Re: [spam score 3/10 -pobox] RE: Router with bandwidth management

[Brian Candler <B.Candler at pobox.com>]

On Mon, May 19, 2003 at 10:30:35AM +0300, Mark Tinka wrote:
> Are you then saying that the service provider should strive to give the
> client more than the 256Kbps the client isn't feeling satisfied with? 

No - I'm saying that if I buy 256K, I should be given 256K with no packet
loss, not 512K with packet loss.

> In the client-provider SLA - "I can guarantee you 256Kbps as long as you
> keep within 256Kbps or 32Kbps data trasnfer rate. I can't guarantee you full
> passage if you attempt to go beyond this capacity."
> 
> Isn't this what the provider is trying to achieve for the client? If the
> client wants to connect at speeds in excess of the 256Kbps, the provider is
> obliged to bring him down to sanity, or else he upgrades and a new SLA is
> written up.

Yes, but the client almost certainly cannot control it themselves. Here's a
more concrete example:

     ethernet           DSL line (512K)
  PC --------- DSL CPE ---------------- DSL LNS --------- Internet -- FTP
            (e.g. Cisco 8xx)          (e.g. 72xx)                   server

The client runs an FTP client on their PC. How many FTP client programs do
you know which can be configured "don't download faster than 256K"? None
that I know of. The FTP program accepts TCP data as fast as it is presented
to it.

Equally, you can't tell the FTP server "please don't send me data faster
than 256K, because that would put me outside of my contract". It sends as
fast as it can. And in any case, you might be talking to several remote
servers at the same time down the same link; in order to remain within
contract I would have to enforce that the *total* inbound bandwidth for all
those sessions combined is under 256K.

Either of the two Cisco boxes I have shown could slow my inbound data to
256K without dropping packets - but that's not a feature provided by Cisco.

> In what I have experienced, if a client has 128Kbps [16Kbps data transfer
> rate], the application that can hog all this capacity will sustainably
> maintain 16Kbps transfer rates at all times e.g. your favorite p2p software.
> All other clients sourcing the same IP address will suffer because they are
> trying to exceed 128Kbps, and their packets will be dropped. In this case,
> client hasn't kept his side of the SLA.

I don't understand; are you mixing KBps and Kbps ?

If a client is on the end of a 128Kbps leased line, then they should get
16KBps data transfer - agreed.

If the client is on the end of an ethernet, which is downstream of a Cisco
with CAR set to 128Kbps, they will get less than 16KBps data transfer
because of the packet loss, which means backoff delays and possibly useless
out-of-order packets received (i.e. without selective retransmission, those
packets will get sent again)

Regards,

Brian.

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