Hi Pekka Pessi;
a) Does the Sofia-SIP soa module support “Delayed Offer”?
b) How can this call scenario be implemented with the soa module?
SOFIA-SIP (soa)
A (UAC) B (UAS)
| |
|<---------- INVITE ----------|
| |
|------- 100 Trying -------->|
|------- 180 Ringing ------>|
| |
|------- 200 (offer) -------->|
|<----- ACK (answer) ------| | |
c) How can this call scenario be implemented with the soa module?
SOFIA-SIP (soa)
A (UAC) B (UAS)
| |
|---------- INVITE ---------->|
| |
|<------- 100 Trying --------|
|<------- 180 Ringing ------|
| |
|<------ 200 (offer) ---------|
|------ ACK (answer) ----->|
| |
Note: RFC 3261 defines two ways that SDP messages can be sent in the Offer and Answer. These methods are commonly known as Delayed Offer and Early Offer, and support for both methods by User Agent Client/Servers is a mandatory requirement of the specification. In the simplest terms, an initial SIP Invite sent with SDP in the message body defines an Early Offer, whereas an initial SIP Invite without SDP in the message body defines a Delayed Offer.
In an Early Offer, the session initiator (calling device) sends its capabilities (for example, codecs supported) in the SDP contained in the initial Invite (thus allowing the called device to choose its preferred codec for the session). In a Delayed Offer, the session initiator does not send its capabilities in the initial Invite but waits for the called device to send its capabilities first (for example, the list of codecs supported by the called device, thus allowing the calling device to choose the codec to be used for the session).
Best regards
Edson G. Leme
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