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CS 580 Client-Server Programming
Fall Semester, 2000
Tiers & Peers
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© 2000, All Rights Reserved, SDSU & Roger Whitney
San Diego State University -- This page last updated 06-Dec-00
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Contents of Doc 26, Tiers & Peers
References
Overview
of Two- and Three-Tier Client/Server Architectures Gartner Report, via
Governor's Office for Technology, Kentucky, about 1998
http://cdc.state.ky.us/dcs/tiers.htm
Gnutella
news
http://www.gnutellanews.com/
http://gnutella.wego.com/
Gnutella
Protocol 0.04
http://dss.clip2.com/GnutellaProtocol04.pdf
Gnutella:
To the Bandwidth Barrier and Beyond, November 6, 2000
http://dss.clip2.com/gnutella.html
Wired
P2P Pages, Lists of clients, protocols, etc
http://www.wired.com/wired/archive/8.10/p2p_pages.html?pg=1
Independence
Array, Jermoe Kuptz, Wired October, 2000, pp. 236-237
Java
Network Programming 2
nd
Ed, Harold, O'Reilly, 2000, chapter14
Bluetooth
Web site
http://www.bluetooth.com/
Odds
& Ends
How
many Tiers?
Typical
business application is claimed to have:
- Presentation
or Display logic & user interaction
- Business
rules
- Data
access
Three
Tier
- Client
handles presentation
- Server
handles business rule
- Server
gets data from database
Two
Tier
- Client
handles presentation and perhaps business rules
- Server
handles data access and perhaps business rules
Thin
client only handles presentation
Thick
client also handles business rules
Four
Tier
- Presentation
- Flow
control functions
- Business
rules
- Data
access logic
Client
Presentation
To
the user the client is the application
If
the user does not like the interface, they do not like the application
See
User Interface Design for Programmers an on-line book for user interface design
at:
http://joel.editthispage.com/stories/storyReader$51
The
client is not just a way to send the protocol to the server
Peer-to-Peer
Back
to the future
Peer-to-peer
- Clients
communicate with other clients directly
- Clients
are also servers
Why
peer-to-peer
- Environments
that do not have dedicated servers
- Lack
of system administrator
- Ad-hoc
networks
- Wireless
mobile computers
- Avoid
central control
Some
examples
- AppleTalk
networks
- Gnutella
- Bluetooth
Gnutella
Created
by Justin Frankel & Tom Pepper at AOL's Nullsoft
Posted
for a few hours on March 14 2000
The
protocol was reversed-engineered
Many
clones now exist
Gnutella
is a file-sharing program
User
lists files to share with their gnutella client
When
the client is running other gnutella clients can request copies of your files
How
it works
Gnutella
client starts with locations N other clients
Each
client answers the request and sends it on to all clients it knows
TTL
(time to live)
- Number
of times a request will be forwarded to another client
- Maximum
TTL is 7
Radius
- the clients that are within 7 hops
A
radius can have up to 10,000 clients
Protocol
does not scale well, but works better than some thought possible
See
Gnutella: To the Bandwidth Barrier and Beyond, November 6, 2000
http://dss.clip2.com/gnutella.html
for a report on growth of Gnutella networks
Multicast
Sockets
Unicast
sockets
- Provide
point-to-point communication
- Client
needs to know server address
Multicast
sockets
- Each
multicast address is a group of hosts
- Hosts
can leave/join the group dynamically
- Packets
are sent to all hosts in the group
- TTL
of packet indicates how far a packet will be sent
Jini
uses multicast
- Jini
network is an ad-hoc network of services & clients
- Services
use multicast to find a naming service (broker)
- Clients
use multicast to find a naming service to find services
See
http://www.eli.sdsu.edu/courses/spring99/cs696/notes/jiniIntro/jiniIntro.html
and
http://www.sun.com/jini/index.html
for more info on Jini
Bluetooth
Wireless
ad-hoc network standard
Radio
Specs
Range
10 meters
Frequency
band
2.4
Ghz
Max
Data transfer
721kbit/s
+ 3 voice channels
Packet
switching protocol with frequency hopping
1600
hops/second
Piconet
- Up
to 7 devices connected by radio
Multiple
piconets can be linked together dynamically
Uses
error correction and encryption
Started
by Ericsson, IBM, Intel Corporation, Nokia and Toshiba in 1998
Has
wide spread industry support
More
popular in Europe
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