OsmoPCU » History » Revision 26
Revision 25 (laforge, 05/11/2018 11:03 AM) → Revision 26/32 (msuraev, 03/14/2019 02:55 PM)
h1. osmo-pcu
{{>toc}}
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":http://www.sysmocom.de/products/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:
<pre>
socat -t30 -x -v UNIX-LISTEN:/tmp/pcu_bts.socat,mode=755,type=5 UNIX-CONNECT:/tmp/pcu_bts,type=5
</pre>
One might even forward it over network:
<pre>
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
</pre>
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.
h2. Position in a typical Osmocom network
{{graphviz_link()
digraph G {
rankdir = LR;
OsmoBTS -> OsmoBSC [label="Abis/IP"];
OsmoBSC -> OsmoMSC [label="3GPP AoIP"];
OsmoBTS -> OsmoPCU [label="pcu_sock"];
OsmoPCU -> OsmoSGSN [label="Gb/IP"];
OsmoMSC -> OsmoHLR [label="GSUP"];
OsmoSGSN -> OsmoHLR [label="GSUP"];
OsmoSGSN -> OsmoGGSN [label="Gp"];
OsmoGGSN -> Internet [label="Gi"];
OsmoPCU [color=red];
}
}}
h2. 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
h2. 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/
h2. Test Suite
We have a TTCN-3 test suite as part of our [[cellular-infrastructure: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/
h2. 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 [[cellular-infrastructure:MailingListRules]] before posting.
h3. 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)
h3. 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
h2. Authors / Credits
osmo-pcu was originally developed by Ivan Kluchnikov and Andreas Everberg.
Today it is maintaned by Sysmocom.