in client server there are two levels client machine and 
database server machine so client and server are the 
entities to be tested . we check low multimedia type of 
transaction envoirnment and intranet envoirment
in web testing client,server,network are the entities to be 
tested.we do testing in richmultimedia type of transaction 
envoirnment and internet invoirnment

Web applications are essentially client/server 
applications - with web servers and 'browser' clients. 
Consideration should be given to the interactions between 
html pages, TCP/IP communications, Internet connections, 
firewalls, applications that run in web pages (such as 
applets, javascript, plug-in applications), and 
applications that run on the server side (such as cgi 
scripts, database interfaces, logging applications, dynamic 
page generators, asp, etc.). Additionally, there are a wide 
variety of servers and browsers, various versions of each, 
small but sometimes significant differences between them, 
variations in connection speeds, rapidly changing 
technologies, and multiple standards and protocols. The 
result is that testing for web sites can become a major 
ongoing effort.

Client-server: business logic willbe placed in client.but 
in three tier business logic placed in application server.
Client-Server: If ay changes we have to do in client. But 
in three tier no need to do in client we can change in 
application server.
client-server is intranet testing, web testing is internet 
testing