Which of the following organizations developed the open systems interconnection (osi) model?

CS457 Homework 3: Open Systems Interconnection
Robert Rice

The International Standards Organization (ISO) created the OSI model in 1978 as a structural guide to develop systems that allow heterogeneous products to communicate with each other. The word "open" in the architecture description refers to the concept that the system is open to all other systems using the same architecture. OSI is a reference model in that it does not actually represent a architecture in use, but is an idea architecture created from the study of the needs and restrictions of the domain in which it is to operate. It is a standard by which real implementations should be compared.

This architecture was designed to define a modular approach to networking, where each layer is responsible for a discrete aspect of the networking process. A layer on one computer assumes it is only communicating with the same layer on another computer. Each layer is implemented independently of how the surrounding layers are implemented. Ideally, layers can be changed without affecting other layers, provided the interfaces between them remain the same. These layers help to make the difficult process of communication more manageable.

There are seven layers to the OSI model. The bottom four layers provide the basic communications service and as such are implemented by the communications engineer. Programmers implement the remaining layers in order to develop distributed software applications using the network. These layers operate on a sort of assembly/disassembly line process. Ideally, the sending machine assembles the data by running through all seven layers, from the application layer to the physical layer. Then, the receiving machine takes the data at the physical layer and sends it through all seven layers up to the application layer. Each layer is allocated a specific set of functions. These functions help to provide services for, higher layers, while at the same time hiding from the higher layers how these services are implemented. Interfaces are designed to allow layers to access those services provided by lower layers. The seven layers of the OSI are defined as follows:

1. Physical Layer-The physical layer deals with the problem of transmitting raw bits across a physical medium. It deals with the mechanical, electrical, and procedural characteristics to establish, maintain and deactivate the physical link.
2. Data Link Layer-The data link layer provides for the reliable transfer of data across the physical link. It sends blocks of data (frames) with the necessary synchronization, error control and flow control
3. Network Layer-The network layer determines how messages are routed within the network. It provides to transport entities (upper layers) independence from routing and relay considerations. All relay functions are operated within or below this layer. This layer provides switching and routing functions to establish, maintain, and terminate network layer connections and transfer data between users.
4. Transport Layer-The transport layer hides details of any network-dependent information from the higher layers by providing transparent data transfer. The transport layer is concerned with machine to machine transfer rather than process to process. The transport layer will split data into smaller packets, dispatch those packets and at the receiver reassemble the data in the correct sequence. It provides end-to-end error recovery and flow control.
5. Session Layer-The session layer provides the control structure for communication between applications. It establishes, manages and terminates connections (sessions) between cooperating applications.
6. Presentation Layer-The presentation layer transforms application data into common network format. For example the presentation layer may convert EBCDIC to ASCII or carry out text compression or data encryption. It provides services such as encryption, text compression and reformatting.
7. Application Layer-The application layer provides the interface to the communications environment which is used by the application process. It is responsible for communicating application process parameters. The elements include library routines which perform inter-process communication, provide common procedures for constructing application protocols and for accessing the services provided by servers which reside on the network. This layer provides services to the users of the OSI environment, such as FTP, transaction server, network management, etc

In order to arrive at these layers, certain guidelines were considered:

1. A layer should only be created where a different level of abstraction is needed.
2. Each layer should provide a distinct function.
3. Internationally standardized protocols should guide the function designation of each layer.
4. The layer boundaries should be implemented so that a minimal amount of information is passed between layers.
5. The number of layers should be large enough to allow for distinct functions to not be unnecessarily grouped together in the same layer. At the same time, it needs to be small enough that the architecture does not become too large and complex.

These guidelines help to keep each layer logical and distinct.

The OSI model is very closely related to both the Waterfall Method and the Spiral Method of software design. Both methods follow an idea that breaks down problems into smaller problems to decrease the complexity of the problem and facilitate the development of the solution. OSI was created with seven layers to decrease the complexity of allowing communication between heterogeneous systems.

The most appropriate use of this architecture is as a tool for allowing two systems to communicate with each other across a network. As a matter of fact, Microsoft Windows 2000 and later versions use a network system based on the OSI architecture. In the network architecture used in Windows 2000 and later versions of the operating system, the Logical Link Control, Network, and Transport layers are implemented by software drivers known as transport drivers, which are sometimes referred to as protocols, protocol drivers, or protocol modules. TCP/IP is a set of protocols based strongly on the OSI architecture. Inappropriate uses of this architecture lie outside the realm of intercommunication between two systems. The complex process of assembling and disassembling the data through each layer would be unnecessary in a single system. Therefore, any program running on only a single machine would be unnecessarily complex under this kind of architecture.

References
The OSI Reference Model. Gorry Fairhurst . 01/10/2001.
http://www.erg.abdn.ac.uk/users/gorry/eg3561/intro-pages/osi.html TCP/IP's Architecture and the OSI Model.
http://online.matc.edu/cis-105/tcp-ip_osi_model%20.htm The Open System Interconnection (OSI) Architecture.
http://kmh.yeungnam-c.ac.kr/protocol/osi/osi.html The Origins of OSI. William Stallings. 1998.
http://williamstallings.com/Extras/OSI.html The OSI Reference Model.
All contents copyright (c) 2001 RAD Data Communications, Ltd.
http://www.rad.com/networks/1994/osi/osi.htm Windows 2000 and Later Network Architecture and the OSI Model. �2001 OSR Opens Systems Resources, Inc, ALL RIGHTS RESERVED.
http://www.osr.com/ddk/102gen_51ev.htm Software Engineering, 6th Edition. Sommerville, Ian.

Which organization developed the OSI model?

Which layer of the Open Systems Interconnection OSI model is responsible for the logical addressing of end systems and the routing of datagrams on a network?

Which of the following devices typically operates at the network layer of the Open Systems Interconnection OSI model?

Who defined OSI?