Yealink SIP-T54S Administrator's Manual page 766

Administrator's Guide for SIP-T2 Series/T19(P) E2/T4 Series/T5 Series/CP860/CP920 IP Phones
Example of a SIP Notify with the variable value (OK):
Message Header
NOTIFY sip:3583@10.2.40.10:5062 SIP/2.0
Via: SIP/2.0/UDP 10.2.40.27:5063;branch=z9hG4bK4163876675
From: <sip:3586@10.2.1.48>;tag=2900480538
To: "3583" <sip:3583@10.2.1.48>;tag=490600926
Call-ID: 2923387519@10.2.40.10
CSeq: 4 NOTIFY
Contact: <sip:3586@10.2.40.27:5063>
Max-Forwards: 70
User-Agent: Yealink SIP-T46G
Event: ACTION-URI
Content-Type: message/sipfrag
Content-Length: 6
Message Body
key=OK
The following table lists pre-defined variable values:
Variable Value
OK
ENTER
SPEAKER
F_TRANSFER
VOLUME_UP
VOLUME_DOWN
MUTE
F_HOLD/HOLD
F_CONFERENCE
Cancel/CANCEL
X
0-9/*/POUND
740
Phone Action
Press the OK/√ key.
Press the Enter soft key. (not applicable to
SIP-T48S/T48G IP phones)
Press the Speakerphone key (not applicable
to CP860/CP920 IP phones).
Transfers a call to another party.
Increase the volume.
Decrease the volume.
Mute a call.
Place an active call on hold.
Press the Conf/Conference soft key.
Cancel actions or reject incoming calls or end
a call.
Cancel actions or reject incoming calls or
mute or un-mute calls.
Press the keypad (0-9, * or #).