Network topologies are categorized into the
following basic types:
§ BUS
§ RING
§ STAR
§ TREE
§ MESH
More complex networks can be built as
hybrids of two or more of the above basic topologies
BUS TOPOLOGY
Bus networks (not
to be confused with the system bus of a computer) use a common backbone to
connect all devices. A single cable, the backbone functions as a shared
communication medium that devices attach or tap into with an interface
connector. A device wanting to communicate with another device on the network
sends a broadcast message onto the wire that all other devices see, but only
the intended recipient actually accepts and processes the message.
Advantages
· Easy to connect a computer or peripheral to a
linear bus.
· Requires less cable length than a star
topology.
Disadvantages
· Entire network shuts down if there is a break in
the main cable.
· A faulty cable or workstation will take the entire
LAN down
· Terminators are required at both ends of the
backbone cable.
· Difficult to identify the problem if the entire
network shuts down.
· Not meant to be used as a stand-alone solution in a
large building.
RING TOPOLOGY
In a
ring network, every device has exactly two neighbors for communication
purposes. All messages travel through a ring in the same direction (either
"clockwise" or "counterclockwise"). A failure in any cable
or device breaks the loop and can take down the entire network.
To implement a ring network, one typically
uses FDDI, SONET, or Token Ring technology. Ring topologies are
found in some office buildings or school campuses.
Advantages
·
There is no need for network server to control the
connectivity between workstations.
· Additional
components do not affect the performance of network.
· Each
computer has equal access to resources.
Disadvantages
·
If one workstation or port goes down, the entire
network gets affected.
·
Network is
highly dependent on the wire which connects different components.
· MAU’s and network cards are expensive as
compared to Ethernet cards and hubs.
STAR TOPOLOGY
Many home networks
use the star topology. A star network features a central connection point
called a "hub" that may be a hub, switch or router. Devices typically connect to the hub with
Unshielded Twisted Pair (UTP) Ethernet.
Compared to the
bus topology, a star network generally requires more cable, but a failure in
any star network cable will only take down one computer's network access and
not the entire LAN. (If the hub fails, however, the entire network also fails.)
Advantages
Easy to
install, and wire.
· Easy to add new
workstations
· No disruptions to
the network when connecting or removing devices.
· Any non-
centralised failure will have very little effect on the network
· Easy to detect
faults and to remove parts.
· Centralized
control
· Centralized
network/hub monitoring
Disadvantages
· Requires more
cable length than a linear topology.
· If the hub or
concentrator fails, nodes attached are disabled.
· More expensive
than linear bus topologies because of the cost of the concentrators.
TREE TOPOLOGY
Tree topologies
integrate multiple star topologies together onto a bus. In its simplest form,
only hub devices connect directly to the tree bus, and each hub functions as
the "root" of a tree of devices. This bus/star hybrid approach
supports future expandability of the network much better than a bus (limited in
the number of devices due to the broadcast traffic it generates) or a star
(limited by the number of hub connection points) alone.
Advantages
· Point-to-point
wiring for individual segments
Disadvantages
· Overall length of
each segment is limited by the type of cabling used.
· If the backbone line breaks, the entire segment
goes down.
· More difficult to configure and wire than other
topologies.
MESH TOPOLOGY
Mesh topologies
involve the concept of routes. Unlike each of the previous topologies, messages
sent on a mesh network can take any of several possible paths from source to
destination. (Recall that even in a ring, although two cable paths exist, messages
can only travel in one direction.) Some WANs,
most notably the Internet, employ mesh routing.
A mesh network in
which every device connects to every other is called a full mesh. As shown in
the illustration below, partial mesh networks also exist in which some devices
connect only indirectly to others.
ETHERNET
Ethernet is the
most widely-installed local area network ( LAN) technology. Specified in a
standard, IEEE 802.3, Ethernet was originally developed by Xerox from an
earlier specification called Alohanet (for the Palo Alto Research Center Aloha
network) and then developed further by Xerox, DEC, and Intel. An Ethernet LAN
typically uses coaxial cable or special grades of twisted pair wires. Ethernet
is also used in wireless
LOCALTALK
LocalTalk is a
particular implementation of the physical layer of the AppleTalk networking
system from Apple Computer. LocalTalk specifies a system of shielded twisted
pair cabling, plugged into self-terminating transceivers, running at a rate of
230.4 kbit/s.CSMA/CA was implemented as a random multiple access method.
