Transcript COS 338_day22_23 - Ecom and COS classes

COS 338
Day 22
DAY 22 Agenda

Spring 2006 Book List


Lab 7 corrected



Due Dec 5 (last one)
Will drop lowest grade
Exam 3 Graded


Due Dec 1
Assignment 8 Posted


1 A, 1 C, 3 F’s and 1 non-submit
Assignment 7 Posted


Http://perleybrook.umfk.maine.edu/sp2000bl.htm
2 A’s,3 B’s and 1 F
Today (and the next class) we will discuss Network Management and
Networked Applications
2
Schedule for last 4 weeks

Today



Finish Chap 10 and begin chapter 11
Assignment 8 posted
 Due Dec 5
Dec 8



Dec 1




Assignment 7 Due
Finish Chapter 111




Dec 12


Dec 5
Assignment 8 Due
Lab 8
 Due Dec 12
Discussion on Final Group Lab
 Build on SOHO Network in OMS




5 desktops
1 Server
1 Printer
Internet connections
Firewall and/or router
Networked applications

Lab 8 Due
Part 2 of Final Lab
Dec 15


Exam 4
Capstone Progress Report Due
Part 1 of Final lab
 Planning
Part 3 of Final Lab
Dec 19



10-12 noon
Capstones due
10 min presentation of Capstone projects


3
Figure 10-16: Simple Network
Management Protocol (SNMP)

Simple Network Management Protocol (SNMP)

Standard for managing remote devices in a network

Collects information from remote devices to give the
network administrator an overview of the network

Optionally, allows the network administrator to
reconfigure remote devices

Potential for strong labor cost savings
4
Figure 10-16: Simple Network Management
Protocol (SNMP)
Network Management
Software (Manager)
Managed
Device
Manager manages multiple
managed devices from a central
location
RMON Probe
5
Figure 10-16: Simple Network Management
Protocol (SNMP)
Network Management
Software (Manager)
Network
Management
Agent (Agent),
Objects
Network
Management
Agent (Agent),
Objects
Manager talks to an network
management agent on each
managed device
RMON Probe
6
Figure 10-16: Simple Network Management
Protocol (SNMP)
Network Management
Software (Manager)
Network
Management
Agent (Agent),
Objects
Network
Management
Agent (Agent),
Objects
RMON (remote monitoring) probe is
a special agent that collects data
about multiple devices in a region of
in the network. It is like a local
manager that can be queried by the
main manager.
RMON Probe
7
Figure 10-16: Simple Network Management
Protocol (SNMP)
Network Management
Software (Manager)
Management
Information
Base (MIB)
Management
Information
Base (MIB)
MIB stores data about devices.
MIB on manager stores all.
MIB on device stores local information
Management
Information
Base (MIB)
RMON Probe
8
Figure 10-16: Simple Network Management
Protocol (SNMP)
Network Management
Software (Manager)
Management
Information
Base (MIB)
Simple Network
Management Protocol (SNMP)
Management
Information
Base (MIB)
Command (Get, Set, etc.)
Response
Management
Information
Base (MIB)
Trap
RMON Probe
9
Figure 10-17: SNMP Object Model


SNMP Object Model
Management
Information
Base (MIB)

The MIB database schema

Defines objects (parameters) about which
information is stored for each managed device
SNMP System Objects

System name

System description

System contact person

System uptime (since last reboot)
10
Figure 10-17: SNMP Object Model

SNMP IP Objects
Management
Information
Base (MIB)

Forwarding (for routers). Yes if forwarding (routing),
No if not

Subnet mask

Default time to live

Traffic statistics

Number of discards because of resource limitations
11
Figure 10-17: SNMP Object Model

SNMP IP Objects (Continued)
Management
Information
Base (MIB)

Number of discards because could not find route

Number of rows in routing table

Rows discarded because of lack of space

Individual row data in the routing table
12
Figure 10-17: SNMP Object Model

SNMP TCP Objects
Management
Information
Base (MIB)

