PGW:Integrated SLT fails to get ss7 alignment with itu2LSC_LinkFailure reason=0x5 (Two or three invalid BSNs)

Unanswered Question
Sep 20th, 2010


I´m in a trouble with SS7 ITU signaling links. they fails to get alignment witn reason=0x5 (Two or three invalid BSNs). The debug of backhaul lssu reports event=0x6-protocol error cause=0x2 (Abnormal BSN (Backward Sequence Number)).  The links are terminated in a AS5350XM with integrated SLT feature. I Attached a trace of debug ss7 mtp2 *.

Thank you for your help

Juan Manuel Munárriz


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anikas Tue, 09/21/2010 - 05:18

I looked at the debug and this could be any number of things that would caise the BSN failures. Normally this means that there are problems with your facilities. If the facilities are clean on both ends of the link and the error correction is the same (PCR or basic).

Finally, try to collect an ss7 analyser capture of the alignment process and check the SLTMs.

It may be that both ends are not cofigured properly or are in loopback at one side.

You just want to check that the OPC,DPC, SLC and NI are the same on both ends of the link.

JUAN MANUEL MUNARRIZ Thu, 09/23/2010 - 05:20

hi anikas,

thank you very much for you interesting response. The transmision is free of errors. I double checked all the parameters (PCs,NIs,SLCs) and I made testes with the different types of error correction and the problem remains. Anyway with the snooper I can see SLTM interchanges and it seems something extrange. Both sides send SLTM:

12:19:52.414627  1-136-3[03139]       1-081-7[02703]       ITU  SNT.. -> SLTM (11) SLC=1
                                                                         Pr:3 Ni:NTL

********************************** DETAIL **********************************
SIGNALING LINK TEST - SNT                          0x11
   SLC                            0
   LENGTH:                        0x09
  0x54 0x72 0x61 0x6E 0x73 0x50 0x61 0x74 0x68
******************       END_OF_MSG                       ******************

12:19:52.465296  1-081-7[02703]       1-136-3[03139]       ITU  SNT.. -> SLTM (11) SLC=1
                                                                         Pr:0 Ni:NTL

********************************** DETAIL **********************************
SIGNALING LINK TEST - SNT                          0x11
   SLC                            0
   LENGTH:                        0x01
******************       END_OF_MSG                       ******************

But no one send SLTAs.

And the SLTM from my switch  1-136-3[03139] are answered  from another DPC (3703) with a message that the snooper  fails to decode but wireshark sniffer show as:

Cisco Session Management
    SM Message type: PDU Message (0x8000)
    Protocol Type: 0x0001
    Message ID: 0x0000
    Message type: mtp3 from SLT (0x11)
    Channel ID: 0x0000
    Bearer ID: 0x0000
    Length: 16
Message Transfer Part Level 3
    Service information octet
        11.. .... = Network indicator: Reserved for national use (0x03)
        ..00 .... = Spare: 0x00
        .... 1111 = Service indicator: Spare (0x0f)
    Routing label
        .... .... .... .... ..00 1100 0100 0011 = DPC: 3139
        .... 0011 1001 1101 11.. .... .... .... = OPC: 3703
        0001 .... .... .... .... .... .... .... = Signalling Link Selector: 1
Data (11 bytes)

0000  21 90 54 72 61 6e 73 50 61 74 68                  !.TransPath
    Data: 21905472616E7350617468

and as you can see in this packet is enclosed the SLTM pattern (0x21905472616E7350617468). Any idea?

Thank you

Best regards

Juan Manuel Munarriz

econneely Tue, 09/28/2010 - 05:37

Hi Juan

Not sure if you cleared this, but here are my thoughts:

From your IOS debug I see you are sending SIE and receiving SIN. Almost certainly a mismatch in the Point Code and SLC as Anikas illustrated. It appears you are trying to establish a link to an already connected PC? Suggest you check your C7-lnk config against the IOS config on the Media Gateway. If you attach both comfig.mml and the IOS running config, that might allow for further investigation. Perhaps a schematic of the PC interconnect on your network also?


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