Re: [reSIProcate] Why resiprocate just use the branch parameter in via header to distinguish transaction

[Scott Godin <sgodin@xxxxxxxxxxxxxxx>]

Hello,

" First and foremost, the Server should be using Call-ID to distinguish between SIP dialogues.  Before it ever get to looking at Via header Branch-IDs, they should 1^st be looking at Call-ID to establish unique SIP dialogue contexts."

I disagree with your client.  Dialog Id's are higher level than transaction Id's.  There should never be a need to examine the DialogId components (Call Id, To tag, or From tag) to differentiate SIP transactions.  In fact the branch parameter in the Via header is intended to be unique (RFC3261 - Section 8.1.1.7):

"   The branch parameter value MUST be unique across space and time for

   all requests sent by the UA.  The exceptions to this rule are CANCEL

   and ACK for non-2xx responses.  As discussed below, a CANCEL request

   will have the same value of the branch parameter as the request it

   cancels.  As discussed in Section 17.1.1.3, an ACK for a non-2xx

   response will also have the same branch ID as the INVITE whose

   response it acknowledges.

      The uniqueness property of the branch ID parameter, to facilitate

      its use as a transaction ID, was not part of RFC 2543.

   The branch ID inserted by an element compliant with this

   specification MUST always begin with the characters "z9hG4bK".  These

   7 characters are used as a magic cookie (7 is deemed sufficient to

   ensure that an older RFC 2543 implementation would not pick such a

   value), so that servers receiving the request can determine that the

   branch ID was constructed in the fashion described by this

   specification (that is, globally unique).  Beyond this requirement,

   the precise format of the branch token is implementation-defined. "

That being said - resip should be including the sent-by in it's transaction indexing.

17.2.3 Matching Requests to Server Transactions

   When a request is received from the network by the server, it has to

   be matched to an existing transaction.  This is accomplished in the

   following manner.

   The branch parameter in the topmost Via header field of the request

   is examined.  If it is present and begins with the magic cookie

   "z9hG4bK", the request was generated by a client transaction

   compliant to this specification.  Therefore, the branch parameter

   will be unique across all transactions sent by that client.  The

   request matches a transaction if:

      1. the branch parameter in the request is equal to the one in the

         top Via header field of the request that created the

         transaction, and

      2. the sent-by value in the top Via of the request is equal to the

         one in the request that created the transaction, and

      3. the method of the request matches the one that created the

         transaction, except for ACK, where the method of the request

         that created the transaction is INVITE.

   This matching rule applies to both INVITE and non-INVITE transactions

   alike.

      The sent-by value is used as part of the matching process because

      there could be accidental or malicious duplication of branch

      parameters from different clients."

Note:  This has been brought up in the past, but it never did get addressed:

http://list.resiprocate.org/archive/resiprocate-devel/msg08981.html

http://list.resiprocate.org/archive/resiprocate-devel/msg08982.html

Despite the fact that resip really should be including the "sent-by" value in the matching, in practice this has not hindered resip compatibility, since almost all other stack generate the branch parameter using some form of random number generation.

Scott

On Fri, Jun 16, 2017 at 10:23 PM, 海滨 <lhb8859138@xxxxxxx> wrote:

Hi All,

Here is the issue I meet in our product:

1. Client A send the option request to Server with the branch parameter = XXX, sent-by=A

2. Server send the 200 response to the Client A immediatly

3. within 64*T1,Client B send the option request to Server with the same branch parameter =XXX , but sent-by=B.

4. The Server send the last 200 response to Client  A, instead of Client B. So Client B can't receive any response for this option request.

It seems that the resiprocate handle the second option request from Client B with the old transaction and consider this request as retransmission.

Here are my question:

1. In sip standard, the sent-by in via header is also the key value to distinguish transaction. so whether the resiprocate need enhancement for that?

2. The call-ids are different between these two option request, so the designer of clients explain that as below. is he right for the dialog and transaction explanation? in his opinion, the second option request shouldn't handled by the old transaction,because the call-id is different from the first one.

 First and foremost, the Server should be using Call-ID to distinguish between SIP dialogues.  Before it ever get to looking at Via header Branch-IDs, they should 1^st be looking at Call-ID to establish unique SIP dialogue contexts.  From the RFC:

   Call-ID contains a globally unique identifier for this call,

   generated by the combination of a random string and the softphone's

   host name or IP address.  The combination of the To tag, From tag,

   and Call-ID completely defines a peer-to-peer SIP relationship

   between Alice and Bob and is referred to as a dialog.

You are appreciated if can provide help.

Thanks very much.

 

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