OsmoSGSN status report

[Harald Welte]

Hi all!

Since more people are currently looking into using OsmoSGSN, let me write
down some technical notes on its current status:

NS (08.16) implementation (BSS and SGSN side)
	* complete + stable
	* supports NS/UDP/IP and NS/FR/GRE/IP stacking

BSSGP (08.18) implementation
	* no support for per-BSS/per-MS flow control yet, this is WIP
	* otherwise complete and stable

LLC (04.64) implementation, network side
	* No support for Async Balanced Mode (ABM), as to the best of
	  my knowledge, it is not used if IP is transported over GPRS
	* Encryption stub functionality using external plugins for actual
	  GEA encryption.  GEA3 reference code is published, but we cannot
	  redistribute it
	* No full support for the XID mechanism yet

SNDCP (04.65) implementation
	* Fragmentation/defragmentation implenented but not widely tested
	* No full support for the XID mechanism yet
	* No support for any of the header compression formats
		* is optional anyway, but helps performance
	* No support for V.42bis payload compression
		* is optional anyway, but helps performance

GPRS Mobility Management (04.08) implementation
	* Supports GPRS ATTACH, RA UPDATE
	* Known bugs with inter-cell hand-over
	* No access to HLR yet, i.e. all MS are permitted to enter
	* No persistent storage of MM state, i.e. all state is lost
	  if process crashes or restart
	* We don't yet work around a fairly common MS bug which makes
	  them try to do GPRS RA UPD without ever sending GPRS ATTACH first

GPRS Session Management (04.08) implementation
	* Supports only one PDP Context per MS so far
	* Only IPv4, no IPv6 contexts yet
	* No persistent storage of active PDP contexts, i.e. all state
	  is lost if process crashes or restarts
	* only supports one APN, routed to one single GGSN


The TODO list in order of priority is:

* Implement BSSGP flow control (per BSS and per MS)
* Fix MM state machine issues, make sure inter-cell hand-over of GPRS works
* Add access from SGSN to HLR (possibly using libosmo-{tcap,map}, maybe again
  a quick sqlite database hack meanwhile
* Verify encrpytion support in LLC code
* Work on header/payload compression


I don't have a precise schedule yet for it.  Anyone who wants to work on those
issues is of course much welcome.

Meanwhile, if you experience problems with GPRS, please take pcap files of
the A-bis, Gb and GTP links and send them to me, with a detailed description
of what goes wrong when.  I'm happy to look at those issues and resolve them,
if I get sufficiently verbose bug reports.

Regards,
	Harald
-- 
- Harald Welte <laforge at gnumonks.org>           http://laforge.gnumonks.org/
============================================================================
"Privacy in residential applications is a desirable marketing option."
                                                  (ETSI EN 300 175-7 Ch. A6)