rrc setup report v1
DESCRIPTION
RRC Setup Report v1TRANSCRIPT
Presentation TimetablePresentation Timetable
Pilot
Methodology – wk5
Net. IssuesServices
Counters Alarms Drive DataNeighbours – wk5
Performance – wk5
RRC Access – wk7
SHO – wk6
ISHO –wk6
RRC Stp – wk7 Access – wk4
Common Alarms – wk4
Common Failures – wk4
Analysis – wk3
CM Service – wk2
Test No’s – wk3
Script bugs –wk3
CC Disc – wk1
Power Spikes – wk1
HC Failures – EOC
6650 ISHO – wk3
RRC Active – wk7
Inter RNC HO – wk2
TCH/BCH – wk2
Table of ContentsTable of Contents
Introduction
Detailed Descriptions Handover Control
Admission Control
Setup Fail BTS
Setup Fail Trans
Setup Fail Frozen BTS/Internal RNC
Conclusion
RRC Setup PhaseRRC Setup Phase
The RRC Setup phase starts when the UE sends the “RRC CONNECTION REQUEST” message and it is completed when the RNC, after reserving all the necessary resources for the RRC Connection (RNC, BTS, Radio and Transmission), replies with DL “RRC CONNECTION SETUP” message.
During this phase, there are several processes happening between the Node B and the RNC. If any of these processes fail, the Ue will either try again or will fail. In either case the relevant counter will be triggered, giving the Network Analyst clues as to why calls are failing on a particular cell.
A schematic of the Setup phase can be seen on the RHS.
RRC: RRC Connection Request (RACH)
UE RNCNode B
NBAP: Radio Link Setup Request
NBAP: Radio Link Setup Response
ALCAP: Establish Request
ALCAP: Establish Confirm
FP: Downlink Sync
FP: Uplink Sync
NBAP: Synchronisation Indication
RRC: RRC Connection Setup (FACH)
L1 Synchronisation
RRC: RRC Connection Setup Complete (DCH)
RRC: RRC Connection Request (RACH)
UE RNCNode B
NBAP: Radio Link Setup Request
NBAP: Radio Link Setup Response
ALCAP: Establish Request
ALCAP: Establish Confirm
FP: Downlink Sync
FP: Uplink Sync
NBAP: Synchronisation Indication
RRC: RRC Connection Setup (FACH)
L1 Synchronisation
RRC: RRC Connection Setup Complete (DCH)
RRC Setup FailuresRRC Setup Failures
RRC Setup Failure due to Handover Control (HC)
RRC Setup Failure due to Admission Control (AC)
RRC Setup Failure due to BTS
RRC Setup Failure due to Transmission
RRC Setup Failure due to BTS frozen
RRC Setup Failure due to RNC internal reason
Handover ControlHandover Control
Handover Control is the algorithm that is used to allow a Ue connect to two or more cells simultaneously
Handover Control appears to start in the HA3 Program Block during RRC
Setup Procedure
RRC Setup Fail due to HCRRC Setup Fail due to HC
HC Setup Procedure in RNCHC Setup Procedure in RNC
HC Setup appears to reside in the Interface Control and Signalling Unit (ICSU)
ICSU board resides in RNC
ICSU board has redundancy where the redundancy unit is only employed if the active unit fails.
Checked RNC alarms and there were older alarms on ICSU boards
Admission ControlAdmission Control
Admission Control (AC) is the algorithm that decides whether a request to establish a RAB is admitted or not. It is also involved during the handover procedure.
RRC Setup Failure due to ACRRC Setup Failure due to AC
RRC Setup Failure for AC: AC can block the call at RRC level if there is too much noise on a cell. (i.e. Target + Offset is exceeded)
AC also blocks calls if UL or DL is blocking. Check Cell Resource counters (Prx/Ptx total)
In general it’s possible to check the AC blocking in RRC setup phase by checking the Traffic counters(M1002):
- DCH_REQ_LINK_REJ_UL_SRNC
- DCH_REQ_LINK_REJ_DL_SRNC Main failure reasons for AC
- RRC_conn_req_nack (Cell overload on UL or DL)
- No response from BRM - timer expired (indicates a cell availability problem)
RRC Setup failure AC for cell availabilityRRC Setup failure AC for cell availability
A high number of RRC failures for Admission Control does not necessary mean a high traffic or an interference problem but it might reflect a cell availability problem.
