Business Data Communications and Networking
Raymond R. PankoCopyright 2001 Prentice Hall
Revision 1: August 2000
Modified by Nancy Smithfield 2002
Basic Concepts and Principles
Chapter 1
Copyright 2000 Panko
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Part A:Business Data Communications and Networking
What’s in a Title?
6Business
For IS (information systems) students in business schools
– Computer science and electrical engineering students 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, such as banks, government agencies, and manufacturing firms--organizations that use IT (information technology) to get their work done
7Business
The IS Job: Full life cycle support
– To help firms understand how networking will help them work better
– To do needs analysis
– To plan and develop new networks
– To manage new networks after they are developed
8
Network
Network
A Network is an Any-to-Any Communication System– Can connect any station to any other– Stations are called nodes on a network
9
“Connect to GHI”
Network
Each Station has a Unique Network Address– To connect, only need to know the receiver’s address– Like telephone number
ABC
DEF GHI
JKLMNO
10Data Communications
Originally, There was a Sharp Distinction:– Voice and Video Communication versus
– Data Communications, in which one or both parties is a computer
Database Electronic mail World Wide Web
– Distinction is fading because voice and video communication are increasingly computer-based
11Voice and Video Networks
Telephone Network– Customer premises (home or office)– Local loop (access line) connects customer premises to
first switching office
Connection
Switching OfficeLocal Loop
(Access Line)
CustomerPremises
CustomerPremises
12Voice and Video Networks
Telephone Network– Local loop - each telephone has a pair of wires that
goes directly to a telephone company’s nearest office– if a customer (subscriber) attached to a particular office
calls another subscriber attached to the same office, the switching equipment sets up a direct electrical connection between the 2 local loops.
Connection
Switching OfficeLocal Loop(Access Line)
CustomerPremises Customer
Premises
13Voice and Video Networks
Telephone Network– The connection remains intact for the duration of
the call. The call has a “reserved circuit capacity”.
Connection
Switching OfficeLocal Loop(Access Line)
CustomerPremises Customer
Premises
14Voice and Video Networks
If the called telephone is attached to another end office, the the connection will be made through a trunk line. There is a hierarchy of switches
Trunk lines connect switches
Switch
Trunk Line
15Voice and Video Networks
Circuit– End-to-End Connection between Phones– May pass through multiple switches– And trunk lines
CircuitCircuit
16Voice and Video Networks
Reserved Capacity– Circuit capacity is reserved during duration of
each call– At each switch– On each trunk line
Circuit
ReservedCapacity
ReservedCapacity
17Voice and Video Networks
Reserved Capacity– Another name for this type of circuit is circuit
switching– Circuit Switching Characteristics
a connection is established before 2 stations begin transmitting
bandwidth (range of frequencies) is dedicated to the connection until the connection is terminated
18Voice and Video Networks
Reserved Circuit Capacity Guarantees Throughput– Never get less than reserved capacity– Nothing like congestion on the Internet
Reserved Circuit Capacity is Expensive– Pay for it whether you use it or not– Good for voice, because conversations are fairly
constant– Bad for data, because most data transmission is bursty;
e.g., in World Wide Web, download, then stare at screen for a long time until next download
19Packet-Switched Data Networks
Packet Switching– Circuit switching is expensive due to reserved capacity – Packet switching breaks transmissions into messages
– Messages are short (averaging a few hundred bytes) because switches handle short messages efficiently
– Messages are called packets (sometimes, frames or other names)
Message Packets
20Packet-Switched Data Networks
Packet Switching– packets can travel any path to a destination– packets contain destination address and sequencing
information (puts packets back in proper order)– example
class (message) send you to Ruby Tuesday’s in Mall won’t tell you mode of transportation or route how can this be done?
Message Packets
21Packet-Switched Data Networks
Packet Switching– example
class (message) send you to Ruby Tuesday’s in Mall won’t tell you mode of transportation or route use a car, bus or walk (different network
technologies) go towards Ft. Campbell and then down 101st or out
college street? Which door of mall will you enter?
