Re: [hybi] Requirement: extensions and sub protocols

[KOMATSU Kensaku <[e-mail]>]

2010/3/5 Jamie Lokier <[e-mail]>:
>> RTT measurements between client and server will be required for some
>> extensions or sub-protocol. For example, TCP flow-control is so
>> sensitive both content-size and RTT, so these two-parameters will be
>> useful for some application's negotiation-phase which is better to use
>> multiplexing frames in one channel or to use independent channels for
>> each frames.
>
> When you say "use independent channels", do you mean independent TCP
> connections?
>
> Because "channel" is often used to mean the individual flows that are
> carried inside a multiplexed connection.
>
> Assuming you do mean independent TCP connections:

Sorry, your assumption is right. I meant "independent TCP connections".
I'll take care about this from now on.

> Can you say a bit more about the circumstances when an endpoint would
> choose to use them instead of multiplexing?  What kind of parameter values
> are needed for multiple TCPs to be better?
>
> I have not heard of this before, although I appreciate that multiple
> TCPs can be faster than a single shared TCP in some scenarios.  (I'm
> thinking of bonded-ADSL where each TCP is confined to exactly one of
> the links).
>
> Sometimes 4 TCPs is better than 1, but worse than 100, when you have
> 100 individual flows to transport.  But I'm not sure how to decide
> what to use automatically.
>
> Note that full end-to-end RTT, including processing latency, can be
> measured by applications sending each other messages.
>
> -- Jamie
>

Per TCP connection transmission rate is calculated by the formula below.
 <rate> [Mbps] = 65535 / (125 * RTT[msec] )
(I also assumed that TCP receive buffer size = 64KB (winXP's default value))
This formula is reasonable, in my experience, because either the
theory value or the actual measurement value are not so different.

For example.
RTT : 10msec ... 52Mbps
RTT : 15msec ... 35Mbps
RTT : 50msec ... 10Mbps
RTT : 100msec ... 5Mbps

So, if someone wants to provide their service with transmission rate = 10Mbps,
1 tcp connection is enough for RTT < 50msec users. Though, 2 or 3 connection
is required for RTT=100msec users.

I also agree with multiple connections are confortable for web
application developer,
because it offeres an appropriate speed in most cases without
bothersome control.
But this manner requires more connection resources than necessary.

Number of TCP connection affects to connection-sensitive equipment,
global-NAT, proxy, firewall,load-balancer, servers, .... If we use
appropriate number of connection and multiplexing frames for web
applications, the system cost can be made low-priced. And I hope that
this senario will also pleased network providers.

To achieve this senario, preparing some libraries, defining
sub-protocol or extentions and making it easier to use will be
important. That's why I mentioned this-topic before.

For other case, It'll be useful for video service. Because it'll be
useful for the decision of the bandwidth of contents automatically.

Sincerly
---
Kensaku KOMATSU