Bug #4728
closedwrong BSSMAP Cause Value on RLL RELEASE IND
100%
Description
When a phone releases a data link layer (in this specific examply by sending a DM LAPDm message on SAPI3), the BSC translates that to a "SAPI 'n' Reject" message.
What's misleading is that OsmoBSC is using cause value 0x25 (BSS not equipped) in this situation.
As TS 48.058 clearly states, a RLL REL IND is only sent if the datalink is released by the MS. Thre's no cause value giving further diagnostics, but if the MS releases the link, it is clearly not the BSS's fault, and hence "BSS not equipped" is wrong.
Attaching a pcap file.
Files
Updated by fixeria over 3 years ago
- Status changed from New to In Progress
Hi Harald,
What's misleading is that OsmoBSC is using cause value 0x25 (BSS not equipped) in this situation.
here is an extract from 3GPP TS 48.008, section 3.1.18.1.2 (part of "Data Link Control SAPI not Equal to 0"):
Receipt of a layer 3 (DTAP) message from the MSC with the SAPI (indicated in the DLCI) not equal to "0" will cause one of the following actions: ... * the sending of a BSSMAP SAPI "N" REJECT message to the MSC if for any reason the data link cannot be established, A Cause Information Element is included; typical Cause values are: "O&M intervention", "processor overload", "BSS not equipped", "MS not equipped".
I think GSM0808_CAUSE_MS_NOT_EQUIPPED is a better fit in this case (on receipt of RLL REL IND).
Updated by fixeria over 3 years ago
- Status changed from In Progress to Feedback
- % Done changed from 0 to 100
Please see:
https://gerrit.osmocom.org/c/libosmocore/+/19820 gsm0808: add gsm0808_create_sapi_reject_cause()
https://gerrit.osmocom.org/c/osmo-bsc/+/19826 bsc_subscr_conn_fsm: use proper cause values in SAPI N REJECT
Updated by laforge over 3 years ago
- Category deleted (
A interface) - Status changed from Feedback to In Progress
- % Done changed from 100 to 90
patches merged. However, I think we're missing a (TTCN3) test for it. Should be relatively easy to send a RLL RELEASE IND on RSL and check for the SAPI N REJECT cause value.
Updated by fixeria over 3 years ago
- Status changed from In Progress to Feedback
- % Done changed from 90 to 100
It took me a while (more than I initially expected) to get familiarized with the BSC_Tests specific API, and the SAPI/DLCI specifics across both A and A-bis interfaces. Those are actually my first test cases for osmo-bsc, please see:
https://gerrit.osmocom.org/c/osmo-ttcn3-hacks/+/19872 BSSMAP_Templates: add tr_BSSMAP_IE_Cause and tr_BSSMAP_SAPInReject
https://gerrit.osmocom.org/c/osmo-ttcn3-hacks/+/19874 BSC_Tests: add TC_rll_{rel_ind,err_ind,timeout}_sapi_n_reject
I've additionally submitted a bunch of cosmetic / misc changes that will also be needed for #4545:
https://gerrit.osmocom.org/c/osmo-ttcn3-hacks/+/19869 library/GSM_RR_Types: s/MobileAllocation/MobileAllocationLV/g
https://gerrit.osmocom.org/c/osmo-ttcn3-hacks/+/19870 library/GSM_SystemInformation: move 'MobileAllocationT' to GSM_RR_Types
https://gerrit.osmocom.org/c/osmo-ttcn3-hacks/+/19871 library/Osmocom_Types: share RA generation helpers from BTS_Tests
https://gerrit.osmocom.org/c/osmo-ttcn3-hacks/+/19873 library/BSSAP_CodecPort: turn conn_id into a template param
