IntroductionChapter 1
Copyright 1998, 1999 PankoRevised May 1999
2Stars
Material that is especially important, or
Material that is especially difficult or easy to confuse with similar material.
Part A:The Networking Revolution
An overview of trends and the importance of networking to your career
4The Networking Revolution
The Traditional Career Ladder
– Programmer
– Systems Analyst
– IS (information systems) Management
– Chief Information Officer (CIO)
5The Networking Revolution
Many Factors, including Networking, are Changing this Career Ladder
– Networking specialties
– User support specialties (combine PC support and networking support groups of)
– Programmers create groups of programs that interact by exchanging messages across networks, not just stand-alone programs on single machines.
6Changes in IT
Transforming the Corporation
– Intranets: using Internet technology and applications internally
Many good, standardized applications Inexpensive, standardized transmission technology Add security
– Extranets: Using Internet technology to reach business partners and customers
– Enterprise networks connect any two computers in the organization, even if they are at different sites
7Changes in IT
Networking
– High demand for networking skills
– Knowledge beyond wires and bits
TCP/IP standards
Higher-layer standards (applications, etc.)
Systems management (server and client PC management)
8IS versus CS and EE
Hiring Organizations
– CS & EE graduates are trained to work in hardware, software, and networking vendor firms, such as Microsoft, IBM, Oracle, and Cisco Systems.
– IS graduates are trained to work in end user organizations, which use IT to enhance business value, such as banks, government agencies, and manufacturing firms--organizations that use IT to get their work done.
9IS versus CS and EE
Make versus Buy
CS and EE Professionals– Make products for sale
IS Professionals– Buy these products instead of making things
– Must select products appropriately
– Must integrate these products together
10Comparing Products
Dimensions for Comparing Products in Purchase Selection
Performance– Whatever is appropriate for specific user needs– In some cases, speed– In other cases, reliability or something else
Feasibility for the firm– Products based on new standards may be too much work
to implement
Cost (can never be ignored)
11Comparing Products
Costs
Total purchase cost for all hardware and software– Typically, “base price” are only a fraction of total cost
Labor costs to plan, install– Often greatly outweigh product purchase costs
Life cycle costs from initial purchase to final abandonment– Often greatly outweigh initial costs
12Comparing Products
Emphasis: Cost is Always Important– User demands are surging– Budgets are not growing rapidly
You must buy the least expensive technology that will meet user requirements
No comparison of alternatives is complete without a cost analysis
13User Needs
Drive everything else
Must communicate with users to understand their needs
Must support important user needs without bankrupting the firm
14Standards
Standards are rules of operation that are followed by most or all vendors.
Standards allow products from different vendors to work together (interoperate)– You are not limited to buying from one firm.
– Competition will drive down costs and increase options
– You do not have to worry if a single vendor falls behind or fails
Part B:Accessing the World Wide Web from Home
Many students access the World Wide Web from home. Here is how it works, in terms of standards.
16Accessing the WWW from Home
A Common and Important Situation– Must be understood
– Good way of introducing concepts
17The Internet
Network
– A collection of computers that are interconnected so that any computer can send messages to any other computer simply by giving the receiver’s network address at the start of the message.
Key Ideas– Any-to-any. Fully interconnected– Interact through the exchange of messages– Network delivers messages based on their destination
addresses, like the address on a postal envelope
18The Internet
A Worldwide Group of Networks– Not a single network
19The Internet
Messages are Broken into Small Packets for Transmission– More efficient than sending long messages
Message Packets
20The Internet
Routers– Connect the Internet’s networks– Cooperate to give an end to end route for each packet
Routers
Route
21The Internet
Hosts– Any computer attached to the Internet is a host– Webservers are host– Desktop and notebook PCs are hosts too
Host
Host
22The Internet
Host internet addresses– Four number segments separated by dots– For example, 128.171.17.13– Official addresses for hosts– Also called IP addresses
127.18.47.145
127.47.17.47
23The Internet
Internet Addresses
– Really strings of 32 bits (1s and 0s) 10000000101010100001000100001101
– For convenience, divide them into four bytes (also called octets)
10000000 10101010 00010001 00001101
– Both octets and bytes are collections of eight bits
24The Internet
Internet Addresses
– Convert each octet into a decimal number 10000000 is 128 10101011 is 171 00010001 is 17 00001101 is 13
25
Computing Internet Addresses
Value(2N) Bit Decimal
128 1 128
64 0 0
32 1 32
16 0 0
8 0 0
4 0 0
2 1 2
1 1 1
163
Position(N)
7
6
5
4
3
2
1
0
Binary10100011
=Decimal
163
Note: Starts with 0
26The Internet
Host Names– Easy to remember
www.microsoft.com voyager.cba.hawaii.edu Two or more text “labels” separated by dots No relationship between segments and labels
– Like nicknames Not official names If have host name, browser can look up internet
address of host
CNN.COM
27The Internet
Internet Service Providers (ISPs)– You must have an account with an ISP– Connects you to the Internet– Provides other services (e-mail account, etc.)
