CP and IP
have made the interconnection of the world possible, but Ethernet
must be given a silver medal for building up the network from the
ground up. Without Ethernet we would have never evolved organizational
networks and the Internet so quickly. For anyone who has used a
modem from home, and had
to make a dial-up connection, will know how annoying this can be.
But, Ethernet, plug in a cable from a hub to the computer, and it
works seamlessly. No setting dial-ups, no screeching, no flashing
lights, no tying up your phone line, no telephone bills, no bringing
down the network while you connect or disconnect. Nothing. You don't
even have to know what the physical address of the computer is.
So how does it work? Well the key is ARP, as ARP allows a computer
to broadcast a message to the rest of the network, asking for the
MAC address of a given network address. Thus computers can quickly
determine the physical addresses of all the devices on their network
segment, simply by broadcasting an ARP request. So what if the destination
is outside the network segment? Well with this the computer sends
the data frame to the router (as it will know its address from a
previous ARP request), but with the destination network address.
The router detects that the destination address is outside the network
segment, and that the data frame is addressed to itself. It will
then forward to another router, or a network segment.
it seemed unlikely that Ethernet would survive as a provider
of network backbones and for campus networks, and its domain would
stay, in the short-term, with connections to local computers. The
world seemed distended for the global domination of ATM , the true
integrator of real-time and non real-time data . This
was due to Ethernet's lack of support for real-time traffic and
that it does not cope well with traffic rates that approach the
maximum bandwidth of a segment (as the number of collisions
increases with the amount of traffic on a segment). ATM seemed to
be the logical choice as it analyses the type of data being transmitted
and reserves a route for the given quality of service. It looked
as if ATM would migrate down from large-scale networks to the connection
of computers, telephones, and all types of analogue /digital communications
equipment. But, remember, not always the best technological
solution wins the battle for the market - a specialist is normally
always trumped by a good all-rounder.
the best poker player in town. It knows all the tricks. It's a heavyweight
prize fighter. It'll slug it out with anyone, and win. I took Token
Ring on, head to head, and thrashed it. So what would you
choose for your corporate network? Would it be a technology that
was cheap, and could give you 1 Mbps, 10Mbps for your connections to workstations and server, and,
possibly, 1Gbps for your backbone. Ethernet always makes a sensible
choice, as it's cheap and it's going to be around for a lot longer,
yet. Any problems within an Ethernet network can be solved
by segmenting the network, and by relocating servers. And for cable
, it supports twisted-pair, coaxial and fiber. Who would
have believed that you could get 1Gbps down a standard Cat-5 , twisted-pair
does not provide for quality of service and requires other higher-level
protocols, such as IEEE 802.1p. These disadvantages are often outweighed
by its simplicity, its upgradeability, its reliability and its compatibility. One way to overcome the contention problem is to provide
a large enough bandwidth so that the network is not swamped
by sources which burst data onto the network. For this, the
gigabit Ethernet standard is likely to be the best solution for
A key method of
increasing the bandwidth of a network is to replace hubs with
switches, as switches allow simultaneous transmission between connected
ports. Thus if the bandwidth of a single port on a switch is
10 Mbps, then a multi-port switch can give a throughput of
several times this. But, switches have the potential of improving
the configuration of networks.
are now used to open-plan offices, where the physical environment
can be changed as workgroup evolve. This is a concept which is now
appearing in networking, where virtual networks are created.
With this computers connect to switches. The switch then tags
data frames for destination virtual networks and puts the
tagged data frame onto the backbone. Other switches then
read the tag, and, if the destination is connected to one of their
ports, they remove the data tag, and forward the data frame to the
required port. This technique is now standardized with IEEE 802.1q,
an important step in getting any networking technique accepted.
Imagine if whole countries were setup like this. What we would have
is a programmable network, where system administrators could connect
any computer to any network. Presently we are constrained by the
physical location of nodes.
will also bring enhanced security, where it will be possible to
constrain the access to sensitive data. For example a server which
contains data which must be kept secret can be located in a safe
physical environment and only users which a valid MAC address
would be allowed access to the data.
Hats off to the IEEE who have carefully developed the basic technology,
after its initial conception by DEC,
Intel and the Xerox Corporation.