Figure 2.1 Communication requires a message, a transmitter, a ...

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Chapter 2

The Infrastructure

Copyright
© 2003, Addison Wesley

Figure 2.1 This chapter introduces the
technology that makes e
-
commerce possible.

Applications
The World Wide Web
The Internet
The global data communication network
Copyright
© 2003, Addison Wesley

Figure 2.2 Communication requires five
elements.


Message


Information/content


Transmitter


Source or sender


Medium


Path or pipe


Receiver


Sink or destination

Transmitter
Receiver
Medium
Message
Protocol
: a set of rules for
transmitting a message.
Copyright
© 2003, Addison Wesley

Media Types


Cable


Physical wire


Twisted pair, coaxial, fiber optic


Wireless


No physical wire


Cellular, digital cellular, satellite

Copyright
© 2003, Addison Wesley

Connectivity


Ability to operate over a connection


Physical


medium


Logical


protocol


Line types


Baseband


one signal at a time


Broadband


simultaneous signals in parallel


Example


cable TV


Cable can be baseband or broadband


Wireless can be baseband or broadband


Copyright
© 2003, Addison Wesley

Figure 2.3 Plain old telephone service.


The cloud is a common way
to visualize an infrastructure

Central office
Long distance
connection
Source
Central office
Destination
Copyright
© 2003, Addison Wesley

Figure 2.4
Wireless communication.



Both POTS and
wireless use the
same

long distance
infrastructure.

Telephone
Alice
Mobile switching center
Mobile switching center
Long distance
network
Trunk
Trunk
Radio tower
Hub
Base station
Telephone
Bob
Radio tower
Hub
Base station
Copyright
© 2003, Addison Wesley

Figure 2.5 POTS and wireless are alternative access
paths to the long distance infrastructure.



Cable and satellite Internet services use the
same

long
distance lines.

POTS
Wireless service
Long distance infrastructure
Copyright
© 2003, Addison Wesley

Figure 2.6 Bandwidth.


Amount of data a
medium can transmit
in a given time.


Conventions


B


bytes


b


bits


K


1,000


M


1,000,000


G


1,000,000,000









Connection Type
Bandwidth
Local telephone line
56 Kbps
Home satellite service
400 Kbps
DSL
1.44 Mbps
Cable service
2 to 10 Mbps
Leased line (T-1, T-3)
1.5 to 43 Mbps
Fiber optic cable
Up to 10 Gbps
Wireless
2G digital cellular
2.5G digital cellular
3G digital cellular
Bluetooth
Wi-Fi (802.11b)
19.2 Kbps
144 Kbps
2 Mbps
1 Mbps
Up to 11 Mbps
Copyright
© 2003, Addison Wesley

The Last Mile Problem


Speed disparity


Local telephone line


56 Kbps


Long
-
distance line


40+ Mbps


Alternatives


Satellite


400 Kbps


DSL


1.44 Mbps


Cable


2
-
10 Mbps


Fiber optic cable


up to 10 Gbps

Copyright
© 2003, Addison Wesley

Networks


Network
: two or more computers or
devices linked by communication lines.


Each computer/device is a
node


Transmitter and receiver are nodes


The network is the medium


Communication rules are defined by a
protocol

Copyright
© 2003, Addison Wesley

Protocols


Communication protocol


An agreed
-
upon format or procedure for
transmitting data.


Implemented in hardware and/or software


Key issues


Deliver message efficiently


Detect errors


Correct errors


Copyright
© 2003, Addison Wesley

Figure 2.7 An electronic message consists of a
header, a body, and a trailer.


The header carries delivery information


Information
about

the message


The trailer is often optional.


Message
Header
Body
Trailer
Copyright
© 2003, Addison Wesley

Network Structures


LAN (local area network)


Links nodes in close proximity


Point
-
to
-
point or broadcast


WAN (wide area network)


Links geographically disbursed nodes


Typically utilizes common carrier

Copyright
© 2003, Addison Wesley

Figure 2.8 Common LAN topologies.


Topology


Describes shape or form


Defines interconnections

Ring
Bus
Star
Copyright
© 2003, Addison Wesley

Message Delivery


Broadcast


Every message sent to every node


Node picks out messages addressed to it


Bus and some star networks


Point
-
to
-
point


Message moves node
-
to
-
node


Topology or routing determines path


Copyright
© 2003, Addison Wesley

Collisions


LAN traffic management problem


Simultaneous transmission by two or more nodes


Token passing (collision avoidance)


Electronic token passed from node to node


Given node can transmit when it holds token


Collision detection and recovery


Let collision happen


Sense and retransmit affected messages

Copyright
© 2003, Addison Wesley

Figure 2.9 An Ethernet network.

Server
Wiring closet
Wiring closet
Copyright
© 2003, Addison Wesley

Figure 2.10 With point
-
to
-
point transmission,
the signal is routed node by node.


Router 3
Router 4
Router 5
Router 6
Router 7
Router 9
Router 8
Router 1
Router 2
Source
Destination
Copyright
© 2003, Addison Wesley

Figure 2.11 Internetworking.


