[SIPForum-discussion] SIP Glare

Kevin P. Fleming kpfleming at digium.com
Thu Jun 9 14:03:47 UTC 2011

On 06/07/2011 05:56 PM, Aniella Juverdeanu wrote:
> Hi,
> But for SIP signaling one port is used (in majority of the cases port 5060) for multiple calls at each SIP end point.
> If you refer to RTP then you use different ports for - each RTP endpoint will have a port from which will send the RTP packets and will receive the RTP packets for the duration of one call. The ports are sent in SDP m= line - so it doesn't matter that the far end happened to send the same port  as the originator - the ports are at different IP addresses.

All of this is correct, but you haven't described any 'glare' situation 
(a call failing to setup because the two endpoints attempt to use the 
same resource at the same time).

Yes, both ends are probably using the same port number for their SIP 
signaling, but this is irrelevant, because the protocol can easily 
handle multiple dialogs on the same port at the same time.

Kevin P. Fleming
Digium, Inc. | Director of Software Technologies
Jabber: kfleming at digium.com | SIP: kpfleming at digium.com | Skype: kpfleming
445 Jan Davis Drive NW - Huntsville, AL 35806 - USA
Check us out at www.digium.com & www.asterisk.org

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