Ch. 3 FIT5, CIS 110 13F

Chapter 3
The Basics of Networking

Friday, October 18, 13

General Communication
• Synchronous communication:
– (eg) wired telephone network
=> circuit-switched network

• Asynchronous communication:
– (eg) email; the internet
=> packet-switched network
Copyright © 2013 Pearson Education, Inc. Publishing as Pearson Addison-Wesley


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



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


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



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 number
TCP: re-arranges, requests retransmission
– network can optimize packet paths, but..
– prone to chaos



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 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



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


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

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?



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



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 in
browser


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: Assessment
Learning Outcomes - Know the following



Ch. 3 FIT5, CIS 110 13F

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Ch. 3 FIT5, CIS 110 13F