1. Introduction and Overview of Network and Telecommunications

2. Reading for next class Ch 3.1 – 3.12: Internet Communication Models

3. 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?

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

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

6. Video: Warriors of the Net https://www.youtube.com/watch?v=PBWhzz_ Gn10 https://www.youtube.com/watch?v=PBWhzz_ Gn10

7. 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.

8. Why using “protocol layers”?

9. 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

10. 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 Airplane routing Layers: each layer implements a service by Perform certain actions within the layer Using the services of the layer directly below it

11. 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

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

13. 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 ”

14. 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

15. 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

16. Hello World! TCPHTTP message TCPHTTP messageIP TCPHTTP messageIP802.11 TCPHTTP messageIP802.11 TCPHTTP messageIP TCPHTTP message Wire HTML Example HTTP message

17. Another Illustration Think of these nesting dolls: