SDSU CS 580 Client-Server Programming
Fall Semester, 2000
Tiers & Peers
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San Diego State University -- This page last updated 06-Dec-00

Contents of Doc 26, Tiers & Peers


Overview of Two- and Three-Tier Client/Server Architectures Gartner Report, via Governor's Office for Technology, Kentucky, about 1998

Gnutella news

Gnutella Protocol 0.04

Gnutella: To the Bandwidth Barrier and Beyond, November 6, 2000

Wired P2P Pages, Lists of clients, protocols, etc

Independence Array, Jermoe Kuptz, Wired October, 2000, pp. 236-237

Java Network Programming 2 nd Ed, Harold, O'Reilly, 2000, chapter14

Bluetooth Web site

Doc 26, Tiers & Peers Slide # 2
Odds & Ends

How many Tiers?

Typical business application is claimed to have:

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
Flow control functions
Business rules
Data access logic

Doc 26, Tiers & Peers Slide # 3

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:$51

The client is not just a way to send the protocol to the server

Doc 26, Tiers & Peers Slide # 4


Back to the future


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

Doc 26, Tiers & Peers Slide # 5


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

Doc 26, Tiers & Peers Slide # 6
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 for a report on growth of Gnutella networks

Doc 26, Tiers & Peers Slide # 7

Multicast Sockets

Unicast sockets

Multicast sockets

Jini uses multicast

See and for more info on Jini

Doc 26, Tiers & Peers Slide # 8


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


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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2000 SDSU & Roger Whitney, 5500 Campanile Drive, San Diego, CA 92182-7700 USA.
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