[lte][agw] Support nonconsecutive PLMNS

[ulaskozat]

Signed-off-by: Ulas Kozat kozat@fb.com

Summary

• Fixed bug in handling of non-consecutive TACs in TAI list, where the partial lists were not encoded correctly.
• Refactored the code for readability and simplicity.
• Fixed a bug that was not swapping the MNC length during sorting TAIs.

PR limits the TAI list communicated to UE to one partial list that can have up to 16 TAIs. As per the spec TS 124.301 Table 9.9.3.33.1: Tracking area identity list information element:
"The value part of the Tracking area identity list information element consists of one or several partial tracking area identity lists. The length of each partial tracking area identity list can be determined from the 'type of list' field and the 'number of elements'
field in the first octet of the partial tracking area identity list. The UE shall store the complete list received. If more than 16 TAIs are included in this information element, the UE shall store the first 16 TAIs and ignore the remaining
octets of the information element."

Test Plan

Integ tests.

Tested with different entries for consecutive and non-consecutive tacs (by modifying attachedEnodebTacs in gateway.mconfig and restarting the services) and multi-plmn inputs (by modifying the TAC_LIST and TAI_LIST in mme.conf.template file). Checked the pcap entries.

E.g., for
"attachedEnodebTacs": [10181,10183,10185,10187,10188,10283,10284,10287,10288,10383,10384,10387,10388,10483,10487,10488,10583,10584,10587,10588,10683,10684,10687,10783,10784,10787,10883,10884,10887,10983,10984,10987,11083,11084,11183,11184,11283,11288,12888,12988,13088,13188,13288,13388,13488,13588,13684,13688,13784,13788,13884,13888,13984,13988,14084,14088,14184,14188,14284,14384,14484,14584,14684,14784]

Tracking area identity list - TAI list
    Length: 36
    0... .... = Spare bit(s): 0x00
    .00. .... = Type of list: list of TACs belonging to one PLMN, with non-consecutive TAC values (0)
    ...0 1111 = Number of elements: 15
    Mobile Country Code (MCC): Unknown (1)
    Mobile Network Code (MNC): Unknown (01)
    Tracking area code(TAC): 10181
    Tracking area code(TAC): 10183
    Tracking area code(TAC): 10185
    Tracking area code(TAC): 10187
    Tracking area code(TAC): 10188
    Tracking area code(TAC): 10283
    Tracking area code(TAC): 10284
    Tracking area code(TAC): 10287
    Tracking area code(TAC): 10288
    Tracking area code(TAC): 10383
    Tracking area code(TAC): 10384
    Tracking area code(TAC): 10387
    Tracking area code(TAC): 10388
    Tracking area code(TAC): 10483
    Tracking area code(TAC): 10487
    Tracking area code(TAC): 10488

Additional Information

• This change is backwards-breaking

[codecov]

Codecov Report

Merging #6697 (ecec62c) into master (4d5b4c2) will decrease coverage by 0.01%.
The diff coverage is 0.00%.

❗ Current head ecec62c differs from pull request most recent head 15a4948. Consider uploading reports for the commit 15a4948 to get more accurate results

@@            Coverage Diff             @@
##           master    #6697      +/-   ##
==========================================
- Coverage   33.13%   33.11%   -0.02%     
==========================================
  Files        1150     1150              
  Lines      103233   103229       -4     
  Branches     1318     1318              
==========================================
- Hits        34205    34184      -21     
- Misses      65656    65674      +18     
+ Partials     3372     3371       -1     

Flag	Coverage Δ
c_cpp	7.96% <0.00%> (-0.03%)	⬇️
cloud_lint	65.68% <ø> (ø)
feg-lint	56.43% <ø> (-0.13%)	⬇️
lte-test	72.67% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
lte/gateway/c/oai/tasks/nas/api/mme/mme_api.c	0.00% <0.00%> (ø)
lte/gateway/c/oai/tasks/nas/emm/sap/emm_send.c	0.00% <ø> (ø)
...y/services/s8_proxy/servicers/mock_pgw/mock_pgw.go	72.41% <0.00%> (-11.59%)	⬇️
feg/gateway/services/s8_proxy/servicers/senders.go	73.52% <0.00%> (-7.24%)	⬇️
...ateway/services/s8_proxy/servicers/gtp_handlers.go	78.94% <0.00%> (-6.77%)	⬇️
feg/gateway/gtp/gtp_client.go	56.89% <0.00%> (-1.08%)	⬇️
lte/gateway/c/session_manager/StoredState.cpp	93.31% <0.00%> (-0.17%)	⬇️
lte/gateway/c/session_manager/SessionState.cpp	79.63% <0.00%> (-0.08%)	⬇️
lte/gateway/c/session_manager/Types.h	100.00% <0.00%> (ø)
feg/gateway/services/csfb/servicers/csfb.go	42.15% <0.00%> (ø)
... and 12 more

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[ardzoht]

Overall lgtm, with a few comments