2.1 Benefits of networking

Benefits of networking

• Certain hardware can be shared by many computers, such as a printer

• Specialist applications such as email

• Access to an intranet to all employees of a company

LAN (Local Area Network)

• Private network

• Appropriate for a home computer system or for a small enterprise business

• Geography will range from a single room to a single site

• LAN is scalable: more computers can be connected to the LAN

WAN (Wide Area Network)

• Wider geographical area, e.g. within a town

• Can be connected through public telephone network or satellite communications

• Example: the Internet

Client server model

• A client computer application will access various resources and services provided by a server

1. The client software makes a request to the appropriate server

2. The processing of the request is carried out on the server

3. Results of the request are sent back to the client server

• Common applications:
  • File server
  • Email server
  • Print server
  • Database server
  • Web server

• Benefits:
  • Different servers can provide for a wide range of services
  • Provides for the central storage for all files and documents
  • Security, including the administration of user accounts, is centralised

• Drawbacks:
  • Initial set-up costs will be high
  • Requires a specialist network operating system
  • If the server fails, all users are affected

Peer-to-peer networking

• No central server, computers are able to act both as a receiver and a sender

• A peer-to-peer network operates with each peer storing some of the files

• Each peer can request or provide files

• Benefits
  • No dedicated server required
  • Additional computers can join easily
  • Each computer can act as both a provider and receiver of resources

• Drawbacks
  • The system is “de-centralised” and it will be difficult to administer
  • Less control over the identification of malware from other computers in the network

Thin-client computing

• Client provides the server with input, the server does the processing, and the client receives and displays the final output

Thick-client computing

• Client does most of the processing, only accesses the server for data needed by the application

2.2 Network topologies

• Bus topology
  • Single cable connects several computers, with each device as a node
  • One of the node failing will not affect the performance of the network

• Star topology
  • Each node has a point-to-point connection to the central device
  • One of the node failing will not affect the performance of the network
  • Central device must be operational

• Mesh topology
  • Every node has a dedicated point-to-point connection to every other node

• Hybrid topology
  • Mix of different topologies

2.3 Cloud computing

• Based on the principle of a central shared resource

• Public cloud
  • Openly available and likely free
  • E.g. Gmail

• Private cloud
  • Usually paid-for
  • E.g. Apple Music

• Benefits
  • Cost effective
  • Capital expenditure on both hardware software can be avoided
  • Flexibility of access
  • Improved centralised security of data

• Drawbacks
  • Cloud provider has to be reliable to handle sensitive data

2.4 Wired and wireless networks

• Wireless networks are networks without wires, the communication medium must be through electromagnetic waves, e.g. radio waves

• Issues: wireless waves cannot penetrate thick walls

Copper cable

• Twisted-pair
  • A pair of copper cables twisted together to cancel out electromagnetic interference

• Coaxial
  • Central single strand wire that is insulated from the outer multi-strand wire mesh braided around the central insulation
  • E.g. Ethernet

• Pro of Coaxial: electromagnetic interference from other metal objects in close proximity is unlikely to affect the signals

• Bus network uses either of those cables

Fibre-optic cable

• Data is free from any interference

• Will not suffer from loss of strength

• Cabling does not suffer from corrosion

• Data travels at light speed

2.5 Hardware to support a LAN

• Switch
  • Connects devices and forwards data packets to and from those devices

• Network Interface Card (NIC)
  • Allows a device to connect to a network
  • Contain the MAC address

• Wireless Network Interface Card (WNIC)
  • Provides interface to wireless network
  • Receives analogue radio waves
  • Converts them to digital
  • Takes digital input and converts to analogue waves

• Wireless Access Point (WAP)
  • Provides access to a particular wireless network

• Bridge
  • To connect different bus LAN cable segments

• Gateway
  • Used between two dissimilar LANs

• Repeater
  • Boosts the signal when travelling a large distance

• Router
  • Receive data packets from a device
  • Route each packet to its destination address
  • Routing tables show the best possible path for the data packet

2.6 Ethernet

• A protocol

• For data transmission over wired network connections

• Data is transmitted in frames

• Each frame has a source and destination address (IP/MAC)

• And error checking data, so that damaged frames can be resent

Carrier Sense Multiple Access / Collision detection (CSMA/CD)

• Strategy to avoid collision

• Steps:
  • Sending device will listen to the communications line before attempting to transmit
  • If the line is not in use, then the device will transmit immediately
  • More packets are then transmitted with a short time delay between each transmission
  • If the line is in use, the device will wait until the line is later sensed as idle
  • If a collision is detected, the device will stop sending and jam the line to make sure other devices are aware that they are unable to use the line

• Collisions are detected by a voltage change at a node

2.7 Bit streaming

• Bit stream is a sequence of bits, representing a stream of data

• Speed of transmission is the bit rate

Real-time bit streaming

• Streamed in real time

• E.g. live TV, video call

On-demand bit streaming

• Original broadcasts are available to be viewed at a later date

2.8 The World Wide Web and Internet

The Internet

• Global communication infrastructure that links together computers and networks

• Forms a collection of connected internets

• Is an open network, access to it is provided by Internet Service Providers (ISPs)

The World Wide Web (WWW)

• Made up of web pages, made available from web servers

Uniform Resource Locator (URL)

• Resource on the WWW could be a web page, a video clip etc.

Domain Name Service (DNS)

• Web browser requests a resource using the URL

• A piece of software called the DNS resolver contacts a DNS server to determine the resource’s IP address

• If the DNS server does not contain the mapping, it will forward it to a different DNS server

2.9 Hardware to support the Internet

The Public Switched Telephone Network (PSTN)

• Dedicated line between two end-points

• Each use of the network requires a “call setup” in which a connection or circuit is established between the two end-points

• Example of circuit switching

Dedicated lines

• Communication line dedicated for use by an entity’s own computers only

• Provides consistently high data transfer speeds

• High and consistent bandwidth

• Video transmission without buffering and signal degradation

A modem

• If data is sent over the PSTN, there is a problem as the computer uses digital data and the PSTN uses analogue data

• Modem is needed at either end of the communication line

• Wireless network uses modems to convert between digital data and radio waves

Cell phone networks

• Land mass is divided into areas called cells

• At least one transceiver or base station serves each cell

• Common usage is a mobile phone network

2.10 IP addresses and networks

• IPv4: 32 bits, written as four numbers in dotted decimal notation

• IPv6: 128 bits, written as 8 groups of 4 hexadecimal digits

• Blocks of IP addresses have been reserved for private network use

• A public router would ignore any IP addresses from those ranges

• Several devices on a LAN that use different private IP addresses will communicate across the Internet using a single public IP address

• Static IP address is never changed

• When the user requests access to the Internet, the ISP will allocate a dynamic IP address (only when it is needed)