Maximum / minimum retransmission time

Maximum number of TCP connections allowed

Opens / failed connections / resets

Segments sent

Segments retransmitted

Errors in incoming segments

No open port errors

Data on individual connections (sockets, states)
13
Figure 10-17: SNMP Object Model


SNMP UDP Objects

Error: no application on requested port

Traffic statistics
Management
Information
Base (MIB)
SNMP ICMP Objects

Number of errors of various types
14
Figure 10-17: SNMP Object Model

Management
Information
Base (MIB)
SNMP Interface Objects (One per Port)

Type (e.g., 69 is 100Base-FX; 71 is 802.11)

Status: up / down / testing

Speed

MTU (maximum transmission unit—the maximum
packet size)

Traffic statistics: octets, unicast / broadcast /
multicast packets

Errors: discards, unknown protocols, etc.
15
Remote Switch and Router
Management
Figure 10-12: Network Management
Utilities

Remote Switch and Router Management

Telnet

Web interfaces

SSH

TFTP

Saves money compared to traveling to device
17
Figure 10-18: Telnet, Web Management,
SSH, and TFTP

Telnet

Remotely log into managed device as a dumb
terminal

Poor security

Weak password authentication

Passwords are sent in the clear, making them
vulnerable to sniffers

No encryption of traffic
18
Figure 10-18: Telnet, Web Management,
SSH, and TFTP

Web Interfaces

Managed device contains a webserver

Administrator connects to the managed device with
a browser

Can use SSL/TLS but typically does not

Set-up on normally unused port

http://darouter:8888
19
Figure 10-18: Telnet, Web Management,
SSH, and TFTP

SSH

Secure shell protocol

Similar to Telnet but highly secure

Widely installed on Unix computers (including Linux
computers)

Software must be added to Windows devices
20
Figure 10-18: Telnet, Web Management,
SSH, and TFTP

TFTP

Trivial File Transfer Protocol

Similar to file transfer program but simpler


Simple enough to implement on switches and
routers
Often used to download configurations to a switch or
router from a server
21
Figure 10-18: Telnet, Web Management,
SSH, and TFTP

TFTP

No password is needed

Can be used by hackers to download attack
programs

Poor security makes TFTP very dangerous
22
Traffic Management
Figure 10-19: Traffic Management Methods

Traffic Management

Capacity is expensive; it must be used wisely

Especially in WANs
24
Figure 10-19: Traffic Management Methods

Traditional Approaches

Overprovisioning

In Ethernet, install much more capacity than is
needed most of the time

This is wasteful of capacity

Does not require much ongoing management
labor
25
Figure 10-19: Traffic Management Methods

Traditional Approaches

Priority

In Ethernet, assign priority to applications based
on sensitivity to latency

In momentary periods of congestion, send highpriority frames through

Substantial ongoing management labor
26
Figure 10-19: Traffic Management Methods

Traditional Approaches

QoS Reservations

In ATM, reserve capacity on each switch and
transmission line for an application

Allows strong QoS guarantees for voice traffic

Highly labor-intensive

Data gets the scraps—capacity that is not
reserved for voice
27
Figure 10-19: Traffic Management Methods

Traffic Shaping

The Concept

Control traffic coming into the network at access
switches

Filter out unwanted applications

Give a maximum percentage of traffic to other
applications
28
Figure 10-19: Traffic Management Methods

Traffic Shaping

Advantages and Disadvantages

Traffic shaping alone reduces traffic coming into
the network to control costs

Very highly labor intensive

Creates political battles (as do priority and QoS
reservations to a lesser degree)
29
Topics Covered
Topics Covered


