On Wed, 22 Jul 2009 16:23:38 +0530, Sachin T <sachin.sach...@gmail.com> wrote:
>I am downloading it through FTP... One of the biggest factors effecting large file transfers is the TCP window size, especially if you have a high speed connection with significant latency (i.e., a long distance). You will spend most of the time waiting for acknowledgements. The problem: the number of unacknowledged bytes is help in a 16 bit field in the TCP header. After sending that many bytes you have to wait for an Ack. The solution: during the initial TCP handshake, agree to multiply the value in outstanding window field by a scaling factor. Whenever we have had significantly slow TFP transfers over an otherwise fast connection, this has been the problem. We ran into this a LOT when we moved a datacenter and transfers that had been across the computer room floor now had to go 2000 miles. Those transfers that used large scaled windows had no problem; those that were restricted to 64K The Z/OS FTP server has supported window scaling for eons. Most FTP clients supports support it too, but it may not be automatically enabled, and guessing the name of the "knob" to turn it on is anybody's guess. Key phrases to look for when researching this issue: TCP window scale receive window size Long-Fat Networks, or LFN RFC 1323 Good luck. Pat O'Keefe ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@bama.ua.edu with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
