Network Security - MOD2

MODULE 2 - NETWORK TOPOGRAPHY
Understanding Network Topography
Network Topography or Topology is the study of the arrangement of network components, such
as links, nodes, etc., of a computer network. Network topologies are mainly physical or logical.
The physical topology is the physical layout of a network which includes network devices, their
location and the links. The logical topology is how the network traffic actually gets transferred
within the network irrespective of its design.

There are different types of topologies like bus, ring, tree, mesh, etc. However, we will consider
five basic network topologies which are as follows:

Bus Topology
Bus topology is a very popular topology that is used for connecting network components in a local
area network. In this type of topology, a single network cable is made as the main cable, and all
network elements are connected to this cable. The cable has two endpoints and is called a bus. An
example is shown in the below figure:

In this type of topology, if one node gets disconnected or damaged, then all other nodes can get
affected. This is because all the nodes share the same cable for sending and receiving data. The
bus topology is the cheapest to set up among all other topologies. Both ends of the bus cable are
terminated using unique terminators. There are certain advantages as well as disadvantages related
to bus topology. They are as follows:
Advantages:

− Very reliable in tiny networks
− It needs a little amount of cabling to connect the network components.
− It is less expensive than other types of cable structures.
− It is effortless to expand. Repeaters can be used to connect multiple buses together and

expand the bus network.
Disadvantages:

− Bus network can easily slow down if there is heavy network traffic flow on the bus. The
reason for this is that all the devices connected to the bus can transmit data at any given

time and that transmission is not at all controlled. Hence, the signals collide with each
other, and much bandwidth gets wasted, and as a result, the whole network could stop
functioning.
− Every connection between two points tends to weaken the electrical signal going through
the bus.

Ring Topology
In a ring topology, the network cable passes from one node to another in the form of a circle. All
the nodes are connected to that circular cable with two adjacent nodes connected directly to each
other. The link is unidirectional, and it makes sure that the data sent by one node travels around
the cable and back to the node where the signal was generated.

Each packet of data that is sent onto the cable has the address of the node to which the packet is
being sent. The receiving node checks the received packet and figures out whether it is addressed
to itself or not, and if it is, then the node extracts the data inside the packet. In the case when the
packet does not belong to the node, the node sends the packet to the next node attached to the ring.
It is possible to isolate a single node from the ring without altering the network communication.
Whenever a node is switched off, it gets disconnected from the ring, and the information bypasses

that specific node without any obstruction. An example of an implementation of this topology is a
token ring topology. If there is a break in the ring, then the entire network could stop functioning.

Advantages and disadvantages

Advantages:

− A ring network provides high performance in a network where less number of nodes are
present.

− A ring network can be expanded more than other types of networks.
− Unlike bus topology, signal loss is very less in a ring topology. The reason for this is that

the data is reproduced at every hub.
Disadvantages:

− Relatively costly and challenging to setup
− Failure of one node on the network can influence the entire network.
− Finding errors in a ring is troublesome.
− Adding or expelling nodes can cause the network to malfunction.
− It is slower than an Ethernet network under average load.

Star Topology
This type of topology utilises a hub through which all nodes are connected. In a star topology, the
hub is the host node, and each workstation or other network component is connected to the hub
through a link.

Hubs are the central points which are used by nodes to communicate with each other. A lot of
network cable is utilised by a star topology as each terminal is connected back to the hub. This is
even true for a case where two nodes sit beside each other but are located in a building that is
several kilometres away. The hub is the device that makes all the routing decisions.
Advantages and disadvantages
Advantages:

− It is reliable because if one node fails, the network is not affected.
− Network faults can be easily diagnosed from the hub as the faults are easily detected and

the fault can be isolated easily.

− Nodes can easily be connected or removed from the hub without disturbing the rest of the
network.

− Different cable types can be used in the same network.
Disadvantages:

− As more cable length is required to connect all the nodes to the central hub, therefore, a
star topology is more costly to implement than other topologies.

− If the central hub fails, then the whole network could stop functioning.
Mesh Topology
In this topology, the nodes are interconnected with each other via direct links. This also makes
the cabling requirements high. Multiple paths are present for data to reach a particular node
because of which the failure of a node does not affect the operations of a network.

In a mesh network, there are (n-1)/2 physical channels that are used to connect 'n' number of
devices. To connect to these many devices, each device has to have (n-1) input and output ports.

Advantages and disadvantages
Advantages:
− Network traffic can be easily redirected to another node if a node fails to operate.
− Faults can easily be isolated by leveraging point-to-point connections.
− As the data travels along a dedicated path, the privacy between the nodes remains intact.
− It is no problem to diagnose network issues.
Disadvantages:
− Requires a great amount of cabling.
− Devices require a lot of input and output ports.

Tree Topology
This topology is the most common one that is used in networks. Only a single route exists between
any two given nodes is this LAN topology. The way the devices are connected is similar to how
branches come out of a tree, and hence, the name of the topology.

The nodes in this topology are connected to a hub which is in turn connected to a central hub. This
makes it similar to the star topology. A lot of times, networks that are configured with a star
topology are connected to a bus backbone to form a tree topology.
Advantages and disadvantages
Advantages:
− It is easy to set up this type of topology.
− More devices can be connected to the central hub by adding a secondary hub.
− As compared to mesh topology it is very less expensive.
− It is easy to detect faults in the network.
Disadvantages:
− Failure in the central hub could stop the network from functioning.
− It also requires a lot of cable length.