[OpenSIPS-Users] About obstacles to implement the matched Id in event header of NOTIFY(REFER)

Li Cai Li.Cai at comtech.com
Fri Jul 22 20:02:36 UTC 2022

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 -
                <- 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.


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