BaiTip of the Day - December 20th, 2018: Using iPerf to find network bottlenecks resulting in slow speeds


Operators sometime complain low speed issue. As we know in LTE systems, all connected CPEs share the eNB’s resources. CPEs uploading or downloading large files may take many resources while other CPEs start to pass data traffic. All CPEs may suffer noticeable speed slow down issue at the same time, but this is normal case. Operators can check from eNB CPE status page to make sure if it is the case
If it is not the case, we need to check where the bottleneck is. Customers usually do speed test with sites, such as

While I am personally no expert on command line applications such as iPerf, I will attempt to assist our customers analyze where bottlenecks actually exist in the network topology. Currently we can’t run speed test client on eNB, so we can’t rule out backhaul link. To eliminate all backhaul elements and test the eNodeB to client performance, take a laptop to the client side of the cpe and perform ftp or iperf tests again.

Run iperf server on iperf server-Tower, and try iperf test on client PC. i.e, use iperf3 for the test.

Iperf3 TCP Test w/ 8 Parallel Connections - Download

Server: iperf3 -s

Client: iperf3 -c x.x.x.x -P8 -t15 -O5 -R

Iperf3 TCP Test w/ 8 Parallel Connections - Upload

Server: iperf3 -s

Client: iperf3 -c x.x.x.x -P8 -t15 -O5

To test each backhaul link on the data path, we need to add an FTP server/IPERF server at the tower location sharing the same switch with eNBs, and a FTP server/ipserf server right behind ISP switch at the next hop. The typical network topo may look as follows.

Using the same test method as above, but the ipserf server runs on ‘iperf server ISP’. If you can get expected result, than you can say the bottleneck is in external link outside the ISP network; if not, the bottleneck is in the ISP network.

But we need consider multiple UEs share the same eNB and spectrum resources. If many customers have poor RF metrics, it will degrade overall performance of the eNB system.

If the test result is not as expected, please check following:

Make sure the test client PC is the only user of the CPE.

Make sure the CPE’s RF metrics are adequate and stable to support desired speed;

If you still can’t get good result, please save us the eNB logs and report issue to BaiCells.

For more information about iPerf, go to