Network Topologies

A network topology is a way of describing the interconnections and cabling of a group of computers

Physical topology is how the devices or a group of computers are physically connected.

Logical topology is how the network devices communicate with each other

• Each device on the network is connected to a central communication device such as a Hub or switch

If one network cable breaks, the workstation connected to it also fails, but it does not affect the rest of the network

if the central hub fails the whole network will be inoperative as each workstation relies on the central hub for communication.

• central device - hub: network signals reach the hub that are sent out to all connected devices. • The hub just repeats them all on its connections and does not process the signals

• Central device - switch: uses a table that maps each device to the port it is connected to. • switch is able to direct message to correct recipient

• Improves security and speed • messages are transmitted along a specific path from source to destination

• Switch or hub is a central point of failure • if it fails, the connected devices will be unable to communicate or access network resources • failure of individual cables will not affect the network

• If one of the network cables breaks only the computer connected to that cable is affected. • Fast response time and no problems with data collision as each workstation has its own cable. • Security can be installed at the central hub.

• All communication takes place via the central hub and if it fails the whole network will break down. • Uses the most cable which can be expensive to purchase and install. Also long cable runs can cause the data signal to degrade.

• The bus topology has one cable that connects every device on the network which is called the backbone • Each device is connected to the main capable to join the network

• The one cable that connect to a every device on a network.

• At the end of the main capable there is a device called the terminator • The terminator absorbs signals when they reach the end to prevent interference

• Network signals (representing messages between the devices) are sent through the main cable to reach all connected devices. • Each message contains a destination address that identities its intended recipient • MAC address that is hard coded into the Network Interface controller

• If two or more devices try to transmit at the same time, it will cause a collision • if a collision occurs, the devices must stop and try again later • causes the overall performance of the network to deteriorate

• Transmitting signals is a security issue • every device attached to the bus can “read” every message • message needs to be encrypted to not be read

• failure of the main bus capable will bring the whole network to a stop • if there is failure in the cable that connects a single device to the bus, it will only affect just that device

Each device is connected to exactly to other devices creating a single pathway - ring - along which signals travel

• A ring can be uni-directional : the signals can only travel in one direction • break in the capable can lead the network to fail

• signals travel in either direction so the network has more resilience

• Token ring network - a special signal called the token circulates the network • Devices can only communicate when they have the token - there will be no collisions

• Well they can be bi-directional or uni-directional