OsmoPCU » History » Revision 30
Revision 29 (laforge, 08/10/2022 07:20 AM) → Revision 30/33 (dexter, 03/24/2023 04:43 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.
OsmoPCU osmo-pcu is the Osmocom implementation of this PCU functionality.
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.
h2. OsmoPCU in co-location with OsmoBTS
OsmoPCU is usually implements a custom L1 interface that can be used in co-location with [[OsmoBTS:]]. In this scenario all OsmoBTS variants are supported, including
[[OsmoTRX:]] [[OsmoBTS:]] (specifically its "sysmoBTS":http://www.sysmocom.de/products/sysmobts back-end), and PHY based variants, such as "sysmoBTS":https://www.sysmocom.de/products/bts/.
{{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];
{ rank=same OsmoBTS OsmoPCU }
{ rank=same OsmoMSC OsmoSGSN }
}
}}
h2. OsmoPCU in co-location with OsmoBSC
OsmoPCU can also be used in co-location with [[OsmoBSC:]]. This scenario is required to support third party BTSs that
do not include an integrated PCU. This is mainly the case for classic E1 based BTS, such as the [[ericsson-rbs-6xxx:]]
series. [[OsmoTRX:]].
{{graphviz_link()
digraph G {
rankdir = LR;
BTS -> OsmoBSC [label="Abis/IP"];
BTS -> OsmoPCU [label="GPRS/TRAU"];
OsmoBSC -> OsmoMSC [label="3GPP AoIP"];
OsmoBSC -> 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];
{ rank=same OsmoBSC OsmoPCU }
}
}}
The support for BSC co-location in OsmoPCU and OsmoBSC, as well as the hardware specific extensions needed to support
Ericsson RBS2000/RBS6000 base stations have been made possible through funding by the
"NLnet foundation":https://nlnet.nl/ (see also: https://nlnet.nl/project/Osmocom-RBS/).
h2. Interface between OsmoPCU and OsmoBTS/OsmoBSC
The interface between OsmoPCU and OsmoBTS/OsmoBSC OsmoBTS runs over UNIX socket of SOCK_SEQPACKET type. It is used to configure
the network parameters inside the PCU and to exchange signalling information. It also features a custom L1 interface
that allows PDCH MAC blocks. However, for enhanced performance, OsmoPCU also implements a direct PHY acces for some BTS
models.
h3. Documentation
The primitives, which are exchanged between OsmoPCU and OsmoBTS/OsmoBSC are defined in pcuif_proto.h
* pcuif_proto.h: https://gitea.osmocom.org/cellular-infrastructure/osmo-pcu/src/branch/master/include/osmocom/pcu/pcuif_proto.h
Message flow charts that explain PDCH activation and deactivation can be found in the OsmoBTS Abis Protocol Specification
* OsmoBTS Abis Protocol Specification: https://ftp.osmocom.org/docs/osmo-bts/master/osmobts-abis.pdf
h3. Debugging
One of the ways of debugging the PCU socket interface 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: https://ftp.osmocom.org/docs/latest/osmopcu-usermanual.pdf
* VTY Reference: https://ftp.osmocom.org/docs/latest/osmopcu-vty-reference.pdf
* Gb/IP Manual: https://ftp.osmocom.org/docs/latest/osmopcu-gb.pdf
h2. Source Code
The source code is available from https://gitea.osmocom.org/cellular-infrastructure/osmo-pcu.git
You can browse it online via https://gitea.osmocom.org/cellular-infrastructure/osmo-pcu
h2. Test Suite
We have a TTCN-3 test suite as part of our [[cellular-infrastructure:Titan_TTCN3_Testsuites]]
* source code: https://gitea.osmocom.org/ttcn3/osmo-ttcn3-hacks/src/branch/master/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.
h2. Features
osmo-pcu is considered stable and is performing useful service for a number of users, but due to the complexity of GPRS
there is still plenty of area for improvement.
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)
* Ericsson RBS2000/RBS6000 support (BSC co-located)
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.
{{include(cellular-infrastructure:MacroCommercialSupport)}}
