Transcript The Internet - Seneca - School of Information & Communications

Week 1 Lecture Review
Do you remember?
1. Definition of The Internet
2. “internet” vs “The Internet”
3. 3 types of networks
4. Why was the “internetworking project”
at ARPA funded by the US DoD ?
5. What was the role of Bush, Taylor, Cerf,
Berners-Lee, Andreeson?
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1
Week 1 Lecture Review
The Internet
a specific worldwide network of
interconnected networks
communication protocols are used to
specify a common language so that
these different computers can exchange
messages
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2
Week 1 Lecture Review
Networks That Became The Internet
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source: http://www.course.com/
3
Week 1 Lecture Review
Did you....
1. Do the required reading?
2. Do lab 1b at home?
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Week 1 Lab Review
Do you remember?
1. Your learn ID
2. Your matrix ID and Password
3. How to get help with your accounts
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Week 1 Lab Review
Do you remember?
Have you accessed your “matrix”
account from home using telnet?
The answers to the questions at the
end of lab1
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This Week
Intro to the Internet continued
Some basic UNIX commands
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Protocols
Definition: Communication protocol
an agreement that specifies a common
language that two computers use to
exchange messages.
A protocol is a set of agreed upon rules
ex. a “lecture protocol” – raise your hand to ask
a question
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Definition: TCP/IP
Transmission Control Protocol/Internet Protocol
The communications protocols used to connect hosts
on the Internet.
TCP/IP:
1. uses several protocols - the two main ones are
TCP and IP.
2. TCP/IP is built into the UNIX operating system
and is used by the Internet
3. It is the standard for transmitting data over
networks.
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Definition: TCP
“The part of the TCP/IP set of rules for sending data
over a network that includes the rules that
computers on a network use to establish and break
connections”
source:The Internet, Perry & Schneider
The TCP protocol
1. is a “connection-oriented” service that enables two
hosts to establish a connection and exchange
streams of data.
2. guarantees delivery of data
3. guarantees that packets will be reassembled in
the same order in which they were sent.
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source: www.webopedia.com
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Definition: The Internet Protocol (IP)
The part of the TCP/IP set of rules for sending
data over a network that includes the rules for
routing of individual data packets
The IP protocol
1. specifies how a packet is created
2. specifies how a router must forward each packet
to its destination
3. IP is “connectionless” – it does not try to
establish a connection with its peer before
sending data
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Definition: packet or datagram
“A unit of data sent across a network”.
When a large block of data is to be sent over
a network, it is broken up into several packets,
sent, and the reassembled at the other end...

The exact layout of an individual packet is
determined by the protocol being used.

