[eepro100] collisions

[Donald Becker]

On Mon, 22 Jan 2001, Pooya Woodcock wrote:

> The ethernet card is connected to a cable modem (the computer itself is a
> makeshift linux router), and as such is "forced" to deal with a measly
> 10Mbit/sec half-duplex connection. You may not care about this, but
> whenever I download something I get around 510KBytes/sec (byte not bit).
> Where is this in relation to T1 speed, and also how is this possible on a
> 10baseT-HD forced connection with lots of collisions?

A 10baseT connection should sustain about 1050 KB/sec after TCP+IP
overhead.  With full duplex that should increase to a little over 1100.

> I thought that the "real" speed of ethernet was only about
> 3Mbits/sec.

????
What token ring salesman did you hear that from?

[[ T-R proponents used to tout simplified analysis that showed the
theoretical throughput of Aloha-style contention networks was between
0.30 and 0.35.  But Ethernet is much more clever than Aloha was, in part
due to having both carrier sense and collision detection.  The effective
utilization is well above 90%. ]]

> Am I really getting 
> 510Kbytes * (8 bits/1 byte) = 4080 KBits/sec?

Yes.  That is comfortably within 10baseT capability.
I would put anything else on the slow network -- you'll want the link to
go directly to a firewall/NAT box, and from there to an inexpensive
100baseTx switch for the internal machines.

Donald Becker				becker@scyld.com
Scyld Computing Corporation		http://www.scyld.com
410 Severn Ave. Suite 210		Second Generation Beowulf Clusters
Annapolis MD 21403			410-990-9993