window Switch

The window switch sets the size of the "streaming window," or buffer, during a ZMODEM file transfer. This is the format of the window switch:
 
window:size

where size is the largest number of bytes that can be transferred before waiting for an acknowledgment. For example:
 

ztransmit/window:1024 *.exe
zreceive -window:128 *.*

Normally, for maximum speed, ZMODEM transfers do not wait for acknowledgments or look for error-correction information until the file is entirely transferred (but the default window size can be set with the Autfix program). With bursty line noise, with an unreliable modem connection, or on busy systems, this can make file transfers very inefficient. If you experience frequent retries during ZMODEM transfers, try using the window switch to make the transfer pause more frequently for acknowledgments (thus requiring less data to be retransferred in the event of an error). A smaller window means less efficiency on a good connection, but better efficiency on a poor connection.

The window switch can be used with these file transfer commands:
 

ztransmit and zreceive