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laforge, 02/19/2016 10:48 PM
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= OsmoSGSN =
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OsmoSGSN (also spelled {{{osmo-sgsn}}} when referring to the program name) is a Free Software implementation of the GPRS
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Serving GPRS Support Node (SGSN).  As such it implements the GPRS Mobility Management (GMM) and SM (Session Management).
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The SGSN connects via the Gb-Interface to the BSS (e.g. the ip.access nanoBTS), and it connects via the GTP protocol
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to a Gateway GPRS Support Node (GGSN) like [wiki:OpenGGSN].
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It is currently very experimental.  The Gb protocol stack and the LLC implementation are quite robust, and signalling
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for GMM and SM seems to run pretty fine.  However, the user plane including SNDCP fragmentation is in pre-alpha quality.
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OsmoSGSN is part of the openbsc git repository.  In order to build it, you will need a libgtp installation from the
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OpenGGSN project.
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== TODO list ==
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 * use the HLR to identify (and possibly authenticate) subscribers
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 * proper error messages in SM (e.g. activation of an already active PDP context)
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 * secondary PDP contexts
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 * proper de-fragmentation of segmented SN-PDUs into N-PDUs
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 * support for multiple GGSNs
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 * persistent storage of GMM and SM state
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 * recovery from GGSN outages
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 * SNDCP header and data compression
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 * use proper XID exchange and actually use the results to configure the LLC SAPIs
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 * GEA3 encryption
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 * make sure LLC and SNDCP entities are cleaned up on PDP CTX DEACT
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 * make sure PDP contexts are deactivated on IMSI DETACH
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 * PS PAGING in case MS has entered GMM-SUSPEND
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 * SMS delivery via GPRS
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 * network-initiated PDP context activation
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