Chapter 2 Communication

2.1 Networking

Networking devices

LAN - local area network

A typical LAN consists of a number of computers and devices (such as printers) connected to hubs or switches. One of the hubs or switches is usually connected to a router and/or modem to allow the LAN to connect to the internet or become part of a WAN

WLAN - wireless LAN

Devices connected are known as wireless access points (WAPs)

WAN - wide area network - formed by a number of LANs connected together; large geo area

MAN - Metropolitan area network

Client-server and peer-to-peer networking models

client-server model - network that uses separate dedicated servers and specific client workstations. All client computers are connected to the dedicated servers

• thin clients - heavily dependent on having access to a server

  • pros: less expensive to expand, server can offer protection against hacking and malware
  • cons: high reliance on server, start-up costs can be high

• thick clients - can work offline or online

  • pros: more robust (can work offline), clients have more control
  • cons: less secure, data integrity

peer-to-peer model - network in which each node can share its files with all the other nodes. Each node has its own data and there is no central server

Network topologies

• bus networks
• star networks
• mesh networks
• hybrid networks

Public and private cloud computing

Cloud storage

• public cloud; private cloud; hybird cloud
• pros: access anywhere; a remote back-up to data; unlimited capacity
• cons: high cost; slow internet connection; potential failure of cloud storage company

Cloud software

Wired and wireless networking

Wireless

• Bandwidth: infrared > microwaves > radio waves
• Penetration: radio waves > microwaves > infrared
• Attenuation: radio waves > microwaves > infrared

WIred

• twisted pair cables
• coaxial cables
• fibre optic cables

Bit Streaming

contiguous sequence of bits, representing a stream of data, transmitted continuously over a communications path, serially (one at a time)

• real-time streaming

  • An event is captured live
  • The video signal is encoded to streaming media files
  • The encoded feed is then uploaded to a file server
  • Streaming servers duplicate the feed and send it to all clients requesting it in real time

• on-demand streaming - Video is stored on a server as streaming media files

2.2 The internet

Difference between Internet and WWW

Internet (interconnected network) - a massive network of networks, uses TCP/IP protocals

World Wide Web (WWW) - a collection of multimedia web pages and other documents which are stored on websites

Hardware and software needed to support the internet

1. Public switched telephone network (PSTN)
2. Phone calls using the internet
3. Cellular networks and satellites

IP addresses

IPv4 - based on 32bits split into four groups of 8bits, each giving a range of 0 to 255

e.g. 192.25.0.255

network ID: 192.25.0

host ID: 255

IPv6 - based on 128-bit split into 8 groups of 16 bits, adopts the hexadecimal notation

e.g. A8FB:7A88:FFF0:0FFF:3D21:2085:66FB:F0FA

zero compression of IPV6

e.g. 900B:3E4A:AE41::AFF7:DD44:F1FF

Uniform resource locators (URL)

protocol://website address/path/filename

https://www.apple.com.cn/mac/index.html

website address: domain host (www) + domain name (apple) + domain type (.com) + (sometimes) a country code (.cn)

Sequence of Events when Viewing a Website

1. User specifies a URL in their client
2. Client sends DNS lookup request to convert URL to an IP address and initiates a TCP connection to server
3. Server acknowledges TCP connection, client sends HTTP requests to retrieve content for the URL.
4. Server replies with content for web page and browser retrieves content from the HTTP packets and renders

• Client-side script: code that runs on client written using language supported by browser e.g. Javascript. Enables web pages to be scripted; to have different and changing content depending on user input, or other variables.
• Server-side script: code that runs on server written using language supported by server e.g. PHP. Used to provide interface for client & to limit client access to databases