
Internetworking Communications Introduction Introduction Communication refers to the transfer of information from one place to another The simplest communication system consists of the following: Message Receiver Sender Medium Example Voice Telephone Set Telephone Set Telephone Line
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Message
Receiver
Sender
Medium
In order to allow 2 computers at different location to communicate over a telephone line, a modem is needed to change the data from digital to analog signal and vice versa.
Encode
Transmission
Decode
Signal transmitted
by telephone line
Sending device
Receiving device
A Network is a collection of
computers
and
peripherals
via communication media such as cable and telephone line.
Benefits of using network:
OK! I let you print.
I want to print.
The network supervisor
better security
measures
centralized
control over all
facilities and
resources
Server
Install
new
software
Use new software
Use new
software
Use new
software
It refers to the way by which the network hardware (called nodes) are arranged and the means if data flow.
whole network breaks down
Node fails,
network not affected
Configuration is simple
Star architectureI know u love me,
but I hate u !
Oh, not for me, I will
pass the message
All Computer are nodes
What! The deadline
has changed??
Not my message,
I won’t pick up
Not my message,
I won’t pick up
It’s my message,
I will pick it up
Node
BUS
Not my message,
I won’t pick up
You have to hand
in your homework
today!
What! The deadline
has changed??
Not my message,
I won’t pick up
It’s my message,
I will pick it up
Node
What will happen?
BUS
Not my message,
I won’t pick up
You have to hand
in your homework
today!
Both computer networks and mainframes allow users to communicate and share data and resources. Why computer networks still supersede Mainframes?
It is because computer networks have higher reliability and performance over price ratio. It is also much easier to expand a computer network than a mainframe.
1. Direct Mode Transmission
Signals are transmitted to a particular receiver
Signals are transmitted to all directions
In the late 1960s, the U.S. Defense Department began the Internet as a military research project. The government created a network that covered a large geographic area and could withstand nuclear attack. If part of the network failed, information could still find new route around the disabled computers.
C
A
D
H
E
G
F
Suppose A, B, C, D, E, F, G and H are LANs in different geographic area.They are connected together to form a larger computer system
1.Makes messages of different sizes to become packets of standard size --> standard size buffer can be used in transmitting the packets.
2.Packets of the same message can take different route to the destination --> increase flexibility of the network
3.When a transmission error occurs, only the contaminated packet needs to be re-transmitted.
Client
Server
Web Server in SLCSS
Http:/www.slcss.edu.hk
Computer at home
Let’s try your email account provided by HKedCity!
Hotmail (Web-Mail)
DEMO: http://www.scsite.com/dc2000/
Yahoo! Messenger ICQ
http://206.16.0.204/ is the same as http://www.cnet.com/.
While there may be 38 servers at a given company, each with its own IP address, they all share a common domain name, such as CNET.COM.
Domain Name
ExamplesGeographical Domain Name
(means the organization is located in HK)
http://www.dmedia.com.hk/edu/flash/3_4_a_4a.htm
Http://www.cnet.com/Content/Features/Techno/Networks/index.html
http://www.dmedia.com.hk/edu/flash/3_4_a_7b.htm
http://www.dmedia.com.hk/edu/flash/3_4_a_7a.htm
Internet
ISP
Public Phone Line
In return, you have to pay the necessary fees to the ISP.
modem
Receiving Email1. ISP is 24-hour a day connected to the Internet. Mails to you can always reach your ISP via the Internet.
Internet
ISP
MailBox
modem
Receiving Email2. Your mails are stored in your mailbox maintained by your ISP.
Internet
ISP
MailBox
modem
Receiving Email3. When you run your mail client, it contacts your ISP and your mails in your mail in your mailbox will be transmitted to your computer.
Internet
ISP
MailBox
A scheme for encoding and conveying one’s felling as small text “glyphs”
:-) happy
:-( disappointment
:-< really sad
%-( angry
:-X lips are sealed
The Unofficial Smiley Dictionary :
http://www.eff.org/papers/eegtti/eeg_286.htm/