Carrier– Connects you to the ISP– You pay for this separately from your ISP charges
ISPCarrier Line
28The Internet
The Internet is Not Free– You pay your ISP around $20 per month– Part of this pays for ISP expenses– Part of this pays the Internet backbone to carry your
messages
You Also Pay the Carrier Separately for the Carrier Line
ISPCarrier Line
29The Internet
Internet Backbone– Consists of competing carriers called network service
providers (NSPs)
– NSPs are all interconnected for any-any communication among hosts
Internet Backbone
NSPs
ISPISP
30The Internet
ISPs and NSPs– Began in the United States
– Is being copied and adapted by other countries
– However, not universal
31Internet Standards
Framework for standards setting is called TCP/IP
– Originally under DARPA (Defense Advanced Research Projects Agency)
– Now under an independent body, the IETF (Internet Engineering Task Force)
32Internet Standards
TCP/IP Standards are Layered– Application– Transport– Internet– Subnet Application
Transport
Internet
Subnet
33Internet Standards
Application Layer Standards– allow two application programs to work together, even
if they come from different vendors– For example, browser on user PC and webserver
application program on webserver
Browser
WebserverApplication
Program
34Internet Standards
HTTP (HyperText Transfer Protocol)– World Wide Web standard for browser-webserver
application program exchanges
Browser
WebserverApplication
Program
HTTP
35Internet Standards
Protocol
– A standard to govern communication between peer processes at the same layer on different systems
– Browser and webserver programs are at the same layer (application)
– Browser and webserver programs are on different machines (user PC and webserver)
– So HTTP is a protocol.
36Internet Standards
Transport Layer Protocols– allow any two computers to exchange messages even if
they come from different vendors and even if they are of different platform types
– For instance, PC and non-PC webserver
PCPC or
Other Computer
37Internet Standards
The Transport Layer Gives Platform Independence– Two computers do not have to be of the same platform
type
A PC user does not even know what kind of computer the webserver is
PC?
38Internet Standards
HTTP Requires the Use of the TCP Transport Standard– Transmission Control Protocol– The TCP in TCP/IP
TCP
39Internet Standards
Internet Layer Protocols– allow packets to be routed across multiple routers from
a source host to a destination host, even if the routers come from different vendors
Route
40Internet Standards
The Internet Protocol (IP) is the Main Protocol for Routing Packets Across the Internet.– The IP in “TCP/IP”
IP
41Internet Standards
Subnets– Single networks (LANs, WANs, point-to-point link)– A packet will pass through several subnets along its
route across the Internet
Subnet
Subnet
Subnet
42Internet Standards
Different Subnets Can Have Different Subnet Protocols– IP at the internet layer routes across different protocols
at the subnet layer
LAN SubnetProtocol 1
WAN SubnetProtocol 2
Point-to-Point Subnet Protocol 3
43Internet Standards
The IETF Does Not Create Subnet Standards– Uses standards from another architecture, OSI– Reference Model of Open Systems Interconnection
Application
Transport
Internet
Subnet: Use OSI Standards
44Internet Standards
OSI Divides Subnet Standards into Two Layers– Data Link– Physical
Application
Transport
Internet
SubnetOSI
Standards
Data Link
Physical
45Internet Standards
Link– Transmission connection in which there is only one
possible path between any two stations
– Simplest is a point-to-point link
Point-to-
Point
46Internet Standards
Link– Other possibilities for a single possible route between
any two stations
Multidrop Ring
HierarchyStarDaisy Chain
47Internet Standards
Data Link Layer Standards– organize transmissions into collections of bits called
frames and manage the transmission of these frames within a single network (subnet)
10010001001
Data Link
Frame
48Internet Standards
Data Link Layer Standards– For accessing the Internet from home ...
