[SIPForum-discussion] SIP Glare

Rohan Almeida almeida.rohan at gmail.com
Tue Jun 14 15:07:28 UTC 2011

I agree with kevin, there cant be Glare situation in SIP  be due to
resource conflict.

Glare occurs when both the endpoints send re-invite at the same time.

This situation can is handled by sending 'retry-after' header in 491
or 500 response i.e is 'endpoint 1'  has sent re-Invite to 'endpoint
2' and it receives re-invite from  'endpoint 2'  it should reject the
re-invite with 491 or 500 response.

the link provided by Garron James
explains this in detail.

Rohan Almeida

On 6/9/11, Kevin P. Fleming <kpfleming at digium.com> wrote:
> 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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