Cellular Network Infrastructure » Radio Access Network » OsmoBTS

during our lunch discussion we were considering the L3 sequence numbers (2bit) might be related. However, they only exists in MM/CC/SMS/SS - there are no L3 sequence number in RR messages. So that can be excluded.

laforge: I noticed that, I guess RR has no sequence number because those messages never leave the BSS domain (unlike the others).

I have done some more tests on that issue. I was fearing that the problem could be a regression in osmo-bts. I checked the problem against osmo-bts-trx and there everything functions normally - so it seems to be ineed an octphy specific problem. There is more research to be done on this. However on our testphones I can see that the ASSIGNMENT COMMAND is received an an ASSIGNMENT COMPLETE is sent out. I wonder why it never arrived (Wrong channel?).

I have tried the experiment again. This time I have included the gsmtap output from osmo-bts-octphy in the capture. The trace only contains one MO call. One can see the assignment command at frame 2091 on RSL level. Then it appears again on frame 2264 in GSMTAP. A few frames later at 3064 An Assignment Failure is visible in the GSMTAP. An Establish Indication is not visible in the trace. I wonder why the Assignment Failure is not visible in the RSL data. Shouldn't it be forwarded to the BSC?.

I have done the test with a K800i (external mncc, call to test number), the results contradict with the test I did last time with the trace mobile.

I have retried the experiment with the trace mobile. The result is different. At Frame 2453 we can see the incoming assignment command. At Frame 2644 we see the Assignment command re-appearing in the GSMTAP data. After that there is not Assigment Complete and no Assignment Fail visible. Also no Establish Indication is visible.

On the trace mobile the result is somewhat weird. The Assignment command seems to be responded with an Assignment complete, but shortly after that, an Assignment Failure is send out. However, I do not see any of those messages in the trace.

As a follow up, I attached the screen-shots I took on the trace mobile.

dexter wrote:

On the trace mobile the result is somewhat weird. The Assignment command seems to be responded with an Assignment complete, but shortly after that, an Assignment Failure is send out.

Why is that weird? That's exactly the behaviour you would see in any situation where the MS attempts to establish the new radio channel but fails to do so, and then switches back to the old channel to send the assignment failure.

(I am sorry, I confused the configuration when we were talking about the problem last time)

It looks just like that you are right. I tested it again with encryption disabled and it indeed works now.