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Harald Welte laforge at osmocom.orgHi Ivan,
On Thu, Oct 08, 2020 at 01:14:03AM +0300, Ivan Babanov wrote:
> Brief question. Is it possible to debug E1 line by connecting it to the 2nd
> port of the same NIC making a wired loop?
well, you would normally need a series resistor for the tapping port, you cannot
just put them in parallel without signal degradation.
You can check https://osmocom.org/projects/e1-tap/wiki for a small OSHW
device that has the series resistors built in, and which provides two tap
ports (one for each direction). For full-duplex sniffing of one E1 line, you
obviously need two other ports.
> Is it enough to open->ioctl->read
> from /dev/dahdi/channel to get a stream of LAPD SABME messages transmitted
> by BSC?
not /dev/dahdi/channel. On that device you need a special ioctl.
you could look into osmo-e1-recorder, if you wanted to do tracing with DAHDI
ports behind a osmo-e1-tap.
> I'm still trying to bring up BTS Nokia Flexi with OSMO-BSC.
great.
> I'm using an E1 card Digium TE405P on the server side.
> OSMO-BSC is connected with Nokia BTS via a single E1 line.
> Looks like on Level1 everything is ok because BTS can detect the link and
> raise an alarm if the wire is getting disconnected.
great.
> I can observe some data from timeslots on BTS side and if some channel is
> configured as D-Channel in /etc/dahdi/system I see transmission of block
> "01111110".
that's the flag octets
> But the problem is that LAPD link is not establishing. I can't find any
> tries on BTS side and BSC does not receive anything from BTS, just set of
> SABME messages in PCAP file.
That's somewhat of a contradiction.
* SABME is the first frame used to establish a LAPD data link
* it should be sent from BTS to BSC
* the BSC responds with UA
> T200 expires and so on. I tried various T200 values. So, now it looks for
> me like L1 does not receive anything from L2 on BSC side and nothing is
> transmitted over the wire to BTS.
it would be useful to see your configs. I would guess most likely you
didn't select the same timeslot for
signaling on both sides.
--
- Harald Welte <laforge at osmocom.org> http://laforge.gnumonks.org/
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