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Malformed packet in the GSM MAP

Hi,

We couldn't decode some GSM MAP packets in the wireshark.

Kindly check and revert, how to decode it properly in the wireshark.

Thanks, Varghese

Hanosh's avatar
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Hanosh
asked 2018-05-25 06:16:43 +0000
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At the very least you would need to provide the capture that has the issue and your OS and Wireshark version details.

grahamb's avatar grahamb (2018-05-25 08:50:47 +0000) edit
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Thanks for the response. I couldn't attach the trace here, So I just pasted below and Version 1.2.8 (SVN Rev 32676)

[... snipped for brevity ...]

GSM SMS TPDU (GSM 03.40) SMS-DELIVER
    1... .... = TP-RP: TP Reply Path parameter is set in this SMS SUBMIT/DELIVER
    .1.. .... = TP-UDHI: The beginning of the TP UD field contains a Header in addition to the short message
    ..1. .... = TP-SRI: A status report shall be returned to the SME
    .... .1.. = TP-MMS: No more messages are waiting for the MS in this SC
    .... ..00 = TP-MTI: SMS-DELIVER (0)
    TP-Originating-Address - (919566737288)
    TP-PID: 0
    TP-DCS: 0
        00.. .... = Coding Group Bits: General Data Coding indication (0)
        Special case, GSM 7 bit default alphabet
    TP-Service-Centre-Time-Stamp
        Year 18, Month 05, Day 15
        Hour 09, Minutes 59, Seconds 03
        Timezone: GMT + 5 hours 30 minutes
    TP-User-Data-Length: (6) depends on Data-Coding-Scheme
    TP-User-Data
        User-Data Header
            User Data Header Length (32)
            IE: Reserved for ...
(more)
Hanosh's avatar Hanosh (2018-05-25 10:48:47 +0000) edit
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1.2.8 is a very old version (nearly a decade), any chance of trying a modern one that might have fixed the issue?

grahamb's avatar grahamb (2018-05-25 11:54:11 +0000) edit
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1 Answer

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This GSM SMS message really seems to be malformed. It's header indicates that the TP-User-Data-Header is present. So the TP-User-Data 20 58 0E 86 c3 01 starts with a User Data Header. Per 3GPP 23.040 chapter 9.2.3.24, the first byte (here 0x20) is the length of the header. But there are only 5 bytes remaining in the payload and not 32, thus the decoding failure. What was the expected content of the SMS message?

Pascal Quantin's avatar
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Pascal Quantin
answered 2018-05-25 13:59:06 +0000, updated 2018-05-25 13:59:46 +0000
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