Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!tandem.UUCP!rfox
From: rfox@tandem.UUCP (Richard Fox)
Newsgroups: comp.protocols.tcp-ip
Subject: Re:Comments on your RFC 1106
Message-ID: <8906292326.AA22150@tandem.com>
Date: 29 Jun 89 23:26:26 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 55


<of running a host with a high volume of ftp activity, is that I don't
<believe proper window value are being used now, and that opening up
<the possibility of even higher windows will clog all available
<bandwidth, especially when several connections are active with several

In the general networking case this is the case. I don't think anybody would
like a host to open its window to 100K and try and shovel that much data out
onto the internet to traverse arbitrary paths to a destination. At least
not now......

  But what about the case where a site has a private t1 satellite for there
disposal?  Running standard tcp over this link even with the window fully
opened doesn't fully utilize the link. It utilizes about 50% of the link at 
best. The users of this link might not really desire to use a link of this
nature. At NASA this was the case. There was a t1 ground link and a t1
satellite link to the same location. 
If the performance of the satellite was not comparable or
very close to being comparable to the ground link the users would not use it.
To make the satellite link more appealing we needed to make the bandwidth
utilization comparable to the ground link. Thus, the use of big windows fits the
bill. Now the links can be used in the following ways: ground link is used for
telnet type traffic and the satellite is used for bulk file transfers. 

Notice this was just one example of where big windows can make a difference. 
With todays networks becoming faster each year the use of bigger windows
will become very important. Already some local area networks can support
mtus greater than 64K. Thus to fully utilize these networks, big windows
will be neccessary. Even if our goal isn;t to fully utilize the lan but just
to get "better performance out of them" it might make sense to use an mtu close
to the mediums capability and have >64K windows. 

Another obvious place that big windows will come useful is in the giga-bit
bandwidth range. The arguments for this is just an extrapolation of the last
argument. Also for a good argument read 1077.

<now...(not to mention *where* we're going to find the address space to
<hold the retransmission buffers)...

This is a good argument. But remember memory is becoming cheaper and
cheaper..... we are already starting to make 4meg chips. In a few years
it might not be uncommon to see workstations with 32 megs.... Thus buffer
space might become just another cheap commodity. A good argument for this
can be found in a very recent paper by Craig Partridge that was presented
at the INARC last month.



Frank, I hope this gives some insight as to why the work was done and to why
it might be a very important idea in the near future. I appreciate your
comments and would be interested in any follow up.



rich