3. Data Communications

3.4 Internet – Internet Connection

Internet/Intranet The development of the Internet The development of IT as a timeline Difference between intranet and the

Internet Functions of a typical school intranet

The development of the Internet

It was conceived by the Advanced Research Projects Agency (ARPA) of the U.S. government in 1969 and was first known as the Advanced Research Projects Agency Network. The original aim was to create a network that would allow users of a research computer at one university to be able to "talk to" research computers at other universities.

Extracted from whatis.com

The development of the Internet

A side benefit of ARPANet's design was that, because messages could be routed or rerouted in more than one direction, the network could continue to function even if parts of it were destroyed in the event of a military attack or other disaster.

Extracted from whatis.com

The development of the Internet

A global network connecting millions of computers. As of 1999, the Internet has more than 200 million users worldwide, and that number is growing rapidly. More than 100 countries are linked into exchanges of data, news and opinions.

Extracted from pcwebopaedia.com

The development of IT as a timeline

Please refer to the following website

spider.georgetowncollege.edu/infoweb/AcademicSupport/classes/ITClass/Powerpoint/it1/sld007.htm

The development of IT as a timeline

1880s 1930s

1840s

Fax

Telephone

TelevisionTelegraph

1800s 1970s

Satellite

Cellular

Fibre Optics

1950s

Computer

1890s

Radio

Intranet Share information Less expensive to build and manage than private

networks A network based on TCP/IP protocols Belong to an organisation, usually a corporation Accessible only by the organisation’s members,

employees or others with authorisation An intranet’s web sites look and act like any other

web sites The firewall surrounding an intranet fends off

unauthorised access

Functions of a typical school intranet

E-mailing Password Chat room Message board Notice board File cabinet Question database Library service

Internet Connection Essential components:

– Dial-up software– Telephone lines– ISP– Leased lines

Connection services:– ISDN– Cable– ADSL

Dial-up softwareMicrosoft Dial-up program

Reference links: www.download.com, tucows.hkstar.com

Telephone lines

www.techweb.com/encyclopedia/

Registered Jack-11 (RJ-11)

ISPs in HK

HKIX

ISPISP ISP

The Internet

ISP – Internet Services ProviderHKIX – Hong Kong Information Exchange

Leased lines a permanent telephone connection between

two points set up by a telecommunications common carrier.

are typically used by businesses to connect geographically distant offices

always active The fee for the connection is a fixed monthly

rate the carrier can assure a given level of quality

Leased lines a T-1 channel is a type of leased line

that provides a maximum transmission speed of 1.544 Mbps

You can divide the connection into different lines for data and voice communication or use the channel for one high speed data circuit

ISDN Integrated Services Digital Network is an

international communications standard for sending voice, video, and data over digital telephone lines or normal telephone wires

ISDN supports data transfer rates of 64 Kbps two lines at once, called B (bearer) channels one for voice and the other for data, or you can

use both lines for data to give you data rates of 128 Kbps

Detailed references: www.webopaedia.com, www.techweb.com/encyclopedia

ISDN

ISDN

Cable modem A modem used to connect a computer to a cable

TV service that provides Internet access. Cable modems can dramatically increase the

bandwidth between the user's computer and the Internet service provider

Cable modems link to the computer via Ethernet, which makes the service online all the time

the speed will vary depending on how many customers on that cable segment are using the Web at the same time

Cable modem

Cable modem

ADSL Asymmetric Digital Subscriber Line, a new

technology that allows more data to be sent over existing copper telephone lines (POTS).

ADSL supports data rates of from 1.5 to 9 Mbps when receiving data (known as the downstream rate) and from 16 to 640 Kbps when sending data (known as the upstream rate).

TCP/IP A protocol is a set of special rules

governing transmitting and receiving of data between end points

TCP – Transmission Control Protocol IP – Internet Protocol Refer to the handouts of chapter 3.2

for the functions of TCP and IP

IP Address An identifier for a computer or device

on a TCP/IP network The format of an IP address is a 32-bit

numeric address written as four numbers separated by periods.

Each number can be zero to 255. For example, 1.160.10.240 could be an IP address.

IP address classes Class A addresses are for large

networks with many devices. Class B addresses are for

medium-sized networks. Class C addresses are for small

networks (fewer than 256 devices). Class D addresses are multicast

addresses.

