Migrating to SIP Trunks: Not Plug and Play

You may have been operating on T1 and PRI connections to the PSTN for years and have been happy with how things have gone, experiencing very few trouble tickets. But if your provider is terminating the T1 and PRI services it offers, perhaps you're considering migrating to SIP trunks.

I've said it before, but I'll say it again, moving to SIP trunks should be a no brainer. However, this is not a plug-and-play job. Old questions that were resolved with T1 and PRI services have to be answered all over again.

Migration Is Inevitable

Migration to SIP trunks can be voluntary or mandatory. SIP trunks can provide the same kind of access to the PSTN as T1 and PRI trunks. However, the SIP trunk is a completely different technology with a higher degree of intelligence. On the other hand, it is a technology with new problems including implementation and security issues.

You chose SIP trunks because they are flexible, cost-effective, and scalable. Even if you are being forced into SIP trunks, the migration can look very positive for your operation and budget.

Flexibility is a Major Factor

The traditional T1 connection had 24 channels. The traditional North American PRI has 23 channels. You have to buy in these unit sizes and do not have the flexibility to buy in smaller units. SIP trunks can be ordered in many sizes. When you consider flexibility, you have to also consider how the provider offers the SIP trunking service. The technology used to implement SIP trunks offers a great deal of freedom, so you should choose a provider that delivers that freedom.

Here are some things you should consider:

• Look for a user-friendly self-service portal that gives you control as a customer over the provider.
• Most businesses and organizations have seasonal traffic variations. You want to be able to change and provision the number of simultaneous SIP sessions in a short period of time, instantaneously or within a few hours. Be careful and watch the bills -- you may be spending more than you think.
• DIDs are probably part of your environment as well as toll-free numbers. You want to be able to easily purchase and activate these from your portal.
• The SIP trunk is a complex technology compared to T1 and PRI. You need more reporting of the conditions and operation so you can perform analytics and gain insight as to how well the SIP trunk is operating and what problems you may encounter.

Voice Quality -- Not So Easy

Voice quality is probably the most important factor when evaluating and operating a SIP trunk. You probably have had very good experience with the T1 and PRI connections. Now you are operating on an IP network that is best-effort delivery rather than guaranteed bandwidth.

Providers that use the Internet for access cannot guarantee voice quality because they can't guarantee the network quality on the Internet. You should be asking the potential providers how they implement the SIP access network. Is any form of QoS access supported?

Capacity Planning

There is a simple way of determining the number of such sessions you need. Take a look at your T1 PRI connections and just duplicate the number of sessions. However, this is probably over design. You have implemented T1s and PRIs for your maximum traffic. With SIP trunks, you can tune the number of simultaneous sessions to suit your business needs.

The first decision is how much bandwidth you need for the SIP trunk itself. You should never order exactly what you need in bandwidth. Order more for growth. Your organization will grow, so you have to expand the number of such sessions in the future or you may have to expand them seasonally. Where the flexibly comes in is that you can have varying number of SIP sessions and just pay for what you need.

You have to remember that the number of SIP licenses for IP PBX and in your session border controller are fixed, not variable. You can't buy them and give them back, so you have to allocate enough licenses for your maximum SIP trunk capacity. (See my blog, "SIP Trunk Bandwidth: How Much?.")

Don't Forget These

At Enterprise Connect Orlando, coming up in just a few short weeks, I will be moderating a panel session, "SIP Trunking Case Studies: Current Challenges and Opportunities." The panelists will be discussing many of the SIP trunk issues they have encountered and the questions they have had along the way. Some of the questions we'll be going over include:

• Is caller ID correct?
• Is the enterprise protected from Telephony Denial of Service (TDoS)?
• Do 911 and E911 work in every location?
• What is the FAX support, T.30 or T.38 or none? (this seems to be a prevalent problem).
• How does call recording work?
• Are TLS and SRTP supported for security?
• Are 800 numbers blocked?
• Can and how is number porting done?
• How does call trace work?
• Are TDD, modems, and relay stations supported?

Incumbent or Competition, Which Cost?

Implementing the SIP trunk is different than implementing the common T1 or PRI. The major difference is that there are a number of SIP trunking providers that are not traditional carriers, so the competition has opened up. Some of the non-carrier providers have been in the business for quite a number of years and do have the experience. Use this competition to your advantage when you are negotiating and exploring SIP trunking. The competition can help you get more services, cheaper services, or services in geographic areas that you had not anticipated.

Learn more about SIP and SIP trunking at Enterprise Connect 2017, March 27 to 30, in Orlando, Fla. View the SIP/SIP Trunking track, and register now using the code NOJITTER to receive $300 off an Entire Event pass or a free Expo Plus pass.