Sensors and Troubleshooting › CA Application Delivery Analysis Sensors › Retransmission Time

Retransmission Time

The Retransmission Time sensor looks for patterns in retransmissions.

TCP retransmission behavior has a significantly negative effect on application performance and network use. Communication across the affected connection can slow to a halt until a missing segment is retransmitted successfully. Only a limited number of missing segments can remain outstanding at any time.

Troubleshooting a Retransmission Time Alert

An anomaly in retransmission delay typically is caused by several critical components:

• Congested Path: Retransmission delay can increase when interfaces between the clients and servers are congested.
• QoS: A misapplied QoS policy for a particular application may cause increased buffer or queue drops.
• Backup/Routing Issue: A change in the per hop route may cause the issue. Additional retransmission delay may result from routing changes that add congestion to a pipe that is already congested or a pipe that is smaller, such as a backup link.

Identify sources of packet loss along the traffic paths. Keep in mind that the paths going to the server may be different from the paths coming from the server. If that is the case, analyze all paths.