementation with SIP trunks needs to be carefully thought out. They work great when properly configured.


For more information on SIP trunks or to check availability in your area, call Glenn at Top Speed Data 707-283-2710 x716 or email glenn@topspeeddata.com

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At Top Speed Data, we perform a complete audit of your voice, data and wireless services. We listen to your requirements, bid out services to all major carriers and provide one complete proposal for all providers. We specialize in reducing costs, increasing network performance and providing overall telecom project management. We do all of this at no charge to our customers.

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