osmocombb: TS 3 -> TS failed

jolly andreas at eversberg.eu
Mon Jan 14 10:40:37 UTC 2013


hi,

i just encountered the following problem:

the network assigns me from TS 1 to TS 3 it worked, but not when it did
another assigment from TS 3 to TS4. i just got noise instead of valid
SACCH frames.

TS Chg forth: 1 -> 3 | 1856
...
TS Chg forth: 3 -> 4 | 1875


this is the wireshark trace of both assignments. they only differ in the
assigned slot:

Frame 3225: 81 bytes on wire (648 bits), 81 bytes captured (648 bits)
Ethernet II, Src: 00:00:00_00:00:00 (00:00:00:00:00:00), Dst:
00:00:00_00:00:00 (00:00:00:00:00:00)
Internet Protocol Version 4, Src: 127.0.0.1 (127.0.0.1), Dst: 127.0.0.1
(127.0.0.1)
User Datagram Protocol, Src Port: 52261 (52261), Dst Port: gsmtap (4729)
GSM TAP Header, ARFCN: 34 (Downlink), TS: 1, Channel: SDCCH/8 (0)
Link Access Procedure, Channel Dm (LAPDm)
GSM A-I/F DTAP - Assignment Command
    Protocol Discriminator: Radio Resources Management messages
    DTAP Radio Resources Management Message Type: Assignment Command (0x2e)
    Channel Description 2 - Description of the First Channel, after time
        0000 1... = TCH/F + FACCH/F and SACCH/F
        .... .011 = Timeslot: 3
        000. .... = Training Sequence: 0
        ...1 .... = Hopping channel: Yes
        Hopping channel: MAIO 0
        Hopping channel: HSN 0
    Power Command
        0... .... = Spare: 0
        .0.. .... = EPC_mode: Channel(s) not in EPC mode
        ..0. .... = FPC_EPC: FPC not in use/C not in use for uplink
power control
        ...0 0101 = POWER LEVEL: 5
    Frequency List - Frequency List, after time
        Element ID: 5
        Length: 16
        00.. 000. = Format Identifier: bit map 0 (0x00)
        List of ARFCNs = 99 34
    Channel Mode - Mode of the First Channel(Channel Set 1)
        Element ID: 99
        Channel Mode: speech full rate or half rate version 2(GSM EFR) (33)

No.     Time        Source                Destination           Protocol
Info
   3243 464.672890  127.0.0.1             127.0.0.1             LAPDm   
I, N(R)=1, N(S)=2(DTAP) (RR) Assignment Command

Frame 3243: 81 bytes on wire (648 bits), 81 bytes captured (648 bits)
Ethernet II, Src: 00:00:00_00:00:00 (00:00:00:00:00:00), Dst:
00:00:00_00:00:00 (00:00:00:00:00:00)
Internet Protocol Version 4, Src: 127.0.0.1 (127.0.0.1), Dst: 127.0.0.1
(127.0.0.1)
User Datagram Protocol, Src Port: 52261 (52261), Dst Port: gsmtap (4729)
GSM TAP Header, ARFCN: 99 (Downlink), TS: 3, Channel: FACCH/F (0)
Link Access Procedure, Channel Dm (LAPDm)
GSM A-I/F DTAP - Assignment Command
    Protocol Discriminator: Radio Resources Management messages
    DTAP Radio Resources Management Message Type: Assignment Command (0x2e)
    Channel Description 2 - Description of the First Channel, after time
        0000 1... = TCH/F + FACCH/F and SACCH/F
        .... .100 = Timeslot: 4
        000. .... = Training Sequence: 0
        ...1 .... = Hopping channel: Yes
        Hopping channel: MAIO 0
        Hopping channel: HSN 0
    Power Command
        0... .... = Spare: 0
        .0.. .... = EPC_mode: Channel(s) not in EPC mode
        ..0. .... = FPC_EPC: FPC not in use/C not in use for uplink
power control
        ...0 0101 = POWER LEVEL: 5
    Frequency List - Frequency List, after time
        Element ID: 5
        Length: 16
        00.. 000. = Format Identifier: bit map 0 (0x00)
        List of ARFCNs = 99 34
    Channel Mode - Mode of the First Channel(Channel Set 1)
        Element ID: 99
        Channel Mode: speech full rate or half rate version 2(GSM EFR) (33)


any idea why this does not work? i used the "[WIP] Ugly hack to
compensate lost time on TS change (high TS -> low TS)" path.

regards,

andreas





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