Ch. 5 slides from Fluency w/Info. Tech. 5ed (Pearson)

1. Chapter 3
The Basics of Networking
Friday, October 18, 13

2. General Communication
• Synchronous communication:
– (eg) wired telephone network
=> circuit-switched network
• Asynchronous communication:
– (eg) email; the internet
=> packet-switched network
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Friday, October 18, 13

3. Internet’s Communication Properties
• point-to-point, asynchronous
communication
• fast enough to mimic synchronous
communication (e.g., VOIP)
• Multicasting is possible (chat rooms, radio,
tv)
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4. Internet Schematic Diagram
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5. Client/Server Structure
• Most Internet applications are client/server
interaction
– click a hyperlink: your computer connects to server
– page returned => connection ends
– Next connection is brand new => Stateless protocol
No memory of prior connection
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6. Basic Client/Server Interaction
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7. Many Brief Relationships
• server can handle many clients at a time
• server is busy only for as long as it takes to
perform your request
• Google:
5,134,000,000 searches/day (2012)
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8. Client/Server Relationships
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9. Internet Protocol (IP) Address
• Each computer on the Internet has a
unique IP address
– four numbers separated by dots:
128.223.223.85 => “dotted quad”
– each number is 0–255 (one byte / 8bits each)
=> “octet”
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10. IP Addresses
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11. IPv4 Address Exhaustion
– each of the four numbers is
• in the range 0–255
• requires one byte (8 bits) of memory
=> “octet”
– IP address is 4x8= 32 bits long
=> IP addresses in short supply. Why?
2^32 = 4.3 billion, a finite number
(ask Google the exact value)
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Friday, October 18, 13

12. IPv6: 128 bit addresses
– IPv6 addresses will have 16, 8-bit, fields
2^128 = 10^38
– 10^28 times as many addresses as IPv4
– new switching hardware/software is required to
handle IPv6
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Friday, October 18, 13

13. Domain Names
– symbolic names (human-readable)
vs. IP addresses
– based on hierarchy of domains
– domain: related group of networked
computers
– (eg) pages.uoregon.edu
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Friday, October 18, 13

14. Domain Names
• Domain name hiearchy reads right-to-left
ix.cs.uoregon.edu
– top-level domain: edu
– subdomain uoregon
– next subdomain cs
– server is ix
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15. The .edu Domain
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16. DNS Servers
• Domain Name System (DNS):
translates domain names into IP address
• Every Internet host knows the IP address of its
nearest DNS name server
• How the DNS Works (youtube, 00:02:25)
http://bit.ly/ab4s50
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17. DNS Servers
• your computer asks a DNS name server to
translate a name to an IP address
• If the address is not stored on the DNS name
server), the server asks an authoritative name
server
• 13 root name servers keep the complete list of all
authoritative name servers
Tagged A..M here: www.root-servers.org
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18. DNS Root Servers
• 13 root name servers (A..M) scattered around the
world
• Plus 243 mirror sites
=> DNS is the world’s largest distributed
database
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Friday, October 18, 13

19. TCP/IP
• TCP/IP Postcard Analogy
– The Internet is like sending a novel to your
publisher using postcards
– Packet Switching Flash Demo
– Packet Layer in OSI Network Model
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20. TCP/IP
• packets routed around failed nodes
– ensures delivery of entire message
– large scale, built-in redundancy
– crucial to reliability
• packet switching => rapid store-&-forward
design
• node receives a packet, stores it
• determines best route to destination
• sends it to next node
Copyright © 2013 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Friday, October 18, 13

21. TCP/IP:
The Language of the Internet
– analogy: “postcards” = IP packets
– travel different routes / arrive out of order
– can be lost
IP: stamps packet w/address & packet number
TCP: re-arranges, requests retransmission
– network can optimize packet paths, but..
– prone to chaos
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Friday, October 18, 13

22. Ethernet
• Ethernet uses a physical channel
– wire, cable, or optical fiber
– media layer / physical layer
• Key point: Each packet seen by all
computers on the local network
=> store-&-forward design
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Friday, October 18, 13

23. Ethernet Analogy
Party Protocol
• How an Ethernet network works:
– two people start speaking at same time
=> collision
• Collision Resolution policy
– wait random amt of time
– try again
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Friday, October 18, 13

24. Ethernet Analogy
• How an Ethernet network works:
– Party Protocol
– two people start speaking at same time
=> collision
• Collision Resolution
– wait random amt of time
– try again
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Friday, October 18, 13

25. Figure 3.9. Media Layer
Robert Metalfe’s original drawing of the Ethernet-computers “tap” onto the wire labeled “The Ether”
Slide 3Friday, October 18, 13

26. The World Wide Web (http)
• client/server protocol
• requests: URL (a.k.a. URI)
• client & server both “speak” HTTP
Jeopardy Category: Application Layer
Q: The World Wide Web
A: What is, an Internet Application?
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Friday, October 18, 13

27. File Systems:
How to Organize your Folders
• Folders on the server are called Directories
• Directory Hierarchy
– folders can contain folders as well as files
=> the file system, or directory hierarchy
• Think of any hierarchy as a tree
– folders are branches
– files are the leaves
– root directory is at the top of the hierachy
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28. Copyright © 2013 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
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29. File System Pathnames
• Files are identified by the path from the
root diretory to the file:
– (eg) /fluency/part1/chapter3/file-structure/
directory-hierarchy/figure-3-13.pdf
• Note: do not use spaces or special
characters in a Unix pathname
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30. Pathnames & URIs
• Part of a web page file’s pathname is used
in the URI:
URL: pages.uoregon.edu/susanq/110/
Unix pathname on server:
/home7/susanq/public_html/110/
URL: pages.uoregon.edu/susanq/110/p2/index.html
Unix pathname on server:
/home7/susanq/public_html/110/p2/index.html
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Friday, October 18, 13

31. Web Directories:
The Default Document
• When a URL ends in a slash:
=> browser automatically looks in that
folder for a file called index.html or
default.html
=> default document
=> supresses directory listing in
browser
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Friday, October 18, 13

32. Organize your Folders
• Why have a hierarchy?
– organize your thinking & work
– directories/folders cost nothing
– work on the server and your computer
=> highly recommended
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Friday, October 18, 13

33. Ch. 3: Assessment
Learning Outcomes - Know the following
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