Fixed Random TLLI (RTLLI) Management for 2G M2M devices is intended
to expand the operator's control of TLLI (temporary logical link identifier) in
the following scenario:
When multiple M2M devices attempt PS Attaches, with the same fixed
RTLLI coming from different NSEIs (network service entity identifier), the SGSN
cannot distinguish between the devices. The SGSN functions
as if the first device bearing an RTLLI is no longer attached and begins
to communicate with the next device using that same RTLLI. With multiple M2M
devices attempting attaches - all with the same RTLLI - the result is TLLI
collision and dropped calls.
How It Works
This feature deals with Attach problems due to simultaneous IMSI
attaches, all with the same fixed RTLLI.
Beginning with Release 16.3, it became possible to configure the SGSN
to discard/drop Attach Request messages received from an MS with an RTLLI
already in use on the SGSN by adding validation of the NSEI. Attach gets
processed if the attach is coming from a different NSEI. This functionality is
disabled by default.
Beginning with Release 19.3, to further reduce jumbling of
authentication vectors across subscribers, the Fixed Random TLLI Handling
mechanism extends the functionality noted above. A new verification table has
been added to the GbMgr. The table maintains a list of TLLI + NSEI and if an
incoming Attach Request includes a TLLI + NSEI already on the table then the
call is dropped. This functionality is disabled by default.
No new commands or
keywords have been added to the command line interface (CLI) in support of
Fixed Random TLLI Management. Enabling / disabling this mechanism is integrated
into existing CLI.
about the commands, parameters and parameter values, please check your
Interface Reference manual for each of the commands listed below.
configurations should be performed during system boot up. It is not advisable
to enable/disable this TLLI management functionality during runtime.
the RTLLI and the NSEI
To enable the SGSN
to handle Attach Requests with the same fixed RTLLI by verifying both the RTLLI
and the NSEI, use the following configuration:
provides information for monitoring and/or troubleshooting the RTLLI Management
To see the
statistics of attach drops that are due to same-RTLLI collisions, execute the
show commands listed below. When you are looking at the generated statistics,
consider the following:
If the generated counter
values are not increasing then collisions are not occurring.
If the generated counter
values are increasing then it means collisions are occurring and attaches were
Verify Both RTLLI and NSEI
attach-with-tlli-in-use discard-message only-on-same-nseiis configured then the following show command can give the drop
count of attaches caused by same RTLLI and NSEI:
show gbmgr all parser statistics all | grep useIMSI Key: 1487 P-TMSI Key: 0 attach with tlli in use : 592 <-- drops from existing table
Add P-TMSI Key: 0 attach drop tlli in use(pre tlli check): 297 <-- drops from new table
IMSI Key : 1190 P-TMSI Key : 594 attach with tlli in use : 395Add P-TMSI Key : 0 attach drop tlli in use(pre tlli check) : 198
Verify Only RTLLI
attach-with-tlli-in-use discard-message" is configured then the following show
command can give the drop count of attaches caused by same RTLLI:
show gbmgr all parser statistics all | grep use IMSI Key: 1487 P-TMSI Key: 0 attach with tlli in use : 592 <-- drops from existing table
with RTLLIAdd P-TMSI Key: 0 attach drop tlli in use(pre tlli check): 297 <-- drops from new table
with RTLLIIMSI Key : 1190 P-TMSI Key : 594 attach with tlli in use : 395Add P-TMSI Key : 0 attach drop tlli in use(pre tlli check) : 198
Rejects due to Same RTLLI
The following show
command generates SessMgr counters that track the Attach Rejects due to same
show gmm sm stats | grep Same random tlli collisionSame random tlli collision: 10
Release 19.3.5, the 'sgsn-implicit-detach(237)' session disconnect reason pegs
when the 2G-SGSN rejects the Attach Request due to same RTLLI collision.
Beginning in Release
19.4, the following show command identifies the two bulk statistics the SGSN
uses to track the number of times the SGSN rejects Attach Requests or Combined
Attach Requests due to same RTLLI collision.