– Point-to-Point Protocol (PPP) dominates
– Only used between home and ISP!
– Low performance. Other subnets connecting routers are likely to use different subnet protocols!
ISPPPP
49Internet Standards
Physical Layer Standards– standardize connector plugs, transmission media,
electrical signaling, and other physical matters you can see and touch, even if they come from different vendors
– Work bit by bit. No frame organization.
50Internet Standards
Physical Layer Standards in Internet Access from Home– Telephone jack (RJ11)– Telephone wire– Serial port connection to external modem– Modem
SerialPort
External Modem TelephoneWire Wall Jack
51Internet Standards
Subnet Versus Internet Layer Standards– Internet layer provides routing across multiple subnets– Subnet layer standards (data link and physical) provide
for transmission within a single network
InternetLayer
Subnet Layer
52Internet Standards
Subnet Versus Internet Layer Standards– Internet layer provides routing across multiple subnets– Subnet layer standards (data link and physical) provide
for transmission within a single network
Analogy for Subnet versus Internet– Take a vacation– Route from beginning to end (like internet layer)– For different parts, may travel by car, airplane, or boat
(like subnet layer)
53Internet Standards
5-Layer Hybrid TCP/IP-OSI Framework
Use TCP/IP for Higher Layers, OSI for Subnets– Application– Transport– Internet– Data link– Physical
54Internet Standards
Accessing the WWW from Home
AppApp
TransTrans
IntInt
DLDL
PhyPhy
User PC
IntInt
DLDL
PhyPhy
Router
AppApp
TransTrans
IntInt
DLDL
PhyPhy
Webserver
HTTP
TCP
IP
PPP
Modem
IP
?
?
55Internet Standards
End-to-End Layers– Between peer processes on hosts
AppApp
TransTrans
IntInt
DLDL
PhyPhy
User PC
IntInt
DLDL
PhyPhy
Router
AppApp
TransTrans
IntInt
DLDL
PhyPhy
Webserver
HTTP
TCP
End-to-EndLayers
56Internet Standards
Communication Between Host and First Router
AppApp
TransTrans
IntInt
DLDL
PhyPhy
User PC
IntInt
DLDL
PhyPhy
FirstRouter
AppApp
TransTrans
IntInt
DLDL
PhyPhy
Webserver
IP
PPP
Modem
BetweenHost and
First Router
57Internet Standards
Other Connections– Router-Router and Router-Destination-Host– IP at internet layer– Subnet standard is unknown to user PC
IntInt
DLDL
PhyPhy
Next or LastRouter
AppApp
TransTrans
IntInt
DLDL
PhyPhy
Webserver
IP
?
?
IntInt
DLDL
PhyPhy
FirstRouter
IP
?
?
