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laforge, 02/19/2016 10:48 PM
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OsmoSGSN (also spelled {{{osmo-sgsn}}} when referring to the program name) is a Free Software implementation of the GPRS
Serving GPRS Support Node (SGSN). As such it implements the GPRS Mobility Management (GMM) and SM (Session Management).

The SGSN connects via the Gb-Interface to the BSS (e.g. the ip.access nanoBTS), and it connects via the GTP protocol
to a Gateway GPRS Support Node (GGSN) like [wiki:OpenGGSN].

It is currently very experimental. The Gb protocol stack and the LLC implementation are quite robust, and signalling
for GMM and SM seems to run pretty fine. However, the user plane including SNDCP fragmentation is in pre-alpha quality.

OsmoSGSN is part of the openbsc git repository. In order to build it, you will need a libgtp installation from the
OpenGGSN project.

TODO list * use the HLR to identify (and possibly authenticate) subscribers * proper error messages in SM (e.g. activation of an already active PDP context) * secondary PDP contexts * proper de-fragmentation of segmented SN-PDUs into N-PDUs * support for multiple GGSNs * persistent storage of GMM and SM state * recovery from GGSN outages * SNDCP header and data compression * use proper XID exchange and actually use the results to configure the LLC SAPIs * GEA3 encryption * make sure LLC and SNDCP entities are cleaned up on PDP CTX DEACT * make sure PDP contexts are deactivated on IMSI DETACH * PS PAGING in case MS has entered GMM-SUSPEND * SMS delivery via GPRS * network-initiated PDP context activation