Hi experts,
I'm working on the implementation for '2.4.6 Multiple REFER Requests in a
Dialog' of RFC3515 in a B2B SIP Proxy. Right now, I got stuck with two problems
in the solution. Please see the paragraph from RFC-
A REFER creates an implicit subscription sharing the dialog
identifiers in the REFER request. If more than one REFER is issued
in the same dialog (a second attempt at transferring a call for
example), the dialog identifiers do not provide enough information to
associate the resulting NOTIFYs with the proper REFER.
Thus, for the second and subsequent REFER requests a UA receives in a
given dialog, it MUST include an id parameter[2] in the Event header
field of each NOTIFY containing the sequence number (the number from
the CSeq header field value) of the REFER this NOTIFY is associated
with. This id parameter MAY be included in NOTIFYs to the first
REFER a UA receives in a given dialog. A SUBSCRIBE sent to refresh
or terminate this subscription MUST contain this id parameter.
Different from the definition in RFC, the NOTIFY forwarded by the proxy
contains the same Id in Event header as the other side. Please see the below
chart -
B2BProxy
|
<- REFER 2 (Cseq=2) | <-REFER 1 (Cseq=1003)
. . . | . . .
->NOTIFY 1 (event:id=2) | ->NOTIFY 2 (event:id=2)
The current problem is, the above NOTIFY on the right side should include
'id=1003' instead of 'id=2'.
The solution I'm trying is as in the following flow -
1. get CSeq 1 of REFER 1 in route[b2b_request]{} ->
2. get CSeq 2 of REFER 2 in local_route{}, then save the
pair(key=CSeq2, value=CSeq1) in a map set->
3. get Id from NOTIFY 1 event in route[b2b_request]{} ->
4. use Id as key then get matched CSeq1 from the map set, use
remove_hf() and append_hf() to modify the event header in local_route{}
My two questions are:
1. To transfer Cseq 1 from step1 to step2, I tried a variable in the AVP
type but it didn't work. The script variable can work but it doesn't fit
because the processing is based on per request. Can I ask if you have any
suggest on how to transfer the value from route[b2b_request]{} to local_route{}?
2. In the step2, I tried to create and operate a JSON map set to save the
CSeq pairs. But the JSON data didn't work for me.
My source :
$json(csList) = ""; # Initialize the
data set, not sure if it's correct
$json(csList/"$cs") = "$avp(csNum)";
The error I got:
ERROR:core:do_assign: setting PV failed
ERROR:core:do_assign: error at
/usr/local//et/opensips/opensips.cfg:531
Thank you very much for the help! Any your suggests are very welcomed.
Thanks,
Li
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