58Flexibility of Layering
Can Change Only One or Two Layer Standards for Different Application– Base Case: Accessing the WWW from home with a
V.90 modem
– Application HTTP– Transport TCP– Internet IP– Data Link PPP– Physical Serial Port, V.90 Modem,
telephone
59Flexibility of Layering
Can Change Only One or Two Layer Standards for Different Application
– New Case: Accessing a File Transfer Protocol (FTP) host from home with a V.90 modem
– Application FTP instead of HTTP– Transport TCP: No change– Internet IP: No change– Data Link PPP: No change– Physical Serial Port, V.90 Modem,
telephone:No change
60Flexibility of Layering
Can Change Only One or Two Layer Standards for Different Application– New Case: Accessing an POP mail host (see Ch. 7) from
home with a V.34 modem. Compared to Base Case:
– Application POP instead of HTTP– Transport TCP: No change– Internet IP: No change– Data Link PPP: No change– Physical Serial Port, V.34 modem instead
of V.90 modem, telephone
Part C:Platforms
The networking implications of the main computer platforms--file server program access, client/server processing, and mainframes--and of less common platforms
62PC Networks
The Most Common Platform in Organizations– Allows PCs to share resources– Both Wintel (Windows/Intel) PCs and Macintoshes
Network
63PC Network Components
Desktop Machines are Called Client PCs– The customers of services– Large networks have thousands of client PCs– ~$50 in hardware makes a stand-alone PC a client PC
Client PC
64PC Network Components
Servers Provide Services to Client PCs– Most PC networks have several servers– Large PC networks can have hundreds of servers
Service
ServerClient PC
65PC Network Components
File Servers– Store files (data files and programs)– The most common type of server in PC networks– Almost all file servers are themselves PCs
File Server
66File Server Program Access
The Most Common Way to Execute Programs in PC Networks– Program files are stored on the file server before
execution
File ServerClient PC
Storedon the
FileServer
67File Server Program Access
File Server Program Access– Program and data files are downloaded (copied) to the
Client PC– Executed on the client PC, not on the file server– File server merely stores programs and data files
File ServerClient PC
Downloaded toClient PC,Executed There
68File Server Program Access
PC Processing Power Limits FSPA Programs– Client PCs have slow processors, limited RAM– Can only execute small programs: WP, Email, etc.– This is especially true of older client PCs, which still
must be supported.
File ServerClient PC
Executed on theClient PC
69Client/Server Processing
Client and Server Machines– Neither has to be a PC– Platform independent
Client Machine Server
70Client/Server Processing
Two Programs– Client program on client machine– Server program on server machine– Work together to do the required processing
Client Machine Server
Client ProgramServer
Program
71Client/Server Processing
Division of Labor– Client program handles lighter user interface chores
and light processing chores
– Server program handles heavy work, such as database retrieval
Client Machine Server
Client ProgramServer
Program
72Client/Server Processing
Cooperation Through Message Exchange– Client program sends Request, such as a database
retrieval request
– Server program sends a Response message to deliver the requested information or an explanation for failure
Client Machine Server
Client ProgramServer
Program
Request
Response
73Client/Server Processing
Widely Used on the Internet
For instance, webservice– Client program (browser) sends an HTTP request (GET
command) asking for a webserver file
– Server program (webserver application program) sends an HTTP response message with the requested webpage
HTTP Request Message
HTTP Response Message
74Client/Server Processing
On the Internet, a Single Client Program--the Browser (also known as the client suite)--Works with Many Kinds of C/S server applications– WWW, E-mail, etc.
Browser
Webserver
E-mailServer
75Terminal-Host Systems
Created in the 1960s– Central host computer does all the processing– Terminal is dumb--only a remote screen and keyboard– Created in the 1960s, microprocessors for terminal
intelligence did not exist
Terminals Host
76Terminal-Host Systems
Sizes
– Mainframes are the largest business hosts Optimized for business uses--file access speed is more
crucial than mathematical processing
– Supercomputers are faster for intensive computations but not necessarily for business applications that have high file access needs
– Minicomputers are smaller hosts than mainframes
– Small business computers are minicomputers optimized for business use (file processing)
77Terminal-Host Systems
Many Mainframe Applications Were Created in the 1960s through 1980s– No longer cost effective
– Legacy systems--systems created by your predecessors
