Improving Slow Transfers

If you are experiencing slow transfer speeds, try fine-tuning CuteFTP as described below.

Make sure that Mode Z is turned on

Mode Z compression compresses files as they are transferred. Reducing the file size reduces the necessary bandwidth and improves transfer times. If this option is turned on, CuteFTP will take advantage of any server that supports Mode Z.

Tweak the receive and send buffers

Setting these buffers allow you to fine tune transfers over high latency or lossy connections like those over satellite links or with legacy CDMA wireless connections. It is unlikely you will ever need to adjust this setting, but if you have problems with successful transfers and suspect the latency or quality of the connection is at fault, try tweaking these buffers. The receive buffer holds data until CuteFTP is ready to read it; the send buffer holds data until it can be sent to the server. Typically, both send and receive buffers should be set to the same size. The default is set at 65536 bytes, the normal maximum window size of TCP. You can measure the latency and estimate the available bandwidth with network monitoring tools. There is some guesswork involved, as most tools are not entirely accurate, but they can guide you to finding a sweet spot where transmissions are successful. If you have a lossy connection, try lowering the buffer size. If you have high latency, a higher buffer size might help.

Normally, the optimal buffer size is your bandwidth times the latency of the link. So,

bandwidth (in bits) * latency (round trip time in seconds) = socket buffer size (in bits)

Convert bits to bytes (bits divided by 8 equals bytes) for the buffer size.

So, if your bandwidth is 1,536,000 bps and you have a latency of 200ms (.2 seconds), your socket buffers should be set to 38400:

1536000*.2=307200 bits

307200/8=38,400 bytes

You can also try halving or doubling the buffer size. For example, if the buffer is set to 65536 (64kb), try 32768 (32kb).

  1. On the main menu, click Tools > Global Options.

  2. Click the Transfer node.

  3. In Receive buffer and Send buffer boxes, change the values as needed. (See guidelines above.)

  4. Click Apply if you are going to make changes to other pages; click OK to save changes and close the Global Options dialog box.

Turn off the time stamp in logs

Try using multi-part transfers

Check the global bandwidth limit