Wireshark · Wireshark-bugs: [Wireshark-bugs] [Bug 9643] GSM_MAP: false BER error indicated when IMSI is present in segmented TCA

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Comment # 5 on bug 9643 from Robert Gahan

Thanks Anders and Pascal for your feedback, 

> > 
> > The idea behind my change is that opcode 46 (mo-ForwardSm) 
> > was only introduced in MAP phase 3 and does not exist in previous 
> > phases. 
> > 
> > So if the application context is absent, and opcode 46 is 
> > used perhaps then we can decode as a MO-FSM-V3.
> > (As opcode 46 is only associated with V3). 
> 
> The way the code is made it looks like that is not true(or the code is
> wrong?).
>   case 46: /*mo-forwardSM(v3) or ForwardSM(v1/v2)*/
>     if (application_context_version == 3)
>       offset=dissect_gsm_map_sm_MO_ForwardSM_Arg(FALSE, tvb, offset, actx,
> tree, -1);
>     else {
>       offset=dissect_gsm_old_ForwardSM_Arg(FALSE, tvb, offset, actx, tree,
> -1);
>     }
>     break;
> 

>From my reading of the specifications, it would seem that the code is wrong. 
But please let me know if you disagree


> > 
> > Regarding "If version 3 is widely used and v1/v2 are obsolete,". 
> > 
> > From what I have seen, V3 is certainly most popular but I guess there is
> > legacy v1 infrastructure and I have (or am about to) log some V1 related
> > decoding bugs.
> 
> As time goes by I guess V3 will be more common so I think changing the
> preference to V3 is a good idea.
> 
> Blame 3GPP for not making the protocol backwards compatible...
> 
> Regards
> Anders

I agree that the default phase assumed should be three. 
However, this is my understanding:

(*) TC-Continue not used with Phase 1
(*) For a TC-Begin absence of a dialogue portion is taken to mean Phase 1

So if a dialogue portion is absent, can we:
-- if TC-Begin: assume phase 1. 
-- If TC-Continue: assume default. (phase 3)

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