8. The Application Layer
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The Application Layer
Receives services from the transport layer and provides
services to users (humans or software)
Provides user interfaces and support services such as e-mail,
remote file access and transfer, access to the WWW
Three general issues related to the application layer:
network
application architecture (mostly the client-server paradigm)
,
addressing
, and
services
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8.1 Network Application Architecture
We write programs that
Run on (different) end systems
Communicate over a network; e.g., web server software
communicates with browser software
Here the interest is
not
to write software for network-core devices
Network-core devices do not run user applications
Three application architectures
Client-server
Peer-to-Peer (P2P)
Hybrid of client-server and P2P
The Client-Server Model
A computer runs a program to either
request
a service from
another computer (
client
) or to
provide
a service to another
computer (
server
)
