Ethereal-users: Re: [Ethereal-users] Problem with h245 dissector

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From: Guy Harris <guy@xxxxxxxxxxxx>
Date: Wed, 19 Nov 2003 16:23:55 -0800

On Nov 19, 2003, at 10:47 AM, Paul Higgs (CA/EUS) wrote:

I have found a problem with the dissector for H245 in regards to displaying the signalType of a UserInputIndication. The signalType prints as a ? when it is actually an !

H.225.0 CS
    H323_UserInformation
        H323_UU_PDU
            h323_message_body
                h323_message_body: .... .110 : facility (6)
                    FacilityUUIE
                        ProtocolIdentifier: 0.0.8.2250.0.4
                        FacilityReason
                            transportedInformation
                        CallIdentifier
                            guid: 2AFA51A97C0000102143204166275475
                        multipleCalls: 0... .... False
                        maintainConnection: 0... .... False
            h245Tunneling: 1... .... True
            h245Control
                Item 0
                    Octet String Length: 7
                    H.245
                        MultimediaSystemControlMessage
                            PDU Type: .11. .... : Indication (3)
                                IndicationMessage
                                    Indication Type: .... 1101 : UserInputIndication (13)
                                        UserInputIndication
                                            signal
                                                UserInputIndication_signal
                                                    signalType: ?
                                                    duration: 400

0000  00 80 37 84 fb 9c 00 10 b5 75 ac 1d 08 00 45 00   ..7......u....E. 0010  00 6a bb 17 40 00 80 06 93 e7 c0 a8 15 32 c0 a8   [email protected].. 0020  15 0c 75 5a 0f a1 e5 77 18 df 95 c4 e6 f4 50 18   ..uZ...w......P. 0030  43 3a b0 d2 00 00 03 00 00 42 08 02 12 76 62 1c   C:.......B...vb. 0040  00 7e 00 34 05 26 80 06 00 08 91 4a 00 04 86 01   .~.4.&.....J.... 0050  00 1f 01 80 11 00 2a fa 51 a9 7c 00 00 10 21 43   ......*.Q.|...!C 0060  20 41 66 27 54 75 01 00 01 00 10 c0 01 80 09 01    Af'Tu..........
0070  07 6d 81 04 44 20 01 8f                           .m..D ..

I looked in the codebase and it seems that this element is not dissceted as an IA5string but with some other method.

It's dissected as a restricted character string - but the set of characters in that string includes "!".

What does the H.245 spec say that element is? And, if it's a restricted character string:

	1) what's the alphabet for it?

	2) what's the numerical value of the first (and only) character in it)?

According to

	http://www.packetizer.com/iptel/h245/h245_asn.html

the ASN.1 for it is

	signalType
                IA5String(SIZE (1) ^ FROM ("0123456789#*ABCD!")),

but the alphabet string passed to "dissect_per_restricted_character_string()" is "!#*0123456789ABCD".