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source: www.netdictionary.com
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IP Address
Each host in the Internet is assigned to a
unique number for identification.
Such a number is called the IP address of
the host.
To improve readability, IP addresses are
split up into four numbers. The range of
each number falls into 0-255, inclusive.
For example, the host
robin.cse.cuhk.edu.hk has an IP address of
137.189.90.184.
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source: John Hunter
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Network Number/Host number
IP addresses are split into a network
number, and a host number.
For example, 137.189 is the network
number of CUHK, while 90.184 is the host
number of the host robin.cse.cuhk.edu.hk.
Network numbers are assigned by a
central authority, the The Internet
Corporation for Assigned Names and
Numbers (ICANN).
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source: John Hunter
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Class Networks
Class A comprises networks 1.0.0.0
through 127.0.0.0. The network number is
contained in the first quad. It allows
roughly 16 million hosts per network.
Class B contains networks 128.0.0.0
through 191.255.0.0. The network number
is in the first two quads. This class allows
for 16,320 nets with 65,024 hosts each.
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source: John Hunter
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Class Networks
Class C networks range from 192.0.0.0
through 223.255.255.0, with the network
number contained in the first three octets.
This class allows for nearly 2 million networks
with up to 254 hosts.
Classes D, E, and F Addresses falling into
the range of 224.0.0.0 through 254.0.0.0 are
either experimental or are reserved for
special purpose use.
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source: John Hunter
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Subnet
The Internet is structured hierarchically.
For example, CUHK consists of many
academic departments and
administrative bodies, each maintaining
their own network.
IP allows you to subdivide a network into
several subnets. For example, CSE and
CSC are two subnets inside CUHK.
Each subnet is identified by a subnet
number.
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source: John Hunter
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Subnet
For example, we have a different way to
interpret the IP address 137.189.90.184,
 137.189 refers to the network number of
CUHK;
 90 refers to the subnet number of CSE;
and
 184 refers to the host number of robin.
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source: John Hunter
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Example: The Chinese University of Hong Kong
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source: John Hunter
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IP Routing
Remember? The Internet is a packet
switching network.
The process of transmitting a data
packet from the source to the
destination via a series of
intermediate stations is called
routing.
source: John Hunter
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IP Routing
IP routing works as follows:
Each data packet is labeled with the
IP address of the destination host.
When a packet is being delivered,
the IP address of the destination
attached is examined.
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source: John Hunter
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IP Routing
For example:
When a packet is
destined to:
robin.cse.cuhk.edu.hk
(137.189.90.184)
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source: John Hunter
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IP Routing
137.189.90.184
1500 bytes Data here
First - the network number is
extracted as 137.189, which is the
network number of CUHK. The
packet is thus sent to Hong Kong
and then to CUHK.
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source: John Hunter
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IP Routing
137.189.90.184
1500 bytes Data here
Inside CUHK, the subnet number is
examined and is found to be 90, which
is the subnet number of CSE. The
packet is thus sent to CSE.
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source: John Hunter
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IP Routing
1500 bytes Data here
137.189.90.184
source: John Hunter
Inside CSE, the host number
is examined and is found to be
184, which is the host number
of robin.
Finally, the packet is sent to
robin, the destination.
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Making it more human
Humans have trouble remembering IP
addresses.
Therefore URLs, Domain Names, and Host
Names were created.
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source: Inge McLaurin
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Domain and Domain Name
A domain is a logical grouping of
computers on a network. It may include
multiple networks. It may also just be a
subset of a network of computers.
Just like people, domains need to have
names.
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source: Inge McLaurin
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Top Level Domain
Some top level domains (TLD) of the Internet
 com: for commercial entities
 edu: for four-year educational institutions
 gov: for non-military, US federal gov.
institutions
 net: for network operations and Internet
Service Providers (ISP)
 org: for non-profit organizations
There are also domain names for each country
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source: Inge McLaurin
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Top Level Domain
There are also domain names for each
country
 ca: Canada
 cn: China
 uk: United Kingdom
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source: Ling Zhu
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Host and Host Name
A host is a computer that is enabled to function
on a network.
To be a host on the Internet, a computer must
meet 4 requirements:
1. Use the Internet Protocol (IP)
2. Be assigned a unique IP address; eg.,
206.96.248.226
3. Have a network connection that provides a
route to the Internet
4. Have a domain name (optional)
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source: Inge McLaurin
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Domain and Host Names
A given domain can, potentially, contain
millions of host names as long as they are
all unique within that domain.
www.senecac.on.ca
cns.senecac.on.ca
cs.senecac.on.ca
learn.senecac.on.ca
phobos.senecac.on.ca
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142.204.1.1
142.204.119.46
142.204.57.12
142.204.1.21
142.204.57.136
source: Inge McLaurin
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Qualified Domain Name
The host name, and domain name
combine to give a qualified domain name
Qualified Domain Name
cns.senecac.on.ca/
Host Name
Domain Name
TLD
siris.senecac.on.ca/
Qualified Domain Name
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source: Inge McLaurin
Examples
http://www.yahoo.com/
http://www.howstuffworks.com/
http://cns.senecac.on.ca/~fac/
http://htmlgoodies.earthweb.com/
Host Name
Domain Name
Top Level Domain (TLD)
Qualified Domain Name
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source: Inge McLaurin
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Domain Name to IP address
All of the machines use names called IP
Addresses to refer to one another.
For example,
 the machine that humans refer to as
www.howstuffworks.com
 has an IP address of 216.27.61.137.
Every time you use a domain name, you use the
Internet's domain name servers (DNS) to translate
the human-readable domain name into the
machine-readable IP address.
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source: Inge McLaurin
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The DNS does a lot of work
Domain name servers translate domain names to
IP addresses. That sounds simple and it would
be except for 5 things:
1. There are billions of IP addresses currently in use, and
most have a human readable name as well.
2. There are many billions of requests made from domain
name servers every day.
3. Domain names and IP addresses change daily.
4. New domain names get created daily.
5. Millions of people do the work to change and add
domain names and IP addresses every day.
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source: Inge McLaurin
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The DNS database
The DNS system is a database
No other database on the planet gets this many
requests.
No other database has millions of people
changing it every day either.
That is what makes the DNS system so unique!
www.senecac.on.ca
A machine
running a
DNS
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DNS systemthroughout the world
Every domain has a domain name server
somewhere that handles its requests, and there is
a person maintaining the records in that DNS.
This is one of the most amazing parts of the DNS
system -- it is completely distributed throughout
the world on millions of machines administered by
millions of people, yet it behaves like a single,
integrated database!
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source: Inge McLaurin
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ISP (Internet Service Provider)
Companies that provide access to the
Internet
the ISP provides your computer with a
different IP address each time you
connect
this way the ISP only needs enough IP
addresses for all the users that are
connected simultaneously.
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ISP’s (Internet Service Providers)
Network Access Providers (NAPS)
Sell Access to:
Internet Service Providers (ISP’s)
Sell Access to:
Large Firms
Small ISP’s
Sell Access to:
Small Firms
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Individuals
40
source: The Internet, Perry & Schneider
Internet Accounts – PPP & SLIP
Definition: Point-to-Point Protocol (PPP)
“a method of connecting a computer to the
Internet that:
1. is more stable than the older SLIP protocol
2. provides error checking features.
3. sends the computer's TCP/IP packets to a
server that puts them onto the Internet
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source: www.webopedia.com
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Internet Accounts – PPP & SLIP
Definition: SLIP (PPP)
“a method of connecting a computer to the
Internet that:
source: www.webopedia.com
1. a protocol used to connect to an ISP using a dial-up
telephone line
2. is older and simpler than PPP
3. is not much different from connecting to the Internet via
PPP from a practical perspective
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Internet Accounts
In general, service providers offer only one
protocol....
Which does yours offer?
What about Seneca dial-up?
Once connected does PPP “give you
more” of the Internet than SLIP?
Additional Reading (Optional)
http://www.ccsi.com/survival-kit/slip-vs-ppp.html
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Internet Services
1.
2.
3.
4.
5.
World Wide Web (WWW)
Email
Newsgroups (Usenet)
Internet Relay Chats (IRC)
File Transfer
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Internet Services
1.
2.
3.
4.
5.
World Wide Web (WWW)
Email
Newsgroups
Internet Relay Chats (IRC)
File Transfer
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1. The World Wide Web
Isn’t the definition of
“The World Wide Web”
Definition:
Wait a minute!!!!!
the same as the definition
of the Internet?
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The Web
 The Internet
• The Web is just one of the ways that
information can be sent over the Internet.
 The Web uses the HTTP protocol, only
one of the languages spoken over the
Internet, to transmit data.
The Internet, not the Web, is also used for email, which relies on SMTP, Usenet news
groups, instant messaging and FTP.
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source: www.webopedia.com
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Internet Services
1. The World Wide Web
Definition:
“A system of Internet servers that support
documents formatted in a script called HTML
(HyperText Markup Language). These
documents support links to other documents,
as well as graphics, audio, and video files.”


