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utils.py: Add helper method to parse ePDG Selection info TLV

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ePDG selection information TLV data object is made of following elements:

ePDG Selection Information Tag '80' (1 Byte)
Length 5n Note
PLMN 1 (3 Bytes)
ePDG Priority (2 Bytes)
ePDG FQDN format '00' or '01' (1 Byte)
...

PLMN n
...

Note: The length is coded according to ISO/IEC 8825-1 [35]

Note 2: Inconsistency in spec: 3GPP TS 31.102 version 15.2.0 Release 15, 4.2.104

As per spec, Length field value is 5n, where n is number of PLMNs
But, each PLMN entry is made of PLMN (3 Bytes) + ePDG Priority (2 Bytes) + ePDG FQDN format (1 Byte)
Totalling to 6 Bytes, maybe Length should be 6n and not 5n

Change-Id: I0f9f38961a589e3f9a53d2288a3dc6fa71a4b1b0
This commit is contained in:
Supreeth Herle
2020-03-24 12:49:16 +01:00
committed by herlesupreeth
parent 5d8cd9b378
commit 95b4e8d4fa
1 changed files with 54 additions and 0 deletions
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54
pySim/utils.py
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@@ -609,3 +609,57 @@ def init_reader(opts):
sl = SerialSimLink(device=opts.device, baudrate=opts.baudrate)
return sl
def dec_ePDGSelection(sixhexbytes):
"""
Decode ePDGSelection to get EF.ePDGSelection or EF.ePDGSelectionEm.
See 3GPP TS 31.102 version 15.2.0 Release 15, section 4.2.104 and 4.2.106.
"""
res = {'mcc': 0, 'mnc': 0, 'epdg_priority': 0, 'epdg_fqdn_format': ''}
plmn_chars = 6
epdg_priority_chars = 4
epdg_fqdn_format_chars = 2
# first three bytes (six ascii hex chars)
plmn_str = sixhexbytes[:plmn_chars]
# two bytes after first three bytes
epdg_priority_str = sixhexbytes[plmn_chars:plmn_chars + epdg_priority_chars]
# one byte after first five bytes
epdg_fqdn_format_str = sixhexbytes[plmn_chars + epdg_priority_chars:plmn_chars + epdg_priority_chars + epdg_fqdn_format_chars]
res['mcc'] = dec_mcc_from_plmn(plmn_str)
res['mnc'] = dec_mnc_from_plmn(plmn_str)
res['epdg_priority'] = epdg_priority_str
res['epdg_fqdn_format'] = epdg_fqdn_format_str == '00' and 'Operator Identifier FQDN' or 'Location based FQDN'
return res
def format_ePDGSelection(hexstr):
ePDGSelection_info_tag_chars = 2
ePDGSelection_info_tag_str = hexstr[:2]
# Minimum length
len_chars = 2
# TODO: Need to determine length properly - definite length support only
# Inconsistency in spec: 3GPP TS 31.102 version 15.2.0 Release 15, 4.2.104
# As per spec, length is 5n, n - number of PLMNs
# But, each PLMN entry is made of PLMN (3 Bytes) + ePDG Priority (2 Bytes) + ePDG FQDN format (1 Byte)
# Totalling to 6 Bytes, maybe length should be 6n
len_str = hexstr[ePDGSelection_info_tag_chars:ePDGSelection_info_tag_chars+len_chars]
if len_str[0] == '8':
# The bits 7 to 1 denotes the number of length octets if length > 127
if int(len_str[1]) > 0:
# Update number of length octets
len_chars = len_chars * int(len_str[1])
len_str = hexstr[ePDGSelection_info_tag_chars:len_chars]
content_str = hexstr[ePDGSelection_info_tag_chars+len_chars:]
# Right pad to prevent index out of range - multiple of 6 bytes
content_str = rpad(content_str, len(content_str) + (12 - (len(content_str) % 12)))
s = ""
for rec_data in hexstr_to_Nbytearr(content_str, 6):
rec_info = dec_ePDGSelection(rec_data)
if rec_info['mcc'] == 0xFFF and rec_info['mnc'] == 0xFFF:
rec_str = "unused"
else:
rec_str = "MCC: %03d MNC: %03d ePDG Priority: %s ePDG FQDN format: %s" % \
(rec_info['mcc'], rec_info['mnc'], rec_info['epdg_priority'], rec_info['epdg_fqdn_format'])
s += "\t%s # %s\n" % (rec_data, rec_str)
return s