Process of
linking two
or more
networks.

Server
Bridge
Gateway
Server
Workstation
Workstation
Workstation
Server
Workstation
Workstation
Workstation
Workstation
Workstation
Workstation
Workstation
A bridge links
similar networks

A gateway links
dissimilar networks

Copyright
© 2003, Addison Wesley

A router accepts a message at one of several input
ports and forwards it to the appropriate output port.


In
Out
Router
Routers are faster
and less expensive
than computers at
performing the
highly specialized
task of routing
messages.

Copyright
© 2003, Addison Wesley

Figure 2.12 A client/server network.


Server



Controls resource


Normally software


Term sometimes applied
to hardware


Client



Requests resource


Workstation

File system
Printer
Server
Client
Client
Client
Client
Copyright
© 2003, Addison Wesley

Figure 2.13 Most users access the Internet
through an Internet Service Provider (ISP).


Access network


Communication link


Most ISPs offer


E
-
mail, data access,
chat rooms, site
hosting, …


Host or end system


Runs server software


Workstation
ISP
Workstation
ISP
Internet

http//thelist.internet.com

Copyright
© 2003, Addison Wesley

Figure 2.14 The backbone.

Network Service Provider (NSP)
Network
Access Point
(NAP)
Network
Access Point
(NAP)
Network Service Provider (NSP)
Regional ISP
Regional ISP
Regional ISP
Local ISP
Local ISP
Local ISP
Major ISP
Major ISP
Major
corporate
network
Major
corporate
network
Major
corporate
network
Copyright
© 2003, Addison Wesley

The Backbone


Network Service Provider (NSP)


National wide
-
area network


Lease bandwidth to ISPs


Network Access Point (NAP)


Place where NSPs meet and exchange data


Chicago NAP


Regional ISP


Statewide of regional backbones

Copyright
© 2003, Addison Wesley

Figure 2.15 Miami’s network structure.


Large organizations
lease high
-
speed
server
-
to
-
Internet
connections.


Host
muohio

is a
LAN
-
to
-
LAN gateway

muohio
sba
a&s
edu
engr
E-mail host
Data access host
Router
Internet
Regional ISP
Copyright
© 2003, Addison Wesley

Figure 2.16 Packet switching.


Objective:


Efficiently utilize
bandwidth


Process


Break message into
packets


Transmit packets
independently


Multiple messages
share line


Reassemble message
at receiving end

Packet A1
Packet A2
Packet A3
Message A
Packet A1
Packet A2
Packet A3
Message A
Packet A3
Packet
Packet
Packet
Packet A2
Packet
Open
Packet
Packet
Packet A1
Packet
Open
Packet
Packet
Open
Packet
Packet
Packet
Copyright
© 2003, Addison Wesley

Figure 2.17 A message’s packets can
follow different paths.

Router 3
Router 4
Router 6
Router 7
Router 9
Router 8
Router 1
Router 2
Router 4
Router 5
Router 5
Router 5
Copyright
© 2003, Addison Wesley

Figure 2.18 The TCP/IP model.


Application layer
Transport layer
Internet layer
Network access layer
The top two layers work with
the message.
The bottom two layers work with
packets and control the network.
Copyright
© 2003, Addison Wesley

Figure 2.19
The Open
Systems
Interconnect
(OSI) model.

OSI layer
Responsibilities
Application
Provides a logical link between an application program and
the lower-level protocols.
Presentation
Performs necessary data representation and/or syntax
conversions; e.g., encryption/decryption.
Session
Establishes, maintains, and terminates a connection.
Transport
Breaks the message into packets. Ensures error free, end-to-
end delivery of the complete message.
Network
Determines the best route for sending a packet from the
source node to the destination node.
Data-link
Formats a packet for transmission to the next node.
Physical
Interfaces with the physical communication medium.
The top four layers work with the message.
The bottom three layers work with packets and control the network.
A blueprint.

Copyright
© 2003, Addison Wesley

Figure 2.20 The application layer
protocols support application programs.

Application layer
Transport layer
Internet layer
Network access layer
FTP
POP
telnet
SNMP
http
SMTP
Other
DNS
From application program
To transport layer
Copyright
© 2003, Addison Wesley

Figure 2.21 Some common application
layer protocols.










Acronym
FTP
HTTP
POP
SMTP
SNMP
Telnet
Hypertext transfer protocol
File transfer protocol
Name
Post office protocol
Simple mail transfer
protocol
Simple network
management protocol
Terminal emulation
protocol
Send an e-mail message from the originator's
computer to the recipient's mail server.
Function
Download a file from or upload a file to
another computer.
Request and download a web page. HTTP is
the standard Web surfing protocol.
Deliver accumulated mail from a mail server
to the recipient's computer.
Monitor the activity of a network's hardware
and software components.
Log into a remote computer. System operators
use telnet to remotely control a server.
Copyright
© 2003, Addison Wesley

Figure 2.22 The application layer FTP
protocol adds a header.