Typical detection through counters and KPIs: High RRC Setup Failure AC Rate : There may also be a huge number of RRC attempts
(see example). This indicates that the problem is continuous. Traffic counters may or may not reflect the full extent of the problem: in some cases the
traffic counters are not incremented because the request is not even received by the Admission Control.(e.g. MHA Faulty)
Cell Availability << 100% (see example). Alarm may or may not be present
Solution: Cell Availability needs to be monitored and corrected as soon as possible after it
occurs Cell Reset might help.
Cell Availability ExampleCell Availability Example
Site GLN0395 shows high number of RRC Setup Failures for Admission Control on March 15.
From Service Level counters huge number of RRC attemptsRRC repetitions.
From Cell Resource counters:
Average PrxTotal shows nearly no traffic nor interference
Cell Availability problem from 17:30
Alarm in the cell
RRC Setup Failure BTSRRC Setup Failure BTS
RRC Setup Failure for BTS: main failure reasons can be:
- RL_setup_failure (not enough resources) might be a WSP problem
- RL_setup_failure (hardware overload): might be some internal BTS issue
These fails can be seen in the counters :- SETUP_FAIL_RL_NOT_ENOUGH_RES
- SETUP_FAIL_FIRST_RL_HW_RES
RRC Setup Failure TransRRC Setup Failure Trans
RRC Setup Failure due to Transmission: main failure reasons is:
- serv_req_nack_from_nrm meaning some problem in setting up AAL2 transmission resources in Iub
NRM (Network Resource Model) is in-charge of Iub capacity
After capacity check, AAL2 signalling starts
Counter RRC_CONN_STP_FAIL_TRANS is incremented if: Not enough Iub capacity
AAL2 setup fails
RRC Setup Failures TransRRC Setup Failures Trans It appears that the problem may be in this part of the setup protocol
Reason for fail is usually: Not enough Iub capacity
AAL2 setup fails
1 ©NOKIA
AAL2 user plane setup over Iub (MOC)
RNCBTS (WAM)
UE AAL2 SIG CAC CAC AAL2SIG ATM RMRRC: connection request
resource reservation
AAL2 connection establishementERQ (SUGR)
resource reservation
ECF
AAL2 conn. estab. confirmation
RRC:connection setup
RRC
Transport res. reserv. req.
Possible NACK
Possible NACK
AAL2 Setup over IubAAL2 Setup over Iub
Iub resource reservation is performed in order such that all CAC reservations for RNC internal and external (AAL2 path) resources are done before signaling.
If the CAC actions are successfully completed, the signaling is started and the RNC asks the BTS to arrange its resources accordingly.
If the CAC actions fail, the signaling phase is not started at all and the signaling counters are not aware of the connections rejected due to RNC AAL2 layer CAC.
Others RRC Setup FailuresOthers RRC Setup Failures
RRC Setup Failure Frozen BTS: the AC blocks RL establishment to allow the setup of an emergency call(in case of pre-emption, when BTS is frozen no new RRC connection are allowed)
RRC Setup Failure for RNC internal reason: all other failure reasons (e.g. parameter mismatch, timer expiry)
RRC Setup Fail RNCRRC Setup Fail RNC
•Problem should affect the entire RNC (ALL THE CELLS)•Reasons are due to RNC Software/Hardware
RRC Setup Fails on Croydon RNCRRC Setup Fails on Croydon RNC
AC, BTS and TRANS are the most common fails on Croydon RNC
Numbers of fails can be huge but this does not indicate that the issue is necessarily RNC wide. It is probably 1 site with a huge number of fails, possibly due to repeated registration attempts.
The other fails should be at or near 0.
ConclusionConclusion
Setup Fails generally occur due to hardware issues in a low traffic situation. They are the first counters triggered by any attempt to access the network
The counters give us clues where to look
Some Setup Fails will occur repeatedly in response to a single issue causing the counter appear worse than the problem really is. Conversely, in some cases, the counters may not trigger when a fault is occurring but this can be seen by a drop in traffic.