Subject: [Fwd: Re: [IMRG] New "Available Bandwidth" Measurement tool]

From: "Jin Guojun [NCS]" <[email-masked]>
Date: Thu, 21 Aug 2003 17:50:08 -0700

Since I am not on the mailing list, I do not know how many replies
you may already get on it. Here is the link:

	http://www-2.cs.cmu.edu/~hnn/igi/

It is a nice paper because it has systematically discussed more
details of the technology used IGI/PTR, which is modified Pathload
algorithm for efficiency. The problem is the accuracy is lower.

Most current bandwidth measurement research has ignored the system
capability to handle high-speed network I/O; or the designers have
no idea about system capability at all because system issues belong
to the engineer. This creates a significant problem on network 
bandwidth measurement tool development:
10 years ago, we have been able to measure the 100 Mb/s network; 
however, most new tools are only able to measure 100 Mb/s path now.
IT IS USELESS regardless how wonderful the algorithms are.

The new problem is toward to two directions in the future -- 

	accuracy and capability

Accuracy is the old problem and capability is the new one
because the network speed has exceeded the system I/O bandwidth.
All methods except algorithm used in pathchar are requiring the
system I/O is higher than the network bandwidth in order to make
measurement.
Due to this issue, we need to find a very different algorithm to use
low-speed packets to measure high-speed network, such as pathchar.
Research on the packet-pair-dispersion-based algorithm that requires
packets' speed higher than the network available bandwidth and very
high resolution system timer has no more valuable to the real world,
but the pure research. More information can be found at:

	http://dsd.lbl.gov/DIDC/papers/imc-2003.pdf

100 Gb/s network will be available very soon. If new tools still
work only for O(100 Mb/s) network, then, the memory is wasted.
I hope to see some new algorithms for 1 Tb/s, but no more tool for
O(100 Mb/s) measurement.

	-Jin

-------- Original Message --------
>>> From: Yeggy Easwaran <[email-masked]>
>>> Date: Tue Aug 12, 2003  1:41:43 PM America/Los_Angeles
>>> To: [email-masked]
>>> Subject: [IMRG] New "Available Bandwidth" Measurement tool
>>>
>>> Ningning Hu, Peter Steenkiste. Evaluation and Characterization of
>>> Available Bandwidth Probing Techniques. In the IEEE JSAC Special
>> Issue
>>> in Internet and WWW Measurement, Mapping, and Modeling, Vol. 21(6),
>>> Aug. 2003
>>>
>>> talks about a technique called IGI/PTR for measuring available
>>> bandwidth. This technique is supposed to measure available bandwidth
>>> in a network path faster than Pathload
>>>
>>>  (``End-to-End Available Bandwidth: Measurement methodology,
>> Dynamics,
>>> and Relation with TCP Throughput'', in Proceedings of ACM SIGCOMM,
>>> August 2002 (also look at an extended version, to appear in the
>>> ACM/IEEE Transactions on Networking, 2003).
>>>
>>> Does anybody have more information/insights on this?

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---

From: Vinay Joseph Ribeiro <[email-masked]>
Date: Fri, 22 Aug 2003 11:50:50 -0500 (CDT)

Hi all,

	While Jin has made some excellent points, I would beg to differ
with him on some issues.

The point that "network bandwidth has exceeded system I/O bandwidth" is
misleading. It gives one the impression that machines connected to Gigabit
networks cannot read data at 1Gbps (or close to it) which is not quite
true. The real issue with high-speed NIC cards is that they "coalesce"
packet arrival interrupts. For example if a NIC receives three 1000byte
packets spaced 10 micro-sec apart it may send just 1 interrupt to the
higher layer at the end of the 30 micro-sec interval rather than bother
the cpu with 3 interrupts one for each packet. This improves efficiency
and actually IMPROVES the total system I/O bandwidth.

Coalescence clusters packets and so affects packet dispersion techniques
that expect only cross-traffic to disperse packets.

Several solutions suggest themselves that would allow the use of current
packet dispersion techniques.

1. Make use of the larger MTU size. While 1000byte packets can be spaced
as close as 8micro-sec on a Giga network, 8000byte packets will be spaced
64micro-sec apart. From my preliminary experiments on a Gigabit testbed I
observed that the NIC cards did not coalesce packets spaced this far
apart. This solution will require the path MTU to be larger than
1500 bytes.

A strong case has been made by Phil Dyksta for the use of jumbo frames:
http://sd.wareonearth.com/~phil/jumbo.html

Another link by Mathis:
http://www.psc.edu/~mathis/MTU/

2. Modify NIC cards to provide time stamps of when packets arrive at the
NIC. If this is achieved then it does not matter for how long packets are
delayed in the NIC due to coalescence. With this solution it will not
matter if the network speed is 1Gbps or 1Tbps for that matter.

I take this opportunity to advertise "pathChirp", a tool that uses special
exponentially spaced packet trains to estimate available bandwidth.

http://www.spin.rice.edu/Software/pathChirp/

Please feel free to comment/correct any of my opinions. Thanks.

Vinay Ribeiro

Rice University | [email-masked] | www.ece.rice.edu/~vinay | 713.348.2285