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
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
- 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.
* Different twist rate to reduce interference
* Bundled lines
* Unbundled lines
|* Optic Fibres|
|Usage||1. 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
- 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
|Permission||Need landowner permission||Need government permission|
|Home / Small offices||Equally efficient.|
|Phone calls||Traditional phones||Cell phones|
|Long-range||Uses 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
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.
- 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
“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.
“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.
“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|
(-> 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.
|Location||Any computer system||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. (-> 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:
- 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.
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.
“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 (deanery)||Net ID bytes||Host ID bytes|
|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: 220.127.116.11/21 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.