Cost

Exploding demand, slow budget growth

Hardware, software, labor costs

Fully-configured hardware versus base prices

Total cost of ownership: cost over entire life cycle
Network Simulation

Model the network on a computer

Explore alternatives

Cheaper than building alternatives
31
Topics Covered


IP Subnet Planning

Organization is given its network part

Divides remaining bits of IP address into subnet and
host part

Must balance number of subnets with hosts per
subnet
Directory Servers

Hierarchical data storage

LDAP
32
Topics Covered


Configuring Routers

Time-consuming; important skill

Cisco IOS is the dominant router operating system

Command-line interface (CLI)
Network Management Utilities

Both network managers and hackers love them

Host diagnostic tools. Is the connection working?
 127.0.0.1
 Windows XP: Connection Properties
33
Topics Covered

Network Management Utilities

Packet capture and display programs

Traffic summarization program (Etherpeek)

Netstat to show active connections

Route analysis: Ping and Tracert

Network mapping tools (nmap)
34
Topics Covered

Simple Network Management Protocol (SNMP)

Manager, managed devices, agents

Get and set commands

MIB

RMON probe

SNMP object model (MIB schema)
35
Topics Covered

Remote Switch and Management Utilities

Saves money compared to traveling to device

Telnet

Web interfaces

SSH

TFTP
36
Topics Covered

Traffic Management

Capacity is expensive on WANs

Overprovisioning is too wasteful on WANs

Priority is good but expensive to manage

QoS reservations only allow strong guarantees for
some services; rest get the scraps

Traffic shaping: only select certain type of traffic
 Drop certain traffic or limit it to a certain amount
37
Networked Applications
Chapter 11
Copyright 2004 Prentice-Hall
Panko’s Business Data Networks and Telecommunications
5th edition
Application Architectures
Figure 11-1: Simple Terminal-Host System
All Processing is
Done on the Host
Slow Response Time
Monochrome Text
Little Graphics
Dumb
Terminal
Modem
Dumb
Terminal
Telephone
Network
Modem
Host
40
Figure 11-2: Client/Server Computing
File Server Program Access
1.
Program
Stored on
File Server
File Server
2.
Program
Downloaded to
Client PC
When Called
3.
Program
Executed on
Client PC Client PC!
Only useful for small programs (e-mail, word processing, etc.)
Because clients do not get very large
41
Figure 11-2: Client/Server Computing
Client/Server Processing with Request-Response Cycle
Request Message
Client Program
Response Message
Does Light I/O and
Post-Download
Processing
Client PC
Server Program
Does Heavy
Database
and Other Heavy
Processing
Server
Highly scalable: Use larger server as number of clients increases
42
Figure 11-3: Web-Enabled Application (E-Mail)
HTTP Request Message
Client is Browser
HTTP Response Message
Server Program
Almost all client PCs
now have browsers.
No need to install new software.
Client PC
E-Mail Server
43
E-Mail
Figure 11-4: E-Mail

Importance of E-Mail

Universal service on the Internet

Attachments make e-mail a general file delivery
mechanism

Viruses, worms, and spam, and other abuses
45
Figure 11-5: E-Mail Standards
SMTP
To Send
SMTP
To Send
Sender’s Mail
Server
Sending
E-Mail
Client
Receiver’s Mail
Server
Simple Mail Transfer Protocol
(SMTP) to transmit mail in real
time to a user’s mail server or
between mail servers
Receiving
E-Mail
Client
Sender-initiated
46
Figure 11-5: E-Mail Standards
Sender’s Mail
Server
Sending E-Mail
Client
Receiver’s Mail
Server
POP or IMAP to download mail to
receiver when the receiver is next
capable of downloading mail.
POP or
IMAP
To Receive
Receiving
E-Mail
Client
Receiver-initiated
47
Figure 11-4: E-Mail

