Session Timer - Yealink SIP-T2 SERIES Administrator's Manual

Administrator's Guide for SIP-T2 Series/T19(P) E2/T4 Series/CP860 IP Phones
Enter the desired value in the SIP Session Timer T4 (2.5~60s) field.
4.
The default value is 5.
Click Confirm to accept the change.
5.

Session Timer

Session timer allows a periodic refresh of SIP sessions through an UPDATE request, to determine
whether a SIP session is still active. Session timer is specified in
refresher modes: UAC and UAS. Whether the endpoint functions as a UAC or a UAS depends on
the UA that initiates the SIP request. If the initiator is configured as UAC, the other client or the
SIP server will function as a UAS. If the initiator is configured as UAS, the other client or the SIP
server will function as a UAC. The session expiration is negotiated via the Session-Expires header
in the INVITE message. The negotiated refresher is always the UAC and it will send an UPDATE
or request at the negotiated session expiration. The value "refresher=uac" included in the
UPDATE message means that the UAC performs the refresh.
Example of UPDATE message (UAC mode):
UPDATE sip:1058@10.10.20.34:5060 SIP/2.0
Via: SIP/2.0/UDP 10.10.20.32:5060;branch=z9hG4bK2104991394
From: "10111" <sip:10111@10.2.1.48:5060>;tag=2170397024
To: <sip:1058@10.2.1.48:5060>;tag=200382096
Call-ID: 4_1556494084@10.10.20.32
CSeq: 2 UPDATE
Contact: <sip:10111@10.10.20.32:5060>
Max-Forwards: 70
User-Agent: Yealink SIP-T23G 44.80.0.60
Session-Expires: 90;refresher=uac
350
RFC 4028. IP phones support two