Re: Fragmentation for headers: why jumbo != continuation.

Hi Roberto,

On Thu, Jul 10, 2014 at 05:34:37PM -0700, Roberto Peon wrote:
> The amount of latency induced depends mainly on size and bandwidth.
> Assuming that the header size is 8k, and a link is 1Mb/s (as still happens
> often for mobile devices), we're talking about 62ms of buffering before it
> can forward, even if it has all of the headers necessary for routing within
> the first few ms.

But here you're speaking about the serialization time on the proxy itself,
it's irrelevant to the slow bandwidth, because I'm assuming you're not
connecting your proxies using an 1 Mbps arcnet link :-)

> As a concrete usecase, think of any entity that needs to forward requests
> from a slow link to a fast link.

I'm still failing to see the use case I'm afraid, because what will be
added in this case is the time needed to serialize over the fast link.
The problematic case would be if you insert multiple proxies over a
slow link, which really does not make much sense.

> Additionally, in cases where there are multiple proxies as part of a load
> balancing infrastructure, there is no need to examine the full set of
> headers on any but one of them.. and for the response headers (of one
> trusts the server, which can happen if one is running both proxy and
> server), there may never be a need to examine them before forwarding.

It depends, because if you stack multiple proxies, each of them will have
a different usage. One may be a cache, another one may be used to perform
anti-virus processing etc... Also, we're speaking about devices where the
added time is measured in microseconds and is not noticeable by the client
(the request serialization time is lower than the TCP connection time to
the next hop).

For example, here at home a request to youtube, with all the fat cookies
tracking my activity is 669 bytes. That's 21 ms over my 256kB ADSL line.
When it reaches your gateways, it will take an extra 5 microseconds if
they are connected using GigE, or 500 nanoseconds if connected over 10GE.
The round-trip time when the link is empty is 25 milliseconds in comparison,
so that completely dominates the serialization time on all your proxies.

Regards,
Willy

Received on Friday, 11 July 2014 05:02:09 UTC