E-Mail Standards

Downloading mail to client

Post Office Protocol (POP): Simple and widely
used

Internet Message Application Program (IMAP):
More powerful, can manage messages on the
receiver’s mail host, less widely used
48
Figure 11-5: E-Mail Standards
Sender’s Mail
Server
Receiver’s Mail
Server
Message Body Format Standard
Sending
E-Mail
Client
Message
RFC 822 or 2822
HTML body
UNICODE
Receiving
E-Mail
Client
49
Figure 11-4: E-Mail

E-Mail Standards

Message body standards

Receiver must understand sender’s message

RFC 822 and RFC 2822 for all-text bodies

HTML bodies with fancy text and graphics

UNICODE for non-English languages
50
Figure 11-6: Interactions in the Simple
Mail Transfer Protocol (SMTP)
Actor
Command
Comment
When a TCP connection
is opened, the receiver
signals that is is ready.
Sender asks to begin
HELO Voyager.cba.Hawaii.edu Sending a message.
Gives own identity.
Receiver signals that it
250 Mail.Panko.Com
Is ready to begin
Receiving a message.
Receiving SMTP
220 Mail.Panko.Com Ready
Process
Sending SMTP
Process
Receiver
51
Figure 11-6: Interactions in the Simple
Mail Transfer Protocol (SMTP)
Actor
Command
Comment
Sender
MAIL FROM: Panko@
voyager.cba.hawaii.edu
Sender identifies the sender
(mail author, not SMTP
process).
Receiver 250 OK
Accepts author. However,
May reject mail from others.
Sender
Identifies first mail recipient.
RCPT TO: [email protected]
Receiver 250 OK
Accepts first recipient
52
Figure 11-6: Interactions in the Simple
Mail Transfer Protocol (SMTP)
Actor
Command
Sender
RCPT TO:[email protected]
Comment
Sender
DATA
Identifies second mail
Recipient.
Does not accept second
Recipient. However will
deliver to first recipient.
Message will follow.
Receiver
354 Start mail input; end with
<CRLF>.<CRLF>
Gives permission to send
message.
Receiver 550 No such user here
53
Figure 11-6: Interactions in the Simple
Mail Transfer Protocol (SMTP)
Actor
Sender
Command
Comment
When in the course …
The message. Multiple lines
Of text. Ends with line
Containing only a single
Period: <CRLF>.<CRLF>
Receiver 250 OK
Receiver accepts message.
Sender
QUIT
Requests termination of
Session.
Receiver
221 Mail.Panko.Com Service
Closing transmission channel
End of transmission.
54
Figure 11-4: E-Mail

Viruses, Worms, and Trojan Horses

Widespread Problems

Often delivered by e-mail attachments

Use of antivirus software is almost universal but
not fully effective
55
Figure 11-4: E-Mail

Viruses, Worms, and Trojan Horses

Where to Do Scanning?


On client PCs

But users often turn off their software,

Fail to download virus definitions regularly

Or let their contracts lapse
On the corporate mail server or application
firewall

Users cannot turn off
56
Figure 11-4: E-Mail

Viruses, Worms, and Trojan Horses

Where to Do Scanning?


At an antivirus outsourcing company

Before mail ever reaches the company

High level of expertise
Defense in Depth

Do it in at least two places
57
Figure 11-4: E-Mail

Spam

Unsolicited commercial e-mail

Why filter?

Potential sexual harassment suits

Time consumed by users deleting them

Time consumed by staff to delete them

Bandwidth and storage consumed

Legitimate messages lost because overlooked
58
Figure 4-11: E-Mail

Spam

Separating SPAM from legitimate e-mail is difficult

Many spam messages get through to users

Some legitimate messages are deleted

Some firms merely mark messages as probable
spam
59
COS 338
Day 23
DAY 23 Agenda

Spring 2006 Book List

Http://perleybrook.umfk.maine.edu/sp2000bl.htm

Assignment 7 Due

Assignment 8 Posted


Due Dec 5 (last one)

Will drop lowest grade
Two labs left to grade (13 & 14)


Will drop the lowest grade
Today we will discuss Network Applications
61
Schedule for last 3 weeks

Today




Assignment 7 Due
Finish Chapter 111



Dec 5



Dec 8
Assignment 8 Due
Lab 8
 Due Dec 12
Discussion on Final Group Lab
 Build SOHO Network in OMS

5 Toshiba desktops
XP Pro and Linux?
1 Toshiba Server
Server 2003
1 HP 4SI Printer
JetDirect Office-connect
170x Print Server
Internet connections
Cisco Firewall and/or Router
Networked applications
Web Server
DHCP
??