– Too expensive to rewrite all legacy applications at once
– Must live with many host legacy applications
– T-H transmission will be important for some years to come
– Mainframes are beginning to be used as very servers in client/server processing
78“Host” on the Internet
In terminal-host systems, a host is a central computer with many terminals
Originally, only such hosts connected to the Internet
By the time smaller computers, such as PCs, connected to the Internet, the term “host” had stuck
So now any computer connected to the Internet is called a host
79Program Functionality (Size)
File Server Program Access– Poor: many client PCs are small
Client/Server Processing– Good: not limited to client PC processing power– Heavy work can be done on the server machine
Terminal-Host Systems– Good: Hosts can be very large
80Scalability (Ability to Grow)
File Server Program Access– Poor: client PC sizes are limited
Client/Server Processing– Very good: Platform independence allows servers to be
larger than PCs– To grow, leave client machine the same, increase the size
of the server machine
Terminal-Host Systems– Excellent: hosts have an enormous range of processing
power
81Platform Independence
File Server Program Access– Poor: Only works with PC clients and PC file servers– OK for word processing, etc.– Unacceptable for large databases
Client/Server Processing– Excellent: use any server you want, also any client
Terminal-Host Systems– Poor: Hosts require terminals and only work with a few
terminal types
82User Interface
File Server Program Access– Very good: uses local PC processing power
Client/Server Processing– Very good: uses local PC processing power for user
interface
Terminal-Host System– Poor: Relies on distant hosts. User interface quality
limited by transmission costs. Monochrome, text-only screen. No animation
83Response Time (When User Hits a Key)
File Server Program Access– Very good: uses local PC processing power
Client/Server Processing– Very good: local PC processing power for user interface– But retrievals from the server can cause delays
Terminal-Host System– Poor: Relies on distant hosts. Long delays if overloaded.– Some systems use smart terminals with limited editing
capability to reduce response time for simple editing tasks only
84Less Common Platforms
Workstations– More powerful (and expensive) than PCs
– Do not use standard Intel PC microprocessors
– Usually run the UNIX operating system
– Client and server workstations
– Confusingly, Windows NT client operating system is called Windows NT Workstation, where workstation is synonymous with “client”
– Workstation servers are often used as client/server servers
85Less Common Platforms
Network Computers– Clients are simple machines without hard drives– Programs downloaded from NC servers as needed– Much like file server program access– But only run programs written in Java– Cannot run programs written for Windows
NC Java
86Less Common Platforms
Network Computers
– Originally offered to reduce costs
– Low-cost Wintel (Windows/Intel) machines are minimizing the cost advantages
– Use mostly in traditional terminal-host environments, providing more processing power than dumb terminals
87Less Common Platforms
Distributed Processing– Programs are small units called objects– Run on multiple machines (not just 2 as in C/S)– Coordinate by exchanging messages– Should be important in the future
Obj
Obj
Obj
Obj
Message
88Less Common Platforms
Information Appliances– Distributed processing pushed to its limits– Even coffeemakers may become intelligent– Small devices everywhere may coordinate with one
another
C.Standards Architectures
Beyond TCP/IP, to work with different platforms
90Standards Architectures
Standards Cannot be Created in Isolation– Must work together
to provide completeconnection betweentwo applicationprograms on differentcomputers, perhapson different networks
Application Standards
Transport Standards
Internet Standards
Data Link Standards
Physical Standards
91Standards Architecture
Begin With an Architecture (Framework)– General plan for dividing up the work of allowing
application programs to work together across a network– Defines individual layers– Defines how layers work together
Then Create Standards for Individual Layers
We Have Already Seen One Architecture: TCP/IP– Layers: application, transport, internet, subnet
92Standards Architectures
Usually, Multiple Standards at Each Layer– For instance, HTTP and e-mail standards at the
application layer
– To allow customization for individual application needs
– To allow new technology to be supported
– Inability of standards agencies to reach agreement
93Standards Architectures
Standards Agencies– Responsible for the standards architecture– In TCP/IP, this is the IETF (Internet Engineering Task
Force)
94TCP/IP
TCP/IP is the Dominant Architecture above the Subnet Layer
