TCP/IP - [Part 2] - APPLICATION LAYER PROTOCOLS

Application Layer = Transport Layer + Presentation Layer + Session Layer [OSI Model]

Application Layer is combination of Transport, Presentation and Session Layer of OSI Model

Application Layer

• Provide a user interface and allow to access network resources.
• Application Layer is the first layer of the OSI Model and this layer is responsible to provide interface among users and the software application.
• It plays a role of intermediates between actual software application and the users.
• We can say that, application layer plays a front-end role, where user actually communicate or interact, other remaining layers play a back-end role.
• File transfer, emails etc. are the example of application layer where users interact.

Presentation Layer

• It is responsible to present data to the Application layer 
• Presentation Layer is responsible for data translation, conversion and code formatting like 

1. Data compression/Decompression
2. Data Encryption/Decryption
3. Graphic handling
4. Character/string conversion

• A data-transfer technique -  Data will be in standard format before transmission. After that computers will receive generically formatted data and then convert the data back into its native format for actual reading. 
• This layer ensures that data transferred from the Application layer of one system can be read by the Application layer of another system.
• So presentation layer is responsible for integrating all data formats into a standard format for efficient and effective communication. Best example is  EBCDIC (Extended Binary Coded Decimal Interchange Code) to ASCII (American Standard Code for Information Interchange) conversion. 

Session Layer

• Session Layer provides appropriate sessions between users and software, actually where users interacts.
• It is responsible for sessions establishment, session management, session termination and synchronization. Example : Online payment session and IRCTC login session
• It is also provides dialog control between devices, or nodes.

Below protocols come under the Process/Application Layer :- 

Telnet (Teletype Network Protocol)

• Telnet provides a command line interface for communication with a remote device or server.
• We can use it for remote management and also for initial device setup like network hardware.
• There is no any encryption. So it is less secure
• Via telnet a program on one host (Telnet client) may access the resources of other host (Telnet server) as through the client were a local terminal connect to the server.
• You can use telnet via command telnet [host name or ip address].

File Transfer Protocol (FTP)

• FTP basically use to transfer the files between any two machine.
• It is also allow to access both directories and files and can perform certain type of directories operation, like relocating into different ones.
• It is secured with password and username, which implemented by system administrators to restrict access.
• FTP is mostly used to download a file from a server using the internet or to upload a file to server.
• You can use FTP, if you do not need to transfer those files securely. Because FTP for transferring data, usernames and passwords sent along with the file request in the clear format for all to see without encryption.

Trivial File Transfer Protocol (TFTP)

• TFTP is simpler to use than the FTP but less capable. 
• TFTP is similar to FTP, but it is used where user authentication and directory visibility are not required.
• TFTP uses the UDP.

Network File System (NFS)

• It was developed by Sun Microsystems. 
• It allows two different types of file systems to interoperate.
• It is an open standard, so anyone can implement the protocol
• NFS protocol allows a user on a client computer to access files over a network in the same way, such as they would access a local storage file.

Simple Mail Transfer Protocol (SMTP)

• SMTP basically used to send e-mail over the Internet. 
• E-mail client like Outlook and Mac OS X Mail uses Simple Mail Transfer Protocol to send a message to the mail server, after that mail server uses SMTP to relay that message to the correct receiving mail server.

Post Office Protocol (POP)

• Post Office Protocol (POP) provide a storage facility for incoming mail, and the latest version is POP3.
• POP3 is used by local email software clients to retrieve emails from a remote mail server over a TCP/IP connection
• POP traffic is not encrypted, It will send authentication information in plain text.

POP Vs IMAP

• Both POP  and IMAP allow to access email from a remote server. 
• POP basically downloads email to your computer, and usually deletes the email from the remote server. It did not allows the user to synchronize their email among multiple devices like desktop, laptop, tablet or phone.
• Suppose if you have more than one device like desktop, laptop, tablet or phone, where you access your mail. Then you will have to delete or file the same email on every device, so you will have to logging into each device, and you will see lots of unread emails with no indication of which you deleted, read, flagged or filed any folders you created and organize on one device will not be replicated on the other devices. So IMAP came to break this barrier.
• IMAP allows users to store their email on remote servers. This two-way protocol also allows the user to synchronize their email among multiple devices like desktop, laptop, tablet or phone.

Internet Message Access Protocol (IMAP)

• Both POP  and IMAP allow to access email from a remote server. 
• IMAP allows users to store their email on remote servers. This two-way protocol also allows the user to synchronize their email among multiple devices like desktop, laptop, tablet or phone.

