Transcript Ch 5 Network Communication

Introduction to Management Information Systems
Chapter 5 Data Communications
and Internet Technology
HTM 304
Fall 07
Today – The Internet & Enterprise Network
Internet (Public)
Enterprise Network (Private)
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The Internet
Note: Capitalized “I”, the only one, public access
Also called “the Net”
“internet” = inter-connected networks (LANs or WANs) 
there are many.
The Internet: A global WAN that connects approximately
1 million inter organizational computer networks in more
than 200 countries on all continents
Origin: ARPANET – (DoD, 1969)
Original purpose  exchange messages, transfer files
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Connecting the Internet
ISP: Internet Service Provider
Name several well-known ISPs
How to find a local ISP: http://www.thelist.com
Internet Backbone
Providing connectivity in many cities
Has many network access points (NAPs)
Local ISPs rent NAPs to access
the backbone
Who owns the backbone?
ARPAnet (DoD, 1969 – 1986)
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NSFnet – educational (1986- now)
Domain Name Systems (DNS)
To publish on the Internet:  Apply for a public domain name
Organization: ICANN (Internet Corporation for Assigned Names
and Numbers, www.icann.org ), 13 root servers maintain lists of
IP addresses of Internet servers
Purpose of Domain Name:
To get user-friendly names rather than IP addresses.
Components of a Domain Name:
www.sina.com.cn
From the rightmost: Regional code  top-level domains (types of
institutes)  name of the institute  www (or www2, the main
server), or a specific computer in the domain
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The Naming System
Regional Code:
E.g. “cn”, “fr”, “de”, “it”, “uk”, “au”, “jp”, …etc.
What is the regional code for the United States?
Top-Level Domains (type of the site)
com / edu / gov / net, etc.
See page 143 for a complete list (note: in some country, .com is short as
“.co”, e.g www.amazon.co.uk)
Name of the institute (e.g. csusm.edu, microsoft.com)
The leftmost:
www: world wide web – generally go to the predefined main server of the
institute
A particular machine or subnet:
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E.g. fangfang.csusm.edu, sandiego.craigslist.org
Exercise:
Based on the following domain name, describe
the type of the institute.
sandiego.craigslist.org
www.ebay.com.au
www.tsinghua.edu.cn
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Public IP address
Any computer with direct Internet Access needs a public
IP address.
IPv4 and IPv6
Some small business/home LANs only obtains one IP
addresses for the router or server
Router has two IP addresses (one public, one private)
The other computers obtain private IP addresses from routers
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Issues with Domain Name System
Use Fake Domain Names to acquire users’ private
information
Using similar names to gain visits
E.g. www.craiglist.com, www.wikipeda.org, www.goggle.com, etc.
Cybersquatting: register domain names in hoping
companies would want it later: gauge for money.
Anti-cybersquatting Consumer Protection Act. Nov 1999.
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The future of the Internet
The current Internet is UNSATISFACTORY
Too slow for data intensive applications
Unreliable, insecure
Article: the internet is broken – call for a complete redesign
Three initiatives underway
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Internet 2
Develops and deploys advanced network applications such as remote
medical diagnosis, digital libraries, distance education, online simulation
and virtual libraries. (http://www.Internet2.edu)
Next Generation Internet (NGI)
Government sponsored initiative aimed at creating an Internet that is
fast, always on, everywhere, natural, intelligent, easy and trusted.
(http://www.ngi.gov )
vBNS
high-speed network designed to support the academic Internet2 and the
NGI. Goal: 2.4 gigabits per second.
Enterprise Networks
Major Components of Enterprise Networks
LANs – a small size network in a single location (e.g. a building).
Small company, home business, a department in a big organization
(e.g. embedded LAN for large enterprise)
WANs – connects computers (or LANs) located at physically
separated sites. (see Figure 5-12 on page 126)
Generally provided by common carriers (e.g. Verizon, AT&T, etc.)
