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UNIVERSITY OF NAIROBI
COLLEGE OF EDUCATION AND EXTERNAL STUDIES
KENYA SCIENCE CAMPUS
SCHOOL OF COMPUTING AND INFORMATICS
REG NUMBER: E46/5422/2014
NAME: KIETI DENIS MUSYOKA
UNIT CODE: ICS 230
UNIT NAME: DATA COMMUNICATIONS AND NETWORK
LECTURER: MR. COLLINS ODUOR
TASK:
ASSIGNEMENT
QUESTION 1
Discuss the difference between physical and logical topology.
Physical Topology is the physical layout of nodes, workstations and cables in the
network; while logical topology is the way information flows between different
components. The logical topology in contrast, is the way that the signals act on the
network media, or the way that the data passes through the network from one device to
the next without regard to the physical interconnection of the devices. A network's logical
topology is not necessarily the same as its physical topology. For example, the original
twisted pair Ethernet using repeater hubs was a logical bus topology with a physical star
topology layout. Token Ring is a logical ring topology, but is wired a physical star from the
Media Access Unit.
Under the physical network topology there is a number of sub categories of network. They
include the following:
Bus topology
Ring topology
Star topology
Tree topology
Mesh topology
In the star network topology, there is a central computer or server to which all the
workstations are directly connected. Every workstation is indirectly connected to every
other through the central computer.
In the ring network topology, the workstations are connected in a closed loop
configuration. Adjacent pairs of workstations are directly connected. Other pairs of
workstations are indirectly connected, the data passing through one or more intermediate
nodes.
In the bus network topology, every workstation is connected to a main cable called the
bus. Therefore, in effect, each workstation is directly connected to every other
workstation in the network.
The mesh network topology employs either of two schemes, called full mesh and partial
mesh. In the full mesh topology, each workstation is connected directly to each of the
others. In the partial mesh topology, some workstations are connected to all the others,
and some are connected only to those other nodes with which they exchange the most
data.
The tree network topology uses two or more star networks connected together. The
central computers of the star networks are connected to a main bus. Thus, a tree network
is a bus network of star networks.
Logical (or signal) topology refers to the nature of the paths the signals follow from node
to node. In many instances, the logical topology is the same as the physical topology. But
this is not always the case. For example, some networks are physically laid out in a star
configuration, but they operate logically as bus or ring networks.
Token passing controls network access by passing an electronic token
sequentially to each host. When a host receives the token, it can send data on the
network. If the host has no data to send, it passes the token to the next host and
the process repeats itself.
In a broadcast topology, each host addresses either data to a particular host or to
all hosts connected on a network. There is no order that the hosts must follow to
use the network
QUESTION 2
Describe the various kinds of LAN physical topologies stating a brief
introduction, advantages and disadvantages with necessary diagrams.
As mentioned above, there are several varieties of local area network under the physical
topologies.
STAR TOPOLOGY
A star topology is designed with each node (file server, workstations, and peripherals)
connected directly to a central network hub, switch.
All the data on the star topology passes through the central device before reaching the
intended destination. Hub acts as a junction to connect different nodes present in Star
Network, and at the same time it manages and controls whole of the network. Depending
on which central device is used, “hub” can act as repeater or signal booster. Central
device can also communicate with other hubs of different network.
Data on a star network passes through the hub, switch, or concentrator before continuing
to its destination. The hub, switch, or concentrator manages and controls all functions of
the network. It also acts as a repeater for the data flow. This configuration is common with
twisted pair cable; however, it can also be used with coaxial cable or fiber optic cable.
Advantages of Star Topology
Easy to connect new nodes or devices. In star topology new nodes can be added
easily without affecting rest of the network. Similarly components can also be
removed easily.
Centralized management. It helps in monitoring the network.
Failure of one node or link doesn’t affect the rest of network. At the same time its
easy to detect the failure and troubleshoot it.
No disruptions to the network when connecting or removing devices.
Easy to detect faults and to remove parts.
Disadvantages of Star Topology
Performance and as well number of nodes which can be added in such topology is
depended on capacity of central device.
Requires more cable length than a linear topology.
More expensive than linear bus topologies because of the cost of the hubs, etc.
Too much dependency on central device has its own drawbacks. If it fails whole
network goes down.
The use of hub, a router or a switch as central device increases the overall cost of
the network.
BUS TOPOLOGY
Is a kind of network physical topology where every computer in the network is attached to
the cable called backbone. 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 of a Linear Bus Topology
Easy to connect a computer or peripheral to a linear bus
Requires less cable length than a star topology
Is cost effective
It’s easy to expand
Disadvantages of a Linear Bus Topology
Entire network shuts down if there is a break in the main cable.
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 Ring Topology, all the nodes are connected to each-other in such a way that they make
a closed loop. Each workstation is connected to two other components on either side, and
it communicates with these two adjacent neighbors. Data travels around the network, in
one direction. Sending and receiving of data takes place by the help of token. Token
contains a piece of information which along with data is sent by the source computer. This
token then passes to next node, which checks if the signal is intended to it. If yes, it
receives it and passes the empty to into the network, otherwise passes token along with
the data to next node. This process continues until the signal reaches its intended
destination.
The nodes with token are the ones only allowed to send data. Other nodes have to wait
for an empty token to reach them. This network is usually found in offices, schools and
small buildings.
Advantages of Ring Topology
 This type of network topology is very organized
 Even when the load on the network increases, its performance is better than that of
Bus topology
 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 of Ring Topology
 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.
MESH TOPOLOGY
In a mesh network topology, each of the network node, computer and other devices, are
interconnected with one another. Every node not only sends its own signals but also
relays data from other nodes. In fact a true mesh topology is the one where every node is
connected to every other node in the network. This type of topology is very expensive as
there are many redundant connections, thus it is not mostly used in computer networks. It
is commonly used in wireless networks. Flooding or routing technique is used in mesh
topology.
Advantages of Mesh topology
Data can be transmitted from different devices simultaneously. This topology can
withstand high traffic.
Even if one of the components fails there is always an alternative present. So data
transfer doesn’t get affected.
Expansion and modification in topology can be done without disrupting other
nodes.
Disadvantages of Mesh topology
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Overall cost of this network is way too high as compared to other network
topologies.
Set-up and maintenance of this topology is very difficult. Even administration of the
network is tough.
There are high chances of redundancy in many of the network connections.