More on WANs

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 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 802.11 • g@54 Mbps, n@150 Mbps, ac@867 Mbps • Uses access point/router • Physically connected to an ISP’s modem • Capable of broadcastingandreceiving 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 http://cs.millersville.edu/~zoppetti/101/index.html • The URL has three main parts: • Protocoltells the computers how to handle the file • Server computer’s nameor the name given by the domain hierarchy • Page’s pathnametells 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 • 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: • Downin the hierarchy means into subfolders (towards the leaves) • Upin 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.