The Transmission Control Protocol/Internet Protocol (TCP/IP) suite was designed and implemented by the Department of Defense (DoD) to ensure and preserve data integrity as well as maintain communications in the event of catastrophic war. So it follows that if designed and implemented correctly, a TCP/IP network can be a secure, dependable and resilient one.
The DoD model is a condensed version of the OSI model, composed of four layers instead of seven, but is nonetheless like the OSI model in that it can be used to describe packet creation and devices and protocols can be mapped to its layers.
A Brief History of TCP/IP
TCP first came on the scene way back in 1973, and in 1978, it was divided into two distinct protocols: TCP and IP. Later, in 1983, TCP/IP replaced the Network Control Protocol (NCP) and was authorized as the official means of data transport for anything connecting to ARPAnet, the Internet’s ancestor. The DoD’s Advanced Research Projects Agency (ARPA) created this ancient network way back in 1957 in a cold war reaction to the Soviet’s launching of Sputnik. Also in 1983, ARPA was redubbed DARPA and divided into ARPAnet and MILNET until both were finally dissolved in 1990. It may be counterintuitive, but most of the development work on TCP/IP happened at UC Berkeley in Northern California, where a group of scientists were simultaneously working on the Berkeley version of UNIX, which soon became known as the Berkeley Software Distribution (BSD) series of UNIX versions. Of course, because TCP/IP worked so well, it was packaged into subsequent releases of BSD Unix and offered to other universities and institutions if they bought the distribution tape. So basically, BSD Unix bundled with TCP/ IP began as shareware in the world of academia. As a result, it became the foundation for the tremendous success and unprecedented growth of today’s Internet as well as smaller, private and corporate intranets. As usual, what started as a small group of TCP/IP aficionados evolved, and as it did, the US government created a program to test any new published standards and make sure they passed certain criteria. This was to protect TCP/IP’s integrity and to ensure that no developer changed anything too dramatically or added any proprietary features. It’s this very quality—this open-systems approach to the TCP/IP family of protocols— that sealed its popularity because this quality guarantees a solid connection between myriad hardware and software platforms with no strings attached.
TCP/IP and the DoD Model
The DoD model is basically a condensed version of the OSI model that comprises four instead of seven layers:
History
In the late 1970s, the International Organization for Standardization (ISO) conducted a program to develop general standards and methods of networking. A similar process evolved at the International Telegraph and Telephone Consultative Committee (CCITT, from French: Comité Consultatif International Téléphonique et Télégraphique). Both bodies developed documents that defined similar networking models. In 1983, these two documents were merged to form a standard called The Basic Reference Model for Open Systems Interconnection. The standard is usually referred to as Open Systems Interconnection Reference Model, OSI Reference Model, or simply OSI model. It was published in 1984 by both the ISO, as standard ISO 7498, and the renamed CCITT (now called the Telecommunications Standardization Sector of the International Telecommunication Union or ITU-T) as standard X.200. OSI had two major components, an abstract model of networking, called the Basic Reference Model or seven-layer model, and a set of specific protocols. The concept of a seven-layer model was provided by the work of Charles Bachman at Honeywell Information Services. Various aspects of OSI design evolved from experiences with the ARPANET, NPLNET, EIN, CYCLADES network and the work in IFIP WG6.1. The new design was documented in ISO 7498 and its various addenda. In this model, a networking system was divided into layers. Within each layer, one or more entities implement its functionality. Each entity interacted directly only with the layer immediately beneath it, and provided facilities for use by the layer above it. Protocols enable an entity in one host to interact with a corresponding entity at the same layer in another host. Service definitions abstractly describe the functionality provided to an (N)-layer by an (N-1) layer, where N was one of the seven layers of protocols operating in the local host.
The DoD model is a condensed version of the OSI model, composed of four layers instead of seven, but is nonetheless like the OSI model in that it can be used to describe packet creation and devices and protocols can be mapped to its layers.
