November 6, 2013

SIP Trunk Equipment Issues, How to Avoid Them

Session Initiation Protocol (SIP) trunk implementation issues not only include the provider, but there is also equipment that can be the source of problems. The SIP trunking problems encountered with equipment vendors have in some cases improved and in others have become worse since 2012. Every year The SIP School™ performs an international survey, "The SIP Survey 2013," discussing the status and problems relating to SIP trunk implementations. This year's free survey report points out that some problems still persist when compared to the 2012 survey. 

The problems that have not been resolved or have deteriorated in the last year are at issue. One would expect that with the growth and maturing of SIP trunking and the experience that equipment vendors have attained, the problem situations would have improved in time. Not so. 

The 2013 SIP Survey posed many questions. The two questions for the respondents dealing with the equipment side of SIP trunking are discussed in the TechNote. The survey answers were then compared to the 2012 survey results.

IP PBX Problems

(1) Survey question 1: If the problems were found to be with your SIP/ VoIP based PBX, what were they?

Five areas of concern with the IP PBX vendors SIP trunks support were questioned. Some have improved or remained the same.

"No SIP Licenses" is hard to believe. This begs the question - How much knowledge do enterprises have of the IP PBX they have implemented? This should be a no-brain problem that should not occur. Check first with your vendor about license requirements before deploying SIP trunks. The SIP license may not be included in your procurements. You also may not have enough session licenses installed, thereby limiting the number of simultaneous sessions supported. 

"SIP Registration Failures" to the Internet Telephony Service Provider (ITSP) have remained the same as reported in the 2012 survey. There should have been improvement in this area. Lack of improvement is probably due to improper configuration on the part of the IT staff supporting the IP PBX or more likely the VAR. In either case, I question the enterprise and VAR training, as well as the vendor documentation. Is it just poor typing skills and/or unverified data entry? This problem should be eliminated with adequate cutover testing.

"SIP Trunks Keep Dropping" has declined slightly as a problem area. If this is an issue for your company, determine if the problem occurs during heavy traffic. If so, it may very well be a provider problem.

"Codec Issues" have increased since the 2012 survey. This is most likely due to mis-match configuration problems. If you have codec issues, check the settings carefully. Ensure that the default codec matches the SBC setting.

"PBX Firmware Upgrades" have become less of a problem area. However, upgrades still remain the biggest problem. Check with your VAR or vendor to determine if there are updates that may affect SIP trunk deployment and operation. Postponing the updates could shut down the operation. Make sure that the updates are matched properly with the SBC settings.

Edge Device Problems

(2) Survey question: If your problems were with your SBC / Edge devices, what were they?


First, some SBC / edge device problems have diminished. For example, the "No Audio" and "Calls to the PSTN Blocked" have decreased as problem areas. However, the problems in six other categories have increased since the 2012 survey.

"SBC Failures," such as a crash or lock-up, have increased but remain a minor problem. This problem is preventable by ensuring that the SBC is properly tested. Increased SBC failures may be due to the lack of installing an update or improper configuration.

"Codec Issues" is the second most common problem area. These types of issues should not be on the rise as those working with this 'specialized' equipment should have a good understanding of codecs. The enterprise staff and VARs that are able to work with others involved in an implementation should ensure that codecs are configured correctly and tested thoroughly (the real issue).

"Required Firmware Updates" to fix problems is an area that worsened considerably. These issues appear to be negligence on the part of the VAR or IT department. It is also possible that the SBC vendor is not being diligent in updating their firmware downloads.

The biggest problem - "One Way Audio" - remains the primary headache with the SBC. This was the worst problem area reported in 2012 and remains the worst problem area in 2013. The rise in this number is significant. This issue strongly highlights the importance of testing all components together before deploying and initializing the SIP trunking service. The results of such testing could influence the purchasing decisions of edge devices. 

"One Way Audio" is frequently the result of "NAT breaking SIP" which means that since SIP operates at the Application Layer and the NAT is created at the transport layer of the network, media often cannot reach the SIP device being used in the network because it's private IP address is not routable outside the Local Area Network. One of the beneficial functions of the SBC is to resolve that NAT traversal issue and to rewrite the header information so that SIP can reach those devices.

"QoS Issues" is another problem area most likely due to mis-configuration. QoS could also be a trunk provider problem if there is not enough bandwidth for all the simultaneous sessions to be running.

"SIP Registration Failures" are most likely configuration problems.

Test Enough

These types of equipment problems point out that the initial configuring and testing was done incorrectly, incompletely, or with negligence on the part of the technicians, VAR vendor, and/or IT staff. You have to test to ensure that the features and functions are working. 

You should also test the features and functions under a full traffic load. Full load testing will help to determine the actual performance, not theoretical performance, is delivered. Full load testing means passing the maximum traffic (number of simultaneous sessions) through the equipment to see if it can deliver the capacity promised. You may also find that the call establishment rate (calls per second that are generated by the IP PBX) cannot be handled by the SBC. It is during the full load testing period when unknown problems will surface.

Tweaking for Results Creates Problems

Some enterprise and VAR technicians like to continue to change the configuration and software settings until the device works properly. This should be avoided as the tweaking can turn off features, change security settings by discontinuing a security feature or blocking calls, or produce a liability that will produce new problems in the future. When changes are made to solve a problem, ensure that the documentation of the changes is produced so that there is a useful record available if new issues emerge in the future. If not, the change procedure starts all over again, delaying resolution, and the enterprise will continue to encounter outages or poor operation.

Finally, remember that there are five participants in this SIP trunking configuration: (1) the IP PBX vendor, (2) the SBC vendor, (3) VAR, (4) the SIP trunking provider, and (5) the enterprise staff. How much they know about each other is very important. Lack of knowledge and experience dealing with the interoperability issues may be the real problem, not the products or services offered.

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