Taiwan Mobile RRC State Change Problems

While TMN doesn't let me use their 3G network with my German SIM card as reported in an earlier post, they do offer SIM cards for Internet access which are interesting for occasional use or travelers in the country for a couple of days. For the details on the offer see here. While the throughput in their network is quite o.k. and in the range of 3 MBit/s, their network has some compatibility issues with my 3G dongles.

I don't see such issues often anymore but TMN is one of those networks that still seem to have a strange RAN software version running that make my 3G dongles get stuck every now and then when an RRC state change occurs. Sometimes the connection recovers after a minute or so, sometimes I have to reset the connection entirely. The only thing that helps is a constant ping to keep the RRC connection in Cell-DCH.

TMN, you might want to run a compatibility check against some mainstream UMTS hardware not necessarily sold in Taiwan…

7 thoughts on “Taiwan Mobile RRC State Change Problems”

  1. Hi! Martin,
    I am curious about the issue you mentioned, can you tell me the brand and model of the dongles in question? Thanks in advance!

  2. Hi Andy,

    very common ones here in Europe: An old Huawei E220 (3.6 MBit/s HSDPA only) and a Huawei E176 (HSDPA 7.2, HSUPA).

    Cheers,
    Martin

  3. Hi Martin,

    I really enjoy your blog!

    One question though, could you tell me which tools you use to capture signaling messages exchanged between your devices and the network?

    Thanks

    Bayani

  4. Hi Bayani,

    I didnt use special software. You can observe the state changes based on the LED on the device that changes color when the UE goes from DCH to FACH/IDLE and vice versa. The second thing you can use to observe state changes is the ping round trip time. Sub 100 ms indicate DCH state while 300 ms indicate that the device is in FACH state. Then you do some timing measurements to find out how long it takes the network to switch the UE from FACH to IDLE or PCH. Once you have that you can deduct when the mobile goes into that state. And from those observatons you can deduct, as in this case, if there is a problem with state changes.

    Martin

  5. Ok nice, thanks for the info.

    By any chance do you know of any end user device on which I would be able to trace the signaling on the Uu or Um interfaces?

    Thanks

    Bayani

  7. Hi Martin,
    Welcome to TAIWAN! A quite common RRM policy you can observe in TMN is that firstly NW directs UE into CELL_FACH and tears HSDPA channel down in the mean time. Then directs UE into CELL_PCH state after 4 ~ 5 seconds inactivity period. It has to take UE 2 seconds or so to finish performing CU to get into CELL_FACH then waiting for HSDPA resource allocation. (if everything goes well) The RRM policy in CHT is quite different and can be more “NRT-bearer-services-friendly”.

    IMHO, it’s hard to tell if compatibility issues exist w/o detailed UE traces in such a bursty behavior scenario. Do you have any other reason to guess so?

Comments are closed.