As the Internet gets more congested, new technologies are being developed to
increase the amount of information that can be moved in a given
time period. This is usually refered to as increasing the bandwidth. In
addition, new technologies are being developed that allow faster and more efficient
transfer of data packets between network devices. Below are somewhat simplified
explanations of how these network technologies work.
Ethernet:
Standard Ethernet has a bandwidth of 10 megabits per second (Mb/s), which means
about 1.25 megabytes (MB/s) of information per second can be moving on the network.
This bandwidth is shared among users of your local network, so while Fred down the hall
is transferring a file at .6 MB/s, other users on the network might
notice slower network performance.
One solution to network congestion is to increase the bandwidth, or as some
would say the "size of the pipe." Some networks now use what is called
"Fast Ethernet," which runs at 100 megabits per second or 12.5 megabytes per second.
This allows more information to be transferred over the net at any given time. Fast Ethernet
usually requires new network wire, hubs and cards. Some computers are not fast
enough to take full advantage of this increased speed.
An even faster form of Ethernet, called Gigabit
Ethernet, will allow 125 megabytes to be transferred each second. Gigabit
Ethernet will not work over long distances, and it is not intended for
desktop computers. It is currently being proposed as a backbone for large organizations
using Fast Ethernet (100Mb/s Ethernet).
FDDI:
ATM:
A computer's Ethernet network card sends information onto an Ethernet network in the
following way: the card first determines whether any other computer is sending
packets; if not, it tries to send a packet. On uncongested networks this usually
works, but, on busy networks packets can collide with each other. This requires
both sending machines to try again. Ethernet networks work well until
the traffic increases to a point where the number of collisions is high. By
its design, Ethernet cannot reach its full bandwidth potential because
as it approaches it's theoretical limit, collisions increase.
Fiber Distributed Data Interface or FDDI has been around for a long time. It was
originally designed as a network backbone technology. FDDI runs at 100Mb/s, and
uses a timed token technology. In a typical campus backbone a token is passed from
one FDDI router to the other. When a given router has the token it can send information
and all the other routers listen. FDDI is very fault tolerant and allows segments
of the network to work even if a cable is cut. FDDI has the advantage of allowing
large packet sizes and can come close to achieving it's full theoretical bandwidth
of 100Mb/sec. Many feel that FDDI backbones will eventually be replaced with ATM
backbones.
Asynchronous Transfer Mode (ATM) is a networking technology fundamentally different
from Ethernet and FDDI. The fundamental ATM data unit is a "cell" rather than a packet.
ATM hardware at each end of a network circuit negotiates the operating speed for
the type of data being sent. ATM hardware operates at either 25.4Mb/s, 155Mb/s, or even 622Mb/s.
ATM technology can allocate specific amounts of bandwidth for specific applications, so
Johnny's 50MB FTP transfer need not interupt other users who also using the network.
Unlike Ethernet or FDDI, ATM's ability to allocate bandwidth allows it to carry data,
voice and video reliably.
ATM can be sent over copper wire or fiber. Currently most ATM desktops are connected at 25Mb/s,
while ATM network backbones run at 155Mb/s or 622Mb/s. At this time, it is not clear if ATM
on the desktop will become common, but it is already
widely used for high-speed network backbones.
Additional Information:
Articles and Reviews:
InfoWorld [1.8.96 ] Gigabit Ethernet may Ease Congestion
Updated: Monday, November 11, 1996, 1:05 pm
Peter DeVries (pdevries@cs.wisc.edu)
Copyright © 1996 InterNIC Internet Scout