Which layer in eNB varifies Short-MACI sended by UE in Re-establishment message?

Question

What is content of Short-MACI and how it verified by Receiver? please explain?

Answer 1

Hi,

It is a 16 bit integer which is calculated based on the source cell security algorithm. It is used to verify the rrc-reestablishment message. This verification done at RRC layer.

Answer 2

ShortMAC-I is the 16 least significant bits of calculated MAC-I. Usually when a RRC message is exchanged between UE and eNodeB it is integrity & ciphered protected. This protected message is transmitted over DCCH (Dedicated control channel).
In this particular RRC re-establishment, message is sent from UE to eNodeB over CCCH (common control channel). This common control channel is neither integrity protected nor the ciphered.

RRC at eNodeB receives un-protected and un-ciphered RRC Re-establishment Request message. After receiving this message, eNodeB first gets UE context from the received "Re-establish UE Identity" and then does verification of short-MAC-I.

MAC-I is calculated by using the stored Key RRCint, VarShortMAC-I message. In formula it can be written like
MAC- I = f(key, varShortMAC-I, count, bearer, direction). Here varShortMAC-I is prepared by using (current cellId, pci of source cell and C-RNTI of old cell). Other parameters like count, bearer and direction set to all 1.

Comments

Hi Rupam,

can you please provide me some specification reference to verify ShortMAC-I in eNodeB???