Development issues regarding the cerowrt test router project
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From: Sebastian Moeller <moeller0@gmx.de>
To: Michael Richardson <mcr@sandelman.ca>
Cc: cerowrt-devel@lists.bufferbloat.net
Subject: Re: [Cerowrt-devel] Ideas on how to simplify and popularize bufferbloat control for consideration.
Date: Fri, 1 Aug 2014 20:28:56 +0200	[thread overview]
Message-ID: <70BB6CDF-5A8C-4F44-A308-8681536BB085@gmx.de> (raw)
In-Reply-To: <11000.1406866900@sandelman.ca>

HI Michael,


On Aug 1, 2014, at 06:21 , Michael Richardson <mcr@sandelman.ca> wrote:

> 
> On symmetric links, particularly PPP ones, one can use the LCP layer to do
> echo requests to the first layer-3 device.  This can be used to measure RTT
> and through some math, the bandwidth.

	Sure.

> 
> On assymetric links, my instinct is that if you can measure the downlink
> speed through another mechanism, that one might be able to subtract, but I
> can't think exactly how right now.
> I'm thinking that one can observe the downlink speed by observing packet
> arrival times/sizes for awhile --- the calculation might be too low if the
> sender is congested otherwise, but the average should go up slowly.

	If you go this rout, I would rather look at the minimum delay between incoming packets as a function of the size of the second packet.

> 
> At first, this means that subtracting the downlink bandwidth from the uplink
> bandwidth will, I think, result in too high an uplink speed, which will
> result in rate limiting to a too high value, which is bad.

	But given all the uncertainties right now finding the proper shaping bandwidths is an iterative process anyway, but one that is best started with a decent initial guess. My thinking is that with binary search I would want to definitely see decent latency under load after the first reduction...

>  
> 
> But, if there something wrong with my notion?
> 
> My other notion is that the LCP packets could be time stamped by the PPP(oE)
> gateway, and this would solve the asymmetry.  

	If both devices are time synchronized to a close enough delta that would be great. Initial testing with icmp timestamp request makes me doubt the quality of synchronization (at least right now).

> This would take an IETF action
> to make standard and a decade to get deployed, but it might be a clearly
> measureable marketing win for ISPs.

	But if the “grown ups” can be made to act wouldn’t we rather see nice end-user query-able SNMP information about the current up and downlink rates (and in what protocol level, e.g. 2400Mbps down, 1103Kbps up ATM carrier) (For all I know the DSLAMs/BRASes might already support this)

Best Regards
	Sebastian

> 
> -- 
> Michael Richardson
> -on the road-
> 
> 
> 
> _______________________________________________
> Cerowrt-devel mailing list
> Cerowrt-devel@lists.bufferbloat.net
> https://lists.bufferbloat.net/listinfo/cerowrt-devel


  reply	other threads:[~2014-08-01 18:29 UTC|newest]

Thread overview: 51+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-05-24 14:03 R.
2014-07-25 18:37 ` Valdis.Kletnieks
2014-07-25 21:03   ` David Lang
2014-07-26 11:30     ` Sebastian Moeller
2014-07-26 20:39       ` David Lang
2014-07-26 21:25         ` Sebastian Moeller
2014-07-26 21:45           ` David Lang
2014-07-26 22:24             ` David Lang
2014-07-27  9:50               ` Sebastian Moeller
2014-07-26 22:39             ` Sebastian Moeller
2014-07-26 22:53               ` David Lang
2014-07-26 23:39                 ` Sebastian Moeller
2014-07-27  0:49                   ` David Lang
2014-07-27 11:17                     ` Sebastian Moeller
2014-08-01  4:21       ` Michael Richardson
2014-08-01 18:28         ` Sebastian Moeller [this message]
2014-07-25 20:48 ` Wes Felter
2014-07-25 20:57   ` David Lang
2014-07-26 11:18     ` Sebastian Moeller
2014-07-26 20:21       ` David Lang
2014-07-26 20:54         ` Sebastian Moeller
2014-07-26 21:14           ` David Lang
2014-07-26 21:48             ` Sebastian Moeller
2014-07-26 22:23               ` David Lang
2014-07-26 23:08                 ` Sebastian Moeller
2014-07-27  1:04                   ` David Lang
2014-07-27 11:38                     ` Sebastian Moeller
2014-08-01  4:51                       ` Michael Richardson
2014-08-01 18:04                         ` Sebastian Moeller
2014-08-02 20:17                           ` Michael Richardson
2014-08-01  4:40       ` Michael Richardson
2014-07-26 11:01   ` Sebastian Moeller
  -- strict thread matches above, loose matches on Subject: below --
2014-05-24 14:12 R.
2014-05-24 17:31 ` Sebastian Moeller
2014-05-24 19:05 ` David P. Reed
2014-05-20 22:11 Frits Riep
2014-05-20 23:14 ` Dave Taht
2014-05-21 11:42   ` Frits Riep
2014-05-21 14:51     ` dpreed
2014-05-21 15:19       ` Dave Taht
2014-05-21 16:03         ` dpreed
2014-05-21 16:30           ` Dave Taht
2014-05-21 17:55             ` dpreed
2014-05-21 17:47           ` Jim Gettys
2014-05-21 17:53             ` Dave Taht
2014-05-21 17:56               ` dpreed
2014-05-21 17:57                 ` Jim Gettys
2014-05-21 18:31                   ` Dave Taht
2014-05-21 15:07     ` Dave Taht
2014-05-21 16:50       ` Michael Richardson
2014-05-21 17:58       ` David Lang

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