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Some L2TP Users on ME60 V6R2 Functioning Had Low Internet Access Speed Because of User-Queue Applied to Downlink Traffic

Publication Date:  2013-09-30 Views:  9 Downloads:  0
Issue Description
An ME60 running V600R002C00SPC700 + patch SPH038 functioned as an LNS to receive and transmit L2TP services. The downlink traffic was limited in user-queue mode. In peak hours (the number of L2TP users under the LNS was about 6000), some L2TP users had low Internet access speed and non-L2TP users had normal Internet access speed.
Handling Process

Huawei performed the following operations to address the problem:

1. Excluded that the problem was caused by a website fault or poor link quality as not all L2TP users had low Internet access speed.

2. Checked bandwidths of all interfaces on the ME60.

The bandwidths were normal and no traffic overflow occurred.

3. Analyzed the downlink traffic limitation mechanism in user-queue mode.

The user-queue resources on a tunnel board were allocated for 4000 users. If more than 4000 users were online, the excessive users shared a 1 Gbit/s bandwidth. In the peak hours, the ME60 had about 6000 online L2TP users. Therefore, about 2000 users shared a 1 Gbit/s bandwidth. Packet loss occurred when the downlink traffic of the 2000 users was greater than 1 Gbit/s, resulting in low Internet access speed.

      a. Ran display access-user. User-car was applied to the uplink traffic and user-queue was applied to the downlink traffic.

Inbound qos configuration     : User-CAR

  Inbound cir                   : 4096(kbps)

  Inbound pir                   : 4096(kbps)

  Inbound cbs                   : 765952(bytes)

  Inbound pbs                   : 765952(bytes)

  Outbound qos configuration    : User-queue

  Outbound cir                  : 6144(kbps)

  Outbound pir                  : 6144(kbps)

      b. When the number of L2TP users on an LNS was 5700, 1700 users shared a 1 Gbit/s bandwidth.

  ------------------------------------------------------------------------------

  Domain name           State        CAR Access-limit   Online  BODNum RptVSMNum

  ------------------------------------------------------------------------------

  139.com               Active         0       279552     5751       0         0

  ------------------------------------------------------------------------------
Root Cause
With the user-queue scheme applied to downlink traffic, board resources were insufficient in peak hours.
Solution

1. Configure qos rate-limit-mode car outbound in the LNS-side user domain to apply CAR to downlink LNS users. This configuration takes effect after L2TP users go offline and online again.

2. Add tunnel boards (BSUF-21/40, VSUA) to evenly share L2TP traffic at the LNS side. 
Suggestions
None

END