Re: Ethernet auto-select and concurrent 10, 100 and 1000 connections

[mlelstv%serpens.de@localhost (Michael van Elst)]

tlaronde%polynum.com@localhost writes:

>Is the speed adapted to each connected device? Or does the serving card
>fix the speed, during a slice of time, for all connexions to the minimum
>speed?

Autonegotiation means that the card and the switch communicate and
agree on a speed.


>What is the "cost" of switching the speed or, in other words, is
>connecting a 10base card able to slow done the whole throughput of the
>card even for other devices---due to the overhead of switching the speed
>depending on connected devices?

The speed isn't switched unless you disconnect or reconnect the
ethernet cable, but if the configuration is unchanged, card and
switch will usually agree on the same speed as before.


>(The other question relates to the switch but not to NetBSD: does the
>switch have a table for the connected devices and buffers the
>transactions, rewriting the packets to adjust for the speed of each of
>the devices?).

Almost all switches will allow to connect devices with different
speeds and packets that are received at one speed are buffered and
sent out at possibly a different speed. The packets don't need to
be rewritten.

Differences in speed between sender and receiver are usually handled
by higher level protocols (e.g. TCP) or by lower level protocols
(802.3x) when device and switch support it.

-- 
-- 
                                Michael van Elst
Internet: mlelstv%serpens.de@localhost
                                "A potential Snark may lurk in every tree."