NSS-ICT‎ > ‎Unit C‎ > ‎

Chapter 16

  • P.217 - 219
  • Chapter 16 HW:
  • MC Q1-10
  • Short Questions: Q1-5
4th Oct, 2016

The networking and Internet Basics

16.1 Basic Concepts of Computer Networks
Internet is the world's largest computer network

16.2 Local Area Networks and Wide Area Networks
 cover small geographical area (within 1km) cover large geographical area
 use private cable - Physical security is possible

Wi-Fi: encryption is a MUST
 use public carrier such as telephone lines, leased lines, microwave, satellites.

 Physical security is NOT feasible.
 Encryption is needed.

Usually, It consists of 2 or more remote LAN

Intercept: steal the data when it transmit in the network.

Peer to Peer (P2P). e.g. BT is a P2P services. Each computer upload/download files.
- suitable to small network.
- No need to setup a server.

Client /Server
- suitable to large network. In our school campus, we have around 10 server (Physical and Virtual), over 200 desktop computers as client computer.
- need to set up a server.

 Peer to peerClient / Server 
 No need to set a server
 Lower cost and easy to setup
 server - centralized management

Home network
Share Internet (via modem, router)
Share data (Share a folder in your PC to others)
Smart home (Able to control home appliance via network or Internet)
Share printer
IP cam.

Procedure of sharing a Printer/Folder in a peer to peer network 
1. Connect Printer to computer A
2. Share the printer/folder (e.g. PrinterShare/FolderShare) and set sharing permission in computer A. 
     (In home network, set the same account user name and password in Both Computer)
3. In the other computer, map the printer share. (e.g. \\<IP address>\PrinterShare) or the folder share (e.g.\\<IP address>\FolderShare)

16.3 Network services
- Hardware Sharing  (Harddisk, printer, scanner)
- Software Sharing (web services) Count the number of simultaneous sign-in
- Data/ File sharing (Centralized Data Management, information backup, security)
- Communications (Internet Access service sharing, Network conference)

Class work
You have 3 computers at home. You want to share one broadband connection, printer, network drive.
Draw a network diagram at your home.

Common Server:
FIle server
Print server.
Log-on/sign-in server (Windows: Domain server) 
     Directory Server (LDAP), authentication server
     Single Sign-on (Similar to Google. You can sign on App Inventor using Google account)
VPN server. 
     Logon a VPN server in school over the Internet. The sign-in account can map network drive, browse the internal network. Just like working in school 
     Transmission of data is encrypted. (Tunneling)

16.4 Connecting to a computer network

16.4.1 A network interface card: RJ45
- Media Access Control (MAC) Access, used within a LAN segment. In the switch, a table of MAC address and IP address is stored.
  also called Hardware address. 48 bits address. 
  The first 24 bits can used to identify the manufacturer. http://aruljohn.com/mac.pl (Exercise)
  Security issue: MAC spoofing. (Demonstration)
- Obtain an IP address from DHCP server
- common bandwidth: 100Mbps, 1Gbps
- connector: RJ45 (common) , BNC (outdated), fiber.
- Expansion bus: PCI, on board, USB

Windows Networking Commands: ipconfig, arp, nslookup, ping, netstat

Network Connecting devices
 Repeater and HubNo intelligence. Receive a signal and amplify the signal and sends to connected device 

Repeater: 2 ports. resolve the problem of signal attenuation over long distance.
Hub: more ports, connect multiple device.
 Bridge and SwitchTable of IP address, MAC address, ports are stored in the Device. Forward the traffic to the port connected to the computer/device. 
Switch: central connecting point in a home network.
 Router Connect between different type of LAN, between LAN and Internet 

16.4.2 Modem
Dial up modem. It converts digital signals from your computer into analog signals that can travel over telephone lines and vice versa. Maximum speed: 56 kbps
Still used in fax machine.

Cable modem. via cable TV line
DSL, ADSL modem: also via telephone line.

16.4.3 Cables
Twisted Pair cable 
Coaxial Cable Optical Fiber Cable 
 Up to 1Gbpsused in TV system. Not common in LAN High bandwidth: 10Gbps depends on Connecting device
 UTP: subject to EMILess EMI Not affect by EMI 
electrical signal electrical signalOptical signal 
 Low cost  High cost 
up to 100M distance over 100mUp to km distance 
 suitable to connect to PC Backbone in school, over long distance, high bandwidth is needed 

Transmission over Power line. (Demonstration)

16.4.4 Radio Connections

Satellite broadband. in plane, cruise.

Microwave: up to km, direct line of sight is needed.

Wi-Fi Connections: up to 100m, use radio signal.


16.5 Methods of Internet Access

Internet Service Provider.

Dial up connection: up to 56 kbps (56000 bit per second)
Dial up modem: convert digital signal into analog signal and vice versa.

ISDN (Integrated Services Digital Network)
- not popular in HK.
- up to 128 kbps

- 10Mbps, 100 Mbps, 1000Mbps is common in HK. (Bandwidth connected to ISP)
- DSL (Digital subscription line) modem (SDSL, ADSL) using telephone line
  Many years ago, PCCW only provides ADSL to school, upload speed is 1.5Mbps. Download speed is 10Mbps. 
  We switch to use HGC because of symmetric bandwidth.
- Cable modem (using TV network)
- Direct Ethernet (Fast Ethernet) 

T-carrier (Leased line)
- Nowadays, no school using it to connect to Internet. It is not cost effective. It is very expensive.
- It connect two points in a WAN with guarantee bandwidth. With better security.
- can be leased by hours, days etc. Suitable for video conference meeting. or connect 2 offices in different area.

Wireless Internet Access.
- Wi-Fi hot spots - provided by different ISP. Usually free for 3G/4G subscriber.
  11Mbps, 54Mbps, can be over 100Mbps.

- Mobile phone, GPRS/2.5G (115.2 kbps), 3G (2-28Mbps), 4G LTE (up to 100Mbps)

P.216 Self Assessment Corner Q1-10 
           Do it in exercise book
P.218 Short questions Q1-3

workbook P.45 - P.49
Q2  A bridge is a switch but with two ports only
Q10   WAP 

Short Questions
Q1. P.181
Q2. P.193 - 194
a)  fibre not affect by EMI 
      STP / coaxial : fairly resistant to EMI


MC answer