Transport Layer Security (TLS)

• Transport Layer Security is the replacement for Secure Sockets Layer . Both are cryptographic protocols designed to provide communications security over a computer network.
• It is used to encrypt sensitive information sent over the Web and to prevent eavesdropping and tampering.
• It allow secure online data transfer activities such as browsing the Web, instant messaging, Internet faxing etc.

Session Initiation Protocol (SIP)

• SIP is signaling protocol used to construct and deconstruct multimedia communication sessions for many things like voice and video calls, video conferencing, streaming multimedia distribution, instant messaging, presence information, and online games over the Internet
• It is used in VoIP (Voice Over Internet Protocol) technology

Real-time Transport Protocol (RTP)

• RTP is used to delivering audio and video over IP networks or Internet.
• Initially it is designed as a multicast protocol, but now we can used for unicast application too

Line Printer Daemon (LPD) and Line Printer Remote (LPR)

• Basically LPD  is used for printer sharing. 
• Line Printer Remote protocol (LPR) is used for submitting print jobs to a remote printer.
• LPD software is installed in the printer or print server and the LPR software is installed in the client device. 
• LPR client sends the print request to the IP address of the LPD printer/server, LPD handles the printers and print the jobs. 

Domain Name Service (DNS)

• Domain Name Service (DNS) resolves host-name into the IP address

X Window

• X Window System is open source, which provides a GUI in a distributed network environment.
• Basically it is cross platform and client-server computer software system, which is designed for client/server operations - A single server controls the input/output hardware, like screen, keyboard, and mouse, all application programs act as clients, interacting with the user and with the other clients via the server. 

Simple Network Management Protocol (SNMP)

• Simple Network Management Protocol (SNMP) is used to  managing devices on IP networks". 
• Devices routers, switches, servers, workstations, printers, modem, racks and more support the SNMP.
• Basically SNMP is used in Network Management Systems (NMS) to monitor the network-attached devices.

Secure Shell (SSH)

• SSH, is a cryptographic network protocol, used to allow remote login. 
• It provides a secure channel over a network in a client-server architecture, by connecting an SSH client application with an SSH server.

Hypertext Transfer Protocol (HTTP)

• Basically It is used to manage communications between web browsers and web servers and opens the right resource when user click on a link.

Hypertext Transfer Protocol Secure (HTTPS)

• Hypertext Transfer Protocol Secure (HTTPS) is also known as Secure Hypertext Transfer Protocol/HTTP over TLS/HTTP over SSL/HTTP Secure. 
• It uses Transport Layer Security or its predecessor Secure Sockets Layer for encryption to provide secure communication over a computer network .
• Main purpose of HTTPS is authentication of the visited website and It is used to protect the privacy and integrity of the exchanged data.

Network Time Protocol (NTP)

• NTP is a protocol used to synchronize the clocks of computers over a network.

Network News Transfer Protocol (NNTP)

• The Network News Transfer Protocol (NNTP) is an application protocol used for transporting Usenet news articles (netnews) between news servers and for reading and posting articles by end user client applications.

Secure Copy Protocol (SCP)

• You can use FTP, if you do not need to transfer those files securely. Because FTP for transferring data, usernames and passwords sent along with the file request in the clear format for all to see without encryption. So SCP came with encryption for security purpose
• SCP whole purpose is to protect your files through SSH. It provides a secure, encrypted connection between the sending and receiving hosts until file transfer is complete.

Lightweight Directory Access Protocol (LDAP)

• The Lightweight Directory Access Protocol  is used for accessing and maintaining distributed directory information services over an IP network.
• As examples, directory services provide an organized set of records with a hierarchical structure, like corporate email directory, telephone directory.

Internet Group Management Protocol (IGMP)

• IGMP is used by host and adjacent router to establish multicast group memberships, it allows a host to advertise its multicast group membership to neighboring switches and adjacent routers. It is used to achieve dynamic multicasting like online streaming video and gaming.

Dynamic Host Configuration Protocol (DHCP)

• DHCP Server is automatically provides and assigns IP addresses, default gateways and other network parameters to client devices. 
• DHCP server can provide - IP address, Subnet mask, Domain name, Default gateway (routers), DNS server address and WINS server address

Automatic Private IP Addressing (APIPA)

• Automatic Private IP Addressing (APIPA) is enables a computer to automatically assign itself an IP address when there is no DHCP server available. APIPA is enabled by default
• APIPA range of address - from 169.254.0.1 - 169.254.255.254

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Anubhav Upadhyay

Hello and welcome to networktopic Blog. My name is Anubhav. I am a Senior Network Egineer. I have created this blog specially to serve interview questions and answer on Network Routing and Switching, I will try my best to serve correct and updated networking knowledge for you as per my corporate experience.

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