Bitmap printing performance with Zebra printer

I am trying to print a (fairly big) bitmap (827x1166) on a Zebra Technologies ZTC 140XiIIIPlus-200dpi with ZPL.

While printing of the bitmaps actually works, performance is quite bad. It takes more than a second (probably more than 1.5 seconds) until the print starts.

The network trace shows that more than a second is spend sending the 71 KB (via TCP 9100 WLAN - LAN) PNG. 343 ms are used waiting for the first ACK alone.

  ~DYR:xxx.PNG,p,p,35769,103,<hex png>
  ^XA
  ^PW827
  ^LH0,0
  ^LL1166
  ^FO0,0
  ^XGR:xxx.PNG,1,1
  ^XZ

Sending the image as GRF (increasing the data size to 250 KB) does not change that.

Any ideas?

Solution

Tests with newer printer models (eg Zebra ZT 410) have shown that there is no delay before printing starts. We have als switched to LPR protcol (to allow multiple computers to use the same printer).