LTE: RRC Connection Reject

Direction: E-UTRAN => UE
Signalling Radio Bearer: SRB0
RLC Mode: TM
Logical Channel: CCCH
Transport Channel: DL-SCH

The RRC CONNECTION REJECT message is used to reject the RRC connection establishment. This message includes the IE waitTime which can be in the range from 0 to 16 seconds. Optionally, the NW can include the IE extendedWaitTime for the purpose of Delay Tolerant access requests
          Upon receiving the RRC CONNECTION REJECT message, the UE should start timer T302, with the timer value set to waitTime. The UE is not allowed to send another RRCConnectionRequest for mobile originating calls, mobile originating signalling, mobile terminating access and mobile originating CS fallback on the same cell on which RRC CONNECTION REJECT is received until the expiry of T302

The following differences are noted as compared to UMTS RRC CONNECTION REJECT:
  1. There is no RejectionCause in the case of LTE
  2. RedirectionInfo which is used to redirect the UE to another frequency/RAT is not present in the case of LTE
  3. LTE requires the higher layers to initiate new RRC CONNECTION REQUEST after receiving RRC CONNECTION REJECT, where as in the case of UMTS, the procedure is repeated for N300 times
Example: RRC CONNECTION REJECT Message








Reference: 3GPP TS 36.331 and 3GPP TS 25.331
Posted by KP
Labels: ,

15 comments:

  1. hi2friendsNovember 8, 2013 at 5:05 AM

    Hi Kumar,

    There is Typo:

    "LTE requires the higher layers to initiate new RRC CONNECTION REJECT after receiving RRC CONNECTION REJECT, where as in the case of UMTS, the procedure is repeated for N300 times"

    Thanks,
    Rajdeep

    ReplyDelete
  2. KPNovember 8, 2013 at 5:40 AM

    Thanks. Type corrected

    ReplyDelete
  3. UnknownMay 8, 2014 at 10:50 PM

    what are the reasons of the RRC rejections from the eNB??

    ReplyDelete
  4. AnonymousSeptember 16, 2014 at 8:14 PM

    Hi Pankaj,
    eNodeB may send RRC Connection Reject in response to the UE’s RRC Connection Request. This typically happens if the cell is congested and the necessary radio resources for the connection setup cannot be provided and/or the eNodeB is overloaded. According to the 3GPP TS 36.331 , 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.

    ReplyDelete
  5. UnknownDecember 1, 2015 at 9:34 AM

    Hi Kumar,

    How will MAC know whether it has received Setup or Reject?
    Do we need to add CRI mac subheader in Reject message also?

    ReplyDelete
    Replies
    1. KPDecember 9, 2015 at 8:53 AM

      Hi Shuaib,

      The MAC will never know if this setup or reject. Only RRC will be able to understand this. CRI subheader is part of contention resolution procedure which is separate from receiving RRC Connection setup/reject. Some networks transmit CRI along with setup/reject and some networks do it separately (CRI first)

      Delete
  6. hamoooo271087November 13, 2016 at 1:43 AM

    Hello Kumar,

    Do we have to check utilization counters like Resource blocks utilization or max number of users in a manner similar to UMTS to check the cause of RRC rejection or it wouldn't help

    Thanks

    ReplyDelete
  7. UnknownDecember 8, 2016 at 3:16 AM

    Hi Kumar,

    ENB sending RRC connection reject if UE sending MMEC in rrc connection request and MMEC does not match with any MME in pool.
    Is it expected behavior?

    Thanks

    ReplyDelete
    Replies
    1. KPDecember 8, 2016 at 10:08 AM

      Hi,
      You mean MMEC in S-TMSI? If yes, I think that the eNodeB shouldn't reject the connection establishment procedure based on the fact that the MMEC doesn't match with any of the MMEs in the pool. Frankly, I am not 100% sure.
      Are you sure about the reason for rejection? In any case, please update the progress here, I am interested to know this. In the meantime, I can spend time in checking more about it.

      Delete
  8. UnknownAugust 4, 2017 at 10:01 AM

    Hi,
    As I know UE even can send random number instead of s-TMSI and eNB still accepting that, so undefined MMEC should not be a reason for rejecting the request.
    on the other hand if MME grouping is used, then eNB will check the load balance of each then forward the UE to it.

    ReplyDelete
  9. AnonymousApril 26, 2020 at 5:14 PM

    How RRC can decide whether to accept or reject the connection? If it is based on cell congestion control, looking for some references for that.

    ReplyDelete
  10. AnonymousJune 7, 2020 at 8:20 AM

    What if the UE sends a rrcConnectionRequest with an invalid TMSI? Would it receive rrcConnectionReject and then attempt to perform imsi attach?

    ReplyDelete
  11. সুদীপ্তJune 9, 2020 at 8:41 AM

    Hi Kumaraswamy, how it is determined whether rrcconnectionrelease will contain redirectedCarrierInfo or not?

    ReplyDelete
  12. AnonymousJune 8, 2023 at 9:27 AM

    71726

    ReplyDelete

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