Ask Your Question

NGAP AllowedNSSAI IE not decoded correctly.

asked 2018-09-12 06:06:48 +0000

TheWirelessGuy gravatar image

updated 2018-09-12 06:35:00 +0000

The AllowedNSSAI IE in NGAP message Initial Context Setup Request (3GPP TS 38413, vf00) doesn't seem to be decoded correctly.

The SD IE in S-NSSAI is optional. So, the optional bit field for presence has to be set/checked while encoding/decoding. However, wireshark seems to expect this IE to be mandatory. What version of the spec is wireshark compliant to?

Below I have the hex for the Initial Context Setup Message with only Allowed-NSSAI IE encoded.

The below hex is decoded (in this the bit field under S-NSSAI is not set)


The below hex fails to decode (gives malformed packet error)


edit retag flag offensive close merge delete

1 Answer

Sort by ยป oldest newest most voted

answered 2018-09-12 10:47:53 +0000

Anders gravatar image

updated 2018-09-12 11:28:11 +0000

The ASN1 code of TS 38.413 15.0.0 which is what Wireshark is based on has:

sST             SST,
sD                  SD,
iE-Extensions       ProtocolExtensionContainer { { S-NSSAI-ExtIEs} }    OPTIONAL,


e.g SD is NOT OPTIONAL. It is my understanding that this will be changed in the next version of the specification but that is not yet available.

edit flag offensive delete link more

Your Answer

Please start posting anonymously - your entry will be published after you log in or create a new account.

Add Answer

Question Tools

1 follower


Asked: 2018-09-12 06:06:48 +0000

Seen: 617 times

Last updated: Sep 12 '18