FTP request
FTP
header
FTP request
Application program
Application layer
Copyright
© 2003, Addison Wesley

Figure 2.23 The next layer down is the
transport layer.

Application layer
Transport layer
Internet layer
Network access layer
TCP
Other
transport
protocol
From application layer
To Internet layer
The transport layer usually uses the TCP protocol.

Copyright
© 2003, Addison Wesley

Figure 2.24 TCP adds its own header.

TCP
header
FTP request
FTP
header
FTP request
FTP
header
FTP request
Application program
Application layer
Transport layer
(each packet)
Copyright
© 2003, Addison Wesley

Figure 2.25 The Internet layer uses the
Internet protocol (IP).

Application layer
Transport layer
Internet layer
Network access layer
IP
From transport layer
To network access layer
ARP
Copyright
© 2003, Addison Wesley

Figure 2.26 IP adds its own header.

FTP request
FTP
header
TCP
header
IP
header
TCP
header
FTP request
FTP
header
FTP request
FTP
header
FTP request
Application program
Application layer
Transport layer
(each packet)
Internet layer
(each packet)
Copyright
© 2003, Addison Wesley

Figure 2.27
The network
access layer
adds another
header.

FTP request
FTP
header
TCP
header
IP
header
TCP
header
FTP request
FTP
header
FTP request
FTP
header
FTP request
Application program
Application layer
Transport layer
(each packet)
Internet layer
(each packet)
FTP request
FTP
header
TCP
header
IP
header
Network
header
Network access
layer
Copyright
© 2003, Addison Wesley

Open standards


TCP/IP is an example


Promotes


Platform independence


Interoperability


Open standards make the Internet a
true public medium.


Copyright
© 2003, Addison Wesley

Figure 2.28 A domain name consists of
two to four words separated by dots.

sbaserver1.sba.muohio.edu
Server within SBA sub-domain
SBA sub-domain
Miami University domain
Top-level domain
Domain: a set of nodes administered as a unit.

Copyright
© 2003, Addison Wesley

The parts of a
domain name are
structured as a
hierarchy.


edu
134
com
org
muohio
134.53
sba
134.53.40
cas
134.53.54
sbaserver1
134.53.40.2
sbadata
134.53.40.4
Copyright
© 2003, Addison Wesley

Figure 2.29 Top
-
level domain names.

Domain Signifies
Domain
Signifies
aero
Air-transport industry
au
Australia
biz
Business organization
br
Brazil
com
US commercial
ca
Canada
coop
Coooeratives
cn
China
edu
US educational
de
Germany
info
Unrestricted
fi
Finland
gov
US government
fr
France
mil
US military
gb
Great Britian
museum Museums
in
India
name
Individuals
it
Italy
net
US network
jp
Japan
org
US non-profit
ru
Russia
pro
Professionals
za
South Africa

Copyright
© 2003, Addison Wesley

Figure 2.30 An IP address.

134.53.40.2
Server within SBA domain
SBA domain
Miami University domain
Top-level domain
Copyright
© 2003, Addison Wesley

Figure 2.31 A domain name and an IP
address convey the same information.



Physical transmission requires IP address


Domain name system converts domain name to
equivalent IP address

sbaserver1.sba.muohio.edu 134.53.40.2
Copyright
© 2003, Addison Wesley

Figure 2.32 The domain name system.

sba
DNS
muohio
DNS
com
= 207
com
DNS
microsoft
=
207.46
microsoft
DNS
service
=
207.46.140.71
s
ervice.microsoft.com
service.microsoft.com
service.microsoft
service
207.46.140.71
207.46
207.46.140.71
1
2
3
4
5
6
7
Copyright
© 2003, Addison Wesley

Figure 2.33 Well
-
known port assignments
.

Port
Used for:

5

RJE (Remote Job Entry)
20
FTP (File Transfer Protocol) data
21
FTP (File Transfer Protocol) control
23
TELNET (Terminal emulator)
25
SMTP (Simple Mail Transfer Protocol)
79 FINGER (Given e-mail address, identify user)
80
HTTP (Hypertext Transfer Protocol)
110
POP3 (Post Office Protocol, Version 3)
119
NNTP (Network News Transfer Protocol)
Port
: endpoint of a logical connection

Copyright
© 2003, Addison Wesley

Socket


Software object consisting of


IP address


right node


Port address


right application program


Application program


Sends message through socket


Accepts message via socket

Copyright
© 2003, Addison Wesley

Figure 2.34 TCP/IP
address translation.



DNS


Domain name to IP


ARP


IP to MAC address


Map logical domain
name to physical
device.


MAC address


Final node


Not directly on Internet

Domain Name
System (DNS)
IP address
Address
Resolution
Protocol (ARP)
MAC address
domain name
Copyright
© 2003, Addison Wesley

Figure 2.35 The e
-
commerce infrastructure.

E-commerce application
Web application
World Wide Web
Internet
Data communication network