RE: iSCSI: Framing Steps

[Paul Koning <ni1d@arrl.net>]

Excerpt of message (sent 29 January 2002) by Somesh Gupta:
> While I support a generic direct data placement model,
> the following are additional points for consideration for
> analysis of memory bandwidths and sizes.
> 
> 1. A 10G link dropping packets will not do TCP at 10Gbps.
> The rate drops as the packet loss increases. I don't recall
> but Franco or Victor from Nortel had posted an equation once.

A very old (40 years?) rule of thumb is that 1% loss costs you 50% in
throughput.  I expect that it gets a lot worse as links get faster.
> ...
> 3. The analysis of 10Gbps, half way round the world
> was initially used in this debate. ALthough interesting, the person
> with the scenario above is not going to blink at the cost of
> 256MBytes of fastest memory considering what they are paying
> for the link.

Exactly.

One reason ATM failed as a LAN is that its design was burdened with
complexity based on that sort of scenario.  (In other words: "it has
to work at umpteen Gig, across the globe, and only use a tiny little
bit of memory because implementations can't handle a megabyte of
buffers".) 

A design optimized for the combination of very high bit rate and very
long latency will inevitably be way overpriced for the predominant
case, which is the LAN case.

      paul