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Codec List in SIP-Initiated Offer
Overview
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 4-5 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 4-6 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.
SIP INVITE
INVITE sip:5087@10.10.1.203:5060 SIP/2.0
Via: SIP/2.0/UDP 10.10.1.32
To: 5087<sip:5087@10.10.1.203:5060>
From: 00000000<sip:00000000@10.10.1.32:5060>;tag=19353246318f
Call-ID: EXCEL-CSP255.78f.12687.680@10.10.1.32
Contact: 00000000<sip:00000000@10.10.1.32:5060>
User-Agent: Excel_CSP/83.1.115
Supported: timer
Session-Expires: 40
Min-SE: 39
CSeq: 1 INVITE
Content-Type: application/sdp
Content-Length: 142
v=0
o=sip 946686677 946686677 IN IP4 10.10.1.32
s=SIP_Call
c=IN IP4 10.10.1.37
t=0 0
m=audio 23440 RTP/AVP 0 8 18
a=rtpmap:0 PCMU/8000