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SIP Troubleshooting with the AUKUA Packet Capture Tool

I see more people using softphones on their computers, phones and tablets. Why not, it’s convenient and gives us so much control of how we can stay in touch.

In some cases, you might have multiple sip accounts and end up using a third-party SIP client. This is when you might run into configuration “inconsistencies”. Even I experienced this issue on my SIP client softphone application.

The problem I experienced was that my softphone client would seldom successfully connect and constantly reported “SIP Registration Failure” on the application status bar. I did some research and looked through the SIP vendor’s forum and the consensus was that the network was blocking, or dropping the SIP packets required for the call setup. Some blamed NAT’ing and others blamed the SIP client software since the “free apps are all garbage”. Pretty strong accusation which I promptly ignored.

In my case, the network theory could not be the issue since I had an ATA configured with the same settings and it worked without a problem.

Today I decided I was going to try and figure this out once and for all.

The main issue I run into is how to capture packets from a WIFI device. In this case, the easiest solution was to place my Aukua MGA2510 ( between the switch ports and capture the packets from the Android phone after it traverses the access point.

I received a MGA2510 Packet capture appliance from AUKUA and thought let’s put it to the test. It didn’t take long to set up and I placed it in line between two switches that the access point is connected to. I then set up an IP capture filter and got my packets.

I wanted to just mirror/span/monitor the access point but the switch was unmanaged. In many cases when I go to client jobs, I don’t have access to their switches or they can’t configure span ports on the fly, so it’s the same thing as having an unmanaged switch.

I also considered inserting a TAP inline but was concerned that my laptop would be able to keep up with the current traffic flow. According to the Aukua, the max bandwidth going across the switch spiked up to 400 Mbps and approximately 12,000 packets/sec one way. The other practical issue was that I wasn’t physically located close to the switch uplink ports/tap.

As you can see from the trace the SIP error message was pretty obvious and fairly specific so I found the settings in my softphone client and now it works 100% of the time with no issue.

When I perform VOIP or softphone baselines or troubleshooting reports, I try to document all the SIP commands.


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