Yealink SIP-T54S Administrator's Manual page 468

Administrator's Guide for SIP-T2 Series/T19(P) E2/T4 Series/T5 Series/CP860/CP920 IP Phones
a call on hold.
If it is set to 1 (Enabled), SDP media direction attribute "a=inactive" is used when placing a
call on hold. RTP packets will not be sent or received.
X ranges from 1 to 16 (for SIP-T54S/T48G/T48S/T46G/T46S/T29G)
X ranges from 1 to 12 (for SIP-T52S/T42G/T42S)
X ranges from 1 to 6 (for SIP-T41P/T41S/T27P/T27G)
X ranges from 1 to 3 (for SIP-T40P/T40G/T23P/T23G)
X ranges from 1 to 2 (for SIP-T21(P) E2)
X is equal to 1 (for SIP-T19(P) E2/CP860/CP920)
Note: It works only if the value of the parameter "sip.rfc2543_hold" is set to 0 (Disabled).
Web User Interface:
None
Phone User Interface:
None
To configure call hold tone and call hold tone delay via web user interface:
Click on Features->General Information.
1.
Select the desired value from the pull-down list of Play Hold Tone.
2.
Enter the desired time in the Play Hold Tone Delay field.
3.
Click Confirm to accept the change.
4.
To configure call hold method via web user interface:
Click on Features->General Information.
1.
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Parameters Permitted Values Default