OsmoPCU Debugging¶

In order to debug issues with OsmoPCU, it is important to have protocol traces from all related interfaces.

Fundamentally, this includes

1. the Gb interface (NS-over-IP from PCU to SGSN, showing NS/BSSGP/LLC and higher layer protocols)
   • this one is easy, you just have to capture the UDP traffic on the ip/port as specified in your configuration for this NS-VC (from OsmoBSC or OsmoNITB
2. the Um interface (RLC/MAC between MS and PCU)
   • Um frames transmitted/received via OsmoPCU (on PACCH, PTCCH, PDTCH)
   • Um frames transmitted/received via OsmoBTS on behalf of OsmoPCU (on PCH and AGCH)

The instructions below will help you to set this up

Setting up capturing¶

NS-over-IP traffic¶

FIXME

Um frames of OsmoPCU via GSMTAP¶

You must call the specific OsmoPCU binary for your BTS hardware with the -i option to enable GSMTAP and specify a remote IP address where to send it to¹.
The IP address could be the localhost/loopback device, in case you want to capture packets locally.

For example, on a sysmoBTS device the normal command to start osmo-bts (by the systemd service) is:

/usr/bin/osmo-pcu -c /etc/osmocom/osmo-pcu.cfg

but we now need to start it as

/usr/bin/osmo-pcu -c /etc/osmocom/osmo-pcu.cfg -i 127.0.0.1

¹ As of this writing, OsmoPCU actually will send GSMTAP automatically by default to 127.0.0.1 but this is scheduled to change. Explicitly specifying the GSMTAP via the command-line argument as described here will work with both older and future versions of OsmoPCU

Um frames of OsmoBTS via GSMTAP¶

You must call the specific OsmoBTS binary for your BTS hardware with the -i option to enable GSMTAP and specify a remote IP address where to send it to.
The IP address could be the localhost/loopback device, in case you want to capture packets locally.

For example, on a sysmoBTS device the normal command to start osmo-bts (by the systemd service) is:

/usr/bin/osmo-bts-sysmo -s -c /etc/osmocom/osmo-bts.cfg -M

but we now need to start it as

/usr/bin/osmo-bts-sysmo -s -c /etc/osmocom/osmo-bts.cfg -M -i 127.0.0.1

In osmo-bts.cfg you need to enable the following gsmtap SAPIs:

bts 0
 ...
 gsmtap-sapi ccch
 gsmtap-sapi rach
 gsmtap-sapi agch
 gsmtap-sapi pch
 ...