[c-nsp] ASIC to switch port mapping

Pavel Skovajsa pavel.skovajsa at gmail.com
Mon Sep 13 11:09:56 EDT 2010

Interesting enough, yesterday James Ventre posted a note where he
found at least some minimal info about the 2960/3560/3750 buffer
amount: http://networking.ventrefamily.com/2010/09/3560ge-and-3750ge-buffers.html

Also, I have to say I have exactly the same experience as Gert - IPTV
streaming box connected via 1Gbps, generating about 65Mbps, that no
Cisco "Enterprise level switch" (aka 2960/3560/3750 or even ME3400)
was able to forward to a 100Mbps port without output drops. When we
sniffed it we found that in a given discrete period of 1 second, the
streaming box is absolutely idle for the first 900 ms, and then
quickly pushes 80Megs in the last 100 ms.

My guess is that due to the functionality of the MPEG box, it needs to
gather some uncompressed picture frames first, and only after that it
is able to produce the MPEG output....which makes it hurry too much :)


On Mon, Sep 13, 2010 at 12:55 PM, Gert Doering <gert at greenie.muc.de> wrote:
> Hi,
> On Mon, Sep 13, 2010 at 11:06:48AM +0100, Nick Hilliard wrote:
>> On 13/09/2010 10:44, Gert Doering wrote:
>> >(spreading out the packets), while most other streaming software creates
>> >somewhat massive wirespeed bursts, and then waits some milliseconds, and
>> >then generates a new wirespeed burst.
>> ew, that is pretty horrible :-(
> Trade-off between server load ("send out as many packets as can be
> stuffed into the hardware in one go") and network load ("smooth out
> stuff, but have more context switches, interrupts, ... etc. in the
> server").
> Now if I had more time :-) it might be worth investigating the (Linux)
> streaming server software used, whether it can be changed to invest a bit
> more CPU to better smooth out the packets...  OTOH, the kernel might
> just wreck this, and smear it all togehter again.  (*Now* we really get
> even more off-topic for c-nsp than usual)
> gert
> --
> USENET is *not* the non-clickable part of WWW!
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> Gert Doering - Munich, Germany                             gert at greenie.muc.de
> fax: +49-89-35655025                        gert at net.informatik.tu-muenchen.de
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