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SIP Trunking – The Role of the Service Provider

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This is the second in my series on SIP trunking – designed to explain how companies can take advantage of the benefits this communications protocol provides. In my first blog post, I shared the basics. In this one, I’ll explore the value a service provider can bring to your business communications strategy.

To enable your business to make and receive SIP phone calls, you need three key components.

  1. SIP phones for making and receiving the calls.
  2. SIP server in the network that can support all of the SIP phones.
  3. Security solution that allows you to safely connect your network to the Internet or external IP network.

To place a call, enter the number you want to call into your phone. The phone then reaches out to the SIP server and asks it to assist in making the call. The SIP server looks the destination up in the network’s directory names server (DNS) to determine the IP address of the destination and then launches the call through your security system, across the network, to the indicated destination.

On the other side, the person you are trying to call must have the same set-up in their network. The request is received, allowed past the network security and delivered to the SIP server on their internal network. The server looks at the request to determine who you want to speak with and then compares this information with the information available on all the SIP phones that have previously registered.

When it finds a match, it forwards your request on to the intended destination device. At this point, the two phones exchange a couple of messages to determine the type of communications they want to have and the phone call occurs.

One thing clear from the above scenario is that it is possible to make phone calls using SIP directly from one enterprise to another. Other than resolving the IP address, the SIP infrastructure on either side can work together to enable the call without much network support. However, what wasn’t mentioned were the assumptions needed to make it happen.

The above scenario assumed that the person you wanted to speak with worked for a company that had set up a SIP registrar and security solution in order to support SIP voice calls. In reality, this isn’t a stretch. Legacy interfaces such as ISDN, TDM, and analog still carry more calls to and from the enterprise than IP but this is rapidly changing. More and more companies are seeing the advantages of SIP trunking and deploying this very infrastructure in their networks.

Secondly, and this is the big one, it assumes that the company where your friend works will accept inbound SIP calls off the open network. This is almost never the case today because of concerns over whether or not a given request to connect is legitimate.

When you get a request today, you can confirm that the request is coming from a server owned by that requestor. This is analogous to the way you can confirm that the site you are visiting on the Web is really owned by the store you want to buy from before you provide your credit card information.

Beyond that, however, there isn’t a way to confirm that the person trying to reach you isn’t malicious and will not try to flood you with requests in an attempt to take down your network. It’s similar to the website analogy above. You can confirm that the site you are interacting with is part of the store you were visiting. But if you have never done business with them before, how do you know you can trust them with your credit card information?

So while it is possible to make those phone calls on an enterprise-to-enterprise basis across the network, it isn’t really practical today – unless you add a SIP trunking provider to the solution. SIP trunking providers enable a solution that doesn’t rely on everyone being on the Internet, that doesn’t require the enterprise to worry about how good or bad the caller is, and helps ensure your calls sound good.

With a SIP trunking provider, you are still required to have the SIP infrastructure on your side. But your SIP infrastructure is more limited in scope and should be more easily deployed. The key is that you only communicate via SIP with the service provider. All of your outbound requests come from your service provider. And you only accept inbound request from them. You know all of the inbound requests are trust-worthy because they all come from the service provider you know and trust.

Service providers also bridge your SIP connection to the legacy PSTN and the world of good, old-fashioned phone numbers. You no longer are relying on everyone you want to reach having their own SIP infrastructure in place because you dial them via the PSTN. And you no longer have to worry about publishing your information in DNS or accepting malicious requests because people reach you via the PSTN using your phone number.

For phone calls, the SIP trunking providers play a crucial role in making it easier for you to get the benefits of SIP trunking. They limit the complexity of your SIP infrastructure, provide you with a bridge to the PSTN, and enable all of this without opening you up to the additional security risks of accepting voice connections off the internet.

For voice calling, SIP trunking provides the answer. But with the increasing importance of unified communications, the use of video, IM, and presence is taking people beyond the simple voice call into the world of richer communications. What happens then?  It isn’t necessary to provide a bridge to the PSTN if your goal is a video call. But you still need security, yes?  How will the role of the service provider change over time?  A very interesting question but one I will have to cover next time.