Not all Internet servers are part of the World Wide Web
HTTP (Hypertext Transfer protocol) defines how
messages are formatted and transmitted and what actions
Web servers and browsers take
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source: www.webopedia.com
Web Pages
Definition: a web page is a file written in
HTML (Hyper Text Mark-Up Language)
• HTML is the computer language used to
specify the contents and format of documents in
the WWW
• to access a web page you need the URL
(Uniform Resource Locator) which specifies its
location
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Internet Services
1.
2.
3.
4.
5.
World Wide Web (WWW)
Email
Newsgroups
Internet Relay Chats (IRC)
File Transfer
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Internet Services
2. Email
Definition: the transmission of text
messages over communications
networks
Interesting Note – According to “How Stuff Works”...
• The first e-mail message was sent in 1971 by an
engineer named Ray Tomlinson.
• before this, you could only send messages to users on a
single machine.
• Tomlinson's breakthrough was the ability to send
messages to other machines on the Internet, using the
@ sign to designate the receiving machine.
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Internet Services
2. Mail Clients
You use an “e-mail client” to look at the email you receive.
ex. Outlook Express, Eudora (or in a web page like
Hotmail)
Email clients do 4 things
1. shows you message headers
2. lets you select and read messages
3. lets you create and send messages
4. lets you add attachments, save attachments
you receive
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Internet Services
2. Mail servers
Remember....
machines on the Internet can run software
applications that act as servers.
Well.....
these applications listen to specific “ports”
waiting for people or programs to attach to the
port
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Internet Services:
2. Mail servers
Definition: port
“ an endpoint to a logical connection.”
The port number identifies what type of
port it is. For example, port 80 is used for
HTTP traffic”
This is NOT the same as the “physical” ports in
Hardware 101....Sorry!
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Mail Protocols
Messages are retrieved by an e-mail
client using either POP or IMAP.
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Mail Protocol - POP
Definition: Post Office Protocol
a protocol used to retrieve e-mail
from a mail server.
“POP3” is the newest version of POP
 unlike the older version it can be used with
or without SMTP.

