Application layer

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An application layer is an abstraction layer that specifies the shared communication protocols and interface methods used by hosts in a communications network. [1] An application layer abstraction is specified in both the Internet Protocol Suite (TCP/IP) and the OSI model. [2] Although both models use the same term for their respective highest-level layer, the detailed definitions and purposes are different. [3]

Contents

Internet protocol suite

In the Internet protocol suite, the application layer contains the communications protocols and interface methods used in process-to-process communications across an Internet Protocol (IP) computer network. [4] The application layer only standardizes communication and depends upon the underlying transport layer protocols to establish host-to-host data transfer channels and manage the data exchange in a client–server or peer-to-peer networking model. [5] Though the TCP/IP application layer does not describe specific rules or data formats that applications must consider when communicating, the original specification (in RFC   1123) does rely on and recommend the robustness principle for application design. [6] [7]

OSI model

In the OSI model, the definition of the application layer is narrower in scope. [9] The OSI model defines the application layer as only the interface responsible for communicating with host-based and user-facing applications. [10] OSI then explicitly distinguishes the functionality of two additional layers, the session layer and presentation layer, as separate levels below the application layer and above the transport layer. OSI specifies a strict modular separation of functionality at these layers and provides protocol implementations for each. In contrast, the Internet Protocol Suite compiles these functions into a single layer. [10]

Sublayers

Originally the OSI model consisted of two kinds of application layer services with their related protocols. [11] These two sublayers are the common application service element (CASE) and specific application service element (SASE). [12] Generally, an application layer protocol is realized by the use of the functionality of a number of application service elements. [13] Some application service elements invoke different procedures based on the version of the session service available. [14]

CASE

The common application service element sublayer provides services for the application layer and request services from the session layer. It provides support for common application services, such as:

SASE

The specific application service element sublayer provides application-specific services (protocols), such as:

  • FTAM (File Transfer, Access and Manager)
  • VT (Virtual Terminal)
  • MOTIS (Message Oriented Text Interchange Standard)
  • CMIP (Common Management Information Protocol)
  • JTM (Job Transfer and Manipulation) [15]
  • MMS (Manufacturing Messaging Specification)
  • RDA (Remote Database Access)
  • DTP (Distributed Transaction Processing)

Protocols

The IETF definition document for the application layer in the Internet Protocol Suite is RFC 1123. It provided an initial set of protocols that covered the major aspects of the functionality of the early Internet: [6]

Examples

Additional notable application-layer protocols include the following:

Related Research Articles

The Internet protocol suite, commonly known as TCP/IP, is a framework for organizing the set of communication protocols used in the Internet and similar computer networks according to functional criteria. The foundational protocols in the suite are the Transmission Control Protocol (TCP), the User Datagram Protocol (UDP), and the Internet Protocol (IP). Early versions of this networking model were known as the Department of Defense (DoD) model because the research and development were funded by the United States Department of Defense through DARPA.

<span class="mw-page-title-main">OSI model</span> Model of communication of seven abstraction layers

The Open Systems Interconnection (OSI) model is a reference model from the International Organization for Standardization (ISO) that "provides a common basis for the coordination of standards development for the purpose of systems interconnection." In the OSI reference model, the communications between systems are split into seven different abstraction layers: Physical, Data Link, Network, Transport, Session, Presentation, and Application.

Xerox Network Systems (XNS) is a computer networking protocol suite developed by Xerox within the Xerox Network Systems Architecture. It provided general purpose network communications, internetwork routing and packet delivery, and higher level functions such as a reliable stream, and remote procedure calls. XNS predated and influenced the development of the Open Systems Interconnection (OSI) networking model, and was very influential in local area networking designs during the 1980s.

In the seven-layer OSI model of computer networking, the network layer is layer 3. The network layer is responsible for packet forwarding including routing through intermediate routers.

In the seven-layer OSI model of computer networking, the session layer is layer 5.

<span class="mw-page-title-main">Transport layer</span> Layer in the OSI and TCP/IP models providing host-to-host communication services for applications

In computer networking, the transport layer is a conceptual division of methods in the layered architecture of protocols in the network stack in the Internet protocol suite and the OSI model. The protocols of this layer provide end-to-end communication services for applications. It provides services such as connection-oriented communication, reliability, flow control, and multiplexing.

The data link layer, or layer 2, is the second layer of the seven-layer OSI model of computer networking. This layer is the protocol layer that transfers data between nodes on a network segment across the physical layer. The data link layer provides the functional and procedural means to transfer data between network entities and may also provide the means to detect and possibly correct errors that can occur in the physical layer.

NetBIOS is an acronym for Network Basic Input/Output System. It provides services related to the session layer of the OSI model allowing applications on separate computers to communicate over a local area network. As strictly an API, NetBIOS is not a networking protocol. Operating systems of the 1980s ran NetBIOS over IEEE 802.2 and IPX/SPX using the NetBIOS Frames (NBF) and NetBIOS over IPX/SPX (NBX) protocols, respectively. In modern networks, NetBIOS normally runs over TCP/IP via the NetBIOS over TCP/IP (NBT) protocol. This results in each computer in the network having both an IP address and a NetBIOS name corresponding to a host name. NetBIOS is also used for identifying system names in TCP/IP (Windows). Simply stated, it is a protocol that allows communication of data for files and printers through the Session Layer of the OSI Model in a LAN.

