Transcript Internet

The Internet
• What is the ‘Net’
• Is this all just a craze?
• How does it work?
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The Internet
• Looking at ….
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What is the ‘Net’?
Protocols
IP and TCP
Domain Name Service and Domain Names
FTP
Email
Video-conferencing
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The Internet
• What is the Internet ?
• “The Internet is a world-wide system of
computer networks, a network of networks
in which users at any one computer can, if
they have permission, get information from
any other computer”
– http://www.whatis.com
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The Internet
• The Internet is a network of networks
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The Internet
• Comprised of nodes which communicate with each
other using a specific protocol
Node A
Internet
Node B
• protocol used to handle communication through Internet5
Computer Protocol
• HTTP, FTP, Telnet, IP, etc.. are all protocols
• What is a protocol?
– An agreed set of rules
– a standard procedure for regulating data
transmission between nodes (computers)
• why are protocols important?
– Internet comprised of networks of networks
– each network contains different types of
nodes/hosts (Windows, Unix, …)
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Computer Protocol
• Networks may be different and thus
communicate differently
– need a standard !!!!!
• Protocols set standard message types to
enable communication (in various forms)
between computers
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IP (Internet Protocol)
• IP provides every node connected to the
Internet with a unique address
– e.g. 167.252.135.277
• IP is a standard protocol enabling message
passing between nodes
• All nodes connected to Internet agree on
using IP as a standard protocol to enable
communication
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IP Addressing
• All nodes have a unique address
• Each address is represented by 32 bits
– e.g. 10010011111111001000010000101011
– broken into four bytes separated by a decimal
point
– e.g. 10010011. 11111100.10000100.00101011
– and converted to decimal
– e.g. 147.252.132.43
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IP Message Format
• There exists a specific format for messages that
nodes send to each other
• Application data is appended onto the message
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TCP (Transmission
Communication Protocol)
• It ensures that IP messages are delivered
reliably
– IP is not a reliable network protocol
– TCP adds reliability
• IP and TCP exist at two separate levels, or
layers in the protocol stack
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TCP (Transmission
Communication Protocol)
• The final message (or packet) is forwarded
from node to node over the internet which
may exist on different networks
• Nodes look at the destination address of the
packet and forward it
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DNS (Domain Name Service)
• We have seen all nodes connected to the
Internet have a unique IP Address
• How does one node connect to another if it
doesn’t know the IP Address?
• DNS resolves this issue
• Using DNS, every IP Address can be
resolved to a name (Hostname as it is
referred)
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DNS (Domain Name Service)
• IP does not understand what Hostnames are
so DNS acts as a form of ‘translator’
• DNS translates between IP Addresses and
Hostnames
• We must first look at what Domain Names
are
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Domain Names
• Any entity connected to the Internet is located
using a Domain Name
– e.g. www.dit.ie
• www.dit.ie
– represents the Internet address
• The .ie part is the top-level of the domain and
represents an entity located in Ireland
– others include .de, .jp., .com., .edu
• The ‘dit’ part of the address (including the top level) is
the second level domain and represents the
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organisation
Domain Names
• There may be other domain levels in an Address.
– E.g. www.comp.kst.dit.ie
• The Left-most level is the server on which the
resource resides (in this case is ‘www’)
Server
Top Level Domain
www.dit.ie
Second Level Domain
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DNS (Domain Name Service)
• DNS is used to resolve hostnames (www.dit.ie)
and IP Addresses
• It is based on a Tree-like, hierarchical structure
• The root domain is “.” It resides at the top of the
tree and various subdomains branch out
• These subdomains include .com, .ie, .org, ..etc.
• The tree continues to branch with each subdomain
in turn containing various subdomains
– e.g. www.kst.dit.ie
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DNS Tree example
. (root domain)
.ie
dit.ie
kst.dit.ie
.org
tcd.ie
ang.dit.ie
.com
google.com
.edu
stanford.edu
berkeley.edu
cs.stanford.edu
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DNS (Name Servers)
• Each domain (and sub-domain) has its own name
server, a server which contains the host name
information about the hosts and sub-domains within its
domain.
– The dit.ie domain, for example, has a name server that stores
address information about all of the hosts and subdomains in
the dit.ie domain.
– However, authority for a subdomain, such as kst.dit.ie, can be
passed to a name server that has authority for that subdomain.
– When a name resolution request comes to the dit.ie name
server, it just passes the request off to the kst.dit.ie name server.
– In this way, DNS maintains only the information that is
pertinent to that domain
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DNS (Name Resolution)
• Requests are made to the name servers in order to
resolve names
• e.g. to find the IP address for home.kst.dit.ie the
following steps take place
– A DNS server would ask the root server for the address of the
name server for the .ie domain
– The DNS server then can contact the .ie name server and asks
this server for the number of the name server for the dit.ie
domain
– In turn, the DNS server then contacts the dit.ie name server and
asks for the address of the name server for kst.dit.ie domain
– Finally a request is made to the kst.dit.ie domain for the address
of the server named ‘home’. This IP address is returned and can
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be used for communication between nodes
FTP (File Transfer Protocol)
• Used to transfer files over the Internet
between computers
• Downloading using FTP
– file transfer from remote server to local
computer (localhost)
• Uploading using FTP
– file transfer from local computer to remote
server
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FTP (File Transfer Protocol)
• FTP used to transfer files, applications, etc..
• Using FTP
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ftp://
e.g. ftp://www.comp.dit.ie/~mcollins/report.pdf
may require authentication (name & password)
open directly or save to hard drive
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E-mail
• E-mail (Electronic mail)
– Revolutionised old ‘snail mail’!!
• Delivers formatted messages over the
Internet
• E-mail address are unique (no two people
have the same address)
– username@domainname
• A computer in the domain is used as a Mail
server.
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E-mail
• Mail server
– Gathers incoming email, looks at recipient
address and forwards to recipient
– Collects outgoing e-mail and sends onto
Internet
– Incoming e-mail with bad/incorrect addresses
are returned to sender, usually with an error
message
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Video-Conferencing
• aka ‘NetMeeting’
• used mainly in business and work
environments
• facilitates visual, audio and text
communication together over the Internet
• usually requires large bandwidth and
dedicated channel (e.g. ISDN, ADSL, Fiber
Optic connection).
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Video-Conferencing
• Uses include
– File Transfer
– Whiteboard
• (smartboard) for sharing diagrams and enabling
remote editing)
– Talk
• real-time chat with full audio, video and text
exchange)
– Program sharing
• Many VC software packages on market
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Summary
• We have looked at:
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Makeup of Internet
Protocol
IP
TCP
DNS and Domain Names
FTP
E-mail
Video-Conferencing
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