3G update: stable IuCS Location Update

Dear 3G Folks, after various problems with obtaining a stable Location Update of a 3G subscriber on our hNodeB femto-cell, we've finally succeeded today! Basically, after both MM Authentication and Integrity Protection were in place today, the phone finally started to reply to the Location Updating Accept with the expected TMSI Reallocation Complete message. After that, the phone was still cycling new Location Update Requests every half minute or so, because we were replying with the wrong LAC id = 0; Osmo-CSCN (Circuit-Switched Core Network) needs to know which RNC (like a BSC in 2G) has which Location Area Code. The RNC tells us its global RNC ID when it first connects, and the CSCN needs to match the LAC properly from prior knowledge (aka config). Now that both Integrity Protection and the matching LAC are in place during the Location Updating Accept message from the CSCN, the UE happily stays subscribed to the CSCN! It's about time, too. The reasons why it took this long to reach this admittedly meagre sounding milestone were mostly: - The fact that Osmocom did not feature a standalone MSC, which first had to be surgically separated from the BSC part (used to be the NITB). I introduced and then eradicated a few build problems in the process. - Osmocom's libmsc previously was not able to do mere MM Authentication without also enabling Ciphering, so to test MM Authentication on its own I needed a new path in the auth and ciph code. - Osmocom's libmsc so far expected to have precisely one BSC, as part of the NITB, so it simply telepathically knew "the" LAC. Now, libmsc has to figure out the LAC from a table instead. (VTY configuration to match RNCs with LACs is in the making, as well as the RNC and BSC registry itself.) So, in fact, this milestone has much more under the hood than the layman would expect. Now that we have all of these fleas numbered and in the same matchbox, the long overdue stable 3G Location Update on IuCS using the new osmo-cscn finally arrived this afternoon. As soon as this code is configurable and peer reviewed, I will move on to implement 3G paging. I do hope to shift up a gear on that, with new confidence and by now much firmer knowledge of 3G and the "Osmoverse". Lively greetings from sysmocom's open 3G lab in Berlin! Stay tuned for more Updates, soon at this Location. ~Neels -- - Neels Hofmeyr <nhofmeyr(a)sysmocom.de> http://www.sysmocom.de/ ======================================================================= * sysmocom - systems for mobile communications GmbH * Alt-Moabit 93 * 10559 Berlin, Germany * Sitz / Registered office: Berlin, HRB 134158 B * Geschäftsführer / Managing Directors: Holger Freyther, Harald Welte