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.

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

osmo-pcu is now considerd 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.

Source Code

The source code is available from git://

You can browse it online via

Mailing List

There is a mailing list for (development) discussion regarding the PCU: You can subscribe to it (or manage your subscription) at


Information about testing is available here: GPRS-testing


  • GPRS CS1 to CS4 with dynamik link/rate adaption
  • single-slot and multi-slot operation on downlink
  • single-slot operation on uplink

Shortcomings / Limitations / Restrictions

  • Pure GPRS PCU, no EGPRS (EDGE) functionality (yet)
  • Timeslots have to be assigned dedicated as a PDCH, no dynamic PDCH/TCH switching
  • No support for hand-over of any sort yet
  • No support of processing measurement reports
  • No timing advance loop, i.e. maximum cell radius 2-3 km
  • 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

Authors / Credits

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

Today it is maintaned by Holger Freyther and Jacob Erlbeck at sysmocom.

Last modified 6 weeks ago Last modified on Oct 16, 2015, 11:38:39 AM

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