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Path: utzoo!mnetor!seismo!sundc!hadron!cos!howard
From: howard@COS.COM (Howard C. Berkowitz)
Newsgroups: comp.dcom.lans
Subject: Re: "Remote" Ethernets?
Message-ID: <203@cos.COM>
Date: Wed, 22-Apr-87 10:55:30 EST
Article-I.D.: cos.203
Posted: Wed Apr 22 10:55:30 1987
Date-Received: Fri, 24-Apr-87 03:29:16 EST
References: <7381@mordor.s1.gov>
Organization: Corporation for Open Systems, McLean, VA
Lines: 34
Summary: MAC bridges, network layer routers

In article <7381@mordor.s1.gov>, kiessig@mordor.s1.gov (Rick Kiessig) writes:
> Has anyone heard of a device which might be used to allow two
> remote ethernets to talk to one another?  About all I can think
> of is using serial lines.  Is there anything better?  The LANs
> are about 50 miles apart, separated by hills.  Thanks,

There are two basic approaches, depending on your performance
needs, budget, and protocols used.  The first is a MAC-layer
bridge, which recognizes Ethernet frames not on the local
LAN and sends them, via hopefully high-speed lines, to
the other LAN.  Bridges are transparent to protocols above
the link control layer.  For performance to be anywhere near
transparent, you would want at least 56 KBPS on a lightly
loaded LAN and 1 MBPS or more on a heavily loaded one.

Vitalink is a major manufacturer of long-haul (i.e., where
you can't run cable or fiber between the bridges of each
LAN); there are others (e.g., DEC) for cases where you can run your own facilities.

Routers are more intelligent than bridges, and might give
better utilization of lower-speed lines.  They are not
transparent to network-layer protocols such as OSI Internet,
DDN IP, DECnet routing layer, etc.

I suspect your major constraint will be the speed of the
line you can get and afford.  56 KBPS is available on
DDS, and in some areas as switched digital service on
an as-needed basis.  For DS1 channels at 1.544 MBPS,
you can get T1 carrier from telephone companies (or
build them yourself), possibly get CATV-based data if
your areas are served by a single cable TV firm, use
satellite (probably overkill), or, if you can get
rights-of-way and can maintain it, a free-space microwave
or laser link.