Re: Efficiency of FTP URLs

Marc VanHeyningen (
Mon, 25 Jul 1994 12:46:53 -0500

Thus wrote:
>> We have been having a small, local discussion on the efficiency of
>>FTP vs. HTTP. One of the items I pointed out was that for serving up an HTML
>>document with inlined images, FTP is very inefficient because of the startup
>>costs for every inlined images. Later I got to thinking that this would be
>>an obvious place for an optimization: leave the FTP open until done parsing
>>the HTML document in case any inlined images (or whatever) might be needed.
>> This morning I confirmed that MacWeb 1.0a2, MacMosaic 2.0a2, XMosaic
>>2.4, and WinMosaic 2.0a2 take the inefficient approach of a separate ftp
>>connection for each inlined image. It would seem that optimizing this would
>>help the load on ftp servers, and response time to the user.
>FTP _is_ an inefficient protocol for serving HTML documents with inlined
>images, period (in fact, I'd be personally inclined to say FTP is an
>inefficient protocol, period. :^) However, NCSA Mosaic for Windows
>and its progeny DO leave the connection open (permanently, as a matter of
>fact, until the server times it out.) I thought this was true of 2a2, but
>it certainly should be of later releases (unless this was changed since I
>left.) AIR Mosaic leaves it open.

Real problem with "leave it open" is how to deal with relative paths
that back up or absolute paths that aren't the same. There's no
general way to CWD up a directory or to go back to the FTP root other
than to break the connection and re-establish it. (Unless you want to
be highly UNIX-centric, which I hope everyone agrees is a bad idea.)
Leaving it open is not an unreasonable optimization for fetching items
from the same directory or subdirectories.

<A HREF="">Marc VanHeyningen</A>