Computer Networking Concepts for DevOps Engineer Part II
Welcome! Its nice to have you here, this is continuation on our series of articles on essential computer networking skills that DevOps engineer should have in their repertoire. You can read the Part I if you haven't or if you need to refresh your memory on basic knowledge on computer networking in order to better understand all we would cover in this article.
The OSI Model
What is the OSI Model?
The open systems interconnection (OSI) model is a conceptual model created by the International Organization for Standardization which enables diverse communication systems to communicate using standard protocols. In plain English, the OSI provides a standard for different computer systems to be able to communicate with each other.
The OSI Model can be seen as a universal language for computer networking. It’s based on the concept of splitting up a communication system into seven abstract layers, each one stacked upon the last.
The seven abstraction layers of the OSI model can be defined as follows, from top to bottom
Application Layer
The application layer is used by end-user software such as web browsers and email clients. It provides protocols that allow the software to send and receive information and present it in a meaningful format to the user. A few examples of application layer protocols are the Hypertext Transfer Protocol (HTTP), File Transfer Protocol (FTP), Post Office Protocol (POP), Simple Mail Transfer Protocol (SMTP), and Domain Name System (DNS).
Presentation Layer
The presentation layer prepares data for the application layer. It defines how two devices should encode, encrypt, and compress data so it is received correctly on the other end. The presentation layer takes any data transmitted by the application layer and prepares it for transmission over the session layer.
Session Layer
The session layer creates communication channels, called sessions, between devices. It is responsible for opening sessions, ensuring they remain open and functional while data is being transferred, and closing them when communication ends. The session layer can also set checkpoints during a data transfer — if the session is interrupted, devices can resume data transfer from the last checkpoint.
Transport Layer
The transport layer takes data transferred in the session layer and breaks it into “segments” on the transmitting end. It is responsible for reassembling the segments on the receiving end, turning them back into data that can be used by the session layer. The transport layer carries outflow control, sending data at a rate that matches the connection speed of the receiving device, and error control, checking if data was received incorrectly and if not, request it again.
Network Layer
The network layer has two main functions. One is breaking up segments into network packets, and reassembling the packets on the receiving end. The other is routing packets by discovering the best path across a physical network. The network layer uses network addresses (typically Internet Protocol addresses) to route packets to a destination node.
Data Link Layer
The data link layer establishes and terminates a connection between two physically-connected nodes on a network. It breaks up packets into frames and sends them from source to destination. This layer is composed of two parts — Logical Link Control (LLC), which identifies network protocols, performs error checking and synchronizes frames, and Media Access Control (MAC) which uses MAC addresses to connect devices and define permissions to transmit and receive data.
Physical Layer
The physical layer is responsible for the physical cable or wireless connection between network nodes. It defines the connector, the electrical cable, or wireless technology connecting the devices, and is responsible for the transmission of the raw data, which is simply a series of 0s and 1s while taking care of bit rate control.
