Administrator’s Guide for SIP-T2 Series/T4 Series/T5 Series/CP920 IP Phones
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X is the account ID. For T54S/T48S/T48G/T46S/T46G/T29G, X=1-16; for T52S/T42G/T42S, X=1-12; for T41P/T41S/T27G,
X=1-6; for T40P/T40G/T23P/T23G, X=1-3; for T21(P) E2, X=1-2.
Call Completion
When you place a call and the callee is temporarily unavailable to answer the call, call completion allows your phone to
monitor the busy party and establish a call after the busy party becomes available to receive a call.
Two factors commonly prevent a call from connecting successfully:
l Callee does not answer
l Callee actively rejects the incoming call before answering
Yealink IP phones support call completion using the SUBSCRIBE/NOTIFY method, which is specified in draft-poetzl-sip-
ping-call-completion-00, to subscribe to the busy party and receive notifications of their status changes.
The caller subscribes for update notifications of the dialog event from the busy party. Example of a SUBSCRIBE mes-
sage:
SUBSCRIBE sip:1000@10.10.20.34:5060 SIP/2.0
Via: SIP/2.0/UDP 10.10.20.32:5060;branch=z9hG4bK2880274891
From: "10111" <sip:10111@10.2.1.48:5060>;tag=8643512
To: <sip:1000@10.2.1.48:5060>;tag=4025601441
Call-ID: 4_2103527761@10.10.20.32
CSeq: 2 SUBSCRIBE
Contact: <sip:10111@10.10.20.32:5060>
Accept: application/dialog-info+xml
Max-Forwards: 70
User-Agent: Yealink SIP-T46G 28.82.0.20
Expires: 60
Event: dialog
Content-Length: 0
Example of a NOTIFY message (The subscription (SUBSCRIBE message) of the dialog event “Call Completion” is con-
firmed by the busy party):
NOTIFY sip:10111@10.10.20.32:5060 SIP/2.0
Via: SIP/2.0/UDP 10.10.20.31:5060;branch=z9hG4bK1830418099
From: <sip:1000@10.2.1.48:5060>;tag=1032948194
To: "10111" <sip:10111@10.2.1.48:5060>;tag=722495580
Call-ID: 0_160090766@10.10.20.32
CSeq: 2 NOTIFY
Contact: <sip:1000@10.10.20.31:5060>
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