I am a telecommunications specialist with over twenty years of experience. I own a telecommunications services company that provides network design, management, and administration services as well as telecom consulting services. I've been involved in the education and training of network professionals in areas including IP telephony and networking technologies. I have experience with Cisco's UC solutions since 2003 when Call Manager version 4.1 was still around. I have dealt with live implementations of Cisco's CUCM, Unity, IPCC, Attendant Console, and voice gateway products.
Troubleshooting VoIP issues can be troublesome. When something goes wrong, the lack of direct visibility as to what is occurring on the network with SIP and RTP packets can initially be intimidating to network and voice engineers. However, Wireshark SIP analysis turns ordinary engineers into superheroes, allowing them to see deep into the network and determine exactly what is happening.
In this article, we’ll get our hands dirty by examining a real voice packet capture from a production network. We’ll go through the whole scenario, delving deeply into the details of the voice packets being exchanged. Let’s get started!
When there’s trouble in the network, and voice services are suffering, those in need will call upon you, the networking superhero! As a superhero, you use your x-ray vision to zoom in to the microscopic world of voice packets, to perform a Wireshark packet analysis, and to investigate the malfunction and make things right. Then you will be hailed as the liberator and protector of the network!
When I encounter a problem on a VoIP network that needs troubleshooting, I just wish that I had microscopic X-ray vision, like a superhero who is able to peer into the subatomic level of things. It would be so advantageous to be able to instantaneously see what is going on with transmissions on the network. When you experience voice quality issues, one way or choppy voice, or call setup problems, it would be great to be able to see, are the voice packets arriving? How are they arriving? What kind of signaling is getting through and what is being blocked and where? These are questions I wish I had instant access to, and this is what port mirroring is all about.
You get a call from a user stating that they have experienced poor voice quality issues with their Cisco IP phone. Your mind goes numb, your palms get sweaty, and your eyes glaze over. What do you do? Where do you start? It’s so much easier to deal with problems where something stops working completely, rather than trying to resolve an intermittent fault such as bad voice quality.
Why are poor voice quality issues so difficult to tackle? It’s usually because there is a myriad of different causes, and the methodology to investigate those causes is not always readily or intuitively clear. For voice troubleshooters, it is important to have a battle plan in place to quickly zero in on causes of voice degradation and to diagnose, identify, and resolve them as quickly as possible.
This article will focus on this battle plan so that you can identify the problem quickly, and determine the first troubleshooting steps, which are often the most difficult to decide upon.