NAS Attach Complete message contains 2 security header type IEs and 2 protocol discriminator IEs

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Asked the same on LTE University, just repeating the same here.

I was wondering if you can help me with this issue: I don't understand why the Attach Complete and other NAS messages contain more than 1 Protocol Discriminator IEs and more than 1 Security header type IEs. Are these IEs correlated with the following ESM message container or what could it be the cause?

Here you can find the hex stream of my Attach Complete (only the NAS PDU) packet:
270000000001074300035201c2

posted Jun 23, 2014 by anonymous

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1 Answer

When MME activates integrity and ciphering for NAS messages, it expects UE will send NAS protected message. If you see Attach Complete message content, it doesn't contain any field like MAC (message authentication code and Sequence number, MAC is used for integrity of received message. Attach Complete is a EMM message. If you see message content of "Attach default EPS bearer context accept" , it doesn't have any security related IE. So there is NAS PDU header has been defined which contains information like MAC (message authentication code) and Sequence Number.

answer Jun 24, 2014 by Ganesh

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