Chapter 2: Communication and Information Technology

Nov 20, 2019

Overview of the chapter:

  • 2.1 Transmission Media
  • 2.2 The internet
  • 2.3 Internet supporting hardware
  • 2.4 The World Wide Web
  • 2.5 Client-Server architecture
  • 2.6 Bit-streaming
  • 2.7 IP Addressing
  • 2.8 Domain name
  • 2.9 HTML, JavaScript, and PHP

The current A1 lessons has only reached to 2.7 IPv4. Your EoS exam only covers to section 2.7. Expect 1 structured question in this chapter ion your exam.

Next page: 2.1 Transmission Media


2.1 Transmission Media

Data could be transmitted by cable or wireless.

No matter which method is used, the aims are always the same:

  • Aim1: Fast transmission
    • Bandwidth
  • Aim2: Data integrity
    • High-frequency attenuation
    • Interference
  • Aim3: Low cost
    • Cost
    • Require for repeaters
    • Maintenance

2.1.1 Cable transmission

There are three types of cable to transmit data.

Twisted pairCoaxialFibre-optic
Structure* Copper
* Different twist rate to reduce interference
* Bundled lines
* Copper
* Unbundled lines
* Optic Fibres
Usage1. Connection of telephone handset to line
2. High-speed local area networks
1. Old long-distance telephone cables
2. Cable televisions
1. Long distance phone line
2. Long distance cabling
An image
You need to remember:
a) The different sector of the measurement.
b) Relative performance of the three cables in each of the sector.
  • Fibre-optic performs the best across all sectors, yet it is the most expensive.
  • Twisted pair is the worst, except for “high frequency attenuation”.

Modern is a kind of analog-to-digital convertor. By setting up one at each end, people could connect to the internet through phone lines. (Through POTS / PTSN).

Typically organizations will lease lines for LAN / WAN.

PSTNs (Public Switched Telephone Network) provides internet connection through: Traditional networks lines, public hotspot and cellular connection.

2.1.2 Wireless transmission

Through electromagnetic radiation. Options are radio, microwave and infrared.

  • Most applications: Microwaves
    • Because of band-width limitations of Radio waves
  • Indoor applications: Infrared

2.1.3 Wire vs Wireless

Pros and cons

WireWireless
PermissionNeed landowner permissionNeed government permission
InterferenceGreater
RepeatersMore required

Applications

WireWireless
Home / Small officesEqually efficient.
Phone callsTraditional phonesCell phones
Long-rangeUses undersea cables.Uses satellites.

GEO: Long distance phone and internet connection.
MEO: For GPS.
LEO: Supplement Earth Phone services. Can connect distant components at low cost.

There will be delays in transmission.

Next page: 2.2 The Internet

2.2 The Internet

Network Structure

LAN < WAN < ISP < Internet.

  • LAN: Local Area Network
    • Short distance communication, e.g. In a same building
    • WLAN: Wireless Local Area Network
  • WAN: Wide Area Network
    • Long distance communication, e.g. The whole country
  • ISP (Internet Service Provider)
    • An ISP is a network.
    • Connections between ISP are managed by IXPs. (Internet Exchange Points.
    • The Tier 1 ISPs are the major content providers.
    • Functions of ISPs
      • Initially, functions of ISP is to provide access to Internet. Now these ISP are known as “access ISPs”.
      • They connect to regional ISPs then Tier 1 ISPs.
  • Internet
    • The internet is not a WAN. It is the biggest internetwork in existence.
    • It hasn’t been designed, and there’s no definition of its structure.

The World Wide Web is not a network. It is a distributed application available on the Internet. WWW is not Internet.

WWW contains an enormous collection of websites. Each has one or more web pages. Special Feature: They can contain Hyperlinks — when clicked, gives direct access to other web pages.

Next Page: 2.4 Internet Supporting Hardware

2.4 Internet Supporting hardware

Router

A device that acts as a node on the Internet.

The center of a star topology can be a hub, switch, or a router. When a information is sent to the center:

* A hub broadcasts it to every end-system

* A switch is more intelligent. It can track the address of the devices. So it can sent to the specified end-system in a unicast.

