COS 338
Day 22
DAY 22 Agenda
Spring 2006 Book List
Http://perleybrook.umfk.maine.edu/sp2000bl.htm
Lab 7 corrected
1 A, 1 C, 3 F’s and 1 non-submit
Assignment 7 Posted
Due Dec 1
Assignment 8 Posted
Due Dec 5 (last one)
Will drop lowest grade
Exam 3 Graded
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 Dec 8
Finish Chap 10 and begin chapter 11 Exam 4
Assignment 8 posted Capstone Progress Report Due
Due Dec 5 Part 1 of Final lab
Planning
Dec 1
Assignment 7 Due Dec 12
Finish Chapter 111 Lab 8 Due
Dec 5 Part 2 of Final Lab
Assignment 8 Due Dec 15
Lab 8 Part 3 of Final Lab
Due Dec 12
Dec 19
Discussion on Final Group Lab
10-12 noon
Build on SOHO Network in OMS
5 desktops Capstones due
1 Server
10 min presentation of Capstone projects
1 Printer
Internet connections
Firewall and/or router
Networked applications
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 Managed
Software (Manager) Device
Manager manages multiple
managed devices from a central
location
RMON Probe
5
Figure 10-16: Simple Network Management
Protocol (SNMP)
Network
Network Management
Management
Software (Manager)
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
Network Management
Management
Software (Manager)
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 Management
Software (Manager) Information
Base (MIB)
Management
Information
Base (MIB)
Management
MIB stores data about devices.
Information
MIB on manager stores all. Base (MIB)
MIB on device stores local information
RMON Probe
8
Figure 10-16: Simple Network Management
Protocol (SNMP)
Network Management Management
Software (Manager) Information
Base (MIB)
Simple Network
Management Protocol (SNMP)
Management
Information
Base (MIB)
Command (Get, Set, etc.) Management
Information
Response Base (MIB)
Trap
RMON Probe
9
Figure 10-17: SNMP Object Model
Management
Information
SNMP Object Model 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
Management
Information
SNMP IP Objects 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
Management
Information
SNMP IP Objects (Continued) 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
Management
Information
SNMP TCP Objects 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
Management
Information
SNMP UDP Objects Base (MIB)
Error: no application on requested port
Traffic statistics
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 high-
priority 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
Telephone
Network
Modem Modem
Host
Dumb
Terminal
40
Figure 11-2: Client/Server Computing
File Server Program Access
1. 3.
2. Program
Program
Program Executed on
Stored on
Downloaded to Client PC Client PC!
File Server
Client PC
File Server When Called
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
Response Message
Client Program Server Program
Does Light I/O and
Post-Download Does Heavy
Processing Database
and Other Heavy
Client PC Processing
Server
Highly scalable: Use larger server as number of clients increases
42
Figure 11-3: Web-Enabled Application (E-Mail)
HTTP Request Message
HTTP Response Message
Client is Browser 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 Receiver’s Mail
Server Server
Simple Mail Transfer Protocol
Sending (SMTP) to transmit mail in real Receiving
E-Mail E-Mail
time to a user’s mail server or
Client Client
between mail servers
Sender-initiated
46
Figure 11-5: E-Mail Standards
POP or
IMAP
To Receive
Sender’s Mail Receiver’s Mail
Server Server
POP or IMAP to download mail to
Sending E-Mail Receiving
receiver when the receiver is next
Client E-Mail
capable of downloading 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 Receiver’s Mail
Server Server
Message Body Format Standard
Sending Receiving
E-Mail RFC 822 or 2822 E-Mail
Client Message HTML body Client
UNICODE
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
Receiving SMTP
220 Mail.Panko.Com Ready is opened, the receiver
Process
signals that is is ready.
Sender asks to begin
Sending SMTP
HELO Voyager.cba.Hawaii.edu Sending a message.
Process
Gives own identity.
Receiver signals that it
Receiver 250 Mail.Panko.Com Is ready to begin
Receiving a message.
51
Figure 11-6: Interactions in the Simple
Mail Transfer Protocol (SMTP)
Actor Command Comment
Sender identifies the sender
MAIL FROM: Panko@
Sender (mail author, not SMTP
voyager.cba.hawaii.edu
process).
Accepts author. However,
Receiver 250 OK
May reject mail from others.
Sender RCPT TO: Ray@Panko.com Identifies first mail recipient.
Receiver 250 OK Accepts first recipient
52
Figure 11-6: Interactions in the Simple
Mail Transfer Protocol (SMTP)
Actor Command Comment
Identifies second mail
Sender RCPT TO:Lee@Panko.com
Recipient.
Does not accept second
Receiver 550 No such user here Recipient. However will
deliver to first recipient.
Sender DATA Message will follow.
354 Start mail input; end with Gives permission to send
Receiver
. message.
53
Figure 11-6: Interactions in the Simple
Mail Transfer Protocol (SMTP)
Actor Command Comment
The message. Multiple lines
Of text. Ends with line
Sender When in the course …
Containing only a single
Period: .
Receiver 250 OK Receiver accepts message.
Requests termination of
Sender QUIT
Session.
221 Mail.Panko.Com Service
Receiver End of transmission.
Closing transmission channel
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 Dec 8
Assignment 7 Due Exam 4
Finish Chapter 111 Capstone Progress Report Due
Dec 5 Part 1 of Final lab
Planning
Assignment 8 Due
Lab 8 Dec 12
Due Dec 12 Lab 8 Due
Discussion on Final Group Lab Part 2 of Final Lab
Build SOHO Network in OMS
5 Toshiba desktops
Dec 15
XP Pro and Linux? Part 3 of Final Lab
1 Toshiba Server
Server 2003 Dec 19
1 HP 4SI Printer
JetDirect Office-connect 10-12 noon
170x Print Server
Capstones due
Internet connections
Cisco Firewall and/or Router 10 min presentation of Capstone
Networked applications projects
Web Server
DHCP
??
