TCP Traffic - IGEL Test

Since most popular applications rely on the TCP protocol for their proper functioning, traffic monitoring at the TCP protocol layer can provide good indicators of the performance seen by the applications that use TCP. The most critical metric at the TCP protocol layer is the percentage of retransmissions. Since TCP uses an exponential back-off algorithm for its retransmissions, any retransmission of packets over the network (due to network congestion, noise, data link errors, etc.) can have a significant impact on the throughput seen by applications that use TCP. This test monitors the TCP protocol traffic to and from an IGEL Endpoint, and particularly monitors retransmissions.

Target of the test : An IGEL Endpoint

Agent deploying the test : A remote agent

Outputs of the test : One set of results for each IGEL Endpoint

Configurable parameters for the test
Parameter Description

Test Period

How often should the test be executed.

Host

The nick name of the IGEL Endpoints component for which this test is to be configured.

Port

Refers to the port at which the specified host listens to. By default, this is NULL.

Inside View Using

To obtain the 'inside view' of performance of the IGEL Endpoints - i.e., to measure the internal performance of the IGEL Endpoints - this test uses a light-weight Endpoint Agent software deployed on each of the IGEL Endpoints. The Endpoint Agents collect performance metrics from the IGEL Endpoints and communicate the metrics to the eG remote agent using TCP protocol. Accordingly, by default, this parameter is set to TCP.

Report By User

Since this test runs for an 'IGEL Endpoints' component, this flag is set to Yes by default.

Report Powered OS

Since this test runs for an 'IGEL Endpoints' component, this flag is set to Yes by default.

Is Cloud VMs

Since this test runs for an 'IGEL Endpoints' component, this flag is set to Yes by default.

Segments Sent Min

Specify the minimum threshold for the number of segments sent/transmitted over the network. The default value is 25; in this case, the test will compute/report the TCP retransmit ratio measure only if more than 25 segments are sent over the network – i.e., if the value of the TCP retransmit ratio measure crosses the value 25. On the other hand, if the TCP retransmit ratio measure reports a value less than 25, then the test will not compute/report the TCP retransmit ratio measure. This is done to ensure that no false alerts are generated by the eG Enterprise system for the TCP retransmit ratio measure. You can change this minimum threshold to any value of your choice.

Measurements made by the test
Measurement Description Measurement Unit Interpretation

Segments received

Indicates the rate at which segments are received by this IGEL Endpoint.

Segments/Sec

 

Segments sent

Indicates the rate at which segments are sent to clients
or other IGEL Endpoints.

Segments/Sec

 

Segment retransmissions

Indicates the rate at which segments are being retransmitted by this IGEL Endpoint.

Segments/Sec

 

TCP retransmit ratio

Indicates the ratio of the rate of data retransmissions to the rate of data being sent by this IGEL Endpoint.

Percent

Ideally, the retransmission ratio should be low (< 5%). Most often retransmissions at the TCP layer have significant impact on application performance. Very often a large number of retransmissions are caused by a congested network link, bottlenecks at a router causing buffer/queue overflows, or by lousy network links due to poor physical layer characteristics (e.g., low signal to noise ratio). By tracking the percentage of retransmissions at an endpoint, an administrator can quickly be alerted to problem situations in the network link(s) to the endpoint that may be impacting the service performance.