Lab 8 Due
Part 2 of Final Lab
Dec 15



Dec 12


Exam 4
Capstone Progress Report Due
Part 1 of Final lab
 Planning
Part 3 of Final Lab
Dec 19



10-12 noon
Capstones due
10 min presentation of Capstone
projects



62
HTML and HTTP
Figure 11-7: HTML and HTTP
Webserver
Application
Browser
HTTP Request
HTTP Response
Client PC
HTML Document
Webserver
64
Figure 11-8: Downloading a Complex
Webpage with Two Graphics Files
HTML Document
Browser
Client PC
Webserver
Application
Webserver
As
Displayed
2
Graphics
Files
Webpage Consists of Three Files
Rendered as a Single Page On-Screen
65
Figure 11-8: Downloading a Complex
Webpage with Two Graphics Files
HTML Document
HTML Document
Browser
Client PC
As
Displayed
Webserver
Application
2
Graphics
Files
Webserver
Download Requires 3
HTTP Request-Response Cycles;
Downloads HTML Page First
It has Tags to Identify Other Files
66
Figure 11-8: Downloading a Complex
Webpage with Two Graphics Files
Browser
Client PC
As
Displayed
Webserver
Application
2
Graphics
Files
Webserver
Based on Tags in HTML Document,
Browser Requests Downloads of
Remaining Graphics or Other Files
Browser Renders Combined Webpage on Screen
67
Figure 11-8: Downloading a Complex Webpage
with Two Graphics Files

Quiz: Your browser downloads a webpage with
three graphics images, a sound sequence,
and a Java applet. How many files will your
browser have to download?
68
Figure 11-9: Examples of HTTP Request and
Response Messages

HTTP Request Message

GET /panko/home.htm HTTP/1.1[CRLF]

Host: voyager.cba.hawaii.edu[CRLF]
69
Figure 11-9: Examples of HTTP Request and
Response Messages

HTTP Response Message

HTTP/1.1 200 OK[CRLF]

Date: Tuesday, 20-JAN-2004 18:32:15 GMT[CRLF]

Server: name of server software[CRLF]

MIME-version: 1.0[CRLF]

Content-type: text/plain[CRLF]

[CRLF]

File to be downloaded
70
Actual Response
=~=~=~=~=~=~=~=~=~=~=~= PuTTY log 2005.12.01 13:32:02 =~=~=~=~=~=~=~=~=~=~=~=
GET /start.htm
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>Main Page</title>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
<link href="cos.css" rel="stylesheet" type="text/css" />
</head>
<body background="ClearDay.jpg">
<p><img src="umfkb.gif" width="640" class="box1" /></p>
<p>
<h1 align="left" class="big">Tony Gauvin's Web Site
<img src="best_ne_seal_trans.gif" width="180" height="173" hspace="50" align="absmiddle" /></h1>
</p>
<p class="title">Textbook Lists</p>
<ul>
<li><a href="sp2006BL.htm" target="_blank">Spring 2006</a>
</li>
</ul>
<p class="title">Presentations</p>
<p class="dingbat" >Miscellaneous Presentations </p>
<ul>
<li>
<a href="http://perleybrook.umfk.maine.edu/slides/Tony%20Gauvin%20resume.ppt">Tony
Gauvin's Resume </a>
</li>
<li><a href="http://perleybrook.umfk.maine.edu/slides/hum%20102.ppt">Advice for
new UMFK Business Students </a>
</li>
<li><a href="http://perleybrook.umfk.maine.edu/slides/hum102Comp.ppt">Introduction to UMFK Academics For eCommerce Students</a>
</li>
<li><a href="http://perleybrook.umfk.maine.edu/slides/hum102FP.ppt">Introduction to Information Technologies at UMFK</a>
</li>
<li>
71
MIME

