Subject: [SIP] Overlap Sending

From: "Keith Robinson" <[email-masked]>
Date: Fri, 5 Jan 2001 15:50:45 +0000

I have the following query regarding overlap sending as defined in
rfc2543bis-02:

Section 4.2.1 states the following:

"...the UAS compares the Request-URI with Request-URI of the previous INVITE
request
for the same Call-Id. If the Request-URI  contains additional digits in the
'user' part, the UAS
treats the INVITE as adding additional digits to the original dialed string."

This appears to imply that the subsequent INVITE contains the original dialled
string plus the
additional digits; if this is the case, then there is no need for the UAS to
remember the
previous string, and therefore no need to keep any state regarding the previous
attempt.
The subsequent INVITE can really be a new INVITE., i.e. a new Call-Id.

If, on the other hand, the sending UA only sends additional digits, then the
original digits
will have to be remembered by the UAS, and the INVITE matched up with this state
so
this INVITE must be on the same Call-Id.

This latter case is similar to the way existing telephony protocols transmit
addtional digits
when doing overlap sending.

So, upon receiving a response of 484 Address Incomplete, does the sending UA
send
original digits plus aditional digits on a new Call-Id or additional digits only
on the same
Call-Id with an incremented Cseq.

Regards,

K. Robinson.

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From: Steve Levy <[email-masked]>
Date: Fri, 05 Jan 2001 14:32:00 -0800

Hi Keith, 

I was wondering if in considering overlap sending issues and SIP if you were considering the case of overlap sending across multiple networks with variable length digits.

In this case, in order to avoid post dial delay, the digits need to be passed through the networks to the final destiantion network prior to end of dial (since the destination network is the only network that knows how many digits are required). So in effect there may be additional digits sent after an INVITE has been received and sent downstream to the callee.  

Thanks,
Steve