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source: www.webopedia.com
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Mail Protocol - IMAP
Definition: Internet Message Access Protocol
a protocol used to retrieve e-mail from
a mail server.
IMAP4 is the latest version
 It is similar to POP3 but has some more features
 With IMAP4, you can search through your e-mail
messages while they are still on mail server. You can
then only download the ones you want to your machine.

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source: www.webopedia.com
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Mail Protocols
Remember...
Messages are retrieved by an e-mail client
using either POP or IMAP.
Well,
There is another protocol for sending mail
between servers, and from a client to a server....
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Mail Protocol - SMTP
Definition: Simple Mail Transfer
Protocol : a protocol for sending email messages between servers.
Most e-mail systems that send mail over the
Internet use SMTP to send messages from
one server to another
 SMTP is also used to send messages from a
mail client to a mail server.

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Outgoing mail is handled
by SMTP, the POP3
server allows user to get
their mail
Mail Protocol - SMTP
To: [email protected]
DNS – where is mindspring?
You are here
If the domain for the email
you are sending is
“Mindspring” host SMTP
hands it to to the POP3
server and it is placed in
that users’ mailbox using a
program called the delivery
agent
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Remember
•Outgoing mail is handled by the SMTP server
• the POP3 (or IMAP) server allows users to
get their mail
This is why...
You need to specify BOTH the POP or IMAP
server and the SMTP server when you
configure your e-mail application!
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Internet Services
1.
2.
3.
4.
5.
World Wide Web (WWW)
Email
Newsgroups (Usenet)
Internet Relay Chats (IRC)
File Transfer
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Internet Services - Newsgroups
Usenet News Service or “Usenet”
was founded in 1979 at Duke University
its purpose was to collect and store
information about computing by topic
topic categories are called “newsgroups” or
“forums” or recently “Internet Discussion
groups”
each site that participates in Usenet
chooses which newsgroups it will carry
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Usenet - “distributed database”
• The database is stored in multiple physical
locations – no one location has a complete copy
• It is probably the largest one in the world
• There are over 50,000 newsgroups
• Newsgroups store (or “post”) messages (or
“articles”) on an electronic bulletin board for
users to read
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source: The Internet, Perry & Schneider 64
Usenet
 Mailing List
Copies of messages
are
not
forwarded
to subscribers!
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Newsgroups Hierarchies
The original Usenet News Service had 8
top-level categories:
comp
computers
rec
recreation
sci
science
soc
social issues
news
operation of Usenet
talk
conversations
miscmiscellaneous
alt
controversial topics
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source: The Internet, Perry & Schneider 66
Usenet – News clients
Microsoft’s
Outlook Express
contains a news
client or
“newsreader”
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source: The Internet, Perry & Schneider67
Usenet – News servers
News servers store all the articles for a
newsgroup
News servers compare their articles with
other new servers and copy the ones they
are missing in a “store-and-forward”
process called a “newsfeed”
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source: The Internet, Perry & Schneider
News protocol - NNTP
Definition: Network News Transfer Protocol
the protocol used to post, distribute and
retrieve USEnet messages.
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Your Turn! (i.e. homework)
1.Subscribe to a newsgroup. Ask for help in
the lab if you need it!
Be prepared to explain how you did it and
what the topic you chose was.
2. Look at www.Deja.com
2. What is a “flame”?
3. What is the difference between a
“moderated” and an “unmoderated”
newsgroup.
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Internet Services
1.
2.
3.
4.
5.
World Wide Web (WWW)
Email
Newsgroups
Internet Relay Chats (IRC)
File Transfer
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IRC Chat
Definition: Internet Relay Chat
a program that allows text-based real-time
communication between computers
connected to the Internet

