PageOutline = osmo-pcu =

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 [wiki:OsmoBTS] (specifically its
[http://www.sysmocom.de/products/sysmobts sysmoBTS] back-end), and also with
an unofficial version of OpenBTS that is being created by Fairwaves.

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

osmo-pcu is not fully stable yet, but already performing useful service for a number of users.

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/

The branch to be used with [wiki:OsmoBTS] and sysmoBTS is the 'jolly_merge' branch.

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

Status
Information about testing is available here: [wiki:GPRS-testing]

=== Supported === * GPRS CS1 to CS4 * single-slot and multi-slot operation on downlink * only single-slot operation on uplink

=== Shortcomings / Limitations / Restrictions ===

• Pure GPRS PCU, no EGPRS (EDGE) functionality
• 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 dynamic link adaption for different coding schemes
• No resource-dependent flow control
• Single slot allocation algorithm only allocates the first available PDCH
• Multi slot allocation algorithm
  - only allocates single uplink PDCH
  - limits allocation of type 1 mobile classes to 5 downlink PDCH
  - does not choose other uplink PDCH, if no USF is avaiable
• 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