Class A IP addresses

Class number

Max. networks

Max. hosts

Network ID (bits)

Host ID (bits)

1-127 127 16777214 7 24

0XXXXXXX.xxxxxxxx.xxxxxxxx.xxxxxxxx

Network ID Host ID

Class B IP addresses

Class number

Max. networks

Max. hosts

Network ID (bits)

Host ID (bits)

129-191

16383 65534 14 16

10XXXXXX.XXXXXXXX.xxxxxxxx.xxxxxxxx

Network ID Host ID

Class C IP addresses

Class number

Max. networks

Max. hosts

Network ID (bits)

Host ID (bits)

192-223

2097151 254 21 8

110XXXXX.XXXXXXXX.XXXXXXXX.xxxxxxxx

Network ID Host ID

Class D IP addresses

1110xxxx.xxxxxxxx.xxxxxxxx.xxxxxxxx

Multicast address

Subnet mask The method used for splitting IP networks

into a series of subgroups, or subnets. The mask is a binary pattern that is matched

up with the IP address to turn part of the host ID address field into a field for subnets.

It's called a mask because it can be used to identify the subnet to which an IP address belongs by performing a bitwise AND operation on the mask and the IP address

Subnet maskE.g. with explanations:Subnet mask: 255.255.255.0(11111111.11111111.11111111.00000000)IP address: 150.215.17.9(10010110.11010111.00010001.00001001)Subnet address: 150.215.17.0(10010110.11010111.00010001.00000000)

Subnet maskE.g. with explanations:Subnet mask: 255.255.240.0(11111111.11111111.11110000.00000000)IP address: 150.215.17.9(10010110.11010111.00010001.00001001)Subnet address: 150.215.16.0(10010110.11010111.00010000.00000000)

Default subnet mask numbers

Class Default subnet mask numbers

A 255.0.0.0 (Dec)

B 255.255.0.0 (Dec)

C 255.255.255.0 (Dec)

Reserved IP addresses 127.X.X.X

– Loop back X.X.X.0

– Network X.X.X.255

– Broadcasting

DNS Short for Domain Name System (or Service), an

Internet service that translates domain names into IP addresses

Because domain names are alphabetic, they're easier to remember

The Internet however, is really based on IP addresses Every time you use a domain name, therefore, a DNS

service must translate the name into the corresponding IP address. For example, the domain name www.example.com might translate to 198.105.232.4.

DNS The DNS system is, in fact, its own

network If one DNS server doesn't know how to

translate a particular domain name, it asks another one, and so on, until the correct IP address is returned

Routers A device that forwards data packets from

one local area network (LAN) or wide area network (WAN) to another

Based on routing tables and routing protocols, routers read the network address in each transmitted frame and make a decision on how to send it based on the most expedient route (traffic load, line costs, speed, bad lines, etc.)

Install TCP/IP

Fig. 1Network

Install TCP/IP

Fig. 2

Add

Install TCP/IP

Fig. 3

Protocol

Add

Install TCP/IP

Fig. 4

TCP/IP protocol

Configure TCP/IP

Fig. 5

Dynamic Host Configuration Protocol (DHCP)

Configure TCP/IP

Fig. 6

IP address

Subnet mask

TCP/IP Utilities ping (Packet Inter-Network Groper)

– This is used to test whether the host is reachable or not.

– ping 10.123.48.173– ping www.yahoo.com

TCP/IP Utilities nslookup (name service lookup)

– This is used to find the web address from the IP address or vice and versa

– nslookup 10.123.48.173– nslookup www.yahoo.com

TCP/IP Utilities tracert (trace route)

– This is used to show the path of the packet which has passed through on its way to destination.

– tracert www.koei.co.jp– tracert www.netvigator.com

TCP/IP Utilities netstat (network statistics)

– This is used to view TCP/IP statistics and the current active TCP/IP connections

– netstat

TCP/IP Utilities ipconfig (IP configuration)

– This is used to list the IP configuration of the current computer

– ipconfig– ipconfig /all

TCP/IP Utilities arp (Address Resolution Protocol)

– This is used to displays and modifies the IP-to-Physical address translation tables

– arp -a

Firewall A firewall is special software or

hardware designed to protect a private computer network from unauthorized access. Firewalls are used by corporations, banks and research facilities to keep information private and secure.

Proxy Server A proxy server stores web contents on

local hard disks so that the next visit of the same web addresses will retrieve faster.