3. Data Communications - PowerPoint PPT Presentation

3. Data Communications

3.4 Internet –

Internet Connection

• The development of the Internet
• The development of IT as a timeline
• Difference between intranet and the Internet
• Functions of a typical school intranet

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

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

• 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

• Please refer to the following website

spider.georgetowncollege.edu/infoweb/

AcademicSupport/classes/ITClass/

Powerpoint/it1/sld007.htm

Cellular

Telephone

Telegraph

Television

Satellite

1970s

1800s

1880s

1930s

1890s

1950s

1840s

Fibre Optics

Computer

Fax

Radio

• 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

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

• Essential components:
• Dial-up software
• Telephone lines
• ISP
• Leased lines
• Connection services:
• ISDN
• Cable
• ADSL

Microsoft Dial-up program

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

Registered Jack-11 (RJ-11)

www.techweb.com/encyclopedia/

The Internet

HKIX

ISP

ISP

ISP

ISP – Internet Services

Provider

HKIX – Hong Kong

Information

Exchange

• 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

• 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

• 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

• 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

• 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).

• 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

• 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.

• 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.

0XXXXXXX.xxxxxxxx.xxxxxxxx.xxxxxxxx

Network ID

Host ID

10XXXXXX.XXXXXXXX.xxxxxxxx.xxxxxxxx

Network ID

Host ID

110XXXXX.XXXXXXXX.XXXXXXXX.xxxxxxxx

Network ID

Host ID

1110xxxx.xxxxxxxx.xxxxxxxx.xxxxxxxx

Multicast address

• 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

E.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)

E.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)

• 127.X.X.X
• Loop back
• X.X.X.0
• Network
• X.X.X.255
• Broadcasting

• 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.

• 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

• 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.)

Network

Fig. 1

Add

Fig. 2

Add

Protocol

Fig. 3

TCP/IP protocol

Fig. 4

Dynamic Host

Configuration Protocol

(DHCP)

Fig. 5

IP address

Subnet mask

Fig. 6

• 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

• 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

• 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

• netstat (network statistics)
• This is used to view TCP/IP statistics and the current active TCP/IP connections
• netstat

• ipconfig (IP configuration)
• This is used to list the IP configuration of the current computer
• ipconfig
• ipconfig /all

• arp (Address Resolution Protocol)
• This is used to displays and modifies the IP-to-Physical address translation tables
• arp -a

• 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.

• A proxy server stores web contents on local hard disks so that the next visit of the same web addresses will retrieve faster.