Cellular Network Infrastructure » Core Network (CN) » osmo-gbproxy

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h1. 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 form a NS/UDP/IP (Gb over IP) stacking to a frame-relay based NS/FR/GRE/IP stacking.

Source code available as part of [[OpenBSC]] repository:

<pre>

git clone git://git.osmocom.org/openbsc.git

</pre>

The proxy then forwards NS-DUs (BSSGP PDUs) between the SGSN and the

respective BSS (and vice versa).

{{graphviz_link()

digraph G {

  rankdir=LR;

  nanobts1->OpenBSC  [ label="Abis/IP" ];

  nanobts2->OpenBSC  [ label="Abis/IP" ];

  nanobts1->gb_proxy [ label="Gb/IP" ];

  nanobts2->gb_proxy [ label="Gb/IP" ];

  gb_proxy->SGSN     [ label="Gb/IP or\nGb/FR/GRE/IP" ];

  nanobts2 [ label = "OsmoBTS" ];

  nanobts1 [ label = "nanoBTS" ];

  OpenBSC [ label = "OpenBSC" ]

}

}}

h2. Documentation

* "User manual":https://ftp.osmocom.org/docs/latest/osmogbproxy-usermanual.pdf

* "VTY reference manual":https://ftp.osmocom.org/docs/latest/osmogbproxy-vty-reference.pdf

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 sales@sysmocom.de in case you would want to hear more about its capabilities.

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h2. 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:

<pre>

  -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.

</code></pre>

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

h2. Advanced use cases

h3. 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.

h2. Design documentation

There's a more detailed [[osmo-gbproxy_design|design description]] outlining

details of the proxy.