Ch. 3 FIT5, CIS 110 13F

Chapter 3The Basics of Networking

Friday, October 18, 13

Copyright © 2013 Pearson Education, Inc. Publishing as Pearson Addison-Wesley

General Communication

• Synchronous communication: – (eg) wired telephone network

=> circuit-switched network

• Asynchronous communication:– (eg) email; the internet

=> packet-switched network



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)



Internet Schematic Diagram



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



Basic Client/Server Interaction



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)



Client/Server Relationships



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”



IP Addresses



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)



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



Domain Names

– symbolic names (human-readable)vs. IP addresses

– based on hierarchy of domains

– domain: related group of networked computers

– (eg) pages.uoregon.edu



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



The .edu Domain



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


http://bit.ly/ab4s50

http://bit.ly/ab4s50


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


http://www.root-servers.org

http://www.root-servers.org


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



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


http://www.pbs.org/opb/nerds2.0.1/geek_glossary/packet_switching_flash.html

http://www.pbs.org/opb/nerds2.0.1/geek_glossary/packet_switching_flash.html

http://www.cs.uoregon.edu/Classes/13F/cis110/code/PDFs/OSI-p3.pdf

http://www.cs.uoregon.edu/Classes/13F/cis110/code/PDFs/OSI-p3.pdf


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



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 numberTCP: re-arranges, requests retransmission

– network can optimize packet paths, but..– prone to chaos


http://homework.uoregon.edu/pub/class/155/router.html

http://homework.uoregon.edu/pub/class/155/router.html


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



Ethernet AnalogyParty Protocol

• How an Ethernet network works:– two people start speaking at same time

=> collision

• Collision Resolution policy– wait random amt of time– try again



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


Slide 3-

Figure 3.9. Media LayerRobert Metalfe’s original drawing of the Ethernet-- computers “tap” onto the wire labeled “The Ether”



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 WebA: What is, an Internet Application?



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


Copyright © 2013 Pearson Education, Inc. Publishing as Pearson Addison-WesleyFriday, October 18, 13


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



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



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 inbrowser


http://grooveshark.com/s/Sweet+Child+O+Mine/4KnKby?src=5

http://grooveshark.com/s/Sweet+Child+O+Mine/4KnKby?src=5


Organize your Folders

• Why have a hierarchy?

– organize your thinking & work– directories/folders cost nothing– work on the server and your computer

=> highly recommended



Ch. 3: AssessmentLearning Outcomes - Know the following
