Debugging MS Teams Traffic
Skype client protocols
This page describes how Skype traffic can be analyzed with the Allegro Network Multimeter. The Skype client heavily relies on SSL for all control based traffic and RTP for all audio based traffic.
The Allegro Network Multimeter allows to search for traffic to the microsoft cloud, helps to analyze the response time of the SSL encrypted control traffic and the RTP analytics.
Skype control traffic
The skype control traffic is SSL encrypted. This does not allow to decode and analyse the content of the control connection. As SSL uses the TCP as layer 4 protocol, all quality statistics of the tcp connection can be used for debugging. The most importent quality parameters are:
- TCP handshake response time
- TCP retransmission rates
- TCP Zero window times
Please read the TCP module for more information about this and more counters.
A simple way to get an overview of the response time for skype servers is the IP statistics table. You can use the free text search for "skype" and select the the graph dialog: "tcp response time". This will present you the top IP addresses with a correlated name to skype and their tcp response time.
This graph shows you the delay of the tcp stack to confirm the reception for data. Please note that many tcp stacks wait a few milliseconds if there is no data to respond ( see [Wikipedia TCP delayed acknowledgment]. So any delay below above this value ( usually 40 ms ) shows a significant delay in the roundtrip time. If you have installed the Allegro close to the Skype client, it will be the roundtip time of the tcp packets from your network to the Skype could.
The used DNS names and IP address ranges for can differ for Skype as it is a propietary protocol. a current description for Skype for Business can be found here: [https://techcommunity.microsoft.com/t5/skype-for-business-blog/simplified-port-requirements-for-skype-for-business-online/ba-p/77094]
This can be done also for tcp retransmissions and zero window. If you have installed the Allegro close to the Skype client, this will indicate if the data sent to the Skype server required a retransmission on the WAN link.
Skype audio traffic
The Skype audio traffic is sent by RTP frames with encrypted content but not the RTP header. You can easily debug the RTP traffic with the RTP decoder output of the Allegro Network Multimeter.
To get an overview of which IPs have used RTP, you can use the Applications → RTP statistics.
You can also navigate directly to an IP Address and see all RTP connections of it.