[ale] WAN type connection

[Keith R. Watson]

At 11:41 10/23/2002 -0700, Kevin O'Neill Stoll wrote:
>Hey all,
>
>If I wanted to connect two buildings, that are 1/2 a mile
>apart, to the same network, What would be the best way to
>handle it?
>
>Some issues that would come into play are: possibly
>crossing a roadway, lots of rain and heat.
>
>I remember reading that network mediums have distance
>limitations but I can't remember what they were.
>
>
>
>=====
>Kevin Stoll
>http://kevinstoll.org

Kevin,

It is highly recommended that you do not use copper when wiring networks 
between buildings as there are some rather nasty problems that can occur.

A ground loop can occur when two circuits are connected together that do 
not share a common ground point (as when networking between buildings). 
When there is a difference in ground potential between the two points a 
current starts flowing between the two systems via the ground connection. 
At the best this causes the network to be "flakey" or at its worst it can 
destroy equipment.

Close lightning strikes are a common cause of ground differentials that can 
be as high as 50KV. The induced current can easily destroy the terminating 
equipment as well as systems attached to the network. I have worked on 
equipment destroyed in such a manner and its not pretty.

Due to differences in the composition of the dirt where ground contact is 
made at each site a standing voltage differential can occur between the two 
sites. This is a common problem that is not easily resolved if the sites 
must be connected via copper.

The best solution that solves the ground loop problem is to use fiber. 
Fiber is incapable of conducting electricity so it is completely immune to 
ground differentials, hence no ground loops. Another plus for fiber is the 
immense bandwidth you can push over it. If you use the right kind of fiber 
you can upgrade bandwidth as needed into the terabit ranges by replacing 
the terminating equipment. Just remember the networking maxim: Speed costs, 
how fast can you afford to go?

The down side to fiber is its cost to install, the majority of that being 
labor. There is also the issue of having right-of-way to lay the fiber 
between the buildings. In simple terms this means you must own the land 
between the two points or have purchased or leased the rights to use the 
land or power poles. You also have to protect the fiber from its natural 
enemy the backhoe.

If you can stand to have 10Mb or 54Mb full duplex you can use 802.11b and 
802.11a wireless. With a directional antenna using 802.11b you can get 10Mb 
full duplex as far way as 20 miles with a clear line of sight. Another nice 
feature is you can put the antenna indoors and point it out a window. This 
will protect it from its natural enemy the direct lightning strike. 
Wireless can also be rather tolerant of weather with the possible exception 
of a severe blizzard or sand storm. In either of these cases 802.11a will 
fair better.

The down side to wireless is the lack of security. This can be resolved to 
some degree with adequate planning. Also the fact that your using line of 
sight makes interception of the signal less likely reducing the risk 
considerably.

If wireless looks like a good bet there are innumerable commercial vendors 
of equipment.

Another option is laser, which can work up to several miles and it supports 
most all networking types and bandwidths. It is very secure, you only need 
line of sight, and a rich uncle to pay for it. Did I mention it is the most 
expensive option?

I hope this helps, let me know if you need more info.

keith
-------------

Keith R. Watson                        GTRI/ITD
Systems Support Specialist III         Georgia Tech Research Institute
keith.watson at gtri.gatech.edu           Atlanta, GA  30332-0816
404-894-0836

---
This message has been sent through the ALE general discussion list.
See http://www.ale.org/mailing-lists.shtml for more info. Problems should be 
sent to listmaster at ale dot org.