Hi! I was capturing a RTP communication between two PC, where in each of one the wireshark was sniffing. Finally when the communication finished I stopped the wireshark and then I went to Telephony-->RTP-->Show All Stream, and the values that had each computer in both ways, were different in each computer. Why this happens if they were capturing the same communication? why one computer show me that there are more jitter than the other one?
P.D: I attached the results of both computers!
asked 01 Nov '12, 01:36
As you can see, there are less packets (only one) in one capture. In general, packet loss will have an influence on the jitter calculation. In your case however, it's just one packet. So, that should not have such a big influence (hard to tell without access to the capture file).
There can be a much bigger influence on the jitter calculation. Packets may not arrive in the same order as they were sent (taking different routes, QoS on routers, etc.). So if the packets arrive in a different order, you will get totally different values for jitter.
HOWEVER, your hosts seem to be on the same network (192.168.0). So a packet reordering is rather unlikely.
So, what's the reason for the different jitter values? Some suggestions:
Can you post the capture files (cloudshark.org) for further analysis?
UPDATE/SOLUTION: As already mentioned in my comment below, I was a bit "off track" regarding the packet ordering. The RTP jitter calculation is based (mainly) on the timestamp in the frame (arrival time) and the timestamp in the RTP packet (send time). So, if you calculate the jitter at the sender side, you will get much lower jitter, as the delta between frame timestamp and RTP timestamp is much smaller than at the receiver side. So, it should be "normal" to see different jitter values if you calculate those values at the sender/receiver side.
Looking at the reordered packets. That will also have an influence on the jitter, as the frame timestamp (at the receiver) changes slightly due to the different packet order. HOWEVER, this slightly change will only cause a very small change in the jitter value and can (possibly) be ignored.
answered 01 Nov '12, 03:10
Kurt Knochner ♦
edited 02 Nov '12, 09:44