LTE: How much resource is granted by eNodeB to transmit msg3 ?

Question

Can someone please tell me "How much radio resource is granted on PUSCH" for msg3 (RRC Connection Request or RRC Connection Re-establishment Requet or RRC Connection Reconfiguration Complete).

Answer 1

I have not worked for LTE L2 layers but have some level of basic information.

When an UE needs to send either one of the RRC messages (like RRC Connection Request or RRC Connection Reestablishment Request or RRC Connection Reconfiguration Complete(in case of handover)), it initiates Random access procedure. As part of random access procedure, eNodeB allocates resources on PUSCH channel for msg3 transmission.

I checked 3GPP 36.321 specfication, UL- Grant field has 20 bits long space in RAR pdu.

It my personal thinking since eNodeB already knows what type of messages can be send from UE. So it allocates the resource which is large enough to carry msg3. Most probably Union of {RRC Connection Request, RRC Connection Reestablishment Request, RRC Connection Reconfiguration complete }.

I have not much confidence on my answer it is just a thought. Waiting for others to respond.