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Application Layer

Functionality andProtocols

Network Fundamentals

Chapter 3

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Applications LayerThe Interface between Human & Data Networks

The Application layer(Layer 7)

provides the interface between the applications we use tocommunicate and the underlying network over which our messagesare transmitted.

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Applications: i.e., software program used by people.

Network-aware applications: able to communicate directly with thelower layers protocol.

Services: interface with the network and prepare the data for transfer.

Protocols: define the standards and formats of data.

Applications provide people with a way to create messages.Application layer services establish an interface to thenetwork. Protocols provide the rules that govern how data istreated.

Applications, Services and Protocols

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Client: the device requesting the information.

Server: the device responding to the request.

Application layer protocols describe the format of the requests andresponses between clients and servers. (user data + control info)

The Client/Server Model

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The Peer-to-Peer Model

Two forms:

Peer-to-peer Networks: no dedicated server; decentralized.

Peer-to-peer Applications:

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Widely-known TCP/IP Application layer Protocols

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Application Layer Protocols & Svc Ex. DNS

Domain Name System (DNS) - TCP/UDP Port 53 Service that provides the IP address of a web site or domain nameso a host can connect to it.

uses hierarchy of decentralized DNS servers.

Describe the features of the DNS protocol and how this protocol supports DNSservices.

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Application Layer Protocols & Svc Ex. HTTP

Describe the features of the HTTP protocol and how this protocol supports thedelivery of web pages to the client

Hypertext Transfer Protocol (HTTP) - TCP Port 80

Used to transfer information between web clients and web servers.

Most web pages are accessed using HTTP.

Lab 3.4.2

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Application Layer Protocols & Svc Ex. SMTP/POP

Describe the features of the POP and SMTP protocols, and how these protocolssupport E-mail services

Lab 3.4.3

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Application Layer Protocols & Svc Ex. Telnet

Describe the features of the Telnet protocol and identify several of its uses inexamining and managing networks.

Telnet - TCP Port 23

Service that allows admin to login to a host from a remote locationand control the host as though they were logged in locally.

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Summary

Define the application layer as the source anddestination of data for communication acrossnetworks.

Explain the role of protocols in supportingcommunication between server and client processes.

Describe the features, operation, and use of well-

known TCP/IP application layer services (HTTP,DNS, SMTP).