Can anyone say what happens when MME does not support the security algorithms sent by UE

Question

What is the objective to send the ESM Information Request message to UE ? Does it part of attach procedure ?

Answer 1

Check the following section 33.102 (mine is release 11 document) section 6.4.2 which says -

1) If the MS and the network have no versions of the UEA algorithm in common and the network is not prepared to use an unciphered connection, then the connection shall be released.
2) If the MS and the network have no versions of the UEA algorithm in common and the user (respectively the user's HE) and the network are willing to use an unciphered connection, then an unciphered connection shall be used.
3) If the MS and the network have at least one version of the UEA algorithm in common, then the network shall select one of the mutually acceptable versions of the UEA algorithm for use on that connection.

This text looks to be 3G text but logically the behavior should be same for LTE too. Comments welcome.

Comments

Thanks for your reply Salil, But what about integrity algorithm

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As per my understanding UE and Network should negotiate it as it is used by subsequently in case if support is not there connection should be released.

Answer 2

MME shall send attach reject with EMM cause "UE security capabilities mismatch".
Please go though 3GPP specification 24.301.

As per my knowledge, there are three algorithms NULL, SNOW 3G and AES for both integrity as well as ciphering. Take a case MME supports only AES and UE supports NULL and SNOW 3G, in that case MME responds with Attach reject.