22Circuit-Switched Data Networks
Circuit Switching– example
class (message) send you to Ruby Tuesday’s in Mall reserved 3 busses that will arrive at end of class
– make the reservation ahead of time (establish a circuit)
– pay for 36 seats (12 per bus) - if only 2/3 of the class is here, I have wasted capacity
23Packet-Switched Data Networks
Switching Decision– When a packet arrives at a switch, the switch must
decide which of several ports (connections) to use to send the packet back out
– Complex– Made at each switch
B?
D?
C?
Switch A
B
C
DPacket
24Packet Switched Data Networks
Multiplexing– Packets from many conversations are mixed
(multiplexed) over each trunk line– Only pay for the capacity used– Dramatic trunk line cost savings– The reason for packet switching
Multiplexing onTrunk Line
Part B:More Basic Concepts
Analog and Digital Communication
Modems
LANs and WANs
26Analog Transmission
In analog transmission, the state of the line can vary continuously, rising and falling smoothly in intensity among an infinite number of states– State may be voltage, frequency or another line signal
characteristic– The human voice is like this– When we speak into a telephone, we generate
analogous (similar) electrical signals, hence the name
Time
Strength
New
27Digital Transmission
In digital transmission, time is divided into periods of fixed length called clock cycles
The line is kept constant (in one state) during each clock cycle so that the receiver can sample it anywhere during the cycle and get the same result
Clock CycleTime
Strength
New
28Digital Transmission
The line is kept in one of only a few possible states (conditions) during each clock cycle– 2, 4, 8, 16, 32, rarely more– There are fairly large differences between states– If a signal is near one state but a bit off, the receiver
will still read it correctly as being at that state
Clock CycleTime
Strength
New
29Digital Transmission
At the end of each clock cycle, the line may change abruptly to another of these few states – Can also stay the same
Time
Strength
AbruptChange
Stays Same
Clock Cycle
30Digital Versus Binary Transmission
Digital transmission: a few states (2, 4, 8, 16, etc.)
Binary transmission: exactly two states– One state represents 1, the other 0
Digital Binary
Two StatesFew States
0
1
31Digital Communication
Modems– Computers have digital output
– Telephone network assumes analog input
– Modem translates between digital device and analog line for data transmission over the phone system
DigitalSignal
Modem
AnalogSignal
32LANs and WANs
Networks Have Different Geographical Scopes
Local Area Networks (LANs)– Small Office– Office Building– Industrial Park / University Campus
Wide Area Networks (WANs)– Connect corporate sites or– Connect corporate sites with sites of customers and
suppliers
33Elements of a Simple LAN
Hub or Switch
Wiring
Hub or Switch connects all stations
Wiring is standardbusiness telephone wiring
(4 pairs in a bundle)
34Elements of a Simple LAN
Server
Client PC
Client PC
Server
Client PCs are used byordinary managers and
professionals; receive service
Servers provide servicesto client PCs
Server
35Elements of a Simple LAN
Client PC– Begin with stand-alone PC
– Add a network interface card (NIC) todeal with the network
– Networks have many client PCs
Server– Most PC nets have multiple servers
Part C:Distributed Processing
Terminal-Host Systems
File Server Program Access
Client Server Processing
37What is distributed?
Data Storage - Where and in what type of structure is the data stored (DB or files)
Data Access Logic - Process required to get the correct data
Application Logic - Processing required before and after data is retrieved
Presentation Logic - User Interface, System Commands, Data Entry
38Terminal-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, when microprocessors for
terminal intelligence did not exist
Terminals Host
39Terminal-Host Systems
Sizes
– Mainframes are the largest business hosts Optimized for business uses--file access speed is
more crucial than mathematical processing
40Terminal-Host Systems
Many Mainframe Applications Were Created in the 1960s through 1980s– Legacy systems--systems created by your predecessors
– Would not use the same platform today if built new
– But too expensive to rewrite all legacy applications at once
– Must live with many host legacy applications for now
– Older networks can be legacy systems as well; “legacy system” is not just limited to mainframe applications
41PC Networks
The Most Common Platform in Organizations– Allows PCs to share resources– Both Wintel (Windows/Intel) PCs and Macintoshes
Network
42PC 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
43File Server Program Access
File Server Program Access is 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
44File 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
45File Server Program Access
PC Processing Power Limits FSPA Programs– Client PCs do not get very large– Only programs small enough to operate on limited
client PCs can be used
Data Storage is the only thing done on server
File ServerClient PC
Executed on theClient PC
46Client/Server Processing
Client and Server Machines– Neither has to be a PC– Platform independent
Client Machine Server
47C/S Servers often are Workstation Servers
Workstations– Are computers 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”
48Client/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
49Client/Server Processing
Division of Labor– Client program handles lighter work, such as user
interface chores and light processing chores
– Server program handles heavy work, such as database retrieval
Client Machine Server
Client ProgramServer
Program
50Client/Server Processing
Cooperation Through Message Exchange– Client program sends Request message, 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
51Client/Server Processing
Widely Used on the Internet
For instance, webservice– Client program (browser) sends an HTTP request
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
52Client/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, some E-mail, etc.
