L1 L2 L3 What’s the Difference.
Layer 1: Physical Layer
It covers the physical aspects of networking, and is the lowest and most physical layer of the OSI model. Wiring standards play an important role in this layert. In Layer 1, it utilizes physical cabling and radio frequency standards along with the conversion of data to bits.
Data
Data at this layer is simply bits sent across a wire, many many zeros and ones. This is the network layer where that happens so that it can be transmitted somewhere else.
Equipment
The type of equipment involved in Layer 1 uses little to no logic (DUMB) when operating: copper ethernet cables, fiber optic cables, and ethernet hubs. This is not only limited to physical cables though. The physical transmission aspects of Wi-Fi, Bluetooth, Microwave, and other over the air technologies fall under this layer.
An easy-to-understand non-network example of this is electricity. For the most part you simply plug your appliance into the outlet and power is delivered. In the OSI model, swap out power with data.
Layer 2: Data Link Layer
This layer is primarily involved in transmitting data from one specific node to another. These nodes are usually directly connected, whether that’s via LAN, WAN or MAN.
Two sublayers exist here, Medium Access Control (MAC) and Logical Link Control (LLC). It is important to understand that each protocol implements its lower layers differently. Ethernet follows IEEE 802 and allows for variable sized data, while protocols like ATM (Asynchronous Transfer Mode) have fixed 53 bytes of data that it calls “cells.”
In ethernet, Virtual LAN (VLAN) is an important technology implemented here. VLANs help split up broadcast domains by allowing you to segment devices to their own dedicated LAN. When combining VLANs over a single port, they are differentiated with a VLAN header. 802.1Q is the standard today.
Data
Data at this layer is referred to as a frame. Frames have basic data in them such as a source address and a destination address as well as payload. That basic data is often referred to as a header, a type of metadata.
Equipment
Equipment at this layer is a little more intelligent and consists of switches, bridges, and network cards. It can use the headers of the packet to determine exactly where it goes. A switch can read the destination MAC address and forward it directly to the specific port the MAC address is plugged into.
Layer 2A – Medium Access Control
Medium Access Control entails quite a few important functions. Carrier Sense Multiple Access with Collision Detection (CSMA/CD) is a mechanism ethernet uses to help deal with collisions on half duplex networks.
Layer 2B – Logical Link Control
One of LLC’s main features is that it is a helper layer to assist between Layer 2’s MAC and Layer 3. It does this by providing mechanisms for multiplexing Layer 3 Protocols.
Layer 3: Network Layer
The “IP” in TCP/IP is a Layer 3 protocol. IPX was a very popular Layer 3 protocol within the IPX/SPX protocol group in NetWare’s heyday.
The network layer provides a logical address of an endpoint. Layer 2 addresses are typically automatically generated by the vendor during the manufacturing process. But layer 3 addresses are usually configured. This could be a static IP configuration or a DHCP automated configuration.
Data
Data at this layer is referred to as a packet, which is a stateless grouping of data. Devices that forward packets do not validate that the other end receives the data. Instead, devices leave it to higher layer protocols to implement — should they choose. For example, in the case of Layer 4 protocol TCP, it does. Layer 4 protocol, UDP, however, does not.
Equipment
Routers are the common equipment used at this layer but there are many others. Layer 3 switches are also very common. Those are essentially Layer 2 switches with a router built into the backplane for speed. Firewalls, while able to operate at higher layers, can operate purely at this layer.