Multipurpose Internet Mail Extensions (MIME)

System for identifying format of a file.
 Used in e-mail attachments
 Used in HTTP downloads and other applications

Examples (Top-Level Media Type/Specific Type)
 Text/Plain (plain ASCII text)
 Image/JPEG (JPEG graphic file)
 Octet/Stream (un-interpreted bytes for application)
 Application/Postscript (Postscript application data)
72
E-Commerce
Figure 11-10: Electronic Commerce
Functions
Browser
Webserver
Application
E-Commerce
Server
Customer
PC
External
Bank
Internal
Warehouse
Database
74
Figure 11-10: Electronic Commerce
Functions

Webserver Functionality, Plus…

E-Commerce functionality

Online catalog

Shopping cart

Checkout, including payment

Customer resource management

Links to External Systems
 Credit card number checking
 Bank settlement
75
Figure 11-10: Electronic Commerce
Functions

E-Commerce functionality

Links to internal systems
 Accounting
 Pricing
 Warehousing (Product Availability)
 Shipment
 Etc.
76
Figure 11-11: Application Server (3-Tier
Architecture
Client PC
with
Browser
1.
Form
Webserver
Application
2.
Server
Data
Mainframe
Server of
External Company
Database
Server
77
Figure 11-11: Application Server (3-Tier
Architecture
Client PC
with
Browser
Webserver
3.
Mainframe
Query and
Application
Response
Server
Mainframe
Mainframe CICS and other matters (3)
Database
Server
Server of
External Company
78
Figure 11-11: Application Server (3-Tier
Architecture
Client PC
with
Browser
Webserver
Application
Server
4.
DB Server Mainframe
Query and
Response
5. External Query/
Response
Database Sever Interactions (4, 5)
Application program interfaces (API)
Both internal and external database hosts
Database
Server
Server of
External Company
79
Figure 11-12: E-Commerce Security
Subnet for
Internal Hosts
(Little or No Access
From Outside)
Ethernet
Switch
DMZ
Subnet
(Easy Access from Outside)
Customer
DMZ: Subnet for
Externally-Facing
Servers
Marketing
Client
Accounting
Server
E-Commerce
Server
80
Figure 11-12: E-Commerce Security
SSL/TLS
SSL/TLS provides
protection against
eavesdroppers
Customer
E-Commerce
Server
81
82
83
Web Services
Figure 11-13: Ordinary Webservice versus
Web Service
Ordinary Webservice
HTTP Request
Browser
HTTP Response
Webserver
Application
Webserver
Client PC
HTML Document
Ordinary webservice was created to download documents
85
Figure 11-13: Ordinary Webservice versus
Web Service
Web Service
HTTP Request
Client PC
SOAPCapable
Browser
HTTP Response
SOAP Message
Using XML Syntax
Web
Service
Webserver
-Interface
Properties
Methods
Web services are objects (programs)
Clients send them commands and data
Web services send back results
86
Figure 11-13: Ordinary Webservice versus
Web Service
Web Service
HTTP Request
Client PC
SOAPCapable
Browser
HTTP Response
SOAP Message
Using XML Syntax
Web
Service
Webserver
-Interface
Properties
Methods
Web service requests are sent via FTP
They are sent as SOAP messages written in XML
87
Figure 11-13: Ordinary Webservice versus
Web Service
Web Service
HTTP Request
Client PC
SOAPCapable
Browser
HTTP Response
SOAP Message
Using XML Syntax
Web
Service
Webserver
-Interface
Properties
Methods
Web services have interfaces that will accept commands
Commands contain methods and properties (parameters)
88
Figure 11-14: Simple SOAP Request and Response

