Project

General

Profile

Actions

Bug #5791

closed

mobile: "DLLAPD NOTICE lapdm.c:769 (dl=0x62c000000ef0) EA bit 0 is not allowed in GSM"

Added by fixeria over 1 year ago. Updated over 1 year ago.

Status:
Resolved
Priority:
Normal
Assignee:
Category:
OsmocomBB Firmware
Target version:
-
Start date:
11/25/2022
Due date:
% Done:

100%

Resolution:
Spec Reference:

Description

This message is frequently seen when "talking" to an Osmocom based network.

DLLAPD NOTICE lapdm.c:769 (dl=0x62c000000ef0) EA bit 0 is not allowed in GSM
DLLAPD NOTICE lapdm.c:546 (dl=0x62c000000ef0) sending MDL-ERROR-IND 12

mobile originated GSMTAP traces in Wireshark confirm this warning:

$ tshark -r /tmp/lapdm.pcap -Y "(lapdm.ea == 0)" 
    9   1.786785    127.0.0.1 → 127.0.10.1   LAPDm 81 S, func=RR, N(R)=0
   10   2.258601    127.0.0.1 → 127.0.10.1   LAPDm 81 S, func=RR, N(R)=0
   11   2.728325    127.0.0.1 → 127.0.10.1   LAPDm 81 S, func=RR, N(R)=0

$ tshark -r /tmp/lapdm.pcap -Y "(lapdm.ea == 0)" -V | less
GSM TAP Header, ARFCN: 73 (Downlink), TS: 1, Channel: SDCCH/8 (0)
    Version: 2
    Header Length: 16 bytes
    Payload Type: GSM Um (MS<->BTS) (1)
    Time Slot: 1
    ..00 0000 0100 1001 = ARFCN: 73
    .0.. .... .... .... = Uplink: 0
    0... .... .... .... = PCS band indicator: 0
    Signal Level: -47 dBm
    Signal/Noise Ratio: 0 dB
    GSM Frame Number: 1195166
    Channel Type: SDCCH/8 (8)
    Antenna Number: 0
    Sub-Slot: 0
Link Access Procedure, Channel Dm (LAPDm)
    Address Field: 0x0e
        .00. .... = LPD: Normal GSM (0)
        ...0 11.. = SAPI: SMS/SS (3)
        .... ..1. = C/R: 1
        .... ...0 = EA: More octets (0)
    Control field: S, func=RR, N(R)=0 (0x01)
        000. .... = N(R): 0
        .... 00.. = Supervisory frame type: Receiver ready (0x0)
        .... ..01 = Frame type: Supervisory frame (0x1)
    Length Field: 0x03
        0000 00.. = Length: 0
        .... ..1. = M: More segments (1)
        .... ...1 = EL: Final octet (1)

Looks like the S, func=RR frames are encoded incorrectly by the network side? SAPI: SMS/SS (3) is also suspicious.


Related issues

Related to OsmocomBB - Bug #5133: mishandling of the sacch l1 headerResolved04/26/2021

Actions
Actions

Also available in: Atom PDF

Add picture from clipboard (Maximum size: 48.8 MB)