– Standards are simple Often even have “simple” in the standard’s name Simple standards are developed rapidly
– Simplicity also allows rapid product development
– Simplicity also allows products to be inexpensive and easy to implement
– “Fast to market and inexpensive” because of simplicity has led to TCP/IP’s dominance
95OSI
OSI (Reference Model of Open Systems Interconnection)– Open systems are those that are open to communicating
with all other systems
– “Reference model” is another name for “architecture”
96OSI Standards Agencies
ISO (International Organization for Standardization)– Traditional standards agency for industrial products
ITU-T (International Telecommunications Union-Telecommunications Standards Sector)– Traditional standards agency for telecommunications
Work Together because Networking Involves both Computers and communications
97OSI
TCP/IP versus OSI– OSI Has 7 Layers While TCP/IP Has 4
OSIApplication (7)Presentation (6)
Session (5)Transport (4)
Network (3)
Data Link (2)Physical (1)
TCP/IP
Application
Transport
Internet
Subnet
98OSI Application Layer (OSI Layer 7)
For Communication Between Specific Types of Application Programs– Email-Email– Database-Database
Not Widely Used– Sometimes simplified then adopted by IETF as a
TCP/IP standard
Similar to TCP/IP Application Layer– But not exactly the same
99OSI Presentation Layer (Layer 6)
For Standards Used in Multiple Applications– Standards for text formatting– Standards for graphics formatting– No need to create for each application
To Provide a Generalized Way to Represent Data– Abstract Syntax Notation 1 (ASN1)– Allows for exchanges between machines with different
ways of representing data
Nothing Like this in TCP/IP
100OSI Session Layer (OSI Layer 5)
Provides a Connection Between Application Programs on Different Machines– If the connection is broken, it can be reestablished
– In general, standards at this layer manage exchanges between application programs
TCP/IP Transport Layer Provides Some of this Functionality
Session (5)Transport (4)
Application
Transport
101OSI Transport Layer
Provides Connection Between Different Machines– Needed because machines may be of different platform
types
Similar to TCP/IP Transport Layer– But TCP/IP transport layer also provides some of the
functionality of the OSI Session layer
Session (5)Transport (4)
Application
Transport
102OSI Network Layer (OSI Layer 3)
The Most Difficult to Characterize
Originally Created for Subnets (Single Networks) that had a mesh of switches– Defined a route within a single mesh subnet
103OSI Network Layer (OSI Layer 3)
ISO and ITU-T “Forgot” to Have an Internetting Layer– Internetting--routing across subnets was later added to
Layer 3
So OSI Networking Layer is for BOTH Mesh Subnets AND for Routing Across Subnets– Inelegant
104OSI Network Layer (OSI Layer 3)
However, OSI Only Developed One Three-Layer Subnet Standard (X.25)– All subsequent subnet standards do not use Layer 3– Highest layer is Layer 2
So in practice, OSI Layer 3 is an Internetting Layer
Network (3)Data Link (2)Physical (1)
Internet
Subnet
105OSI Data Link and Physical Layers
We Saw These Earlier
Data Link Layer (OSI Layer 2)– Manages the transmission of frames across a single link
Physical Layer (OSI Layer 2)– For physical and electrical standards within a single
link– Works bit-by-bit
Data Link (2)Physical (1)
Subnet
106OSI Subnet Dominance
OSI Standards are Dominant for Subnet Transmission– Local Area Networks (LANs)– Wide Area Networks (WANs)– TCP/IP Does Not Challenge that Dominance
IETF Generally Does Not Create Subnet Standards for TCP/IP– If it does (as in the case of the Point-to-Point protocol,
by the way), it follows the OSI architecture
107Hybrid TCP/IP-OSI Architecture
As Noted Earlier, Most Firms Today Use a Hybrid TCP/IP-OSI Architecture for Most of their Internal Communication
Application TCP/IP
Transport TCP/IP
Internet TCP/IP
Data Link OSI
Physical OSI
108SNA
Systems Network Architecture– Another Standards Architecture
Proprietary– Controlled by IBM– However, IBM shares specifications, so most mainframe
systems from all vendors use SNA or a variant
Dominant for Mainframe Communication– Still accounts for a very large part of long-distance data
traffic
109IPX/SPX
Created by Novell– For NetWare PC network software
– Novell dominated PC networking for years
– So IPX/SPX is still widely used in PC networking with Novell NetWare servers
– Even Novell is switching to TCP/IP
– However, many PC networks have not converted their Novell servers and clients to TCP/IP
– Must be considered in PC networking
110Recap
Trends in Networking and its Impacts
Standards for WWW Access from Home to Introduce Basic Networking Principles
Popular Computer Platforms Found in Networked Environments
Standards Architectures that Tend to Differ by Platform
The Dominant TCP/IP-OSI Hybrid Architecture
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