Simple Object Access Protocol (SOAP)

Carried in HTTP request or response message

Formatted using XML Syntax

Similar to HTML syntax but
the sender and receiver can
create new tags that
they can then use in
transactions, such as
<price>$33</price>
HTTP Header
SOAP
Body
89
Figure 11-14: Simple SOAP Request and Response

Situation

There is a pricing object that returns the price if
another object sends the part number, quantity, and
shipping type (rush, etc.) on an interface

Objects can be on different computers
Request
(PartNum, Quantity, ShippingType)
Sending
Object
Pricing
Object
Response
(Price)
90
Figure 11-14: Simple SOAP Request and Response

SOAP Request Message
HTTP Request Header pointing to program
<?xml version=“1.0”>
<BODY>
<QuotePrice xmlns=“QuoteInterface”>
<PartNum>QA78d</PartNum>
<Quantity>47</Quantity>
<ShippingType>Rush</ShippingType>
</QuotePrice>
</BODY>
Note: xmlns specifies an XML namespace for the object
91
Figure 11-14: Simple SOAP Request and Response

SOAP Response Message
HTTP Response Header
<?xml version=“1.0”>
<BODY>
<QuotePrice xmlns=“QuoteInterface”>
<Price>$750.33</Price>
</QuotePrice>
</BODY>
92
Web Services: A More Complex Example
New
Not in Book
Service
Via HTTP:
SOAP +
XML
Client PC
With
Browser
Web service
1
(Object)
Server
Service Via HTTP:
SOAP + XML
Web service
2
(Object)
New: Not
In Book
Service Via HTTP:
SOAP + XML
Web service
3
(Object)
Mainframe
Minicomputer
93
Figure 11-15: Universal Description, Discovery, and
Integration (UDDI) Server for Web Services
UDDI Functions:
Client PC
2.
Web Service Interaction
1.
UDDI
Request for
Information,
Response
UDDI Server
Server with
Web Service
Interaction Between
UDDI Servers
to Fulfill a Request
White Pages
By name
Yellow Pages
By type
Green Pages
Details of how
to use,
payment, etc.
UDDI Server
94
Web Service Description Language (WSDL)

Protocol for asking a corporate
webserver about the company’s
SOAP-compliant services
Client PC
New: Not
In Book
WSDL
Request-Response Cycle
Corporate
Webserver
95
Perspective on Web Services


Benefits of Web Services
New: Not
In Book

Offers a way to standardize interactions between
objects over the Internet

Can make distributed computing far simpler once
Web services standards are fully developed
Concerns

High overhead (very chatty)

Standards immaturity

Security is embryonic
96
Peer-to-Peer Computing
Figure 11-16: Traditional Client/Server Application
Client PC
Client PC
Advantage:
Central Control
Client PC
Client PC
Client PC
Disadvantages:
Network Overload at Server
Underused Client Power
Central Control
Server Does Heavy Processing Work
98
Figure 11-17: Simple Peer-to-Peer (P2P) Application
Request
Client PC
Response
Benefits:
End User Freedom
No Network Bottleneck at Serve
Uses Client Capacity Better
Client PC
Problems:
Transient Presence of Clients
Transient Client IP Addresses
Security (No Central Control)
99
P2P Applications

Direct service, although some P2P systems
use facilitating servers for some of the work
Peer
Peer
Peer
Peer
Peer
Peer
100
Figure 11-18: Gnutella: Pure P2P with Viral
Networking
Gnutella
Client (ABC)
1. Init or
Search
Message
2.
Init or Search
Message
2. Init or
Search
Message
Gnutella
Client
(Carol)
3.
Init or Search
Message
Gnutella
Client (DEF)
3. Init or
Search
Message
3. Init or
Search
Message
4.
P2P File Download
HTTP Request-Response Gnutella
Cycle
Client (XYZ)
Gnutella
Client (GHI)
101
Gnutella

