Advantages of Networks:

Communication: it is easier using email / video

Roaming: users are not fixed to one place

Sharing information: it is easy to share files and information

Sharing resources: it is easy to share resources such as printers and software

Central management: can manage the system much more effectively and securely: update Anti-Virus etc

In a star network, each device has its own cable that connects to a switch

Star topologies tend to be found in organisations where high performance is a must

They are also found in home networks, especially those that are wireless

In this case, a router with a wireless access point (WAP) provides the central connection for all devices.

+ Each device is separately connected, so a failure of one device or its transmission media does not affect any other device

+ New devices can be added to the network simply by connecting them to the switch

- Extra hardware is required which add to the cost

- If a switch fails, all the devices connected to it will have no network connection

With the Mesh Topology there is no central connection point. Each device is connected to at least one other device and usually to more than one

There are two types of mesh topology:

full & partial mesh

With a full mesh, each devices is directly connected to every other devices

This enables a message to be sent along many individual routes

+ This topology can withstand high traffic.

+ Even if one of the components fails there is always an alternative

+ Expansion and modification in topology can be done without disrupting other devices

+/- There are high chances of redundancy in many of the network connections

- 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

Router: An interconnection device used on networks to connect two or more devices BUT MOST IMPORTANTLY to connect to the internet

Routers used in homes usually contain a switch and a WAP, enabling a LAN and they contain a modem, which allows users to connect to the internet

A switch is an interconnection device that connects two or more devices together and helps in solving the issue of data collisions

A network interface card allows a computer to connect to a wired OR wireless network

A NIC contains a MAC address which is a physical hardware address

A NIC allows an Ethernet cable to be plugged in OR a wireless connection made

IP Addressing

When connected to a network each device is given a unique IP address. This address consists of four sets of up to three digits, each with a maximum value of 255, which are separated by dots. An example is:

192.168.0.254

When a node wants to send a message to another node, it uses the recipient node's address as the destination. A switch on the network knows where the node with this address is and routes the message to it accordingly.

IP addresses can be static or dynamic.

A node given a static address always keeps the same address. A node given a dynamic address has a different address assigned to it each time it connects to the network. This method is known as dynamic host configuration protocol (DHCP). Static addressing makes it easy for network managers to know which device is which on a network. However, dynamic addressing allows more devices to connect than there are available addresses. When a device disconnects from the network, its address is freed up for another device to use. When the first device reconnects it is assigned any free address.

This method of addressing using four sets of digits is called IPv4 and allows for up to 4.3 billion addresses to be used (4,300,000,000). When IPv4 was devised, this number of addresses allowed was deemed to be enough. However, the huge increase in internet-enabled devices has seen IPv4 run out of addresses. A new version, IPv6 which includes eight sets of four-digit hexadecimal values, separated by colons, has been introduced, greatly increasing the number of possible addresses, to around 340 trillion, trillion, trillion (the actual number is 340,282,366,920,938,463,463,374,607,431,768,211,456).

MAC addressing

A MAC address is a unique serial number assigned to each network interface controller (NIC). This allows a network to uniquely identify any device, even when a dynamic IP address is assigned using DHCP, each time the device connects to a network. The device’s IP address changes depending on the network and the MAC address is unique to the device.

A MAC address consists of a string of hexadecimal numbers. An example is:

1A:5B:6H:98:78:35

The MAC address is assigned by the NIC’s manufacturer and cannot be changed. If a device has more than one NIC, for example a wired NIC and a wireless NIC, each NIC will have its own MAC address.

Other protocols

Many other protocols exist. Some of the more common protocols are:

• TCP/IP - Transmission Control Protocol/Internet Protocol - enables communication over the internet.

• HTTP and HTTPS - Hypertext Transfer Protocol - governs communication between a webserver and a client. HTTPS (secure) includes secure encryption to allow transactions to be made over the internet.

• FTP - File Transfer Protocol - governs the transmission of files across a network and the internet.

• SMTP - Simple Mail Transfer Protocol - governs the sending of email over a network to a mail server.

• POP and IMAP - Post Office Protocol and Internet Message Access Protocol - govern retrieving emails from email servers. POP is an older implementation, largely replaced by IMAP.

Transmission media

Ethernet (Cat 5e / Cat6)

Known as twisted pair

A networking standard

Fibre optic

Very fast cable but also more expensive (often used with WAN or larger LANs)

Coaxial Cable

An older networking standard

WiFI

Allows for wireless devices to connect to a network (either LAN or WAN)

Includes connections through Wifi and Bluetooth

Wi-Fi signals use radio frequencies in the 2.4 and 5 GHz wavebands

2.4 is slower BUT covers a larger area and 5 is faster BUT covers a smaller area

Packet Switching:

Transmissions over a network can be extremely large in size. To send a large message in one go would be impractical

With packet switching, messages are broken up into very small pieces, called packets.

The packets are sent individually across the network and put back together to reform the message at the other end.

Each packet consists of two parts:

header - this includes the sender's and recipient's IP addresses, the packet number, the total number of packets, plus the details of any protocols used

payload - this is part of the actual message itself

The packets are sent individually across the network and put back together at the other end.

In networking, layering means to break up the sending of messages into separate components and activities

Each component handles a different part of the communication

This can be referred to as the Transmission Control Protocol/Internet Protocol (TCP/IP) model

It allows standards to be developed and also to be adapted to new hardware and software over time

Application layer: encodes/decodes the message in a form that is understood by the sender and the recipient

Transport layer: breaks down the message into small chunks (packets). Each packet is given a packet number and the total number of packets

Network layer: adds the sender’s IP address and that of the recipient. The network then knows where to send the message, and where it came from

Data link layer: enables the transfer of packets between nodes on a network, and between one network and another

Virtual Networks:

Within a LAN it is possible to use virtual networks to allow one group of devices to not “see” another group on the network

They share the same network hardware and cabling but software determines what the different virtual networks can access and see/use

Easier to maintain a network and also leads to a flexible network setup

Machines can be added and removed from a virtual network without having to re-wire