If you encounter problems with control characters Please refer to the sz -T command in sz.doc for more help. Flow control between the server and modem is often defective. Experiment with different values to find the best throughput. Terminal servers are designed to accept keyboard input from human operators. They may lose data when a program sends data to the host faster than humans type.
Some servers allow larger input buffers to support file uploads.
Sometimes the terminal server software is defective and must be upgraded. Please contact the network's vendor for corrective procedures. An alternative is to install direct serial ports for users desiring to upload files. Some systems enforce a timeout which disconnects a user after several minutes of no keyboarding. Unfortunately, not all Unix versions support input flow control.