[Asterisk-Users] NIC card failure [was: System freeze]

[Chris Albertson]

VOIP is a very low data rate compared to the bandwidth of
a switched 100BaseT network.  Lets say you are using 100BaseT
to trunk 100 simultainous calls at 64Kbps (How many of us really 
would ever do that?) 100 calls would be 6,400,000 bps.  Well
over what a T1 could handle but is only 6.4% of 100Mbps. or
maybe 25% of the usable bandwidth of a switched 100BaseT
segment. (Ethernet does not work well when loaded over 30% of
it's nominal bandwidth.)

Think of it another way 100BaseT is 100Mbps.  If 100 calls
are on the line each call gets 1000Kbps  So VOIP in an office
enviroment does not even come close to pushing the limits of
Ethernet.

Things like NFS and HTTP cascing with SQUID are much harder
on a network and may push you to things like using gigabit
ethernet but voice is a comparitively low data rate.

How to select a NIC to use under Linux?  Read the drivers.

Pick the NIC with the best driver.  Even a quick scan over the
comments will let you see how much of the NIC's hardware is
being put to use.  Are the bytes being read one at a time with
programmed IO?  With DMA?  Is there a hardware ring buffer being
used?
How about packet filtering on the card?  Take a look, the Reltek
is not a bad choise.


--- Steven Critchfield <critch at basesys.com> wrote:
> On Tue, 2004-02-10 at 07:01, mattf wrote:
> > It is important to note that cheap nic cards that were really
> designed for
> > 1% utilization on a workstation are not well suited for an Asterisk
> server
> > installation with any kind of VOIP traffic. We foolishly put a
> Realtek card
> > in a test server and after a month literally fried the NIC card, It
> was
> > extremely hot when we took it out after seeing thousands of network
> errors.
> > I would recommend a 3com 905CX NIC card, we have these in all of
> our
> > Asterisk servers and they function beautifully, and I have yet to
> hear of
> > one breaking down uder high traffic. Yes, they cost a lot more than
> your
> > average $4 Realtek card, you can pick them up new for about
> $20-$30.
> 
> Just to try and complete the message here, I have plenty of problems
> out
> of 3com cards. I was at an install where we had to jerk all the 3C905
> cards and replace with Davicom cards. 
> 
> As for the Realtek cards, that is what is in my office switch with no
> problems for over a year. I wonder if the card was made by Realtek,
> or
> just the chip. I have had good experiences with the 8139 chip, and it
> may be just better quality cards.
> 
> -- 
> Steven Critchfield  <critch at basesys.com>
> 
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=====
Chris Albertson
  Home:   310-376-1029  chrisalbertson90278 at yahoo.com
  Cell:   310-990-7550
  Office: 310-336-5189  Christopher.J.Albertson at aero.org
  KG6OMK

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