There are 3 types of routing strategies.

1. Hot potato
The message is delivered to the shortest output queue

2. Pre-Determined
In this mode the message itself contains information on how the message should be routed

3. Directory
Routing table: This finds the shortest way possible to arrive to destination
Here the router decides how to forward packets based on a routing table where for a specific destination it will first try the first preference  followed by the second if unsuccessful etc….

A Protocol is a set of rules / instructions

1. Transmission Rate (Flow Control)

Hardware – RTS ¦ CTS
-> Tx (Transmitter) needs to send data so sends a RTS (Request) signal to Rx (Receiver)
-> When Rx is not busy it sends CTS signal to Tx
-> Tx sends packets of data, followed by another RTS signal to Rx

Software – XON ¦ XOFF
-> Tx starts sending data
-> When Rx’s buffer is full the Rx sends an XOFF signal to Tx
-> Tx receives XOFF signal it stops sending
-> When Rx buffer is empty, Rx sends XON signal to Tx
-> Tx starts again

2. Transmission Type (Serial, Parallel, Simplex, Half Duplex, Full Duplex)

Simplex -> One way
Half Duplex -> Two Way, not at them same time
Full Duplex -> Two Way, at the same time

3. Transmission Flow (Asynchronous, Synchronous)

Asynchronous -> Used when data is transmitted at a regular intervals without synchronizing the transmitter with the receiver
Synchronous -> Used between two devices that are continuously sending data to each other in a synchronized fashion, in timed intervals.

4. Error control and compression techniques

-> Parity Check
-> BCC
-> CRC

Linear Bus Topology

The Linear Bus Topology basically is a wire, with all the computers connected to it (as shown in the diagram). Terminators are required because without terminators the BUS will suffer major signal reflection and distortion.

General Information

Developed in 1976
Later IEEE defined the Ethernet standard
The first versions ran at 3 Mbps
The current versions run at 10 Mbps and 100 Mbps
This is a broadcast-based technology
It is inexpensive
Cables used: Thicknet (10Base5 / 100Base5) and Thinnet (10Base2 / 100Base2)

Problem: What happens if 2 devices transmit at the same time?
Each device monitors the line constantly so, a collision will be detected, so as soon as a collision is detected both devices will wait a random time and resend the packet. This process is repeated until a packet is sent successfully. Because of this, the network is not very efficient since there will be many collisions with an increase in workstations.

Problem Solution:
The network can be subdivided logically into smaller segments. and make use of local bridges/switches or routers on smaller segments.

Mesh

This network topology is quite expensive to setup, because it requires too much cable… because every node is physically connected to all the other nodes on the network, with cable. This type of network is used in WAN’s (Wide Area Networks). When you add a new node, you have to connect it to all the other nodes on the network, therefore the more nodes you add, the more cable.

But in some cases particular links can be removed, and you will still have low risk of network failure, this is called Partial Mesh.

Tree

This type of network is a hierarchical network. It consists of a backbone and different types of networks for example you can connect a star network with other type of networks. The backbone is just like a linear bus network, but instead of the nodes, other networks are connected. This is usually used to extend already existent networks into one big network.

Token Ring

This networking topology is very basic. It uses STP cabling and it is more reliable. This network topology does not have collisions like the linear bus topology, because all the nodes are connected in a loop, and a token is used to allow the nodes to send data. A node cannot send data unless it has the token.

It works in a very simple way. A token circles the network and goes from a node to another, when a node has the token it sends the data, and when the receiver gets the token and the data it reads the data and then puts the token back on the network with a flag indicating that the data was read, when the original sender reads that token again, it will empty the token and puts it back on the network.

A disadvantage is, if one node is not working, the whole network will be down, but this is easily solved with an MAU (Multi-Station Access Unit). This connects to the network and if it detects a node that is down it will disable that link and provides a bypass through the MAU.

The extended star topology is exactly like the star topology but, it is modified in a way that two or more star networks are connected. Instead of connecting a node with the central hub, you just connect the other central hub of the other star network.

Star Topology

The star network is a centralized network, because each node is connected to a centralized hub (switch). When a node sends data to another node, the data needs to go through the centralized hub. Usually this network uses UTP cable, but if higher speeds are needed, fiber optic can be used.

The advantages of this network are that you can easily extend it and add more nodes after it has been set up. If one cable or one node is down and not working, the network still works. You can easily detect which node or cable is malfunctioning. But on the other hand, it has some disadvantages too for example it uses much more cable than other linear networks. If the centralized hub is malfunctioning, the entire network is down.