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Application Layer of TCP/IP Protocol

Application layer is the top layer of TCP/IP protocol.  The Application layer includes all the processes that use Transport layer protocols to deliver data to the Internet layer. There are many application protocols, and new protocols are frequently added.

Some common TCP/IP applications include:

• Telnet Protocol
• File Transfer Protocol (FTP)
• Simple Network Management Protocol (SNMP)
• Simple Mail Transfer Protocol (SMTP)
• Dynamic Host Configuration Protocol (DHCP)
• Domain Name System (DNS)
• Network Information Service (NIS)
• Network File System (NFS)
• Secure shell (SSH)
• Secure copy (SCP)

The Application layer handles the details of the particular application. The primary functions of this layer are:

• Formatting data – Data is formatted based on a computer’s architecture. For example, text formatting is done in American Standard Code for Information Interchange (ASCII) on a UNIX® host, and Extended Binary Coded Decimal Interchange Code (EBCDIC) on an IBM mainframe computer. Protocols operating at this layer of the model encapsulate packets into streams or messages.
• Presenting data – If end users specify how they want their data presented to them, the Application layer makes sure that it reaches the end users in this format. A common syntax ensures compatibility between various end-user applications and machines. The Application layer also provides translations between locally represented data and data used for transfer between end systems.
• Transporting data – The Application layer stipulates a transfer syntax, which represents a coding agreement for the data to be formatted and transferred. remote procedure call (RPC) libraries allow high-level language programs to make procedure decisions on other machines on the network to organize the flow of data.

Protocols, such as NIS and NFS, use RPC for session management between clients and servers.

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Understanding Application Layer Protocols

• By Matthew Syme, Philip Goldie.
• Sample Chapter is provided courtesy of Prentice Hall PTR.
• Date: Mar 5, 2004.

Quiz

Q4. True:False:  RPC is supported in Solaris environment.

 A: True

 Q5. TI RPC stands for ____________________ ?

 Ans: Transport - Independent Remote Procedure Call (TI-RPC)

 Q6. ________ resolves the differences in data byte ordering, data type size, representation and alignment between architecture.

 A: XDR

 Q7. XDR stands for _____________________  ?

 A: External Data Representation

160. Which file is used to identify and register the reserved port numbers, services, and protocols for the Internet.  (well know ports)

Ans: /etc/inet/services

161.  Which port is reserved for telnet ?

Ans: 23

162. Which port is reserved for FTP ?

Ans: 23

163. Which port is reserved for HTTP ?

Ans: 80

164. Which init script starts the inetd daemon ?

Ans: /etc/init.d/inetsvc

165. Which command would you use to kill a process by name ?

Ans: pkill

166. Which file dictates what ports inetd will listen for ?

Ans: /etc/inet/inetd.conf

167. Which command will make the inetd reread the inetd.conf file ?

 Ans: pkill –HUP inetd

Last Modified: August 10, 2009