Call_ID in voice calls

[Florin Vancea]

Sorry for O.T., but this is the only place where I may find some help. If
anyone with protocol experience is so kind to read and reply I'd be very
grateful. (all references below are to the n6110.txt document in 0.6.4
source tarball, dir /Docs/protocol)

I am having some problems with my own-developed software doing FBUS with
5110. (not gnokii, scratch-written according to my early protocol digging -
some of the older developers may remember the "cat" document :) ).

In a nutshell, the software runs on a embedded controller and
launches/accepts voice calls on a connected 5110.
As I looked into latest gnokii source, the only things I identified being
different are:
1. I am sending "Answer call part 1" only once, at initialization time (not
for each call answer)
2. When answering the call I am not including the call_id, but merely send
[... 0x06 0x07 0x00 ...] instead [... 0x06 <call_id> 0x00 ...] as gnokii
does.

The whole system works and places/receives calls as supposed. However, after
a while and some inbound/outbound calls (not systematically reproducible) it
stops working. A phone reboot (only phone, not controller) solves it.
I looked into the data flow and I found out that when failing, the phone
always rejects the call with "Call information" / "Remote hang up" but
TWICE. First one contains the call_id (I've seen 01 to 04) but the second
one has call_id 00. The data following is also slightly different.

Does anyone have any answer to the below questions please?

A. Is it normal to see a sequence of call_id in subsequent calls? (i.e. 01,
then 02, then 03, then 04, then 01 again)

B. Is it mandatory to send "Answer call part 1" each time when I answer a
call ?

C. Is it mandatory to specify the call_id when answering? (or my 0x07 should
work, meaning something like "current call")

D. What's the possible meaning of the 00 call_id and the associated call
reject? The error codes appearing later in the data are different. Is there
any reference for the error codes? I saw in n6110.txt the comment "like in
netmon in 39". What does that mean?

If I get no reply, I'll have to start the trial-and-error debugging process,
but being on a embedded system will make it veeeeery slooooow and veeeery
painful. Please, give me a hand.

Thank you a lot,
Florin