Gnutella uses viral networking for initial
identification messages

To announce a client’s presence and see what
other users are available

Time-to-live limited to 5-7 hops to moderate load on
network

Gnutella uses viral networking for searches

Gnutella uses direct interaction for file
download
102
Figure 11-19: Napster
Napster
Index Server
1.
Uploads List
Of Available Files
When Connects
Client PC
2.
Search Query
3.
Response
File List
List of
Available
Files
From All
Current Clients
Client PC
4.
Large P2P
Download
Client PC
103
Figure 11-20: Use of Servers in Instant Messaging
Pure P2P IM
Ongoing
Communication
Client PC A
Client PC B
In pure P2P IM, there are no servers
The clients communicate directly
Finding each other can be difficult because of DHCP
104
Figure 11-20: Use of Servers in Instant Messaging
Use of a Presence Server
1.
Presence
Information
Client PC C
3.
Ongoing
Communication
2.
Presence
Information
Client PC D
Clients register with presence servers
Presence servers notify other clients as appropriate
Clients use this information to communicate directly
105
Figure 11-20: Use of Servers in Instant Messaging
Use of a Relay Server
All Communication
Goes through the
Relay Server
Client PC E
Presence
Information
Client PC F
Relay servers route all IM messages.
This permits security filtering and other services.
It limits privacy because the relay server sees everything.
106
How Grid Computing Works

Using many (>100 and more like 10000)
ordinary computers connected together over a
network to perform a single task or a series of
related tasks

Examples

Seti@home

Beowulf

Factoring large numbers
107
Figure 11-21: SETI@Home Client PC Processor
Sharing
1. I am idle. Give me work.
2. Here is work to do
3. I am busy now. Here are my results.
Idle Client PC
With SETI@home
Screen Saver Program
SETI@home
Server
No Interaction
Busy Client PC
With SETI@home
Screen Saver Program
108
Seti@home
109
Largest number ever factored
110
Perspective on Application Architectures

Driven primarily by the evolution of client
processing power

Terminal-Host: Client processing power was
uneconomical

Client/Server: Client PCs could handle some
of the load

P2P: Clients have rich power to do most
things
111
Topics Covered
Application Architectures

Terminal-Host Computing



Host does all the work
Client/Server Computing

File server program access: client executes the program

Client/server processing: both the client and the server both
do considerable work
Peer-to-Peer (P2P)

The client PCs do most or all of the work

If servers are present, they facilitate the PCs
113
Application Architectures


E-Mail

SMTP to send

POP or IMAP to download

Web-based e-mail uses HTTP
E-Mail Bodies

RFC 822 and RFC 2822 for pure-text messages

HTML bodies

UNICODE for international alphabets
114
Topics Covered

Viruses, Worms, and Trojan horses




Thwarted by antivirus scanning
Where to do the scanning
Spam
HTML and HTTP

HTTP – sending and receiving messages

HTML – body format

Most pages have text, graphics, etc.
 Multiple request-response cycles per webpage
115
Topics Covered

HTTP Request and Response Messages


All-text formats
MIME

Standard for describing file formats
116
Topics Covered


E-Commerce

Functionality beyond webservice

Links to other systems

Application server integrates information
Web Services

Generalized way to send commands to remote
programs and get responses

Formatted in SOAP format which uses XML syntax

UDDI and WSDL
117
Topics Covered

P2P Computing

Exploits the growing processing power of client
PCs

May use servers to facilitate what is primarily a P2P
application

File sharing
 Gnutella does not use facilitating servers
 Napster (the original) did use facilitating servers
118
Topics Covered

P2P Computing

Instant Messaging (IM)
 Pure P2P
 Presence servers
 Relay servers

Processor Sharing (e.g., SETI@home)
119