Yealink CP969 Administrator's Manual page 360

Administrator's Guide for SIP-T5 Series Smart Media Phones
support two call hold methods, one is
to sendonly, recvonly or inactive (e.g., a=sendonly). The other is
(connection addresses for the media streams) in the SDP to zero (e.g., c=0.0.0.0).
Call hold tone allows IP phones to play a warning tone at regular intervals when there is a call on
hold. The warning tone is played through the speakerphone.
Procedure
Call hold can be configured using the following methods.
Central Provisioning
(Configuration File)
Web User Interface
Details of Configuration Parameters:
features.play_hold_tone.enable
338
RFC 3264, which sets the "a" (media attribute) in the SDP
<y0000000000xx>.cfg
Parameters
RFC 2543, which sets the "c"
Configure the call hold tone and call
hold tone delay.
Parameters:
features.play_hold_tone.enable
features.play_hold_tone.delay
Specify whether RFC 2543
(c=0.0.0.0) outgoing hold signaling
is used.
Parameter:
sip.rfc2543_hold
Configure the call hold tone and call
hold tone delay.
Specify whether RFC 2543
(c=0.0.0.0) outgoing hold signaling
is used.
Navigate to:
http://<phoneIPAddress>/servlet?m
=mod_data&p=features-general&q
=load
Permitted Values
0 or 1
Default
1