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Some L2TP Users Connecting to an ME60 Serving as an LNS Had Low Internet Access Speed in Peak Hours

Publication Date:  2013-10-26 Views:  119 Downloads:  0

Issue Description

An ME60 served as an LNS receiving and transmitting 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

To address the issue, Huawei performed the following operations and observed the following information:

1. Ran the display access-user command. 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)

2. Checked the number of L2TP users under the LNS. The number of L2TP users on the LNS was 5700.

  Domain name           State        CAR Access-limit   Online  BODNum RptVSMNum
  ------------------------------------------------------------------------------               Active         0       279552     5751       0         0

Therefore, over 1700 users shared 1 Gbit/s bandwidth. That is, each user could use less than 0.5 Mbit/s bandwidth, much less than 6 Mbit/s. In addition, the 1 Gbit/s bandwidth was not evenly allocated to each user, and therefore, some users might have little downlink bandwidth.

Root Cause

When an ME60 served as an LNS and downlink traffic was limited in user-queue mode, the user-queue resources on a tunnel board were allocated only for 4000 users. If more than 4000 users were online, the excessive users shared 1 Gbit/s bandwidth. In the peak hours, the ME60 had about 6000 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.


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.


Note that resources are sufficient for only 4000 users when an ME60 serves as an LNS and downlink traffic is limited in user-queue mode.