2. More on WANs Fiber Optic Cables Used in Internet backbone
Speeds over 100 Gbps
Team at the University of Southampton achieved a throughput of ~70 Tbps, with the signal traveling at 99.7% the speed of light (New Scientist)

3. Network Tools Available on site like http://ping.eu/ Tools
ping (try millersville.edu)
DNS lookup
Visit site using IP address
Reverse lookup
traceroute
whois (authoritative name servers)

4. Ethernet Uses a wire or fiber, called the channel
Engineers “tap” into the channel to connect a computer
Can then send/recv signals
All computers, including the sender, can detect the signal

6. Ethernet Network Protocol
Rough analogy: conversation at a cocktail party
One person talks, everyone listens
When talker stops, it is briefly quiet, and someone else starts
If two persons start talking, they hear the conflict and pause briefly, until one begins talking again
Decentralized scheme (no plan or schedule control)
Each computer listens to the channel, and if it's quiet, it's free.
A computer starts to transmit; if another starts at the same time, they hear garbled message; both stop for a random time and then try again.
Shortest random wait gets the channel

7. Ethernet vs. Internet Internet Ethernet
Uses point-to-point network to implement point-to-point communications
Allows multiple communications taking place concurrently along its different paths
Ethernet
Uses broadcast network to implement point-to-point communications
Allows only one communication at a time

8. Connecting to the Internet
Two basic methods
Connect via an Internet service provider (ISP)
Connect through a campus or enterprise network

9. 1. Connections by ISP Most home users use ISPs
Modems convert digital output to carrier format

11. 1. Connections by ISP Signals are sent to carrier
Carrier modem receives signals, sends to server
Server connects to the Internet via a gateway
Smart phones also have modems

12. 2. Enterprise Network Connections
Connect via organization’s network
Organization connects to the Internet by a gateway

13. Wireless Networks Variation of a LAN connection
Protocol name is
Mbps, Mbps, Mbps
Uses access point/router
Physically connected to an ISP’s modem
Capable of broadcasting and receiving signals, usually radio frequency (rf ) signals

15. The World Wide Web
Some computers connected to the Internet are Web servers
Supply files to browsers
Web servers and their files comprise the World Wide Web (WWW)

16. The World Wide Web Web pages are files Text Images Video Audio
Programs

17. Requesting a Web Page Web requests use client/server interaction
Browser is client
Web server is server
File specified using URL (Universal Resource Locator)
Web browsers and servers use HTTP protocol

18. Requesting a Web Page The URL has three main parts:
The URL has three main parts:
Protocol tells the computers how to handle the file
Server computer’s name or the name given by the domain hierarchy
Page’s pathname tells the server which file (page) is requested and where to find it

19. Describing a Web Page Servers do not store Web pages as images
Pages are stored in source files as a description of how they should appear on the screen
Browser receives the description and renders image

20. Describing a Web Page
Two advantages to storing and sending the source file
Less space
Browser can adapt image for your machine

22. The Internet and the Web
Some Web servers
Have www as part of their domain name
Add www if you leave it out
Work either way
When is the www required and when is it optional?

23. The Internet and the Web
Web addresses consist of host names
And host names have an IP address
DNS server requires name to match exactly

24. The Internet and the Web
Incorrect name results in
Accessing wrong IP address
google.com vs google.gov
DNS lookup fails (“Server Not Found”)
Web administrators may register similar forms of a URL
yahoo.com

25. File Structure Directory Hierarchy Think of any hierarchy as a tree
Folders can contain folders as well as files
Think of any hierarchy as a tree
folders are the branch points
files are the leaves

26. File Structure Directory Hierarchy
All hierarchies have branch points and leaves
Hierarchy trees are often drawn sideways or upside down
Two terms are standard, however:
Down in the hierarchy means into subfolders (towards the leaves)
Up in the hierarchy means into folders (toward the root)

28. File Structure
Part of the directory hierarchy is shown in the pathnames of URLs: airandspace.si.edu/exhibitions/gal100/pioneer.html
Page is specified by a pathname that specifies file
With each slash (/) we move into a subfolder or to the file

30. Organizing the Folder Last item in pathname is file
Unless URL ends in /, then server looks for “index.html”
Course page example

31. Summary
Point-to-point, multicast, broadcast, synchronous, and asynchronous communications
IP addresses, domains, IP packets, IP protocol, WANS and LANS, Ethernet protocol, ISPs, enterprise networks, and wireless networks

32. Summary
Difference between the Internet and the Web
File hierarchies

33. Quiz How many bytes are in an IPv6 address?
The ______ translates from host names to IP addresses.
TCP/IP is a key ______ used on the Internet.