12/6/00 Doc 26, Tiers & Peers slide # 1 CS 580 Client-Server Programming Fall Semester, 2000 Doc 26 Tiers & Peers Contents How many Tiers? ............................................................................................... 2 Client Presentation ............................................................................................. 3 Peer-to-Peer....................................................................................................... 4 Gnutella........................................................................................................... 5 Multicast Sockets ............................................................................................ 7 Bluetooth......................................................................................................... 8 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 2nd Ed, Harold, O'Reilly, 2000, chapter14 Bluetooth Web site http://www.bluetooth.com/ Copyright ©, All rights reserved. 2000 SDSU & Roger Whitney, 5500 Campanile Drive, San Diego, CA 92182-7700 USA. OpenContent (http://www.opencontent.org/opl.shtml) license defines the copyright on this document. 12/6/00 Doc 26, Tiers & Peers slide # 2 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 12/6/00 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: http://joel.editthispage.com/stories/storyReader$51 The client is not just a way to send the protocol to the server 12/6/00 Doc 26, Tiers & Peers slide # 4 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 12/6/00 Doc 26, Tiers & Peers slide # 5 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 12/6/00 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 http://dss.clip2.com/gnutella.html for a report on growth of Gnutella networks 12/6/00 Doc 26, Tiers & Peers slide # 7 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/j iniIntro.html and http://www.sun.com/jini/index.html for more info on Jini 12/6/00 Doc 26, Tiers & Peers slide # 8 Bluetooth Wireless ad-hoc network standard Radio Specs Range 10 meters Frequency band 2.4 Ghz Max Data transfer721kbit/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.