Network Protocols, Layers and Devices Simplified

What is a Network Protocol?

All computers in a network should be able to communicate with each other. Protocol is a set of standard rules that govern the communication between the computers in a network. The protocol is independent of operating system, device and application. 

What is a Layer in Network Protocol?

For the ease of usage and standardization, network protocols are divided into standard layers forming protocol stack. Each Layer has a specific purpose and work in conjunction for successful data transfer. OSI (Open Systems Interconnection), TCP/IP (Transmission Control Protocol / Internet Protocol) are some of the prominent models used to define layers in network protocol.

  

OSI vs TCP/IP Layers and Devices:

Layers Protocols and Devices

While understanding OSI layering is important, TCP/IP layers are more prominent in enterprise networks. Hence, Updated TCP/IP layers and protocols are discusses below

Application Layer - Layer 5:

Provides services to software application running on a computer. It acts as an interface between software application and network. There are numerous protocols serving application layer and each protocol use specific TCP/IP port to make connections.                                                                                                                    

Transport Layer - Layer 4:

Predominantly, the two protocols serving this layer are Transfer Control Protocol (TCP) and User Datagram Protocol (UDP). This layer is concerned with the reliable delivery of packages and makes connections with application layer using ports. Data received from application layer is broken down to chunks, a header is added  with proper sequencing and then passed down to the network layer. For reliable delivery, transport layer uses error detection, retransmission and acknowledgements.

TCP is generally used for reliable data delivery while UDP is used for broadcasting and multicasting.

Network Layer - Layer 3:

Internet Protocol is used in network layer. This layer deals with the addressing of source and destination node IP addresses are included in the package header and are then transferred to data link layer. Layer 3 devices are capable of routing packages between VLANs. 

Data Link - Layers 2: 

Every NIC, either physical or virtual has a MAC address. MAC (Media Access Control)  address is a unique 6 byte (48bit) address assigned by the hardware manufacturer. Ethernet is the most prominent protocol used in data link layer too. Every node on a network will have at least one MAC address assigned and frames are routed based on MAC address in layer 2. during ethernet encapsulation, source and destination MAC addresses are added in this layer. Link layer is concerned with delivery of packages with in the same VLAN. 

Laptop has 2 MAC addresses assigned. One for  wired communication and another for wireless communication.

Physical Link - Layer 1: 

This layer deals with the physical components of the networks such as cables, RJ45 connectors,  network interface cards (NIC), repeaters. Ethernet is the most popular protocol in this layer for wired transmission. 

Ethernet protocol defines the link speed (10BaseT, 100BaseT), link distance, topology (star, tree and bus) in this layer.