Browser
Webserver
E-mailServer
53Program Functionality (Size)
High program functionality requires large program size
File Server Program Access– Poor: client PCs are small, can only execute small
programs
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
54Platform Independence
File Server Program Access– Poor: Only works with PC clients and PC file servers
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
55Scalability
Ability to grow as demand grows
File Server Program Access– Poor: client PCs do not get very large
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: have an enormous range of processing power
56User 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 high long-distance transmission costs– Monochrome, text-only screen; no animation
57Response 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
Part D: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
59Accessing the WWW from Home
A Common and Important Situation– Must be understood
– Good way of introducing networking concepts
60The Internet
The Internet is a Worldwide Group of Networks– Not a single network
– Individual networks on the Internet are called subnets
61The Internet
Messages are Broken into Small Packets for Transmission, as Noted Earlier– More efficient than sending long messages
Message Packets
62The Internet
Routers– Connect the Internet’s individual networks (subnets)– Cooperate to give an end-to-end route for each packet
Routers
Route
63The Internet
Hosts– Any computer attached to the Internet is a host– Webservers are host– Desktop and notebook PCs are hosts too
Host
Host
64The Internet
Network deliver messages based on network addresses– The Internet has two addressing systems for hosts
IP addresses Host names
Host
Host
65The Internet
Host IP addresses– Strings of 32 ones and zeros– Usually represented by four number segments
separated by dots: dotted decimal notation– For example, 128.171.17.13– Official addresses for hosts
127.18.47.145127.47.17.47
66The Internet
Dotted Decimal Notation
– IP addresses are really strings of 32 bits (1s and 0s) 10000000101010100001000100001101
– To convert this to dotted decimal notation, first, divide them into four bytes (also called octets)
10000000 10101010 00010001 00001101
– Both octets and bytes are collections of eight bits
67The Internet
Dotted Decimal Notation
– Convert each binary (Base 2) octet into decimal (Base 10)
10000000 is 128 10101011 is 171 00010001 is 17 00001101 is 13
68
The Internet
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
Position7
Position0
69The Internet
Why dotted decimal notation?
– Strings of 32 bits are very difficult to memorize
– Dotted decimal representations of IP addresses are (somewhat) easier to remember
– So dotted decimal notation is merely a mnemonic device for representing IP addresses
70The Internet
Host Names– The other network addressing system on the Internet
– Easy to remember www.microsoft.com voyager.cba.hawaii.edu Two or more text “labels” separated by dots No relationship between segments and labels
CNN.COM
71The Internet
Host Names– Like nicknames
Not official addresses Each host must have an IP address But only some hosts have host names If you give it a host name, your browser must look
up IP address of host (Chapter 2 discusses how)
CNN.COM
72The Internet
Internet Service Providers (ISPs)– You must have an account with an ISP– Connects you to the Internet– May provide other services (e-mail account, etc.)
