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How to understand "DPNSS/DASS2-User Adaptation Layer"

asked 2021-02-17 15:59:44 +0000

prokino gravatar image

updated 2021-02-18 09:40:48 +0000

Wireshark detects DPNSS / DASS2 protocol in SCTP packets.
But it cannot recognize the content of DPNSS / DASS2 protocol.
Please tell me where could the error be?
And how can I figure out what's in DPNSS / DASS2?
Here is the screen of Wireshark where DPNSS / DASS2 protocol shown

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There is a pcap attached to "Per-packet memory corrupted" crashes if file contains DUA packets that has a few DUA frames.
Do they look like the decode information you're looking for?

Chuckc gravatar imageChuckc ( 2021-02-18 01:12:09 +0000 )edit

Here is the screen of Wireshark where DPNSS / DASS2 protocol shown Wireshark screen - DPNSS / DASS2 protocol

prokino gravatar imageprokino ( 2021-02-18 09:38:32 +0000 )edit

Are you sure it's DUA over SCTP? Not something else using that ppid?

Anders gravatar imageAnders ( 2021-02-18 12:08:33 +0000 )edit

As stated in RFC4960, the SCTP protocol has no effect on what data it carries. I'm not sure if this is exactly DPNSS / DASS2.

prokino gravatar imageprokino ( 2021-02-18 16:07:45 +0000 )edit
Anders gravatar imageAnders ( 2021-02-19 15:55:40 +0000 )edit

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answered 2021-02-20 16:49:34 +0000

Chuckc gravatar image

If you follow the RFC chain, it seems the DUA data is scrambled.
It seems to be the correct length (56 = 0x38) but the fields, starting with version, don't make sense.
The RFC says only version 1 is supported and the screen shot shows - Version: Unknown (0)

As @Anders asked above, is it possible that this is a different message type using the DUA PPID of 10?


SCTP Payload Protocol Identifiers = 10 (DUA) RFC4129

RFC4129 - Digital Private Network Signaling System (DPNSS)/Digital Access Signaling System 2 (DASS 2) Extensions to the IUA Protocol

   This document defines a mechanism for backhauling Digital Private
   Network Signaling System 1 (DPNSS 1) and Digital Access Signaling
   System 2 (DASS 2) messages over IP by extending the ISDN User
   Adaptation (IUA) Layer Protocol defined in RFC 3057.


RFC4233 (obsoletes RFC3057) - Integrated Services Digital Network (ISDN) Q.921-User Adaptation Layer

3.1.  Common Message Header

   The protocol messages for Q.921-User Adaptation require a message
   header that contains the adaptation layer version, the message type,
   and message length.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Version    |   Reserved    | Message Class | Message Type  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Message Length                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 2.  Common Header Format

   All fields in an IUA message MUST be transmitted in the network byte
   order, unless otherwise stated.

3.1.1.  Version

   The version field contains the version of the IUA adaptation layer.
   The supported versions are the following:

      Value    Version
      -----    -------
        1      Release 1.0

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Asked: 2021-02-17 15:59:44 +0000

Seen: 62 times

Last updated: Feb 20