Packet Loss
by December 13, 2013

Filed under: Networking Technology, Performance Monitoring

This article will be part of a series of articles describing how various network issues are presented by AppNeta Performance Manager. We begin with packet loss.

Packet loss occurs when one or more packets failed to reach its intended destination. This article shows how high packet loss is presented on AppNeta. Packet loss also manifests itself by degrading other network metrics measured by Pathview Cloud. We will see shortly which metrics are affected.

In order to simulate packet loss, we use the Linux tc utility to emulate random loss. We will simulate different rates of loss (from 5% to 50%) to show how this condition is presented in AppNeta.  It is important to note that this simulation is applied to outbound traffic only. AppNeta makes separate measurements for outbound and inbound traffics in dual-ended paths.

Setup

The following setup is used for our simulations:

AppNeta tackles packet loss

The route from Appliance A to Appliance B is routed through an emulator where packet is dropped. A dual-ended data and voice path is created from Appliance A to Appliance B. For this setup, AppNeta monitors the following metrics:

  • Capacity (total, available and utilized in both directions)
  • Data loss (in both directions)
  • Data jitter (in both directions)
  • Latency (outbound only)
  • RTT
  • MOS (in both directions)
  • Voice loss (in both directions)
  • Voice jitter (in both directions)

Packet loss of 5% is simulated ~11:30 am. The loss rate is incremented by 5% every 10 minutes until 50%. The following charts show the measurements from ~11:40 am to 1:50 pm.

Test Results

packet loss with AppNetaCapacity and data loss metrics.

The first chart shows capacity measurements in both directions.  They are not affected by packet loss (up to 50%).

The next chart shows outbound data loss which increased gradually up to 50% as expected. There’s some inbound data loss (< 5%) as well.

packet lossData jitter, MOS and voice loss metrics

The first chart here shows that data jitter is not affected by packet loss.

The next chart shows decreasing MOS in both directions.  The last chart shows increasing voice loss in both directions up to ~50% as expected.

packet lossVoice jitter, network latency and RTT metrics

None of the metrics are affected by packet loss.

Conclusions on Packet Loss

In conclusion, when there’s a packet loss, the following metrics are affected:

  • Data loss (in the direction where loss occurred)
  • Voice loss (if voice traffic is present)
  • MOS

In the next series, we will talk about jitter.

  • If Appneta reports 22% data loss how does that relate to actual packet loss? Are they the same?

    • trjordan

      They are! PathView is synthetically testing for packet loss, so the reported loss is based on our packets. That said, since it’s happening continuously, it matches the networks properties closely, which we’ve confirmed with tests across the same link with unrelated data.

      Now, if you’re asking “how many packets were actually lost during this time”, that will depend on when the packets were sent. If there’s no other network traffic during a time of high data loss, then obviously no data is lost. But in any given period, the data loss the AppNeta measures is the same as the data loss experienced concurrent traffic.