Yealink SIP-T54S Administrator's Manual page 1032

Administrator's Guide for SIP-T2 Series/T19(P) E2/T4 Series/T5 Series/CP860/CP920 IP Phones
What is the difference between enabling and disabling the RFC 2543
Hold feature?
Capturing packets after you enable the RFC 2543 Hold feature. SDP media direction attributes
(such as a=sendonly) per RFC 2543 is used in the INVITE message when placing a call on hold.
Capturing packets after you disable the RFC 2543 Hold feature. SDP media connection address
c=0.0.0.0 per RFC 3264 is used in the INVITE message when placing a call on hold.
For more information on RFC 2543 hold feature, refer to
information on capturing packets, refer to
What is the difference between Shared Call Appearance (SCA) and
Bridge Lines Appearance (BLA)?
SCA and BLA are similar signaling methods that enable more than one phone to share a SIP
line. The method you use varies with the SIP server you are using. In the configuration files, the
relevant configuration parameters of SCA and BLA are different. The barge-in and call pull
feature are not available with BLA; but they are available with SCA.
1006
Call Hold on page 439. For more
Capturing Packets on page 978.