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Introduction and Overview of Network and Telecommunications

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1 Introduction and Overview of Network and Telecommunications

2 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? What is this course about?

3 A Simple Example http://ist.psu.edu/
Can you sketch a diagram to illustrate through what a path your phone gets information? IST Server

4 Cellular Tower Internet Gateway (Phone Company) Server Maps Server Wireless Router Cable Modem Internet Internet Gateway (Map Service Company) Map Data Internet Gateway (Cable Company)

5 Video: Warriors of the Net

6 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.

7 Why using “protocol layers”?

8 Networks are Extremely Complex
Network consists of many “pieces” Hosts Routers Links of various media Applications Hardware, software The network does much for apps 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 We need a form of modularity, to help manage complexity and support reuse

9 Organization of air travel
ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing ticket (complain) baggage (claim) gates (unload) runway landing airplane routing Ticket Baggage Gate Takeoff/Landing Advantage of layering: information hiding and reuse 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

10 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

11 Internet protocol stack
Set of protocols in use in called a protocol stack e.g., web server e.g., web browser e.g., HTTP

12 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, (WiFi), PPP Physical: bits “on the wire”

13 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

14 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

15 <HTML><BODY>Hello World!</BODY></HTML>
HTTP message TCP HTTP message IP TCP HTTP message TCP HTTP message IP 802.11 Wire 802.11 IP TCP HTTP message IP TCP HTTP message TCP HTTP message HTTP message <HTML><BODY>HTML Example</BODY></HTML>

16 Another Illustration Think of these nesting dolls:


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