Saturday, November 5, 2011

RRC Connection Release

Direction: E-UTRAN => UE
Signalling Radio Bearer: SRB1
RLC Mode: AM
Logical Channel: DCCH
Transport Channel: DL-SCH

The RRC CONNECTION RELEASE message is used to command the release of an RRC connection. E-UTRAN initiates the RRC connection release procedure to an UE in RRC_CONNECTED state

The RRC CONNECTION RELEASE procedure with redirection information can also be used for CS-fallback to GERAN or UTRAN

The RRC CONNECTION RELEASE procedure can also be used for MME load balancing. If an MME feels overloaded, it can simply move the calls to other MME in the MME pool. The source MME releases the S1 connections of the UE towards the eNodeB asking the UE to perform a “load balancing TAU”. Then the eNodeB sends RRC CONNECTION RELEASE message to the UE with cause ‘load balancing TAU required'. After receiving this message, the UE initiates Tracking Area Updating procedure which is redirected to another MME

The eNodeB may provide a cell reselection priority for each frequency, by means of separate lists for each RAT (including E-UTRA) in the RRC CONNECTION RELEASE message

There is no RRC CONNECTION RELEASE COMPLETE message defined in LTE. So, UE leaves RRC_CONNECTED state without transmitting RRC CONNECTION RELEASE COMPLETE message

Some of the IEs in RRC CONNECTION RELEASE message
ReleaseCause: The IE releaseCause is used to indicates the reason for releasing the RRC Connection (Ex:- loadBalancingTAUrequired, cs-FallbackHighPriority, or other)
RedirectedCarrierInfo: The redirectedCarrierInfo indicates a carrier frequency which is used to redirect the UE to an E-UTRA or an inter-RAT carrier frequency
IdleModeMobilityControlInfo: This IE provides dedicated cell reselection priorities. 
FreqPriorityListX: Provides a cell reselection priority for each frequency, by means of separate lists for each RAT (including E-UTRA)
SystemInformation: Container for system information of the GERAN cell. Each OCTET STRING in ‘SystemInfoListGERAN’ contains one complete System Information (SI) message as defined in TS 44.018
cellInfoList: Used to provide system information of one or more cells on the redirected inter-RAT carrier frequency. The system information can be used if, upon redirection, the UE selects an inter-RAT cell indicated by the physCellId and carrierFreq (GERAN) or by the physCellId (other RATs).
utra-BCCH-Container: Contains System Information Container message as defined in TS 25.331

 Reference: 3GPP TS 36.331

Example1: Simple RRC CONNECTION RELEASE message













Example2: RRC CONNECTION RELEASE message IdleModeMobilityControlInfo



























Example3: RRC CONNECTION RELEASE message with redirection from E-UTRAN to UTRAN















Example4: RRC CONNECTION RELEASE message with redirection from E-UTRAN to GERAN

20 comments:

  1. HI,
    I am having one doubt, when the connection is being disconnected by the UE, then all the bearers and resources from the UE side get released.
    How the eNb side comes to know about the disconnection and releases its resources and transmits the "RRCConnectionRelease" messege to the UE?

    ReplyDelete
  2. Hi,

    The UE can only release resources after receiving RRC Connection release message from the NW.

    ReplyDelete
  3. Swamy,
    so what is the OTA message for that in QXDM

    Thanks

    ReplyDelete
  4. Replies
    1. OTA is over the air,QXDM does not show LTE message like 3G.You may have to decode and see what type of message.
      If QCAT is installed you can see the decoded content in QXDM directly.

      Delete
    2. I have latest QCAT installed in my PC, but still its not showing the decoded message in QXDM. Still i need to decode it manually. Can any one please tell? Is there any settings we need to set it QXDM?

      Delete
  5. Someone can clarify what means IE ?

    ReplyDelete
  6. IE is an Information Element in an RRC Message in ASN.1 terminalogy. These IEs can be individual fields, a particular structures and so on...For example in the above RRC Connection Release message, 'release cause' is an IE

    ReplyDelete
  7. Is it possible to redirect from UMTS to LTE?

