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

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

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

An estimate of time, in microseconds, that it would take the remote client to 
exhaust the currently advertised remote receive window (RWIN) if no userspace 
consumption of that data occurred. It is based on the observed bandwidth of the 
connection and the variable may return zero if there is not enough data transfer 
yet to make an estimate.

Applications may use this information to schedule the frequency at which they 
read data from the kernel, but it is primarily used by the kernel itself when 
determining the size of RWIN.