---
title: client.socket.tcpi_rttvar
summary: null
url: >-
  https://www.fastly.com/documentation/reference/vcl/variables/client-connection/client-socket-tcpi-rttvar
---

**Type:** INTEGER  
**Access:** read-only

**Available in:** recv, deliver, log, error

The TCP stack's estimate of the smoothed mean deviation of the
round trip time samples used in conjunction with the smoothed
round trip time for loss detection. It is expressed in
microseconds. `client.socket.tcpi_rttvar` is a measurement of variance, 
therefore larger values represent connections with less stable performance than
connections with smaller `client.socket.tcpi_rttvar`.