    ReplyDelete
  8. Hi,

    I have a question.
    I am able to do MO call in both and idle and connected mode in CSFB
    But for MT its happening for idle mode only.

    Can it be due CSFB priority handling.
    Can you tell me what parameters are responsible for it.

    ReplyDelete
  9. Hi,
    I am doing Volte testing, My question is I don't see RRC message between UE and network in qxdm log. Where should it be seen?

    ReplyDelete
  10. Hi,
    I have a question,when UE will go to idle mode ? UE itself will decide or EUTRAN will decide ?

    ReplyDelete
    Replies
    1. The UE does not decide to go into idle. It is directed to do so by the eNodeb, after an inactivity timer expires. The value of the timer is set by the operator.

      Delete
  11. Hi,

    Anyone can help me, I have a question
    we are facing below command & release message but still we can't know the exact reason for receiving it


    [82] [2013-12-10 15:18:24:100] [MME -> eNB_2115] : UEContextReleaseCommand

    1 msgS1apUEContextReleaseCommand_type.uE_S1AP_IDs.choice = 1
    2 msgS1apUEContextReleaseCommand_type.uE_S1AP_IDs.u.uE_S1AP_ID_pair.mME_UE_S1AP_ID = 16853291 (0x101292b)
    3 msgS1apUEContextReleaseCommand_type.uE_S1AP_IDs.u.uE_S1AP_ID_pair.eNB_UE_S1AP_ID = 4401 (0x1131)
    4 msgS1apUEContextReleaseCommand_type.cause.choice = 1
    5 msgS1apUEContextReleaseCommand_type.cause.u.radioNetwork = 21 (0x15)
    6
    7 msgS1apUEContextReleaseCommand_type.rawdata.numocts = 25
    8
    9 msgS1apUEContextReleaseCommand_type.rawdata.data =
    10 00 17 00 15 00 00 02 00 63 00 08 0c 01 01 29 2b ........c.....)+
    11 40 11 31 00 02 40 02 02 a0 @.1..@...



    [83] [2013-12-10 15:18:24:100] [eNB_2115 -> UE] : RRCConnectionRelease

    1 value DL-DCCH-Message ::=
    2 {
    3 message c1 : rrcConnectionRelease :
    4 {
    5 rrc-TransactionIdentifier 0,
    6 criticalExtensions c1 : rrcConnectionRelease-r8 :
    7 {
    8 releaseCause other
    9 }
    10 }
    11 }
    12
    13 RRCConnectionRelease.rawdata.numocts = 2
    14
    15 RRCConnectionRelease.rawdata.data =
    16 28 02 (.


    Thanks everyone

    ReplyDelete
  12. Hi,

    I have a question. If there is no uplink and downlink transmission for a long time, RRC connection will be released. How long should it be? Is any timer counting for that in spec and which spec can find it? I am appreciated for your help.

    ReplyDelete
  13. Yes there is a timer running at eNB and the value of the timer is not specified by 3GPP. This value is operator specific

    ReplyDelete
  14. Hi Kumar Swamy
    As per 23401,i always see CSFB happened with Extended service request and S1AP request & responce with CSFB indicator.(as LTE do attach & default bearer procedure from very begining).could you please explain when CSFB will trigger with RRC connection release with CSFB indicator.please explain with call flow and pratical scenario.

    Thanks in Advance
    Vijay T

    ReplyDelete
  15. I have a question, RRC RELEASE COMMAND with cause as "mmeloadbalancingTAUrequired" is sent to UE from ENB only after the ENB receives UE CONTEXT RELEASE COMMAND with cause as "mmeloadbalancingTAUrequired" right?? is there any scenario where UE receives RELEASE COMMAND from ENB with the cause "mmeloadbalancinfTAUrequired" but the ENB received UE CONTEXT RELEASE COMMAND with an cause "miscellaneous unspecified".
    Could you help me on these as we saw this case from last 2 weeks, I am confused as the specs say something and i am seeing something.

    ReplyDelete
  16. Agree with you and even I think that the UE get RRC Connection Release with cause 'loadBalancingTAUrequired' only when eNB gets the release command for the same but not for unspecified cause.

    ReplyDelete