3G (NodeB / femtocell) roadmap

[Harald Welte]

Hi all,

i just wanted to keep you posted with the 2011 roadmap for 3G integration
into our "Free Software Mobile Network" stack.  This message summarizes
the plan of what I expect to be working on.  Comments welcome.

3G support directly in OpenBSC is, however, a bit more difficult than we
originally anticipated.  The primary problems are:

* 3G and 2G share the same core network (CN = MSC/VLR/HLR/AuC/SGSN/GGSN)
  but have different radio access netowrk (RAN = BTS+BSC vs. NodeB+RNC)

* the interface between RAN and CN is different, i.e. 'A' interface
  (08.08) in GSM case, RANAP in 3G case.

* The encoding of the two protocols could not be any different. Hand-coded
  vs. complex ASN.1 structures

So with OpenBSC, we face the following challenges:

1) We implement the GSM-RAN functionality and the CN in one process,
   without any separation or standardized interfaces between them

2) Implementing RANAP in C can be done, but is probably quite cumbersome
   given the tons of code asn1c generates and how difficult it seems to
   get all the memory allocation/freeing right in all the cases

What we instead decided to do is:

a) Split the BSC part from the CN by implementing the A interface (this
   is already finished, we now have osmo-bsc to do exactly that)

b) Implement a new MSC part, using the A interface towards the BSC
   This is still possible using our existing code in the original
   OpenBSC, though we have not completed/finished it yet.  
     The real goal is to have a new MSC, written in a higher-order language
   that provides proper tools for working with ASN.1 - e.g. Erlang.  I have
   just started working on this and am more or less finished with the lower
   layers like SCCP and am moving into 08.08 and the actual layer3 protocols.
   There is already some initial funding secured for the first months of
   this work, and funding will likely continue.

c) Once the 2G functionality of the Erlang MSC is working, add the RANAP
   interface to it.  
     At this point we should more or less be able to directly
   connect the Alcatel-Lucent femtocells, as they basically consist of
   HomeNodeB plus an internal RNC handling the RRC protocol.

d) Adding support for ip.access/Cisco/AT&T will need an implementation of
   their URSL protocol, which is proprietary.  URSL can either be added
   to the new MSC directly, or a URSL<->RANAP translater be developed.

e) Adding support for the Ubiquisys/SFR femtocell would require us to implement
   the UMA protocol stack.  This can once again be either done as part of
   the MSC or using an external translator/gateway program.

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)