LTE: RRC Connection Setup

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

The RRC CONNECTION SETUP message is used to establish SRB1. It contains configuration information for SRB1. This allows subsequent signaling to use the DCCH logical channel. The configuration for SRB1 can be a specific configuration or the default configuration.

The RRC CONNECTION SETUP message may also contain configuration for PUSCH, PUCCH, PDSCH channels and information regarding uplink power control, CQI reporting, the SRS, antenna configuration and scheduling requests

Example: RRC CONNECTION SETUP

28 comments:

  1. After eNB sent the RRC connection Setup, it wiat for a time waiting the reply from UE by the RRC Connectione setup complete, and if no reply then there is a fail of the RRC.
    what is that timer? and how we can change it?

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    1. It is T300 timer

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    2. It is RRCConnSetupCmp Waiting Timer(s)

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    3. the T300(How much wait time the timer will activate)

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  2. This is known as the defense mechanism timer and it's usually set to 3 seconds.

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  3. What if we don't receive RRC Setup message? Radio conditions are good.

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    1. It needs to be checked on the UE logs where the procedure was stuck. Is RA procedure succesful? at least MSG3 sent out?

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  4. Hi, what is the difference between "RRC Connection Setup message" and "Msg-4" in RACH procedure? Thx

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    1. Msg4 is actually contention resolution. Some NWs transmit RRC Connection Setup message along with Msg4 while the others do it seperately.

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    2. If it is CCCH type RA, then Contention resolution MAC CE would be expected it will be MSG4, if it is of type DXCH then uplink grant addressed by C-RNTI expected as MSG4, And any grant addressed to C-RNTI if PDCCH order triggered

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  5. is it possible that eNB can send data(RRC CONNECTION SETUP IE's) of REl-10(not rel-8) to UE for SRB-1 setup,but UE has setup of rel-8 to decode that data(from ASN encode/decoder) then how the decode will be successful(As of now eNB might or might not be knowing which release UE is supporting ?.

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    1. Could you please point to which Rel-10 IEs in RRC Connection Setup message?

      As far as I can see this message has RRCConnectionSetup-r8-IEs even in release-10. The only change in Rel-10 as compared to rel-8 (initial versions) is the addition of RRCConnectionSetup-v8a0-IEs (contains only non-critical extensions)

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    2. i'm talking about RadioResourceConfigDedicated(first IE in RRCConnectionSetup-r8-IEs)in which we have IE's like RLF-TimersAndConstants-r9, MeasSubframePatternPCell-r10 (in this also we have so many) and these two IE's are not present in REL-8, so how will i decode these two in ue(if we have rel-8 asn encode/decoder). in other words i can say i have a UE of rel-8 and eNB of rel-10 then how UE will decode messages which is of rel-10 coming from eNB? and please tell me whethr this case is possible or not ?

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    3. Normally, eNB wouldn't include any non-rel-8 fields, IEs in the setup message itself. I was checking the RRC specification and found the below point which might be useful for you...

      The UE shall, when receiving an RRC message on any logical channel:
      1> if the message includes a field that the UE does not comprehend:
      2> treat the rest of the message as if the field was absent;

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    4. Thanks for your reply, i got my answer.

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  6. This comment has been removed by the author.

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  7. can u tell me the what are the critical extensions & non critical extensions....any one can give the clarification

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    1. Critical extensions are characterised by a redefinition of the PDU contents and need to be governed by a mechanism for protocol version agreement between the encoder and the decoder of the PDU, such that the encoder is prevented from sending a critically extended version of the PDU type, which is not comprehended by the decoder.

      Non-critical extensions are characterised by the addition of new information to the original specification of the PDU type. If not comprehended, a non-critical extension may be skipped by the decoder, whilst the decoder is still able to complete the decoding of the comprehended parts of the PDU contents

      Please refer to 36.331 Annex A for more details...

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  8. what will be the timer in between the rrc connection setup and rrc connection setup complete?

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    1. I am not sure if the timer value is specified any where. But I have checked a vendor and they have a 4 seconds value which still seemed to be very high.

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    2. It can be configured at enodeB level
      It completely depends on operator what he wants to set it.

      By default I have seen it as 5000ms

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  9. why RRC connection setup is sent again after RRC complete message is received ? the scenario that I have is

    RRC connection request
    RRC connection setup
    RRC connection setup complete
    RRC connection setup ( the message content is exactly like the first setup except for the CFN is different)

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  10. At what time of receiving RRC connection setup UE knows it is his RRC connection setup message

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  11. How UE will know that this msg is rrc connetion setup msg ?
    please can you just explain..

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  12. At the time of receiving rrc connection setup how ue knows that its his rrc connection setup

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    1. We will get CRNTI as UE specific information in RRC connection setup msg through which UE can check that this RRC connection setup msg is for him only.

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    2. So does the RRC connection setup message actually include a C-RNTI? I can't seem to find it in the figure above

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    3. CRC of the thsi PDU is scrambled with the c-rnti , hence UE idenifies the recieeved message is intended for him

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