Computer Network - NetworkTopology

Manoj Kumar
M.Sc.(Computer Science)
Saturday, January 24, 2015 1

 A network as a "group of computers and associated devices
that are connected by communications facilities.“
 A network provides two principle benefits: the ability to
communicate and the ability to share.
A network supports communication among users in ways that other media
cannot. E-mail, the most popular form of network communication,
provides low-cost, printable correspondence with the capability for
forwarding, acknowledgment, storage, retrieval, and attachments.
Sharing involves not only information (database records, e-mail, graphics,
etc.), but also resources (applications, printers, modems, disk space,
scanners, etc.) Through its ability to share, a network promotes
collaboration

 A network can consist of two computers connected
together on a desk or it can consist of many Local
Area Networks (LANs) connected together to form a
Wide Area Network (WAN) across a continent.

 A topology refers to the manner in which the cable is
run to individual workstations on the network.
 Two or more devices connect to a link; two or more
links are forms of topology.
 The topology of network is the geometrical
representation of the relationship of all the links and
linking devices (usually called nodes) one to another.
 A topology is concerned with the physical
arrangement of the network components

TOPOLOGY
MESH
TOPOLOGY
STAR
TOPOLOGY
BUS
TOPOLOGY
RING
TOPOLOGY
TREE
TOPOLOGY
HYBRID
TOPOLOGY

 In mesh topology, every device has a dedicated point
to point link to every other device. The term dedicated
means that the link carries traffic only between the
two devices it connects.
STATION 1
STATION 2
STATION 3 STATION 4
STATION 5
Fig. : MESH TOPOLOGY

 To find the number of physical links in a fully
connected mesh network with n nodes, we first
consider that each node must be connected to n-1
nodes and finally n must be connected to n-1 nodes.
We need n(n-1) physical links. However, if each link
allows communication in both directions, we can
divide the number of links by 2 . We need n(n-1)/2
duplex node links.

1. The use of dedicated links guarantees that each connection
can carry its own data load, thus eliminating the traffic
problems.
2. Mesh topology is robust ;if one link becomes unusable it
does not incapacitate the entire system.
3. There is advantage of privacy or security.
4. There is no need to provide any additional information , i.e.
;source address, along with the packet because each nodes
are connected to each other.
5. Point to point links make fault identification and fault
isolation easy.Saturday, January 24, 2015 8

1. Every device must be connected to every other device.
2. installation and reconnection are difficult.
3. The shear bulk of wiring can be greater than the
available space (in walls, ceilings or floors) can
accommodate.
4. Not flexible ;
5. Poor expandability ;i.e., to add a new node in network
is very cost effective.

 A mesh topology is the connection of telephone
regional offices in which each regional office needs
to be connected to every other regional office.

 In start topology, each device has a dedicated point
to point link only to a central controller, usually called
hub.
The devices are not directly linked to one another.
HUB
STATION
STATION
STATION
STATION
Fig. : STAR TOPOLOGY

A star topology does not allow direct traffic between
devices.
The controller acts as an exchange : if one device
wants to send data to another, it sends the data to the
controller , which then relays the data to the other
connected device.

1. Less expensive than mesh topology, due to less cabling
and ports.
2. It is easy to install and reconfigure because each device
needs only one link and one I/O port to connect it to
any number of other .
3. Provide high speed and great maintainability
4. Robustness: if one link fails, only that link is affected
other link remain active.

1. One big disadvantage of star topology is the
dependency of whole topology on one single point,
the hub.
2. If the hub goes down, the whole system is dead.
3. Often more cabling is required in a star topology
than in some other topologies such as ring or bus
topology.

Star topology is used in local-area networks
(LANs), high-speed LANs often use a star topology
with a central hub.

 A bus topology is multipoint. One long cable acts
as a backbone to link all the devices in a network.
 Nodes are connected to the bus cable by drops lines
and taps.
Station Station
Station station
Cable end Cable end
Fig, :Bus topology

A drop line is a connection running between the device and the main
cable.
A tap is a connector that either splices into the main cable or
punctures the sheathing of a cable to create a contact with the metallic
core.
Full-duplex operation between the station and the tap allows data to
be transmitted onto the bus and received from the bus.
At each end of the bus there is a terminator, which absorbs any
signal, preventing reflection of signal from the endpoints. If the
terminator is not present, the endpoint acts like a mirror and reflects
the signal back causing interference and other problems.
Each station has a unique address in the network, a station copies a
packet only when the destination address of the packet matches with
the self-address.

Ease of installation.
Bus uses less cabling than mesh or star topology.
In the bus, redundancy is eliminated.
A shared link is used, hence it is very cost effective.
Great expandability; One can easily add any new
node or delete any node without affecting other nodes.

Difficult reconnection and fault isolation.
A fault or break in the bus cable stops all transmission.
Because of the shared medium, it is necessary to provide
some extra information about the desired destination, i.e.
to explicitly specify the destination in the packet.
One station is allowed to send data at a time and all other
stations listen to it, as it works in a broadcast mode. Hence,
only one station can transfer the data at any given time.

