[Openbts-discuss] Measurement Report in SABM?

[David B. <da...@ra...>]

Hello -

We have a MultiTech GSM/EDGE modem which (I think) is based on a Sierra Wireless baseband chipset.  It sometimes responds to RR Immediate Assignment with an SABM frame, on the assigned DCCH, containing the RR Measurement Report message.  As far as I know, this message should never appear on a DCCH and should never be in an SABM frame.  Has anyone seen this before?  Any suggestions on how to deal with it?

-- David


BTW, here it is, as seen in Wireshark:

GSM TAP Header, ARFCN: 52 (Uplink), TS: 2, Channel: FACCH/F (0)
    Version: 2
    Header length: 16 bytes
    Payload Type: GSM Um (MS<->BTS) (1)
    Time Slot: 2
    ..00 0000 0011 0100 = ARFCN: 52
    .1.. .... .... .... = Uplink: 1
    Signal/Noise Ratio (dB): 0
    Signal Level (dBm): 0
    GSM Frame Number: 0
    Channel Type: FACCH/F (9)
    Antenna Number: 0
    Sub-Slot: 0
Link Access Procedure, Channel Dm (LAPDm)
    Address Field: 0x01
        .00. .... = LPD: Normal GSM (0)
        ...0 00.. = SAPI: RR/MM/CC (0)
        .... ..0. = C/R: 0
        .... ...1 = EA: Final octet (1)
    Control field: U P, func=SABM (0x3F)
        ...1 .... = Poll: True
        001. 11.. = Command: Set Asynchronous Balanced Mode (0x0b)
        .... ..11 = Frame type: Unnumbered frame (0x03)
    Length Field: 0x49
        0100 10.. = Length: 18
        .... ..0. = M: Last segment (0)
        .... ...1 = EL: Final octet (1)
GSM A-I/F DTAP - Measurement Report
    Protocol Discriminator: Radio Resources Management messages
        .... 0110 = Protocol discriminator: Radio Resources Management messages (0x06)
        0000 .... = Skip Indicator: 0
    DTAP Radio Resources Management Message Type: Measurement Report (0x15)
    Measurement Results
        0... .... = BA-USED: 0
        .0.. .... = DTX-USED: DTX was not used
        ..10 1010 = RXLEV-FULL-SERVING-CELL: -69 <= x < -68 dBm (42)
        0... .... = 3G-BA-USED: 0
        .1.. .... = MEAS-VALID: The measurement results are not valid
        RXLEV-SUB-SERVING-CELL: Unknown (106)
        .000 .... = RXQUAL-FULL-SERVING-CELL: BER < 0.2%, Mean value 0.14% (0)
        .... 000. = RXQUAL-SUB-SERVING-CELL: BER < 0.2%, Mean value 0.14% (0)
        .... ...0  00.. .... = NO-NCELL-M: No neighbour cell measurement result (0)



David A. Burgess, CEO
Range Networks, Inc.
San Francisco
cell +1 707 208 2622
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