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lcsap: fix decode of plmnIdentity 

Corretly decode MNC if it consists of 3 digits
Change to what is called big endinan MNC

   8   7   6   5   4   3   2   1
 +---+---+---+---+---+---+---+---+
 |  MCC digit 2  |  MCC digit 1  |  octet x
 +---------------+---------------+
 |    Filler     |  MCC digit 3  |  octet x+1
 +---------------+---------------+
 |  MNC digit 2  |  MNC digit 1  |  octet x+2
 +---------------+---------------+

 MNC of length 3:

   8   7   6   5   4   3   2   1
 +---+---+---+---+---+---+---+---+
 |  MCC digit 2  |  MCC digit 1  |  octet x
 +---------------+---------------+
 |  MNC digit 1  |  MCC digit 3  |  octet x+1
 +---------------+---------------+
 |  MNC digit 3  |  MNC digit 2  |  octet x+2
 +---------------+---------------+

From 3GPP TS 29.171
7.4.27 PLMN Identity

- digits 0 to 9, encoded 0000 to 1001,
- 1111 used as filler digit, two digits per octet,

- bits 4 to 1 of octet n encoding digit 2n-1
- bits 8 to 5 of octet n encoding digit 2n

The Selected PLMN identity consists of 3 digits from MCC followed by either
- a filler digit plus 2 digits from MNC (in case of 2 digit MNC) or
- 3 digits from MNC (in case of a 3 digit MNC).


(cherry picked from commit 156f9e81fc)
This commit is contained in:
Jonas Falkevik 2020-10-09 22:07:36 +00:00 committed by Pascal Quantin
parent 1d6de11c49
commit 34b41729f9
2 changed files with 2 additions and 2 deletions
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2
epan/dissectors/asn1/lcsap/lcsap.cnf
View File

@ -158,7 +158,7 @@ ProtocolIE-Field/value ie_field_value
if (!parameter_tvb)
return offset;
subtree = proto_item_add_subtree(actx->created_item, ett_lcsap_plmnd_id);
dissect_e212_mcc_mnc(parameter_tvb, actx->pinfo, subtree, 0, E212_NONE, TRUE);
dissect_e212_mcc_mnc(parameter_tvb, actx->pinfo, subtree, 0, E212_NONE, FALSE);
#.END
#.FN_BODY Positioning-Method-And-Usage VAL_PTR = &parameter_tvb

2
epan/dissectors/packet-lcsap.c
View File

@ -1073,7 +1073,7 @@ dissect_lcsap_PLMN_ID(tvbuff_t *tvb _U_, int offset _U_, asn1_ctx_t *actx _U_, p
if (!parameter_tvb)
return offset;
subtree = proto_item_add_subtree(actx->created_item, ett_lcsap_plmnd_id);
dissect_e212_mcc_mnc(parameter_tvb, actx->pinfo, subtree, 0, E212_NONE, TRUE);
dissect_e212_mcc_mnc(parameter_tvb, actx->pinfo, subtree, 0, E212_NONE, FALSE);
return offset;