Backbone Networks: high-speed
central networks which connects
multiple smaller networks
(e.g. LANs or small WANs)
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Types of WANs
Connecting the PC to an ISP via Modems
Home computers, small businesses use
Telephone dial up, DSL line, cable TV line
Networks of Leased Lines (Mostly PSTN)
Lease from telephone companies (a variety of lines, speed ranges
from 1.544Mbps to 40Gbps)
Connecting different sites of the company
Expensive, hard to manage,
sometimes, managed by specialized 3rd parties
Public Switched Data Network (PSDN)
PSDN – a network of computers and leased lines that is developed
and maintained by a vendor
Lease a line from the vendor that connects to PSDN
Virtual Private Network (VPN)
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Uses the public Internet (private internets sometimes) to create virtual
connections
Creating VPN
Tunneling Protocol:
Tunneling: encrypts the data packet to be sent, and places it
inside another packet, which provides confidentiality,
authentication and integrity of the message.
Ensure Security: software encryption.
Offer the benefits of leased lines, but more flexible.
The connections is established upon user request, disconnect at will
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Good for employees on the go, small sites which is too expensive
to lease fixed lines, or business partners with limited data
transfer, etc.
Microsoft windows supports VPN
Criteria for comparing network alternatives
Cost
Initial setup costs, operational costs, and
maintenance costs
Performance
Speed, latency, availability, loss rate,
transparency, performance guarantees
Other
Growth potential, commitment periods,
management time, financial risk, technical risk
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Extensions of Enterprise Network
Intranet vs Extranet
Intranet: a network designed to
serve the internal information
needs to a single organization
Extranet: connects part of the
intranets of different
organizations and allows for
secure communications among
business partners over the
Internet using virtual private
networks (VPNs)
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Extranet
Business partners access modules
such as SCM, CRM, and B2B
Subnet and Subnet Mask
a subnetwork or subnet is a range
of logical addresses (e.g. IP
addresses) that is assigned to an
organization.
Subnet mask is a 32-bit sequence
which is used in conjunction with IP
address to determine whether the
computer is in the subnet.
How? A bitwise “and” operation:
IP address:
143.37.100.27  10001111.00100101.01100100.00011011
Subnet mask: 255.255.255.0  11111111.11111111.11111111.00000000
Bitwise “AND” operation
 10001111.00100101.01100100.00000000
143.
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37.
100.
How many IP addresses can give the same result?
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Some Other Subnet Masks
11111111.11111111.11111111.00000000 (255.255.255.0)
~ supports 256 IP addresses
11111111.11111111.11111110.00000000 (255.255.254.0)
~ supports how many IP addresses?
11111111.11111111.11111111.10000000 (255.255.255.128)
~ supports how many IP addresses?
255.255.255.254 ~ supports how many IP addresses?
If a company has 120 computers, how should the network
administrator configure the subnet mask?
Step1: round up to 2n, (e.g. ~27=128)
Step 2: set all the n digits to be 0 from right to left, and the rest digits as
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e.g. 11111111.11111111.11111111.10000000
Convert to decimal representation of the network address: 255.255.255.128
Exercises
A) what should be the subnet mask if the company has
1000 computers?
B) Are computer A and B in the same subnet?
Computer A: 143.37.100.27
Computer B: 143.37.101.36
Subnet Mask: 255.255.252.0
C) Markstein Hall has both computer labs and offices. The network
administrator needs to separate the computers in the labs and offices
into two separate subnets. The plan is,
Lab computers occupy IP addresses 144.37.2.0~127
Office computers occupy IP addresses 144.37.2.128~255
How should the subnet mask be configured?
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Assignment: the Internet is Broken
Read the article and write your thoughts on this issue on
the blog site.
Answer the following questions and email the answer to
[email protected] by Oct 11 before class starts
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1.
What is the basic flaw of the current Internet design according to
David Clark?
2.
Why nowadays, the basic design flaw has become a much
bigger issue compared to the past?
3.
Explain the saying that “humans are good at ignoring problems”
use your own words.
4.
July 2005, Pew Internet reported ______% of U.S. Internet users
have reported having spyware or adware on their computers
merely by visiting websites.