2015-05-09 4:06 GMT+08:00 Dan Fandrich <dan_at_coneharvesters.com>:
> On Fri, May 08, 2015 at 10:00:14PM +0800, Hongyi Zhao wrote:
>> Hi Daniel,
>>
>> I running the following two commands:
>>
>> curl ftp://ftp.cn.debian.org/debian-cd/8.0.0/amd64/iso-cd/debian-8.0.0-amd64-CD-1.iso
>>
>> and
>>
>> curl -L http://ftp.cn.debian.org/debian-cd/8.0.0/amd64/iso-cd/debian-8.0.0-amd64-CD-1.iso
>>
>> It seems the the second one response more fast the first one. Why the
>> repospons from ftp for curl is so slow than http?
>
> For large downloads over low-latency connections, ftp should not be
> significantly slower. But for shorter downloads over high latency connections,
> the extra setup time for ftp connections can dominate the transfer time.
> If you use the -v option, you'll quickly see why. ftp by default executes a
> single CWD command (which means a network round trip) for every directory
> component, plus it requires extra round trips for authentication and metadata
> discovery, then it also opens a second TCP connection (with its 3 round trips)
> for the data transfer (which goes through TCP's slow start mechanism). You can
> shave some of that off by using --ftp-method NOCWD (or SINGLECWD) if the server
> supports it, but ftp is always going to inherently take (at least) slightly
> longer.

Thanks for your hints.

>
>>>> Dan
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-- 
Hongyi Zhao <hongyi.zhao_at_gmail.com>
Xinjiang Technical Institute of Physics and Chemistry
Chinese Academy of Sciences
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