DID-SDID format subtly different than RFC 8331

[garethsb]

flow_sdianc_data.json has the regex pattern for both DID and SDID as ^0x[0-9a-fA-F]{2}$. There are no examples in the spec repo, but it is clear this requires exactly two hex digits but accepts upper- and lower-case.

On the other hand, the representation in SDP files is governed by RFC 8331 which uses the ABNF:

TwoHex = "0x" 1*2(HEXDIG)
DidSdid = "DID_SDID={" TwoHex "," TwoHex "}"

Where HEXDIG is defined in RFC 2234 by:

DIGIT          =  %x30-39
                       ; 0-9
HEXDIG         =  DIGIT / "A" / "B" / "C" / "D" / "E" / "F"

Therefore, though the examples given in RFC 8331 are like "DID_SDID={0x61,0x02};DID_SDID={0x41,0x05}" which suggests two hex digits is good form, the TwoHex production allows a single hex digit, but requires uppercase for A-F.

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This makes the values "0x41", "0x0c" valid in IS-04 but "{0x41,0x0c}" not valid in SDP, while "{0x41,0xC}" is valid in SDP but "0x41", "0xC" is not valid in IS-04.

This is probably worth at least a little note somewhere.

[peterbrightwell]

Something for a future INFO- implementation guide, assuming that has a section on SDP attributes?