A Brief History of TCP/IP
TCP first came on the scene way back in 1973, and in 1978, it was divided into two distinct protocols: TCP and IP. Later, in 1983, TCP/IP replaced the Network Control Protocol (NCP) and was authorized as the official means of data transport for anything connecting to ARPAnet, the Internet’s ancestor. The DoD’s Advanced Research Projects Agency (ARPA) created this ancient network way back in 1957 in a cold war reaction to the Soviet’s launching of Sputnik. Also in 1983, ARPA was redubbed DARPA and divided into ARPAnet and MILNET until both were finally dissolved in 1990. It may be counterintuitive, but most of the development work on TCP/IP happened at UC Berkeley in Northern California, where a group of scientists were simultaneously working on the Berkeley version of UNIX, which soon became known as the Berkeley Software Distribution (BSD) series of UNIX versions. Of course, because TCP/IP worked so well, it was packaged into subsequent releases of BSD Unix and offered to other universities and institutions if they bought the distribution tape. So basically, BSD Unix bundled with TCP/ IP began as shareware in the world of academia. As a result, it became the foundation for the tremendous success and unprecedented growth of today’s Internet as well as smaller, private and corporate intranets. As usual, what started as a small group of TCP/IP aficionados evolved, and as it did, the US government created a program to test any new published standards and make sure they passed certain criteria. This was to protect TCP/IP’s integrity and to ensure that no developer changed anything too dramatically or added any proprietary features. It’s this very quality—this open-systems approach to the TCP/IP family of protocols— that sealed its popularity because this quality guarantees a solid connection between myriad hardware and software platforms with no strings attached.
TCP/IP and the DoD Model
The DoD model is basically a condensed version of the OSI model that comprises four instead of seven layers:
- Process/Application layer
- Host-to-Host layer/or Transport
- Internet layer
- Network Access layer/or Link
It offers a comparison of the DoD model and the OSI reference model. As you can see, the two are similar in concept, but each has a different number of layers with different names. Cisco may at times use different names for the same layer, such as both “Network Access” and “Link” used to describe the bottom layer.
Note :- When the different protocols in the IP stack are discussed, the layers of the OSI and DoD models are interchangeable.
A vast array of protocols join forces at the DoD model’s Process/Application layer. These processes integrate the various activities and duties spanning the focus of the OSI’s corresponding top three layers (Application, Presentation, and Session).
In short, the Process/Application layer defines protocols for node-to-node application communication and controls user-interface specifications.
The reason TCP/IP became so popular is because there were no set physical layer specifications, so it could run on any existing or future physical network!
The DoD and OSI models are alike in design and concept and have similar functions in similar layers.
The TCP/IP protocol suite
In the DoD model, there are two main reasons for the Internet layer’s existence: routing and providing a single network interface to the upper layers.
The Open Systems Interconnection model (OSI model) is a conceptual model that characterizes and standardizes the communication functions of a telecommunication or computing system without regard to its underlying internal structure and technology. Its goal is the interoperability of diverse communication systems with standard protocols. The model partitions a communication system into abstraction layers.
History
In the late 1970s, the International Organization for Standardization (ISO) conducted a program to develop general standards and methods of networking. A similar process evolved at the International Telegraph and Telephone Consultative Committee (CCITT, from French: Comité Consultatif International Téléphonique et Télégraphique). Both bodies developed documents that defined similar networking models. In 1983, these two documents were merged to form a standard called The Basic Reference Model for Open Systems Interconnection. The standard is usually referred to as Open Systems Interconnection Reference Model, OSI Reference Model, or simply OSI model. It was published in 1984 by both the ISO, as standard ISO 7498, and the renamed CCITT (now called the Telecommunications Standardization Sector of the International Telecommunication Union or ITU-T) as standard X.200. OSI had two major components, an abstract model of networking, called the Basic Reference Model or seven-layer model, and a set of specific protocols. The concept of a seven-layer model was provided by the work of Charles Bachman at Honeywell Information Services. Various aspects of OSI design evolved from experiences with the ARPANET, NPLNET, EIN, CYCLADES network and the work in IFIP WG6.1. The new design was documented in ISO 7498 and its various addenda. In this model, a networking system was divided into layers. Within each layer, one or more entities implement its functionality. Each entity interacted directly only with the layer immediately beneath it, and provided facilities for use by the layer above it. Protocols enable an entity in one host to interact with a corresponding entity at the same layer in another host. Service definitions abstractly describe the functionality provided to an (N)-layer by an (N-1) layer, where N was one of the seven layers of protocols operating in the local host.
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