62
HTML and HTTP
Figure 11-7: HTML and HTTP
Webserver
Browser Application
HTTP Request
HTTP Response
Webserver
Client PC HTML Document
64
Figure 11-8: Downloading a Complex
Webpage with Two Graphics Files
HTML Document
Browser
Webserver
Client PC Application
2
Graphics
Files
Webserver
As Webpage Consists of Three Files
Displayed Rendered as a Single Page On-Screen
65
Figure 11-8: Downloading a Complex
Webpage with Two Graphics Files
HTML Document
HTML Document
Browser Webserver
Client PC Application
2
Graphics
Webserver Files
Download Requires 3
HTTP Request-Response Cycles;
As
Downloads HTML Page First
Displayed
It has Tags to Identify Other Files
66
Figure 11-8: Downloading a Complex
Webpage with Two Graphics Files
Browser Webserver
Application
Client PC 2
Graphics
Webserver Files
Based on Tags in HTML Document,
Browser Requests Downloads of
As Remaining Graphics or Other Files
Displayed
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
Main Page
Tony Gauvin's Web Site
Textbook Lists
Spring 2006
Presentations
Miscellaneous Presentations
Tony
Gauvin's Resume
Advice for
new UMFK Business Students
Introduction to UMFK Academics For eCommerce Students
Introduction to Information Technologies at UMFK
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 E-Commerce
Application Server
Customer
PC
External Internal
Bank 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
Web-
with
server Application
Browser 1. 2. Server
Form Data
Mainframe
Server of Database
External Company Server
77
Figure 11-11: Application Server (3-Tier
Architecture
3.
Client PC Mainframe
Web-
with Query and
server Application
Browser Response
Server
Mainframe
Database
Server
Mainframe CICS and other matters (3)
Server of
External Company 78
Figure 11-11: Application Server (3-Tier
Architecture
Client PC
Web-
with
server Application
Browser
Server
4.
DB Server Mainframe
Query and
Response
5. External Query/
Response
Database Sever Interactions (4, 5) Database
Application program interfaces (API) Server
Both internal and external database hosts Server of
External Company 79
Figure 11-12: E-Commerce Security
Subnet for
Internal Hosts
(Little or No Access
From Outside)
DMZ
Customer
Ethernet Subnet
Switch (Easy Access from Outside)
DMZ: Subnet for
Externally-Facing
Servers
Accounting E-Commerce
Marketing Server
Server
Client
80
Figure 11-12: E-Commerce Security
Customer
SSL/TLS
SSL/TLS provides
protection against E-Commerce
eavesdroppers 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
SOAP- HTTP Response Web
Capable Service
Browser -- Webserver
Client PC
Interface
Properties
SOAP Message Methods
Using XML Syntax
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
SOAP- HTTP Response Web
Capable Service
Browser -- Webserver
Client PC
Interface
Properties
SOAP Message Methods
Using XML Syntax
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
SOAP- HTTP Response Web
Capable Service
Browser -- Webserver
Client PC
Interface
Properties
SOAP Message Methods
Using XML Syntax
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 HTTP Header
create new tags that
they can then use in SOAP
transactions, such as Body
$33
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 Pricing
Object Object
Response
(Price)
90
Figure 11-14: Simple SOAP Request and
Response
SOAP Request Message
HTTP Request Header pointing to program
QA78d
47
Rush
Note: xmlns specifies an XML namespace for the object
91
Figure 11-14: Simple SOAP Request and
Response
SOAP Response Message
HTTP Response Header
$750.33
92
Web Services: A More Complex Example
New New: Not
Not in Book Web service In Book
Service 1
Via HTTP: (Object)
SOAP +
XML Service Via HTTP:
SOAP + XML
Server
Client PC Service Via HTTP: Web service
With SOAP + XML 3
Browser (Object)
Web service
2
(Object) Mainframe
Minicomputer
93
Figure 11-15: Universal Description, Discovery,
and Integration (UDDI) Server for Web Services
Client PC UDDI Functions:
2.
Web Service Interaction
White Pages
By name
Server with
Web Service Yellow Pages
1.
UDDI By type
Request for
Interaction Between Green Pages
Information,
UDDI Servers Details of how
Response
to Fulfill a Request to use,
payment, etc.
UDDI Server UDDI Server
94
Web Service Description Language (WSDL)
New: Not
Protocol for asking a corporate In Book
webserver about the company’s
SOAP-compliant services
WSDL
Client PC
Request-Response Cycle
Corporate
Webserver
95
Perspective on Web Services
New: Not
In Book
Benefits of Web Services
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 Client PC Client PC Client PC
Advantage: Disadvantages:
Central Control 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
Response
Client PC Client PC
Benefits: Problems:
End User Freedom Transient Presence of Clients
No Network Bottleneck at Serve Transient Client IP Addresses
Uses Client Capacity Better 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 2. 3.
Client (ABC) Init or Search Init or Search
1. Init or Message Message
Search
Message Gnutella 3. Init or
Client (DEF) Search
2. Init or Message
Search
Message 3. Init or
Gnutella Search
Client 4. Message
(Carol) P2P File Download
HTTP Request-Response Gnutella Gnutella
Cycle Client (XYZ) 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 File List
1.
List of
Uploads List
Available
Of Available Files
Files
When Connects 2.
From All
Search Query
Current Clients
3.
Response
4.
Large P2P
Download
Client PC Client PC 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. 2.
Presence Presence
Information Information
3.
Ongoing
Client PC C Communication 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 Presence
Relay Server Information
Client PC E 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
SETI@home
With SETI@home
Server
Screen Saver Program
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