TCP Traffic Test

The TCP layer of Windows servers like Microsoft SQL, Exchange, Citrix, etc., will have an additional TCP Traffic test (see Figure 1). This test monitors the TCP protocol traffic to and from a server. Since most popular applications (Web servers, Citrix, Databases, Application servers, etc.) 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.

Target of the test : A host system (Windows servers only)

Agent deploying the test : An Internal agent

Outputs of the test : One set of results for each host system monitored

Configurable parameters for the test
  1. TEST PERIOD – How often should the test be executed
  2. Host - The host for which the test is to be configured.
  3. segments_sent_min - Specify the minimum threshold for the number of segments sent/transmitted over the network. The default value is 10; in this case, the test will compute/report the TCP retransmit ratio measure only if more than 10 segments are sent over the network. On the other hand, if less than 10 segments are sent, 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 the server.

Segments/Sec

 

Segments sent:

Indicates the rate at which segments are sent to clients
or other servers

Segments/Sec

 

Segment retransmissions:

Indicates the rate at which segments are being retransmitted by the server to clients/other servers

Segments/Sec

 

TCP retransmit ratio:

Indicates the ratio of the rate of data retransmissions to the rate of data being sent by the server to clients/other servers

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 a server, an administrator can quickly be alerted to problem situations in the network link(s) to the server that may be impacting the service performance.