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Re: [Discuss-gnuradio] MAC layer development and USRP2
From: |
Jeff Brower |
Subject: |
Re: [Discuss-gnuradio] MAC layer development and USRP2 |
Date: |
Tue, 6 Apr 2010 16:52:29 -0500 (CDT) |
User-agent: |
SquirrelMail/1.4.2-1 |
Charles-
>> I would tend to blame Linux and buffering more than GbE itself (MAC + PHY).
>> Here is an interesting doc where the
>> researchers were asking similar questions:
>>
>> http://www.hep.man.ac.uk/u/rich/atlas/docs/atlas_net_note_draft5.pdf
>>
>> I'm not sure yet how much buffering is done in the USRP2 firmware but we
>> hope to know shortly as a couple of our
>> guys
>> are in the process of taking apart the logic, pulling out non-GbE related
>> sections, and rebuilding.
>>
>> -Jeff
>
> I glanced over the document briefly and was wondering if your analysis
> of the linux issue was because of this document, or a separate source.
> I'm only asking because the document is 10 years old and is using
> RedHat 5 and Pentium 2s. I would assume the linux kernel support for
> GigE has improved since then.
Which part of the Linux issue... sustained throughput or latency? I wouldn't
be surprised to find that latency hasn't
improved substantially because it's not a priority for server software. Even
VoIP applications are not concerned
about a 1 msec improvement... whereas that makes or breaks a wireless MAC.
What I found interesting in that particular document is the authors were
careful not to speculate and to use a logic
analyzer to make exact measurements. For me the key figures are GbE (MAC +
PHY) and PCI latencies, which are likely
not too reducible.
-Jeff
Re: [Discuss-gnuradio] MAC layer development and USRP2, Veljko Pejovic, 2010/04/06