RRC Rejection vs RAB Failure

[abdelrahmase]

What are the reasons for RRC Rejection and RAB Setup failure especial for the OVSF codes?

[praveenku]

Hi,
NodeB may send RRC Connection Reject in response to the UE’s RRC Connection Request. This mostly happens if the cell is congested and the necessary radio resources for the connection setup cannot be provided and/or the NodeB is overloaded. There is no reject cause value specified for the RRC connection reject message in the LTE . However RRC connection reject message provides the wait time parameter. The value of this wait time is an integer number in the range of 1–16. Wait time defines how many seconds the UE should wait after reception of RRC Connection Reject until a new RRC connection request message is sent.

For RAB failures major reasons are like,
i.
When the RNC decides to reject the CS voice RAB request because the admission control entity reports a failure

ii. When the RAB assignment fails due to radio link setup or reconfiguration failure.
iii.When the RNC decides to reject the CS voice RAB request due to transport failure.
iv.When the RNC decides to reject the CS voice RAB request because the admission control entity blocks the radio link establishment to ensure the setup of high priority calls. This happens before the RRC: RADIO BEARER SETUP message would be sent to the UE.
v.When the RNC rejects a CS Voice RAB request due to AMR capacity license exceeded.
vi.When a CS voice traffic class RAB setup fails due to Iu-CS transport resources.

Hope it helps.
Thanks.