Dear Tim!

I hope you don't mind I'm Cc'ing the mailing list. This means that other people can get involved in the discussion - and also means that I only have to write my summary about what needs to be done once, even if you for some reason are unable to complete the actual implementation :)

On Mon, Nov 02, 2009 at 01:25:13PM -0500, Newman, Timothy wrote:

I'm working at Virginia Tech and it looks like we are going to start playing with the cell broadcast gsm stuff. I'd like to just go ahead and add it into openbsc.

This is great news, thanks. Which BTS type are you using with OpenBSC?

Other than the brief read through of some of the 3GPP documents related to cell broadcast, I'm not too familiar with the interworkings of it.

It's not really difficult. What needs to be done 1) enable a channel configuration that adds a CBCH to one of the SDCCH/4 in a combined CCCH, or one of the SDCCH/8. I'd prefer the SDCCH/4, since that is supported by both BS-11 and nanoBTS. However, feel free to implement both options 2) encode the CBCH message (very similar to SMS encoding) TS 03.38 / 03.41 3) have a function to send the CBCH to the BTS over RSL (TS 08.58) 4) later: Implement the Scheduling (Chapter 2.1 of TS 04.12) for DRX

There's two options for cell broadcast: 1) you can set a default cell broadcast message once by the BSC. The BTS then transmit that CB in every idle fame of the CBCH (TS 08.58 SMS BROADCAST CMD) 2) you want to sent multiple different CB messages, then the BSC needs to do the scheduling and send them to the BTS's (TS 08.58 SMS BROADCAST REQ)

I'm a little unclear how long this may take to add this functionality into openbsc. If you had to estimate how long it would take (e.g. 1, 2, 6, 12 months), what would you say? Just give me your estimate and I'll multiply this by 4 because it will be students working on the project and they need a little (a lot) of ramp of time for this also.

If I or any other of the OpenBSC developers was doing it, I would say this is a matter of days, one week max for all of the options described above. However, you need to consider that your studends also have to read up the 3GPP specs, are unfamiliar with the terminlology, don't know the OpenBSC codebase, probably have not that much experience with "plain C" programming in an select-loop single threaded design, ... so a factor of four might not be sufficient.

Regards, Harald

p.s.: I would be interested in learning what you're using OpenBSC for at Virginia Tech. If you have a minute to elaborate on that, I'm very curious. Other people on the mailing list might share that interest, especially those users from academic institutions. If you prefer to respond privately, that would also be OK with me.