Developed by Jarkko Oikarinen in Finland in the late 1980s.

IRC uses a series of dedicated servers and client programs

Other chat programs (like ICQ) use the Internet for chat
communication but do not connect to IRC servers
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IRC Client
A program that runs on your computer
to allow you to send and receive
messages to and from an IRC server.
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IRC Server
The IRC server is responsible for making
sure that all messages are broadcast to
everyone participating in a discussion
• Each discussion is assigned a unique channel
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Internet Services
1.
2.
3.
4.
5.
World Wide Web (WWW)
Email
Newsgroups
Internet Relay Chats (IRC)
File Transfer
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File Transfer
When any kind of file is transferred over
the Internet (spreadsheets, pictures,
movies,sounds, programs)
.... FTP is responsible!
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File Transfer Protocol
Definition: the part of the TCP/IP protocol
set that includes rules for formatting,
ordering and error-checking files sent
across a network
FTP is used to upload files from a
workstation to a FTP server or download
files from a FTP server to a workstation.
It is the way that files get transferred from
one device to another in order for the files
to be available on the Internet
FTP is operating system neutral
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1. FTP – File Transfer Protocol
“ Isn’t that the same as
HTTP – it “transfers” web
pages
over the Internet?
Definition:
Wait
a minute!!!!!
Right?
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FTP
 HTTP
FTP
transfers entire files from one device to
another and copied them into memory
is a two-way system as files are transferred
back and forth between server and
workstation
HTTP
only transfers the contents of a web page into
a browser for viewing
is a one-way system as files are transported
only from the server onto the workstation's
browser.
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FTP Clients
FTP can run from a command-line
interface or an FTP client program
We will use the command-line interface
in Lab 2 this week
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It’s Your Choice!
GUI = Graphical User Interface
CUI = Character User Interface
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FTP Client
resides on your
workstation
WS_FTP LE from
Ipswitch.Inc is a
popular Windows
FTP client
program
there are MANY
others....
(Optional: Look at http://cws.internet.com/ftp-3dftp.html)
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FTP Server
The program that receives files transfer
requests from an FTP client then acts
on those commands.
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Using FTP – Step 1
First connect to the remote computer:
directly

telnet
from your Web Browser

type ftp:// instead of http:// and the site’s URL
from your FTP Client (ex WS_FTP LE)
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Using FTP – Step 2
Then
To login to publicly accessible remote
computers:
user name: anonymous.
password: your email address
“Full-Privilege FTP” is when you have your own
account – you have read and write access to that
space.
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Your Turn! (i.e. homework)
1. FTP a file from your home PC to your
matrix account:
• using telnet
• using WS_FTP or another Windows GUI
FTP client program
(available at http://www.ftpplanet.com/download.htm)
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Internet Services
1.
2.
3.
4.
5.

World Wide Web (WWW)
Email
Newsgroups
Internet Relay Chats (IRC)
File Transfer



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
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Internet Services
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Introduction to UNIX
After Lab1, you should know how to:
log in
change your password
create a file
list the files in your working directory
create a directory
display the name of your working directory
change directories
log out
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Intro to UNIX
The commands you have learned are:
passwd
touch
ls
mkdir
pwd
cd
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