Codec List in SIP-Initiated Offer


The CSP can send a list of up to five supported codecs in an offer to an endpoint when establishing a media session. The receiving endpoint selects one codec from that list and reports the selection back in the answer message to the CSP.

The following applies to this feature:

The codec list is applicable for calls that use SIP or H.323 signaling and is not for clear-channel VoIP calls. For H.323 signaling, refer to Codec List in H.323-Initiated Offers.

The IP Network Interface card must use Profile 2.

The VDAC-ONE card must use Profile 0.

Without this feature, the call might not get established because the CSP could include a codec type that the endpoint will not accept.

The figure below provides an overview of this process.

Figure 5-7 Codec List in Offer


Outseize Control message

The host application provides the codec list and sends the list in the Outseize Control message as shown in the next figure:

Figure 5-8 Host Provides Codec List

TLVs Used

Use the following TLVs in the Outseize Control message to include the codec types:

0x29FF - Local End-Point Media Info

0x2A0E - Media Connection Address

0x2A01 - Per Media Stream Information

0x2A03 - Media Type

0x2A07 - Media Port

0x2A02 - Per Codec Info

The trace below shows how to nest these TLVs in the Outseize Control message. Note that the Outseize Control message cannot exceed 260 bytes.

Important! DO NOT use the following TLVs for these codec types:



0x0100 - RTP Payload Type

0x0101 - RTP Payload Size

0x27B0 - RTP Payload Type

0x27B1 - RTP Payload Size

Outseize Control Message Trace

The following is a message trace for the Outseize Control message followed by the corresponding SIP INVITE message.






INVITE sip:5087@ SIP/2.0

Via: SIP/2.0/UDP

To: 5087<sip:5087@>

From: 00000000<sip:00000000@>;tag=19353246318f

Call-ID: EXCEL-CSP255.78f.12687.680@

Contact: 00000000<sip:00000000@>

User-Agent: Excel_CSP/83.1.115

Supported: timer

Session-Expires: 40

Min-SE: 39


Content-Type: application/sdp

Content-Length: 142



o=sip 946686677 946686677 IN IP4


c=IN IP4

t=0 0

m=audio 23440 RTP/AVP 0 8 18

a=rtpmap:0 PCMU/8000