Carrier Access Line– Usually provided by local telephone carrier– Connects you to the ISP– You pay for this separately from your ISP charges
ISPCarrier Access Line
73The Internet
The Internet is Not Free– You pay your ISP around $20 per month, sometimes
more– Part of this pays for ISP expenses– Part of this pays the Internet backbone to carry your
messages
You Usually Also Pay the Telephone Carrier Separately for the Carrier Access Line
ISPCarrier Access Line
74The Internet
Some ISPs are “free”– More correctly, they are advertiser supported– You must see advertisements every time you use a free
ISP
ISPCarrier Access Line
New
75The Internet
Internet Backbone– Itself consists of many competing but interconnected backbone
carriers
– Sometimes, backbone carriers are also ISPs
– Most are competing carriers called network service providers (NSP)
Internet Backbone
Carriers
ISPISP
76Brief History of the Internet
1957 - USSR launches Sputnik, USA forms Advanced Research Projects Agency (ARPA)
1969 - DoD supports ARPAnet as a research into networks (4 nodes - UCLA, Stanford, UCSB, Univ. of Utah)
1973 - First international nodes in England and Norway
1982 - TCP/IP established as Internet Protocol
77Internet History Continued
1986 - NSF Net established 5 connected supercomputer sites
1988 - NSF Net upgraded to T1(1.54Mbps) with international connections
1991 - Backbone upgraded to T3 (45 Mbps)
1992 - WWW introduced by CERN
1995 - Original NSF retired and replaced with NSP Tier 1, 2, 3, 4
78The Internet
ISPs and NSPs– Began in the United States
– Is being copied and adopted by other countries
– However, not universal
Part E:Standards
Layered Standards Architectures
TCP, IP, and TCP/IP
Other Architectures
80Standards
Standards are rules of operation that most or all vendors follow
Open standards are created and owned by public standards organizations– No single vendor controls these standards
81Standards Are Layered
For Internet Access to a Webserver, standards are set at five layers– Application– Transport– Internet– Data Link– Physical
Together, these standards provide all that is needed for application programs on different hosts on different networks to work together
82Internet Standards
Messages are Exchanged at Multiple Layers
AppApp
TransTrans
IntInt
DLDL
PhyPhy
User PC
IntInt
DLDL
PhyPhy
Router
AppApp
TransTrans
IntInt
DLDL
PhyPhy
Webserver
HTTP
TCP
IP
PPP
Modem
IP
?
?
83Internet Standards
Application Layer Standards– Standards at the application layer specify how two
application programs communicate – For example, browser on user PC and webserver
application program on webserver
Browser
WebserverApplication
Program
84Internet Standards
HTTP (HyperText Transfer Protocol)– World Wide Web standard for browser-webserver
application program exchanges– Other applications (E-mail, etc.) have different
application standards
Browser
WebserverApplication
Program
HTTP
85Internet Standards
Transport Layer Protocols– Standards at the transport layer specify how two host
computers will work together, even if they are of different platform types (PCs, workstations, mainframes, and so forth)
– For instance, PC and non-PC webserver
PCPC or
Other Computer
86Internet 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?
87Internet Standards
HTTP Requires the Use of the TCP Transport Standard– Transmission Control Protocol– TCP messages are called TCP segments
TCP
88Internet Standards
Internet Layer Protocols– Standards at the internet layer specify how hosts and
routers will act to route packets end to end, from the source host to the destination host, across many single networks (subnets) connected by routers
Route
Single Network(Subnet)Host
Host
89Internet Standards
The Internet Protocol (IP) is the Main Protocol for Routing Packets Across the Internet– The IP in “TCP/IP”– IP messages are called packets– All internet layer messages are called packets
IP
Packet
90Internet Standards
Subnets– Single networks (LANs, WANs, point-to-point link) on
the Internet– A packet will pass through several subnets along its
route across the Internet
Subnet
Subnet
Subnet
91Internet Standards
Different Subnets Can Have Different Subnet Protocols– IP at the internet layer routes across different protocols
at the subnet layer
Point-to-Point SubnetProtocol 1
WAN SubnetProtocol 2
LAN Subnet Protocol 3
92Subnets Standards
Subnets are Single Networks on the Internet
Subnet Standards Divided into Two Layers
– Physical layer standards govern the transmission of individual bits within a subnet
– Data Link layer standards govern the transmission of messages within a subnet
Organize individual bits into structured messages
93Internet Standards
Data Link Layer Standards– Standards at the data link layer specify how to transmit
messages within a single network– Messages at the data link layer are called frames
10010001001
Data Link
Frame
94Internet Standards
Data Link Layer Standards– For accessing the Internet from home ...