In computer networking, a network service is an application running at the network application layer and above, that provides data storage, manipulation, presentation, communication or other capability which is often implemented using a client–server or peer-to-peer architecture based on application layer network protocols.

The Common Management Information Protocol (CMIP) is the OSI specified network management protocol.

FTAM, ISO standard 8571, is the OSI application layer protocol for file transfer, access and management.

The Open Systems Interconnection protocols are a family of information exchange standards developed jointly by the ISO and the ITU-T. The standardization process began in 1977.

In computer networks, a tunneling protocol is a communication protocol which allows for the movement of data from one network to another. It can, for example, allow private network communications to be sent across a public network, or for one network protocol to be carried over an incompatible network, through a process called encapsulation.

In computing, Advanced Program to Program Communication or APPC is a protocol which computer programs can use to communicate over a network. APPC is at the application layer in the OSI model, it enables communications between programs on different computers, from portables and workstations to midrange and host computers. APPC is defined as VTAM LU 6.2

A network socket is a software structure within a network node of a computer network that serves as an endpoint for sending and receiving data across the network. The structure and properties of a socket are defined by an application programming interface (API) for the networking architecture. Sockets are created only during the lifetime of a process of an application running in the node.

The internet layer is a group of internetworking methods, protocols, and specifications in the Internet protocol suite that are used to transport network packets from the originating host across network boundaries; if necessary, to the destination host specified by an IP address. The internet layer derives its name from its function facilitating internetworking, which is the concept of connecting multiple networks with each other through gateways.

A communication protocol is a system of rules that allows two or more entities of a communications system to transmit information via any variation of a physical quantity. The protocol defines the rules, syntax, semantics, and synchronization of communication and possible error recovery methods. Protocols may be implemented by hardware, software, or a combination of both.

In computer networking, the link layer is the lowest layer in the Internet protocol suite, the networking architecture of the Internet. The link layer is the group of methods and communications protocols confined to the link that a host is physically connected to. The link is the physical and logical network component used to interconnect hosts or nodes in the network and a link protocol is a suite of methods and standards that operate only between adjacent network nodes of a network segment.

The Protocol Wars were a long-running debate in computer science that occurred from the 1970s to the 1990s, when engineers, organizations and nations became polarized over the issue of which communication protocol would result in the best and most robust networks. This culminated in the Internet–OSI Standards War in the 1980s and early 1990s, which was ultimately "won" by the Internet protocol suite (TCP/IP) by the mid-1990s when it became the dominant protocol through rapid adoption of the Internet.

References

  1. ↑ "Application Layer | Layer 7". The OSI-Model. Retrieved November 5, 2019.
  2. ↑ "Four Layers of TCP/IP model, Comparison and Difference between TCP/IP and OSI models". www.omnisecu.com. Retrieved November 5, 2019.
  3. ↑ "What is the difference between TCP/IP and IP protocol?". SearchNetworking. Retrieved November 5, 2019.
  4. ↑ "What is the difference between TCP/IP and IP protocol?". SearchNetworking. Retrieved November 5, 2019.
  5. ↑ SEO, Bradley Mitchell An MIT graduate who brings years of technical experience to articles on; computers; Networking, Wireless. "What Is Transmission Control Protocol/Internet Protocol (TCP/IP)?". Lifewire. Retrieved November 5, 2019.
  6. 1 2 Robert Braden, ed. (October 1989). "RFC 1123: Requirements for Internet Hosts – Application and Support". Network Working Group of the IETF.
  7. ↑ "What is the Application Layer?". www.tutorialspoint.com. Retrieved November 5, 2019.
  8. ↑ "X.225 : Information technology – Open Systems Interconnection – Connection-oriented Session protocol: Protocol specification". Archived from the original on February 1, 2021. Retrieved March 10, 2023.
  9. ↑ Shaw, Keith (October 22, 2018). "The OSI model explained: How to understand (and remember) the 7 layer network model". Network World. Retrieved November 5, 2019.
  10. 1 2 "What Is The OSI Model?". CloudFlare. 2019. Retrieved November 4, 2019.
  11. ↑ "Application Layer (Layer 7 of the OSI Model)". September 2, 2019.
  12. 1 2 Hura, Gurdeep (2001). "Application Layer". Data and Computer Communications: Networking and Internetworking . CRC Press LLC. pp.  710–712. ISBN   9780849309281.
  13. ↑ Warrier, U.S.; Besaw, L. (April 1989). Common Management Information Services and Protocol over TCP/IP (CMOT) (Report). doi:10.17487/RFC1095.
  14. ↑ Rose, Marshall T. (December 1988). "ISO presentation services on top of TCP/IP based internets".
  15. ↑ a former OSI standard [ permanent dead link ]
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