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

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

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

The TCP stack's current sending slow start threshold expressed
in packets. When the congestion window (CWND) is below this value, the
TCP stack will grow its sending rate more aggressively.

Each connection begins with the
maximum `client.socket.tcpi_snd_ssthresh`, 2147483647, because it wants to 
aggressively probe the network path for available bandwidth. The sender will 
maintain that value until enough data has been transferred to make an estimate
of the available path bandwidth, at which time it will be reduced to a
conservative estimate of the bandwidth delay product of the path. CWND
greater than ssthresh grows at a slower rate (congestion avoidance
mode) than CWND below the threshold (slow start mode).