Bus topology used in the design of early LANs,
Ethernet LANs.

In a ring topology, each device has a dedicated point
to point connection with only two devices on either
side of it.
Ring
Topology
Station 1
Station 2
Station 3 Station 4
Station 5
Station 6
Station 7

RING
TOPOLOGY
SINGLE RING
TOPOLOGY
DOUBLE RING
TOPOLOGY
 Meaning data travels in circular fashion from one computer t
another on the network
Continue…

Station 1
Station 4
Station 3
Station 2
Fig. : Single Ring Topology
SINGLE RING TOPOLOGY
Single ring: A signal is passed along the ring in one direction, from device to device,
until it reaches its destinations.

DOUBLE(DUAL) RING TOPOLOGY
Station 1
Station 4
Station 3
Station 2
Fig. : Dual Ring Topology
Dual ring: A signal is passed along the ring in both direction, from device to device,
until it reaches its destinations.

Easy to install and reconfigure.
Fault isolation is simplified, generally in a ring topology, a signal is
circulating at all times.
Each computer has equal access to resources
 If one device does not receive a signal within a specified period , it can
issue an alarm. The alarm alerts the network operator to the problem
and its location.
Network is highly dependent on the wire which connects different
components.
Extension needs to affect only two neighbored stations, i.e.; good
expandability.

Unidirectional traffic
A break in the ring can disable the entire network.
Each packet of data must pass through all the computers between source
and destination. This makes it slower than star topology.
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.

Ring topology was prevent when IBM introduce ,its
LAN token ring.

 Tree topology is a combination of Bus and Star topology.
 A tree topology is a variation of a star. As in a star, nodes in a
tree are linked to a central hub that controls the traffic to the
network. However, not every device plugs directly into the central
hub.
HUB
HUBHUB
STATION 1 STATION 2
STATION 9STATION 8STATION 7 STATION 12STATION 11STATION 10
STATION 5STATION 4STATION 3
Fig, : Tree topology

Continue…
 The majority of devices connects to a secondary hub that in
turn is connected to the central hub.
 The central hub in the tree is an active hub.
 An active hub contains a repeater, which is a hardware
device that regenerates the received bit patterns before
sending them out.
 Repeating strengthens transmissions and increases the
distance a signal can travel.
 The secondary hubs may be active or passive hubs. A passive
hubs provides a simple physical connection between the
attached devices.

It allow more device to be attached to a single central
hub and can therefore increase the distance a signal can
travel between devices.
 Point to point connection of devices.
It allows the network to isolate and prioritize
communications from different computers.
 Having different levels of the network makes it more
manageable hence easier fault identification and isolation

 Maintenance of the network may be an issue when
the network spans a great area.
 Since it is a variation of bus topology, if the
backbone fails, the entire network is crippled

A good example of this network could be cable TV technology
where the main cable from the main office is divided into main
branches and each branch is divided into smaller branches and
so on. The hubs are used when a cable is divided.

 Hybrid topology use a combination of any two or more topologies.
 In such a way that the resulting network does not exhibit one of the
standard topologies (e.g., bus, star, ring, etc.)
 For example a tree network connected to a tree network is still a tree
network topology.
 A hybrid topology is always produced when two different basic network
topologies are connected.
 Two common examples for Hybrid network are: star ring network and star
bus network.

HUB
BUS HUB
STATION
STATION
STATION
STATION
RING
STATION
STATION
STATION
STATION
Fig, : Hybrid topology
STAR
STAR
Hybrid topology is a combination of Bus, Star and ring topology

Reliable : Unlike other networks, fault detection and troubleshooting is easy in this
type of topology. The part in which fault is detected can be isolated from the rest of
network and required corrective measures can be taken, WITHOUT affecting the
functioning of rest of the network.
Scalable: Its easy to increase the size of network by adding new components,
without disturbing existing architecture.
Flexible: Hybrid Network can be designed according to the requirements of the
organization and by optimizing the available resources. Special care can be given to
nodes where traffic is high as well as where chances of fault are high.
Effective: Hybrid topology is the combination of two or more topologies, so we can
design it in such a way that strengths of constituent topologies are maximized while
there weaknesses are neutralized. For example we saw Ring Topology has good data
reliability (achieved by use of tokens) and Star topology has high tolerance capability
(as each node is not directly connected to other but through central device), so these
two can be used effectively in hybrid star-ring topology.

Complexity of Design: One of the biggest drawback of hybrid
topology is its design. Its not easy to design this type of architecture
and its a tough job for designers. Configuration and installation
process needs to be very efficient.
Costly Hub: The hubs used to connect two distinct networks, are
very expensive. These hubs are different from usual hubs as they need
to be intelligent enough to work with different architectures and
should be function even if a part of network is down.
Costly Infrastructure: As hybrid architectures are usually larger in
scale, they require a lot of cables, cooling systems, sophisticate
network devices, etc.

ANY
QUESTION?

THANK
YOU!

Computer Network - NetworkTopology

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