osmo-pcu¶

• Table of contents
• osmo-pcu
  • Position in a typical Osmocom network
  • Manuals
  • Source Code
  • Test Suite
  • Mailing List
    • Supported
    • Shortcomings / Limitations / Restrictions
  • Authors / Credits

A PCU (Packet Control Unit) is one of the two GPRS elements in the BSS. It implements the RLC and MAC layers of the GPRS
Um (radio) interface on the MS-facing side, as well as the Gb Interface (NS,BSSGP) on the SGSN-facing side.

osmo-pcu is the Osmocom implementation of this PCU functionality.

It implements a custom L1 interface that can be used with OsmoBTS (specifically its
sysmoBTS back-end), and also with
OsmoTRX.

The interface between OsmoPCU and OsmoBTS runs over UNIX socket of SOCK_SEQPACKET type. One of the ways to debug it would be via socat:

socat -t30 -x -v UNIX-LISTEN:/tmp/pcu_bts.socat,mode=755,type=5 UNIX-CONNECT:/tmp/pcu_bts,type=5

One might even forward it over network:

socat -t30 -x -v UDP-LISTEN:1666,reuseaddr,fork UNIX-CONNECT:/tmp/pcu_bts,type=5
socat -t30 -x -v UNIX-LISTEN:/tmp/pcu_bts.socat,mode=755,type=5 UDP-CONNECT:127.0.0.1:1666

Note: in the examples above OsmoBTS (listening side) uses default /tmp/pcu_bts socket while OsmoPCU (connecting side) is configured to use /tmp/pcu_bts.socat via pcu-socket /tmp/pcu_bts.socat config option. It's not recommeded to use outside of TTCN-3 test environment due to amount of traffic over the socket.

Towards the SGSN, the BSSGP and NS protocols are implemented over UDP/IP, sometimes called "NS over IP".
It has been tested with OsmoSGSN as well as an Ericsson SGSN so far.

osmo-pcu is now considered stable and already performing useful service for a number of users, but as one
of the more recent additions to the Osmocom family, there still is plenty of area for improvement.

Position in a typical Osmocom network¶

Manuals¶

• User Manual: http://ftp.osmocom.org/docs/latest/osmopcu-usermanual.pdf
• VTY Reference: http://ftp.osmocom.org/docs/latest/osmopcu-vty-reference.pdf
• Gb/IP Manual: http://ftp.osmocom.org/docs/latest/osmopcu-gb.pdf

Source Code¶

The source code is available from git://git.osmocom.org/osmo-pcu.git

You can browse it online via http://cgit.osmocom.org/cgit/osmo-pcu/

Test Suite¶

We have a TTCN-3 test suite as part of our Titan_TTCN3_Testsuites

• source code: http://git.osmocom.org/osmo-ttcn3-hacks/tree/pcu
• results: https://jenkins.osmocom.org/jenkins/view/TTCN3/job/ttcn3-pcu-test/

Mailing List¶

There is a mailing list for (development) discussion regarding the PCU: osmocom-net-gprs@lists.osmocom.org
You can subscribe to it (or manage your subscription) at http://lists.osmocom.org/cgi-bin/mailman/listinfo/osmocom-net-gprs

Please make sure to read our MailingListRules before posting.

Supported¶

• GPRS CS1 to CS4 with dynamic link/rate adaption
• EDGE MCS1-MCS9 with dynamic link/rate adaption
• Single-slot and multi-slot operation on downlink
• Single-slot operation on uplink
• Independent TFI/USF per PDCH in single-slot allocation mode
• Automatic or fixed PDCH allocation algorithm selection
• Delayed release of downlink TBF
• Active queue management for downlink TBF (!CoDel)
• Initial setting of timing advance based on RACH
• BSSGP BVC flow control support
• Using pchan types of TCH/F_TCH/H_PDCH or TCH/F_PDCH, OsmoBTS supports
  dynamic PDCH/TCH switching (implemented entirely in osmo-bts)

Shortcomings / Limitations / Restrictions¶

Note: this list may be outdated

• No GPRS/EGPRS mixed mode (yet)
• No support for hand-over of any sort yet
• No support of processing measurement reports
• No timing advance loop, i.e. radial movement is limited
• No support for power control
• No Packet Access Reject message on congestion, access is just ignored
• No PCCCH support
• Only "Dynamic allocation RLC data block transfer" is supported
• No network controlled measurement/cell reselection order supported
• No PTCCH support
• No support for Packet Flow Contexts (PFC)
• No support for MS or PFC flow control
• No support for RLC unacknowledged mode operation
• No support for MBMS

Authors / Credits¶

osmo-pcu was originally developed by Ivan Kluchnikov and Andreas Everberg.

Today it is maintaned by Sysmocom.