Fast enough to handle an OC-3 on the upstream side?

[Joshua Snyder]

First you should have no problem running one or more Oc-3's.  The pci bus
has alot more than 33Megabytes/s of bandwidth.  It's a 32 bit bus running
at 33Mhz.  So...

32bit X 33,000,000 =  1056000000 Bit/sec  
1056000000 Bits / 8( 8 bits = one byte ) = 132Megabytes/sec 

Now in realty you can't burst a full 132Meg/sec on a pci bus.  In the real
world you will see around 90-80Meg/sec over a pci bus.  Still far more
than the 19.5Meg/sec of a OC-3.  Also you say that you are not connected
directly to the Oc-3 on your linux box. It's sounds like you are going
over a 100Mbit ethernet to get to the Oc-3, is this correct?  If so, I
think you might have a larger problem with the HUGE number of interrupts
( from the Ethernet device)per sec that you will be seeing on the
machine.  I have seen very busy ethernet segments slamming a machine with
25,000+ interrupts a sec.  The machine will handle the traffic just fine 
but it will not be very responsive.  I would recommend putting a second
GigEthernet card( on the outbound side ) in the machine because most of
them will only interrupt about a 1000 times a second even if they are used
heavily.  I have dealt with all of the above problems first hand, the
company that I work for makes linux based Wan routers (
www.imagestream.com ).  I have been involved with the driver development
& testing for our new Oc-3 Atm( and Atm Ds-3 ) cards ( yes, for linux ).
Are you sure that this isn't an Atm Ds-3, it would be running at
45Mbit/sec?  In which case all of the above is still true, just it might
not be as bad...

					josh 



On Mon, 23 Jul 2001, Greg wrote:

> On Monday 23 July 2001 r, you wrote:
> > Ok, I have to ask. Does anyone have a similar setup, or can anyone tell
> > me, if a dual P2-450 system, with 256 MB of RAM, running Linux 2.4 and
> > Squid, with a gigabit fiber card on the interior side and 100 Mbps UTP
> > card on the exterior side, will be fast enough to handle NATing our
> > network if we get an OC-3 (~45 Mbps)? I want to make sure the box will
> > continue to have enough horsepower, as we may soon be jumping to an OC-3
> > from a T-1 (The state says this, anyway - we'll see what happens. If we
> > upgrade, no one is gonna complain. :), and no one likes complaining users
> > or poorly-used connections, right? Right? :)
> >
> > Derrik Pates      |   Sysadmin, Douglas School   |    #linuxOS on EFnet
> > dpates@dsdk12.net |     District (dsdk12.net)    |    #linuxOS on OPN
> 
> OK well OC-3 == 155.52 mbps
> line rate in packets is 302734 per second
> PCI Bus on an Desktop pci-32 Intel based system is 33Megabytes /s
> 155.52 mbps == 19.375 Megabytes / s
> 
> Now in theory this looks good .. however these calculations are just about
> having a flow of traffic pass through the PCI Bus, and do not include the
> overhead of reading the packets off the device (btw you have a pci32 GE card
> ?) and then applying any routing or firewalling rules to them.  If it was up
> to me I would prolly go with a heaftier board / cpu.. Tyan has a serious
> motherboard that they are going to be releasing very soon .. its a Dual
> Athalon MP (meant to run their new 1.8ghz mp chip's with 1MB L2 cache).
> On top of that it has 5 PCI-64 slots running at 66mhz and 2 onboard 3C920
> 10/100 lan ports that use an ASIC to communicate with the CPU's directly.
> On top of that what is unique to this mobo is that each CPU has its own
> independant Front side bus unlike most smp mobo's that use a shared bus.
> This mobo also has intergrated dual channel adaptec ultra scsi 3 160
> controller, udma 100 port and even a QLogic FiberChannel port on it and
> supports up to 4GB of PC2100 DDR ram.  If you really want to support OC-3 I
> think you might want to adjust the jock strap of your linux-router a tad.
> 
> 
> --
> Lamp Post Networks - http://www.lamp-post.net
>