Welcome to IST 210: Organization of Data

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Transcript Welcome to IST 210: Organization of Data 

Introduction and Overview of Network
and Telecommunications
When you type in a URL on your
mobile phone to visit a web page,
what really happens on the
Internet? Can you sketch a
diagram to illustrate through what
a path your phone gets
information?
A Simple Example
• http://ist.psu.edu/
Can you sketch a diagram to
illustrate through what a path
your phone gets information?
IST Server
Cellular Tower
Internet Gateway
(Phone Company)
Server
Maps Server
Wireless
Router
Cable Modem
Internet
Internet Gateway
Internet Gateway
(Cable Company)
(Map Service Company)
Map Data
Video: Warriors of the Net
• https://www.youtube.com/watch?v=PBWhzz_
Gn10
Some Key Points
• Data is transmitted as packets.
• Packets are handled by equipments at different
layers.
• Each layer has its own protocol to follow.
• At each layer, information, or header, is added
(or removed) based on the protocol before
sending the packet to the lower (or higher) layer.
Why using “protocol layers”?
Networks are Extremely Complex
• Network consists of many “pieces”
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Hosts
Routers
Links of various We
medianeed a form of
Applications modularity, to help
Hardware, software
manage complexity
…
• The network doesand
much
for apps reuse
support
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Make and break connections
Find a path through the network
Transfers information reliably
Send as fast as the network allows
Shares bandwidth among users
Secures information in transit
…
Organization of air travel
ticket (purchase)
ticket (complain)
Ticket
baggage (check)
baggage (claim)
Baggage
gates (load)
gates (unload)
Gate
runway takeoff
runway landing
Takeoff/Landing
airplane routing
airplane routing
Airplane routing
airplane routing
Layers: each layer implements a service by
• Perform certain actions within the layer
• Using the services of the layer directly below it
Protocols and Layers
• Protocols and layering is the main structure
method used to divide up network
functionality
– Each instance of a protocol talks virtually to its
peer using the protocol
– Each instance of a protocol uses only the services
of the lower layer
Internet protocol stack
• Set of protocols in use in called a protocol stack
e.g., web browser
e.g., HTTP
e.g., web server
Internet protocol stack
•
Application: supporting network
applications
– FTP, SMTP, HTTP
•
Transport: process-process data
transfer
– TCP, UDP
•
Internet: routing of datagrams
from source to destination
– IP
•
Link: data transfer between
neighboring network elements
– Ethernet, 802.111 (WiFi), PPP
•
Physical: bits “on the wire”
Internet protocol stack
• An example protocol stack
– Used by a web browser on a
mobile phone that is wirelessly
connected to the Internet
Browser
HTTP
TCP
IP
802.11
Encapsulation
• Encapsulation is the mechanism used to effect
protocol layering
– Lower layer wraps higher layer content, adding its
own information (header) to make a new message
for delivery
– Like sending a letter in an envelope; postal service
doesn’t look inside
<HTML><BODY>Hello World!</BODY></HTML>
HTTP message
802.11
TCP
HTTP message
IP
TCP
HTTP message
IP
TCP
HTTP message
Wire
802.11
IP
TCP
HTTP message
IP
TCP
HTTP message
TCP
HTTP message
HTTP message
<HTML><BODY>HTML Example</BODY></HTML>
Another Illustration
• Think of these nesting dolls: