Re: [LARTC] Modems: Cable or DSL digital blunders that lartc may

From: Ed Wildgoose <lists@wildgooses.com>
To: lartc@vger.kernel.org
Subject: Re: [LARTC] Modems: Cable or DSL digital blunders that lartc may
Date: Wed, 23 Jun 2004 08:15:59 +0000	[thread overview]
Message-ID: <40D93C3F.9060707@wildgooses.com> (raw)
In-Reply-To: <20040622043359.75922.qmail@web11905.mail.yahoo.com>

>Yes, SwFC is lame.  Howerver it would be a good band-aid, to have router
>and modem syncronisation take place.
>  
>

You have got to consider that some devices are asynchronous and some are 
synchronous

>The router(PC) has no idea of the buffer fullness, this is the underlying
>problem!  The cable modem needs to triger a "pause" when it's buffer
>reaches %80 full, regardless of any other rate limiting.  Linux kernel can
>do this with some cards, under heavy CPU strain(htb).
>
>CONFIG_NET_HW_FLOWCONTROL: net/Kconfig
>  
>

Possibly, but this doesn't help you that much.  If your http download is 
whacking out packets then your SSH session will still effectively get 
crowded out.

You want something to queue for a bit and prioritise this extra traffic.

...you have read the LARTC Howto haven't you?

>>You need something which works at IP level or above.  TCP (level higher)
>>    
>>
>No, the DEVICE is not > layer 3.  It's simply a bridge, with a stoplight
>on one end.  The idea is to not make any cars crash, that has nothing todo
>with the ball game a car might want to get too.
>  
>
??

>Yes, ECN will/should be used for routers attached to bridges.
>  
>

Not as far as I am aware? (today)

>>broadly unsupported.  ICMP stuff is frequently dropped by 
>>routers/firewalls making it problematic (look at how difficult it is 
>>just to do MTU discovery!)
>>
>>    
>>
>ECN makes this a non-issue.
>  
>

??? Eh?

>>What's your question though?  Read the LARTC howto and the ADSL QOS 
>>howto.  They are both excellent docs.  Also read up on some basic TCP 
>>notes.  There is nothing really clever that you can do - it's all in the
>>
>>docs you just have to work around the limitations of the protocols
>>
>>    
>>
>I would like to know is maby a ?$6000.00? Cisco cable mobem will not only
>use HwFC but ECN as well?  Thought i'd like to find a $150.00 modem that
>will just do HwFC, maby an internal one?
>  
>

No it won't.  Well, even if it did, I don't think it would help.  Unless 
the rest of the world understands your protocol then you will still have 
problems with incoming connections.

You can get a £250 cisco adsl modem which looks rather powerful.  Try 
that if you want to experiment.

Please, please read the LARTC-Howto and ADSL-qos howto.  I think it has 
everything that you need.

>  
>
>>Ed W
>>
>>    
>>
>
>
>
>		
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