Advanced Operational Features
41-001343-02 REV05 – 07.2014
6-31
Configurable Codec Negotiation Behavior
By default, when the phone receivess an SDP Offer with several codecs defined for the media stream, the phone will reply
with an SDP Answer containing all the codecs present in the Offer (as per RFC 3264).
A configuration parameter (“
sip single codec reply in sdp
”) is available that allows Administrators to change the phone’s
codec negotiation behavior so that the phone will indicate only one preferred codec in the SDP when replying to an SDP
offer (as per 3GPP TS 24.229).
Defining the “
sip single codec reply in sdp
” as “
0
” (disabled) will maintain the default behavior of the phone (as per
RFC3264). Defining the “
sip single codec reply in sdp
” as “
1
” (enabled) will change the phone’s behavior to indicate only
one preferred codec (as per 3GPP TS 24.229).
Configuring Codec Negotiation Behavior
Use the following procedure to configure codec negotiation behavior:
“Call-Info” Header to 200ok Responses for Shared Call Appearance (SCA)
Lines
In earlier versions of the IP phone software releases, a "Call-Info" header was only added to the requests generated by the
phone for Shared Call Appearance (SCA) lines. A “Call-Info” header ia now also included in the 200ok response to an
INVITE, RE-INVITE, and UPDATE messages for SCA lines. No configuration is required for this feature.
Reason Header Field in SIP Message
The IP Phones support the receiving of the Reason Header Field in a SIP CANCEL message, as described in RFC3326. This
allows a call that is answered from somewhere else to still display in the Callers List. Also, the missed calls indicator and
counter do not change.
Limitation
If the call is answered somewhere else, the duration of the call does not display in the Callers List.
Call Failed Message
Administrators can place certain restrictions on users for making outgoing calls (for example, only allow national calls, only
allow internal calls, only allow emergency calls, etc.). Previously when a restriction was active and a user dialed a number
that was not allowed, the PBX sent a certain status code 4xx and the phone displayed “Call Failed” or “Busy”, which was not
very informative to the user.
Now when an outgoing call fails with a status code 4xx or 5xx, the phone will look for the Reason Header (RFC 3326)
in the
status message and display the Reason Header to the user. The reason text is displayed in the center of the screen and is
limited to 20 characters.
If
there is
a Reason Header in the status code message, the reason text (if any) will be displayed on the phone. The tone that
is played follows the status code (i.e., the busy tone for 486 and 503, and the call failed tone for all others).
Note:
The first codec on the compatible codecs list will be selected as the single preferred codec when the “
sip single codec
reply in sdp
” parameter is enabled.
Configuration Files
For the specific parameter you can set in the configuration files, see Appendix A, the section,
on
