R99 Accessibility Congestion

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R99 Accessibility Congestion

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Ericsson Internal R99 Accessibility Congestion 2008-08-272

R99 Accessibility Degradation 2nd carrier was installed at site FLMFU0088 end of

April, 2008 due to increasing traffic R99 accessibility degradation was seen beginning early

May and became the worst around May 5th and 6th.


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RNC Exception

By checking RNC exception, huge amount of AAL2 connection reject was observed and the following can be seen pertaining to site FLMFU0088

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* NciRejType = 2 NciRejCause = 34, 0x22

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* REJECT TYPE = CELLO_AAL2NCI_REMOTE_REJECT (Q2630)

* REJECT CAUSE = Q2630_1_NO_CHANNEL_AVAILABLE

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At first look, it seems to be a bandwidth problem or running out of CIDs. But the P6 VC Utilization counters does not support the idea of running out of bandwidth. See next slide for details.


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VC40 BW Utilization, Transmit• VC40 was utilization as the most around 45%


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VC40 BW Utilization, Receive


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Reason to AAL2 Rejection

The fact that Speech call (which is using AAL2 CLASS A, placed on the same AAL2 path as AAL2 CLASS B, R99) accessibility does not suffer from AAL2 congestion indicate there is no lack of CID either.

This leads us to another direction which is the CAC (Call Admission Control). CAC is the AAL2 admission mechanism which not only perform admission control based on bandwidth, but also based on transmission delay.

At site FLMFU0088, the 2nd AAL2 path is configure to carry QoS class A and B with the QosProfile of ad10bd20. This put Class B traffic under stringent control.


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Reason to AAL2 Rejection (2) Based on previous experience, we suspect the AAL2

rejection was caused by CAC for not able to fulfill the delay characteristics of AAL2 CLASS B.

The current AAL2 configuration is: 1) Aal2Path 1 with Class A CBR 3099 with ad10bd20

2) Aal2Path 2 with Class A_B CBR 3099 with ad10bd20

3) Aal2Path 3 with Class C_D with UBR+ with ad10boff.

We suggested the following changes:

1) Aal2Path 1 with Class A CBR 3099 with ad10bd20

2) Aal2Path 2 with Class A CBR 3099 with ad10bd20

3) Aal2Path 3 with Class B_C_D with UBR+ with ad10boff.


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The above proposal provides two benefits to the existing situation.

1). Allow more speech calls to be admitted into the system as both AAL2 Path 1 and 2 are used to carry CLASS A traffic.

2). Class B traffic is moved to AAL2 Path 3 with QosProfile=ab10boff. This QosProfile does not put AAL2 CLASS B under CAC’s control, so more Class B requests can be permitted in the system, therefore eliminate the possibility of Class B request being rejected due to not able to fulfill delay characteristics.

After the change, KPI indicates no more R99 accessibility degradation. A few other sites adopted the same approach in order to fix R99 congestion problem

Reason to AAL2 Rejection (3)


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Appendix: Detailed AAL2 NCC Trace NCC server trace did not reveal the real problem or it is

not clear on the real problem. Instead it still stated the bandwidth issue.

Rejection Code from NCC trace sendSig_p->RLCReq_r.rejCause = 0[2008-05-14 18:45:30.788] 000100/Ans_aal2ncc2_proc netconn.c:569 TRACE9:aal2NciRejCause = 50000b2, rejectType = 1[2008-05-14 18:45:30.788] 000100/Ans_aal2ncc2_proc netconn.c:3988 TRACE9:nciRejCause = 50000b2, cause = 34sendSig_p->RLCReq_r.rejCause = 34sendSig_p->RLCReq_r.rejCause = 0sendSig_p->RLCReq_r.rejCause = 0sendSig_p->RLCReq_r.rejCause = 0sendSig_p->RLCReq_r.rejCause = 0sendSig_p->RLCReq_r.rejCause = 0sendSig_p->RLCReq_r.rejCause = 0sendSig_p->RLCReq_r.rejCause = 0sendSig_p->RLCReq_r.rejCause = 0sendSig_p->RLCReq_r.rejCause = 0sendSig_p->RLCReq_r.rejCause = 0sendSig_p->RLCReq_r.rejCause = 0

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Appendix: Detailed AAL2 NCC Trace

[2008-05-14 18:45:31.796] 000100/Ans_aal2ncc2_proc netconn.c:569 TRACE9:aal2NciRejCause = 50000b2, rejectType = 1[2008-05-14 18:45:31.796] 000100/Ans_aal2ncc2_proc netconn.c:3988 TRACE9:nciRejCause = 50000b2, cause = 34sendSig_p->RLCReq_r.rejCause = 34sendSig_p->RLCReq_r.rejCause = 0

• RejCode = 50000b2 means the following

#define CELLO_AAL2NCI_CONG_B 0xb2/* This cause indicates that it is not possible to establish a new AAL2*//* connection towards the peer node indicated by the AESA number *//* supplied in the CelloAal2Nci_netConnectReq() call. *//* The reason is that current connection requires a bandwidth greater *//* than the bandwidth available on any of the paths towards that node. *//* The congestion will remain until at least one connection towards *//* that node has been released.


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R99 Accessibility Congestion

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