* A router is the most intelligent. It can decide which specific device to broadcast to.

Routers are the backbones of the Internet. A router can also function as a gateway and network address translation box and firewall.

Chapter 17.03, A2 Computer Science textbook.
Switch a LAN

Gateway

“A device that connects networks of different underlying technologies.”

When different networks needs to connect to the Internet, a Gateway will be needed.

Gateways can be combined with Firewalls and Routers.

Gateway and Switch in a LAN

Server

“A device that provides services via a network.”

There are different types of Servers:

  • Application Server
  • Web Server
  • Domain Name Server (DNS)
  • File Server
  • Proxy Server
Web ServerDomain Name ServerFile ServerProxy Server
Function* Provides access to a web application
(-> Section 2.9)
* A middleware is needed for the transmission of scripting through the network
(-> Section 2.5)
* The client is the web browser.
* Stores server files
* Can be used as cloud storage
* Can act as a Firewall (->Chapter 8)
* Stores a copy of web page as cache. When a page request comes, it, instead of the web server, can respond.
Therefore the web server doesn’t need to search through its file storage every time.
LocationAny computer systemServer Farms, Tier 1 components providers

2.5 Client-server Architecture

In a distributed computer system:

  • The client carries out part of the processing
  • A server carries out the other part
  • A middleware helps them to cooperate.

A web page will be “dynamic” under this architecture. (The information displayed is determined by client’s request.)

Many also require a web-enabled database to be installed on the server. (-> Chapter 8: database)

Next page: 2.6: Bit streaming

2.6 Bit Streaming

Any reference to “streaming media” would imply bit streaming is used.

Process of bit streaming:

  1. Server gains data
    1. For live-streaming data, the main server first sends the data to multiple content servers. They are responsible to send data to users.
    2. The data is compressed. A bit stream is generated.
    3. The bit stream is sent to the user.
  2. Delivery Process:
    1. The incoming data is stored in the buffer.
    2. If the volume of data in the buffer reaches the high water mark, the user’s computer will send a control signal to the server, asking for less data. Vice versa for low water mark.
  3. Playing Process:
    1. The user’s media machine reads the data from the buffer and plays it.

User experience

  • The bit rate user receives should match that of the original file on the server.
    • Transmission speed must be sufficient. (Between server, buffer and player)
    • Transmission to buffer should be faster than file bit rate, to fill up the buffer — avoids unexpected delays.
  • Buffer size should be big enough.

Next page: 2.7 IP Address

2.7 IP Addressing

IP address is a component of TCP/IP protocol. (-> Chapter 17)

It defines from where and to where data is transmitted.

2.7.1 IPv4

“32-bit long, hierarchical address of a device on the internet.”

Components

NetID and Host ID.

  • NetID Defines the network the device belongs.
  • HostID defines the device in that network.

The first 3 bit determines class of the IP address.

First 3 bitsFirst digit range (deanery)Net ID bytesHost ID bytes
Class A0xx0~126First 1 byteLast 3 bytes
Class B10x127~191First 2 bytesLast 2 bytes
Class C110192~255First 3 bytesLast 1 byte

2.7.2 Classless Inter-domain Routing (CIDR)

On the base of IPv4, CIDR adds a furthermore 8 bits to the end. The 8 bits define which bits are for NetID. Like this:

Example of an CIDR: 
11000011000011000000011000001110 / 00010101

Sample Questions:
Q1. Decode following CIDR to IPv4
Solution: convert each 8-bit binary to denary. 
11000011 00001100 | 00000110 00001110 / 00010101
195     .   12    .    6    .    14.  /   21

Final Answer: 195.12.6.14/21

Q2. Find the NetID of this IP address. 
The suffix is 21, meaning :first 21 bits are netID.

110000110000110000000 | 11000001110 / 00010101
|                     |              |           |
|  <---  NetID --->   | <- HostID -> | <-Suffix->|

Solution: the NetID is 110000110000110000000

2.7.3 Sub-netting

Based on class C of IPv4.

Instead of giving each LAN a separate network ID, sub-netting combines all LANs to a router. They all share the same, and only one network ID as the router.

Structure of the IP address also changes.

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