2 Communication and Information Technology
Astatine Tian last edited by John Liu
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
2.1 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
- Aim2: Data integrity
- High-frequency attenuation
- Aim3: Low cost
- Require for repeaters
2.1.1 Cable transmission
There are three types of cable to transmit data.
Twisted pair Coaxial Fibre-optic Structure Copper<br/>Different twist rate to reduce interference<br/>Bundled lines Copper<br/>Unbundled lines Optic Fibres Usage 1. Connection of telephone handset to line<br/>2. High-speed local area networks 1. Old long-distance telephone cables<br/>2. Cable televisions 1. Long distance phone line<br/>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
Wire Wireless Permission Need landowner permission Need government permission Interference Greater Repeaters More required
Wire Wireless Home / Small offices Equally efficient. Phone calls Traditional phones Cell phones Long-range Uses undersea cables. Uses satellites<br /><br />GEO: Long distance phone and internet connection. <br />MEO: For GPS. <br />LEO: Supplement Earth Phone services. Can connect distant components at low cost.<br /><br />There will be delays in transmission.
2.2 The Internet
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
- 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.
- 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 / multimedia.
Characteristics of WWW:
- Uses HTTP to transfer files in HTML formats
- URL specifies location of website.
- They can contain Hyperlinks -- when clicked, gives direct access to other web pages.
2.4 Internet Supporting hardware
"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
"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
"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 Server Domain name Server File Server Proxy Server Function Provides access to a web application (See Section 2.9) <br />A middleware is needed for the transmission of scripting through the network (See Section 2.5) <br />The client is the web browser. Stores server files<br/>Can be used as cloud storage Can act as a Firewall (->Chapter 8)<br/>Stores a copy of web page as cache. When a page request comes, it, instead of the web server, can respond.<br/>Therefore the web server doesn’t need to search through its file storage every time. Location Server 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. (See Chapter 8: database)
2.6 Bit Streaming
Any reference to "streaming media" would imply bit streaming is used.
Process of bit streaming:
- Server gains data
- For live-streaming data, the main server first sends the data to multiple content servers. They are responsible to send data to users.
- The data is compressed. A bit stream is generated.
- The bit stream is sent to the user.
- Delivery Process:
- The incoming data is stored in the buffer.
- 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.
- Playing Process:
- The user's media machine reads the data from the buffer and plays it.
- 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.
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.
"32-bit long, hierarchical address of a device on the internet."
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 bits First digit range (denary) Net ID Host ID Class A 0xx 0~126 First 1 byte Last 3 bytes Class B 10x 127~191 First 2 bytes Last 2 bytes Class C 110 192~255 First 3 bytes Last 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: 188.8.131.52/21 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
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.