The Gb proxy

The purpose of the Gb proxy is to aggregate the Gb links of multiple BSS's and present them in one Gb link to the SGSN.

More specifically, the Gb proxy terminates the NS-VCs of each BSS locally. Furthermore, it establishes one NS-VC with the SGSN.

It also contains support for converting from a NS/UDP/IP (Gb over IP) stacking to a frame-relay based NS/FR/GRE/IP stacking in both directions.

For Gb/IP the Gb proxy supports both IP Access' proprietary dialect but also IP/SNS as specified in 3GPP TS 48.016

The proxy then forwards NS-DUs (BSSGP PDUs) between the SGSN and the
respective BSS (and vice versa).

Deployment scenarios

Overview (also showing circuit switched side)

Mere aggregation of Gb/IP links towards a SGSN

This scenario is used where many Gb/IP links need to be aggregated to wards a SGSN. It is primarily useful in GSM implementations where there is a BTS-colocated PCU (as often seen with small cells, or within Osmocom RAN where OsmoPCU co-located next to OsmoBTS).

Osmo-gbproxy will terminate the NS-VCs from all BSS and to the SGSN. It will then pass through the BSSGP virtual connections from each BSS to the SGSN, while performing special treatment of BVCI=0 (signaling BVCI).

Conversion of Gb/IP to classic Gb over Frame Relay

This scenario is used if you have modern, IP based Gb interface from the RAN, but want to interface with traditional, TDM based SGSNs utilizing Gb over frame relay. osmo-gbproxy doesn't itself directly interface with E1 interface cards, but it uses an external router with frame relay capability which performs Frame Relay encapsulation in GRE over IP.

Vice versa this conversion is also possible: you have traditional Gb FR from the RAN and want to connect it to Gb/iP on the SGSN side:

Binary Packages

Osmocom provides binary packages for several flavors of Debian and Ubuntu GNU/Linux on a variety of architectures (i586, x86_64, armhf, armv7l). Unless you are a software developer interested in developing on Osmocom, it is recommended you use those packages instead of building from source.

For more details see Binary_Packages

User Manuals

Source code

The source code is available from (module osmo-gbproxy).

Public read-only access is available via

git clone

You can browse it via gitea:

Contributions are welcome via Gerrit.

Test Suite

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

Documentation is somewhat minimalistic at this point, as this is not a general-purpose network element but something highly specialized for some niche use cases. Feel free to contact in case you would want to hear more about its capabilities.

Configuring and using osmo-gbproxy

Like other programs in this project, osmo-gbproxy accepts a number of command line arguments
but is generally configured by a configuration file (which can be interactively created/edited
from the VTY).

The command line arguments are:

  -h --help this text
  -d option --debug=DNS:DGPRS,0:0 enable debugging
  -c --config-file filename The config file to use.
  -s --disable-color
  -T --timestamp Prefix every log line with a timestamp
  -V --version. Print the version of [[OpenBSC]].
  -e --log-level number. Set a global loglevel.

There is a wiki page osmo-gbproxy_VTY with a reference for all VTY commands

Advanced use cases

Cascading proxies

You can also cascade multiple Gb proxies behind each other, where a number
of BSS connect to one Gb proxy, which in turn connects to another Gb proxy,
which then finally connects to the SGSN.

The reason for this type of use can be broken or limited Gb implementations
in proprietary BSS equipment, which fails to re-connect the Gb link after some
intermittent network outage.

Design documentation

There's a more detailed design description outlining
details of the proxy.

Contact / Getting Help

Contact us via the osmocom-net-gprs@ mailing list, see Mailing Lists.

You can file issues (bugs / feature requests) using the redmine project you're currently viewing.

Commercial Support

Commercial support as well as development, system integration and training services for this project are available from sysmocom

Files (0)

Updated by osmith 10 days ago ยท 20 revisions

Add picture from clipboard (Maximum size: 48.8 MB)