Toni asks:

> One of my new customer has a Novell Network with 3COM 100 Base-T Hubs.  I
>  sold them HP3000 and HP/J3202A 10-Base/T Hub.  The customer was thinking to
>  keep everything seperate, but now they want HP3000 to be part of their
>  network.  Will 10Base-T work ok connected to 100Base-T? (Will it slow their
>  existing networks' speed?)

Since no one else responded (at least publicly) to Toni's question, and I seem
to responding too much of late, I'll answer the question.

The trivial answer is: yes. Any new device on the LAN will add more packets to
the traffic that's already there and that's bound to have some effect.
However, depending on how busy (or non-busy) the current packet traffic is,
the effect of new packet streams could range from anywhere to neglible to
substantial.

If the LAN is relatively unbusy, they'll never notice the increase in traffic
due to the HP3000. If, on the other hand, the LAN is quite busy and the HP3000
will be serving massive quantities of data to remote devices, it could easily
be the bale of straw that breaks the camel's back.

These conditions are true whether the HP3000 is speaking 10Mbps or 100Mbps.
The great difference between the two is that a 100Mbps packet appears on the
LAN for only 1/10 the period of time that an equal-sized 10Mbps packet would
-- and in this world, short is good. Short packets significantly lower the
possiblity of a packet collision.

LANs are designed around the Chicago taxi cab model of communications, where
every taxi driver works off of the same frequency (a very narrow
communications channel) and in a simplex (one-way-at-a-time) mode. As soon as
the dispatcher finishes saying what he has to say, every taxi driver says "49"
or "91" or whatever his taxi number is, trying to get the dispatcher's
attention. If they all do it simultaneously, the dispatcher says, "Say again!"
And everyone repeats their "packet". And this situation, the process on this
kind of overloaded LAN repeats until the dispatcher can clearly understand one
of the correspondents and says, "Go ahead 73".

A LAN is absolutely identical in construciton; it works only until it gets
this busy. Then it tends to collapse into the same level of inefficiency and
frustration that you see in Chicago taxi cab drivers, where they throw the
microphone across the cab. A 10Mbps or a 100Mbps packet is no different if
collisions are common. It's just that when a 10Mbps packet does get its
chance, it's the same as somebody speaking very s-l-o-w-l-y in an otherwise
high-speed world. If the overall traffic on the channel is reasonably low, it
really doesn't matter all that much. But if the traffic is high enough to
generate collisions commonly, it can matter a great deal.

The bottom line of all of this is then: it just depends.

Wirt Atmar