Optimization Experience: Low FTP Downloading Bit Rate

*A new setup office, FTP downloading bit rate merely 2.2 kB/s after cut over. In theoretical analysis, it may achieve 4kB/s, compare actual downloading BR with the theoretical BR, actual BR is lower than expectation.

*Optimization: From mobile →GPRS network → FTP Server, verify each possible node which may cause the trouble.

Your practical maximum transfer rate can be much lower  due to two factors:

1. if the receiving TCP/IP does not offer maximum window with every acknowledgment packet, i.e., if the TCP/IP does not release the buffer until the destination process has emptied it, which may have an additional delay, and doesnt have extra buffering available, then the round trip time for window buffer allocation may be greater than the round-trip time for packet reception and acknowledgment. Depending on your operating system, the time to checksum and reply may be very close to the time measured by the ping command, while the time to open the window may be significantly greater. A good implementation for high throughput should make these times (ping and window) much closer together.
2. If any of the packets do not get through, the sender has to figure that out and send them again. This is going to take at least two round-trips and generally longer. So network congestion that results in packet loss, or an unreliable link, can drastically reduce your average transfer rate - sometimes fast, other times very slow.

Hi,

You can also consider the technique of "Optimizing TCP with Multiple Streams".

With standard FTP, only one data channel is used. This channel becomes idle during acknowledgement and other housekeeping. By increasing the number  of data streams, there is less “dead air,” as one or more streams is likely to  be sending data at any given time. This method of transferring files is effective when network degradation is not  extreme. However, the process is extremely processor intensive due to the  large number of concurrent threads that must be running

Hi Faizur & Mustafiz,

Thank you for your valuable comment.