Ethereal-users: [Ethereal-users] Question about SAP/SDP interpretation

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From: "John Senior" <johns@xxxxxxxxxx>
Date: Thu, 6 May 2004 10:35:59 -0400
Title: Question about SAP/SDP interpretation

Hello,

My name is John Senior and I work at VBrick Systems developing streaming video solutions.

Our products make extensive use of the SAP/SDP protocols and it seems that our interpretation of the protocol differs slightly from the interpretation used by the Ethereal Network Protocol Analyzer.

Our products allow the user to optionally configure keywords to be included in the SAP/SDP announcements. These keywords are placed in the SAP/SDP using the syntax for keyword attributes as suggested the following paragraph from RFC2327:

      a=keywds:<keywords> Like the cat attribute, this is to assist identifying wanted sessions at the receiver. This allows a receiver to select interesting session based on keywords describing the purpose of the session. It is a session-level attribute. It is a charset dependent attribute, meaning that its value should be interpreted in the charset specified for the session description if one is specified, or by default in ISO 10646/UTF-8.

Ethereal is happy with our SAP/SDP as long as the source is configured with at least one keyword as in the following example:

      a=keywds:LALA

Ethereal reports a [Malformed Packet: SDP] error if our SAP/SDP source is configured with no keywords which results in the following line in our SAP/SDP:

      a=keywds:

We believe that an "empty" keywords attribute line is compliant with the specification and therefore we think this might be a bug in Ethereal.

I have attached two example capture files. "Vbrick-with-category.eth" contains an example of our SAP/SDP packet with keyword LALA configured (Ethereal is happy)  "Default-Vbrick.eth" contains an example of our SAP/SDP with no keywords configured (Ethereal is not happy) Note that the VBrick SAPs are from source address 172.30.47.47 in each of these capture files. 

I am testing with Ethereal Version 0.10.3.

Please let me know what you think of this issue.
VBrick is very committed to standards compliance so we would like to be sure our interpretation of the RFC is valid.

Thanks,

- John

--------------------------------------------------------
John M. Senior
Software Engineering Section Manager
VBrick Systems, Inc.
Phone: 203-303-0117
Fax:: 203-265-6750
Email: johns@xxxxxxxxxx
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