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Bug #3513

unsolicited channel activation acknowledge

Added by stsp 23 days ago. Updated 22 days ago.

Status:
New
Priority:
Normal
Assignee:
Category:
osmo-bts-sysmo
Target version:
-
Start date:
08/31/2018
Due date:
% Done:

0%

Estimated time:
Spec Reference:

Description

While running TTCN3 tests with a sysmobts and osmocom-bb, I ran into test failure "RSL for unknown Dchan"

Specifically, while the BTS is being configured, this code in RSL Emulation is triggered by an
unsolicited channel activation acknowledge RSL message:

                [not dchan_suspended] IPA_PT.receive(tr_RSL(tr_RSL_MsgTypeDR(?))) -> value rx_rsl {
                        /* dispatch to channel based on ChanId */
                        cid := f_cid_by_chan_nr(f_trx_by_streamId(rx_rsl.streamId),
                                                rx_rsl.rsl.ies[0].body.chan_nr);
                        if (cid != -1) {
                                CLIENT_PT.send(rx_rsl.rsl) to ConnectionTable[cid].comp_ref;
                        } else {
                                setverdict(fail, "RSL for unknown Dchan");
                                mtc.stop;
                        }
                }
Frame 396: 76 bytes on wire (608 bits), 76 bytes captured (608 bits) on interface 0
Ethernet II, Src: Sysmocom_00:00:0a (24:62:78:00:00:0a), Dst: WistronI_9e:0e:57 (f0:de:f1:9e:0e:57)
Internet Protocol Version 4, Src: 192.168.100.3, Dst: 192.168.100.11
Transmission Control Protocol, Src Port: 47256, Dst Port: 3003, Seq: 46, Ack: 11, Len: 10
IPA protocol ip.access, type: RSL
    DataLen: 7
    Protocol: RSL (0x00)
Radio Signalling Link (RSL)
    0000 100. = Message discriminator: Dedicated Channel Management messages (4)
    .... ...0 = T bit: Not considered transparent by BTS
    .010 0010 = Message type: CHANnel ACTIVation ACKnowledge (0x22)
    Channel number IE 
        Element identifier: Channel Number (0x01)
        0010 0... = C-bits: SDCCH/4 + ACCH (sub-chan 0) (4)
        .... .000 = Time slot number (TN): 0
    Frame Number IE
        Element identifier: Frame Number (0x08)
        0000 0... = T1': 0
        .... .011 001. .... = T3: 25
        ...1 1000 = T2: 24

Here is another example after changing the control channel 0 to BCCH:

Frame 53997: 76 bytes on wire (608 bits), 76 bytes captured (608 bits) on interface 0
Ethernet II, Src: Sysmocom_00:00:0a (24:62:78:00:00:0a), Dst: WistronI_9e:0e:57 (f0:de:f1:9e:0e:57)
Internet Protocol Version 4, Src: 192.168.100.3, Dst: 192.168.100.11
Transmission Control Protocol, Src Port: 47660, Dst Port: 3003, Seq: 46, Ack: 11, Len: 10
IPA protocol ip.access, type: RSL
    DataLen: 7
    Protocol: RSL (0x00)
Radio Signalling Link (RSL)
    0000 100. = Message discriminator: Dedicated Channel Management messages (4)
    .... ...0 = T bit: Not considered transparent by BTS
    .010 0010 = Message type: CHANnel ACTIVation ACKnowledge (0x22)
    Channel number IE 
        Element identifier: Channel Number (0x01)
        1000 0... = C-bits: BCCH (16)
        .... .000 = Time slot number (TN): 0
    Frame Number IE
        Element identifier: Frame Number (0x08)
        0000 0... = T1': 0
        .... .100 001. .... = T3: 33
        ...0 0110 = T2: 6

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History

#1 Updated by stsp 23 days ago

  • Assignee changed from sysmocom to stsp

#2 Updated by neels 22 days ago

That rings a bell, I've a number of times wondered about Chan Activ Ack right upon BTS startup (sysmoBTS). I kind of assumed it was some bootstrapping necessity and didn't pay closer attention, but of course a Chan Activ Ack without a request shouldn't happen, right?

#3 Updated by laforge 22 days ago

On Sat, Sep 01, 2018 at 09:20:55PM +0000, neels [REDMINE] wrote:

That rings a bell, I've a number of times wondered about Chan Activ Ack right upon BTS startup (sysmoBTS). I kind of assumed it was some bootstrapping necessity and didn't pay closer attention, but of course a Chan Activ Ack without a request shouldn't happen, right?

It shouldn't happen, but it's a known sysmoBTS oddity for many years (maybe forever).

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