Application layer

Application layer is the top layer of the OSI server layer model which provides services that directly support user applications such as database access, e-mail and file transfers. That's why we can say that application layer is not the application itself that is doing the communication. It is a service layer that provides these services.

In the same time it allows applications to communicate with applications on other computers as though they were on the same computer. This is a kind the interface to the communications environment which is used by the application process.

So this layer is responsible for communicating application process parameters. That's why this layer provider different services to the applications. However we can identify that this layer provides services to user defined application processes and not to the end user.If a programmer writes an application program that uses network services, this is the layer that application program will access. However common application layer services provide semantic conversion between associated application processes.

Application Layer includes,

• Protocol
  
  • APPC( Advanced Program-to-Program Communication)
    
  • AMQP( Advanced Message Queuing Protocol)
    
  • BOOTP( Bootstrap Protocol)
    
  • CFDP(Coherent File Distribution Protocol)
    
  • DDS(Data Distribution Service)
    
  • DHCP(Dynamic Host Configuration Protocol)
    
  • DNS,(Domain Name System (Service) Protocol)
    
  • HTTP( HyperText Transfer Protocol)
    
  • IRCP( Internet Relay Chat Protocol)
    
  • LDAP( Lightweight Directory Access Protocol)
    
  • LPD( Line Printer Daemon Protocol)
    
  • NFS( Network File System)
    
  • SSH( Secure Shell)
    
  • SSMS( Secure SMS Messaging Protocol)
    
  • TCAP( Transaction Capabilities Application Part)
    
  • TDS(Tabular Data Stream)
    
  • TELNET( Terminal Emulation Protocol of TCP/IP)
    
  • TFTP(Trivial File Transfer Protocol)
    
  • NTP( Network Time Protocol)
    
  • SMB( Server Message Block)
    
  • SMTP(Simple Mail Transfer Protocol)
    
  • SNMP( Simple Network Management Protocol)
    
  • SNTP(Simple Network Time Protocol)
    
  • SPTP( Secure Parallel Transfer Protocol)
    
  • TSP(Time Stamp Protocol)
    
  • VTP( Virtual Terminal Protocol)
    
  • NIS(Network Information Service)
    
  • NNTP( Network News Transfer Protocol)
    

 

• Software
  
  • Web Browser
    
  • Apache
    
  • FileZilla
    
  • MS-DOS
    
  • Outlook
    
  • MS Outlook
    
  • Utorrent
    

 

Functions & Servicers

 

• Support for file transfers
  
• Ability to print on a network
  
• Browsing the World Wide Web
  
• Electronic mail
  
• Electronic messaging
  
• Virtual terminal access
  
• Network management.
  
• Makes sure that the other party is identified and can be reached
  
• authenticates either the message sender or receiver or both
  
• Makes sure that necessary communication resources exist
  
• Ensures agreement at both ends about error recovery procedures, data integrity and privacy
  
• Determines protocol and data syntax rules at the application level