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Network Applications

2010S3 - 2011/12

Gihan Dias

CS2032

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Network Applications

World-Wide Web

 – Facebook

 – Googledocs

 – YouTube

 – Games

Skype, videoconferencing

BitTorrent

Remote Files

Remote Deskto

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Why Internet Applications?

Without applications, Internet (or anyother network) would be useless

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Application

Transport

Network

Data Link

Physical

2

1

3

4

7

Internet Application

App. Layer in Internet Stack 

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Internet Applications Layer

Model Application talks directly to the transport layer

(TCP or UDP)

Application Layer defined as a protocol – both sides must implement the protocol

APIs usually not defined by IETF

Third-party APIs available – C, Java, VB, XML, etc.

Generally use the client-server model

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Client-Server Model

Some Internet hosts provide a service(servers)

 – web server

 – POP server

 – SIP server

Other hosts (clients) use these services Typically, servers listen on a given port

 – waiting for some client to connect

I’m listening... 

Someone connect to me … 

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Client-server operation (cont.)

Servers should be always on

 – generally sit in a data centre

 – or on the “cloud” 

Clients are often user machines

 – PCs, phones, mobile devices,

 – sometimes other servers

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Common Internet App. Protocols

E-mail

 – Simple Mail Transfer Protocol SMTP

 – Post Office Protocol (V3) POP

 – Interactive Mail Access Protocol IMAP

File Transfer

 – File Transfer Protocol FTP

 – BitTorrent

Domain Name Service DNS

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Common Protocols (cont.)

Web

 – HyperText Transfer Protocol HTTP

Remote Login

 – Telnet

 – rlogin

 – Secure Shell SSH

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Common Protocols (Cont.)

Remote graphics

 – X Window System

 – Microsoft Remote Desktop

 – VNC

Remote File Systems

 – Sun Network File System NFS

 – SMB / CIFS

Network Management

 – Simple Network Management Protocol

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Common Protocols (cont.)

Voice and Teleconferencing

 – Session Initiation Protocol SIP

 – H.323

many others...

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Protocol Format

Many protocols have a similar format

Client - Server

Command / Response

 – text commands

 – numeric responses

Half duplex data exchange

 – why?

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Protocol Format (cont.)

ASCII text commands and responses>> MAIL From:<gihan@mail.mrt.ac.lk> SIZE=54

<< 250 2.1.0 <gihan@mail.mrt.ac.lk>... Sender ok>> RCPT To:<gihan@cse.mrt.ac.lk>

<< 250 2.1.5 <gihan@cse.mrt.ac.lk>... Recipient ok

 – why?

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End