– Point-to-Point Protocol (PPP) dominates
– Only used between home and ISP!
– Other subnets connecting routers are likely to use different subnet protocols!
ISPPPP ?
95Internet Standards
Physical Layer Standards– While the data link layer is concerned with the
organization and transmission of organized messages, standards at the physical layer specify how to transmit single bits one at a time
– Work bit by bit; no frame organization
96Internet 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
97Internet 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
98Internet Standards
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)
InternetLayer
Subnet Layer
99Standards Organizations and Architectures
Architecture is a Design for Standards Creation
– Specifies what types of standards are needed (application, transport, etc.)
– After architecture is designed, individual standards of each type are created
– Analogy: architecture of house specifies what rooms will be needed and their relationships.
– After architecture is settled, individual rooms are designed
100Standards Organizations and Architectures
TCP/IP Standards– Created by the Internet Engineering Task Force (IETF)– Named after its two most widely known standards, TCP
and IP TCP/IP is the architecture, while TCP and IP are
individual standards However, these are not its only standards, even at
the transport and internet layers– IETF standards dominate in corporations at the
application, transport, and internet layers However, application, transport, and internet
standards from other architectures are still used
101Standards Organizations and Architectures
OSI Standards– Reference Model of Open Systems Interconnection
– Created by the International Telecommunications Union-Telecommunications Standards Sector (ITU-T)
– And the International Organization for Standardization (ISO)
– OSI standards dominate the data link and physical layers
Other architectures specify the use of OSI standards at these layers
102Internet Standards
5-Layer Hybrid TCP/IP-OSI Architecture– Most widely used architecture in organizations today– Used on the Internet
Application TCP/IP
Transport TCP/IP
Internet TCP/IP
Data Link OSI
Physical OSI
103Internet Standards
Recap: 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
?
?
104TCP/IP versus OSI
Lowest Four Layers are Comparable in Functionality
TCP/IP OSI
Application ApplicationPresentationSession
Transport TransportInternet NetworkData Link (use OSI) Data LinkPhysical (use OSI) Physical
Box
105OSI Divides the Application Layer
OSI Session Layer– Sets up a connection between two application programs
on different machines– Manage streams of transactions (session); if there is a
break, can resume at the last roll-back point
Transactions
Box
106OSI Divides the Application Layer
OSI Presentation Layer– Handles presentation differences between the two
machines (how data are stored and represented)
– Two presentation layer processes select and use a common format for exchanging data
Application DataExchange in
Common Format
Box
107OSI Divides the Application Layer
OSI Application Layer
– Governs application-to-application communication freed from concerns about presentation format and transaction management
Box
F.Tomorrow
Quality of Service (QoS)
Security
109Quality of Service (QoS)
Throughput Problems and Guarantees
Congestion– When too many transmissions are on a network, traffic
will slow down; this is congestion
Latency– Latency is the amount of time that packets or frames
are delayed because of congestion. Measured in milliseconds (ms),
– Want guarantees of worst-case latency
Throughput– Throughput is the guaranteed speed in bits per second
110Quality of Service (QoS)
Reliability Measures
Availability– Availability is the percentage of time the network is
available to users.– Telephone system has 99.999% availability
Error Rate– Error rate is the percentage of bits or messages that
contain errors – 3% - 6% of all packets are lost on the Internet
111Security
A Growing Problem Encryption for Confidentiality
– Sender encrypts messages before sending them so that anyone intercepting them en route cannot read them
– Receiver can decrypt encrypted messages and read them
– Have confidentiality (unreadability by interceptors)
47 Encryption 101101 Decryption 47
New
112Security
Authentication– Sender of a message must prove their identity– To thwart impostors who impersonate people
Access Control– Prohibits or authorizes access to various resources
(files, programs, etc.)
– Needs authentication but also more
– Access control lists for resources specify what resources the authorized person may use and how they may use them