What Open System Interconnection (OSI) layers do you need to know to become a network engineer?

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Answered by: Rachel, An Expert in the Networking Category
To become a network engineer, numerous and varied skills are needed. In a nutshell, you need to understand how to configure, deploy, and troubleshoot the first four technical layers of the Open System Interconnection (OSI) model of protocols – the physical layer, the data-link layer, the network layer and the transport layer. Once you have the knowledge needed, your skills will get you hired.

Layer 1 of the OSI model is known as the physical layer. This first layer is used to convey bit streams in an electrical, optical or radio format. The physical layer provides hardware as a means of sending and receiving these bit streams. For physical layer format, a network engineer needs to know how to create and test Ethernet cables, crossover cables, and console cables. Although it is not required, knowing how to make fiber cables can also be an excellent skill in your toolbox. You also need to know how to dispatch wiring cleanly and efficiently to and from various equipment via patch panels. This cable cleanliness helps tremendously in future troubleshooting of the physical layer network.

Layer 2 of the OSI model, also known as the data-link layer, is the layer that sets up links across the physical network to send and receive frames on the network. This layer is actually two separate layers, the Logical Link Control (LLC) layer and the Media Access Control (MAC) layer. The LLC layer does error checking, while the MAC layer does controls how devices connected to the network via layer 1 gain access. Once you understand the data-link layer, you will have an understanding to easily learn how to configure switches. Some of the most popular companies that produces switches are Cisco, Juniper, and Brocade.

Layer 3 of the OSI model, also known as the network layer, is where routers are configured and operate. A router is a hardware device that is responsible mainly for providing and defining IP addresses, making choices for a routes based on the IP address of its destination, configuring protocols like OSPF and BGP for the router to make routing choices dynamically, and connecting different layer protocols together, e.g., SONET and Ethernet. In the network layer you will also need to know how to subnet IP addresses and understand the use of datagrams in the network layer. Once you understand the third layer of the OSI model, you will have the skills to learn how to configure routers. Some of the most popular companies that produce routers are Cisco and Juniper.

Layer 4 of the OSI model, also known as the transport layer, provides multiple services for end-to-end communication over the network. You will need to know how these services work. These services include:

     * Setup and maintaining connections between two devices.

     * Multiplex connections to allow numerous applications to send and receive data.

     * Set up transmission methods to be either connection-oriented (TCP) or connectionless (UDP.)

     * Implement a reliable connection via sequences numbers and acknowledgments.

     * Connection control via windowing and flow control.

Once you understand how these services work, it will be easy for you to learn how to configure and troubleshoot multiple routers.

An in-depth understanding of the first four layers of the Open System Interconnection (OSI) protocols are needed to become a network engineer. Understanding each of these layers will help you know how to configure, deploy and troubleshoot networks and protocols. Once you have the knowledge and some experience using some of these layers, you will have a very good chance of being hired as a network engineer.

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