Cellular Network Infrastructure » Radio Access Network » OsmoBSC

I've done some investigation here. My original fear was that the BSC might be trying to open all the TRAU timeslots on the E1 interface, which would then collide with OsmoMGW opening those slots.

• osmo-nitb will open all E1 timeslots that are mentioned in e1 line 0 timeslot 1 ... statements, whether for OML/RSL or for individual timeslots
• osmo-bsc will only open the E1 timeslots carrying singaling, but not those used for TRAU traffic

The reason is found in the e1_reconfig_ts() function, which for the old NITB case contains:

        if (ts_is_tch(ts)) {
                e1_ts = &line->ts[e1_link->e1_ts-1];
                e1inp_ts_config_trau(e1_ts, line, subch_cb);
                subch_demux_activate(&e1_ts->trau.demux, e1_link->e1_ts_ss);
        }

but this section has been removed from osmo-bsc's implementation of e1_reconfig_ts().

Hence, at least on a timeslot level, the BSC and the MGW should not clash with each other. The BSC will only open signaling, and the MGW should only open traffic timeslots.

The E1 line numbering and driver configuration would have to match on both of them, though. This means the section like

e1_input
 e1_line 0 driver e1d
 e1_line 0 port 0

has to be identical in both osmo-bsc and omso-mgw in order to have a common understanding what physical E1 circuit 'line 0' maps to.

assigning to dexter. I think everything on the Abis signalling side is working for all known supported BTS models now, the remainign part of this ticket (inside the BSC) is the handlign of E1 slots via MGCP to OsmoMGW.

Technically osmo-bsc is now ready to use the E1 endpoints on osmo-mgw. However, handover would not work yet. The problem is described/discussed in #2547.

osmo-bsc will use the line number that is configured in osmo-bsc.cfg as trunk number. At the moment osmo-mgw only accepts trunk numbers starting at 1. However, this limitiation is dropped with the following patch: https://gerrit.osmocom.org/c/osmo-mgw/+/19563, once we merge this, osmo-mgw will also accept trunk numbers that start at 0.

dexter wrote:

Technically osmo-bsc is now ready to use the E1 endpoints on osmo-mgw. However, handover would not work yet. The problem is described/discussed in #2547.

I think we should add a separate "handover for E1" feature request ticket for that.

osmo-bsc will use the line number that is configured in osmo-bsc.cfg as trunk number. At the moment osmo-mgw only accepts trunk numbers starting at 1. However, this limitiation is dropped with the following patch: https://gerrit.osmocom.org/c/osmo-mgw/+/19563, once we merge this, osmo-mgw will also accept trunk numbers that start at 0.

that patch has been merged now. Resolving this issue.