[13] in resnet
Re: UTP vs. AUI [0011]
daemon@ATHENA.MIT.EDU (Dennis Baron)
Sat May 15 10:33:26 1993
To: dthumim@Athena.MIT.EDU
Cc: resnet@MIT.EDU
From: dbaron@MIT.EDU (Dennis Baron)
In-Reply-To: [0011]
Date: Sat, 15 May 93 10:33:09 EDT
First, some terminology: A transceiver (MAU) has, by definition, an
attachment unit interface (AUI) connector and a media connector. The
AUI connector goes to the "computer" and the media connector goes to
the network - the "wires". An MAU can connect more than one computer
to the media but can only have one media connecion. In order to
connect two media together you need a repeater and two MAU's. MAU's
are available for use with unshielded twisted pair (UTP) (10bT), thin
Ethernet (10b2), thick Ethernet (10b5), and many other types of media.
A computer can have a "built-in" MAU - these are typically for UTP or
thin media - or any combination of internal MAU's and an AUI interface
for connecting to an external MAU.
For the dorms the media will be UTP - ie: the telephone wiring that is
also used by the dormitory telephones. Computers with "built-in" UTP
MAU's will be able to connect directly to the existing telephone jack.
Others will require an external UTP MAU connected to their AUI
interface. To connect multiple computers in the same room Information
Systems (IS) will provide an MAU and AUI cables to connect to the AUI
interface on each computer. These multi-port MAU's will be returned
when they are no longer needed and reused in other rooms where more
than one computer is going to be connected to MITnet.
All of the recommended Ethernet cards being sold at the MCC have both
a UTP and an AUI connector - ie: the ability to use an external MAU.
Any computer with an AUI connector and an internal or external UTP MAU
will be able to connect to the network in the dorms. Unfortunately,
some manufacturers have chosen not to include an AUI interface on
their computers and have only included an internal MAU for a
particular type of media. This severely limits where and how you can
connect to an Ethernet. Others (eg: Apple, Sun) have developed their
own proprietary AUI-type interfaces - fortunately you can purchase an
adapter that allows you to use a standard MAU from those
manufacturers.
We have decided not to use repeaters - which is what I think you are
suggesting. Repeaters are more complex and more expensive that MAU's.
In addition, the number and location of all the repeaters and all the
media has to be taken into consideration in the overall Ethernet
design. The additional cost of the repeaters and the ongoing cost of
redesigning and redocumenting the network is prohibitive. If your
computer meets our minimal requirements, an AUI connector and an
internal or external UTP MAU, you should be able to move it from room
to room without any problem. I would strongly recommend not
purchasing a computer that locks you in to a particular type of media
by providing only an internal MAU.
Thank you for your interest and question. I hope I have clarified our
plans. Please feel free to forward this message to the athena.dormnet
newsgroup. We are planning on using the resnet mailing list and
Discuss meeting as a public forum to discuss dorm and ILG networking
issues. Additional information will be made available via the
resnet-status mailing list and in TechInfo. We will be announcing
these very soon and will make sure to copy athena.dormnet.
Dennis Baron
Dist. Comp. and Network Svcs.
