Setting up a network and sharing internet

[James Knott]

Lennart Sorensen wrote:
> On Tue, Aug 23, 2005 at 06:08:03AM -0400, Scott Allen wrote:
>>Points below mosly for educational purposes:
>>
>>Actually, there are cable-only methods for more than two machines, 
>>called
>>10-base2 or 10-base5. They link 10M ethernet over a coaxial cable 
>>without
>>hubs.
> 
> I don't think I have ever seen 10base-5 myself.  Few places seemed to
> want single segments of 10mbit ethernet running for up to 500m.  200m
> was plenty for most, and much cheaper to wire too given 10base-2 was
> much more common and the wire much cheaper.

I have worked on one 10base5 installation.  It was a DECNET connecting
several VAX 11/780 computers.  That was my first experience with
ethernet.  However, my first experience with LANs predates that by
several years (1977).  I used to work on a Collins 8500C system, which
used TDM loops, instead of packets, to create a local area network.  A
device that wanted to send data reserverd a time slot and "owned" it,
until released.  IIRC, the high speed "TDX" loop ran at 8 Mb/s and the
low speed TDM loop was 2 Mb.  Devices such as the CPU, tape stands, disk
drives etc., were connected to the TDX loop.  Slower devices, such as
the printer, card reader and a bunch of PDP-11 computers were connected
via the TDM loop.  The interface between the two speeds, was a box that
sat on both the TDX and TDM loops.  The TDM loop used coax, but the TDX
loop used triaxial (two separate shields) cable.


> 
> Of course it was a bit of a pain that to add machines you have to split
> the cable, put in a T and add it to the new machine, causing an
> interruption in the network.
> 
>>The are small differences between using a crossover cable or a 
>>hub/switch, which can slighty affect the way the systems behave.
>>1) With a hub you will get a half-duplex connection. With a switch or 
>>crossover it will likely be full-duplex. As already noted in another 
>>posting in this thread, the difference is generally insignificant.
>>2) The hub/switch will usually always be powered up. Therefore when 
>>one machine is powered off or disconnected, the network connection on 
>>the other machine will still be "alive". With a crossover, when one 
>>machine is powered off or disconnected, the other may see a dead 
>>ethernet link. (I say "may" because some machines will keep the 
>>ethernet active using standby power when "off" to allow for power up 
>>control via ethernet). This may result in more or different error 
>>messages, logs, etc. between one or the other method.
> 
> I think the ability to add and remove machines at will, nice cheap
> twisted pair wire, not having to run the network around through each
> machine, but instead having a central point to connect to just makes way
> more sense, and I sure don't miss 10base-2 at all.
> 

In the Collins network that I mentioned above, the connections were
similar to token ring, in that there were relays, that connected a
device to the loop.  However, the relays were located under the floor,
near the equipment, not at a central location.  Adding or dropping a
device would cause the loop synchronizer to "chirp", while it re-synced.

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