Re: Is round-trip time no longer a concern?

On Mon Feb 20 15:15:23 2006, Eric Rescorla wrote:
> So, what I'm arguing is that except for applications where initial
> connection setup is a large fraction of the cost of the entire
> connection, I think it's not worth optimizing the initial connection
> setup very much. And until you've profiled the protocols in 
> question it's hard to know which case you're in.
> 
> 
I'll have to disagree almost totally.

I think you always basically know what case you're in, because the 
connection setup time is wasted time that's not achieving anything 
useful, it's just staring-at-the-screen time. For a purely 
non-interactive protocol that a real human will never be waiting for 
results from, I suppose you could ignore any setup RTT cost, but I 
struggle to think of an example for this.

For IMAP, where connection setup time is, in principle, a very small 
part of the total session time, it seems odd you're advocating that 
nobody should worry about adding round-trips when there's been 
substantial effort in reducing round-trips in precisely this area. 
Witness the way that the CAPABILITY command has been deprecated into 
a CAPABILITY response code, or the SASL-IR proposal, or RECONNECT - 
the list just goes on.

Moreover, this phase of "reading your mail" is one where the user is 
definitely watching, and essentially nothing useful is happening. You 
absolutely know this is a good place to optimize.

> >> Is it true that we no longer need to worry about regularly adding
> >> extra round-trips to popular protocols that operate over the open
> >> Internet?
> >
> > No.
> >
> > As far as I'm aware, there is no protocol in existence which 
> somebody,
> > somewhere, does not actively use over a mobile phone link, or a 
> slow
> > analogue modem, and this is especially true of TLS enabled 
> protocols
> > such as HTTP, email protocols, etc.
> 
> Well, I hear what you're saying, but when I check my mail over my
> cell phone, it's pretty clear that the time isn't going to TLS
> connection setup.

Nope, but I'll bet that the time you spend waiting, rather than 
reading, is almost entirely round-trip latency, and not actual useful 
octets coming through the ether - silent noise and not shifting bits.

Dave.
-- 
           You see things; and you say "Why?"
   But I dream things that never were; and I say "Why not?"
    - George Bernard Shaw

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