[srslte-users] PLMN-Id decoding and encoding

[nauga+srsran at mailbox.org]

I found the solution. The Hexbytes are encoded in ASN.1. Wireshark does 
the decoding in the background. Alternatively the Python library 
"pycrate" can decode this as well.

Am Montag, 12.07.2021 um 11:23 schrieb nauga+srsran at mailbox.org:
> Hi,
>
> currently I'm having some problems to understand the decoding of 
> PLMN-Id from SIB1. PLMN contains MCC and MNC. According to Standard 
> ETSI TS 129 171 V14.0.0 under “7.4.27 PLMN Identity” the encoding of 
> PLMN-Id is more or less swapping digits in Hexbyte and adding f, if 
> MNC has only 2 digits. This is clear for me.
>
> Unclear for me is what Wireshark is displaying in its Hexbyte window, 
> using a srsue .pcap file or function srsran_vec_fprint_byte() in 
> pdsch_ue.c. For Germany and Provider Vodafone the PLMN-Id is: MCC=262, 
> MNC=02. This is displayed in the tree view of the SIB1 package and 
> should be right according to wikipedia. The encoded PLMN-Id in my 
> understanding according to Standard would be something like: 62f220. 
> But Wireshark is displaying 49 88 05. This difference happens also 
> with other providers and other countries, e.g. 49 88 07 for MCC=262, 
> MNC=03.
>
> So Wireshark is displaying the right decoded PLMN-Id, but in my 
> understanding different Hexbyte as to the standard.
> Is someone to able to explain me these “false” Hexbytes?
>
> Many thanks in advance.
>
> Regards,
> Dom
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