In this chapter of the journey to learn computer networking technology we explain the OSI Reference Model in simple terms, and expand on the different layers of the OSI model.
The OSI model defines the basic building blocks of computer networking, and is an essential part of a complete understanding of modern TCI/IP networks. The theoretical OSI Reference Model is the creation of the European based International Organization for Standardization (ISO), an independent, non-governmental membership organization that creates standards in numerous areas of technology and industry.
Why is the OSI Reference Model important?
An understanding of the concepts of the OSI Reference Model is absolutely necessary for someone learning the role of the Network Administrator or the System Administrator. The OSI model is important because many certification tests use it to determine your understanding of computer networking concepts.
The Open Systems Interconnection Reference Model (OSI Reference Model or OSI Model) was originally created as the basis for designing a universal set of protocols called the OSI Protocol Suite. This suite never achieved widespread success, but the model became a very useful tool for both education and development. The model defines a set of layers and a number of concepts for their use that make understanding networks easier.
The Internet and the TCP/IP family of protocols evolved separately from the OSI model. Often you find teachers, and websites, making direct comparison of the different models. Don't spend too much time trying to compare one versus the other. The two models were developed independently of each other to describe the standards of computer networking.
The TCP/IP Reference Model is not merely a reduced version of the OSI Reference Model with a straight line comparison of the four layers of the TCP/IP model to seven layers of the OSI model. The TCP/IP Reference Model does NOT always line up neatly against the OSI model. People try too hard to make neat comparisons of one model versus the other when there is not always a neat one to one correlation of each aspect.
Simply put the OSI Reference Model is a THEORETICAL model describing a standard of computer networking. The TCP/IP Reference model is based on the ACTUAL standards of the internet which are defined in the collection of Request for Comments (RFC) documents started by Steve Crocker in 1969 to help record unofficial notes on the development of ARPANET. RFCs have since become official documents of Internet specifications, as discussed in the article What is the difference between the Internet and OSI reference model.
To learn more about the evolution of the TCP/IP model check out the Geek History article: The 1980s internet protocols become universal language of computers
If are looking for something less technical that focuses more on using a computer network, rather than understand the core concepts of how it works, please visit our companion website The Guru 42 Universe where we discuss managing technology from the perspective of a business owner or department manager.
Check out the section Business success beyond great ideas and good intentions and specifically the article The System Administrator and successful technology integration.
The role of the Network Administrator or the System Administrator
On a small to mid size network there may be little, if any, distinction between a Systems Administrator and a Network Administrator, and the tasks may all be the responsibility of a single post. As the size of the network grows, the distinction between the areas will become more well defined.
In larger organizations the administrator level technology personnel typically are not the first line of support that works with end users, but rather only work on break and fix issues that could not be resolved at the lower levels.
Network administrators are responsible for making sure computer hardware and the network infrastructure itself is maintained properly. The term network monitoring describes the use of a system that constantly monitors a computer network for slow or failing components and that notifies the network administrator in case of outages via email, pager or other alarms.
The typical Systems Administrator, or sysadmin, leans towards the software and NOS (Network Operating System) side of things. Systems Administrators install software releases, upgrades, and patches, resolve software related problems and performs system backups and recovery.
What is the difference between networking and telecommunications?
In a large organization the distinction of telecommunications and networking can vary depending how the organization is structured. I've worked in smaller companies where anything technology related came under the responsibility of the IT (information technology) department. In larger organizations the roles get a bit more defined and separated. For instance, in a large organization someone specializing in telecommunications may have little or no role in understanding computer servers and network operating systems.
I am answering this from my very personal perspective. I began working in the 1970s in telecommunications. In the military that meant I installed and repaired radio communications and telephone equipment. In the commercial world I had an FCC (Federal Communications License) which allowed me to work on radio communications equipment.
In the 1990s I began working in computer networking, which would be IT (information technology). I see the distinction there as information is data driven. My responsibilities are computer servers and network operating systems. The basic premise of a computer network is to share a resource. The device which allows the resource top be shared is a server. For instance, a print server allows a printer to be shared, a file server allows files to be shared.
In my current position my title includes "telecommunications and networking." My telecommunications responsibilities include telephones. Now with IP (internet protocol) based phones, you have the questions of, is it a phone system problem, or a network problem. The separation was a lot "cleaner" as far as responsibilities before IP based phones. My telecommunications responsibilities also include things like the internal network wiring and dealing with the external issues regarding the connectivity to the building. My networking (IT) responsibilities are the maintenance of the computer servers and the network operating systems that allow resources to be shared.