Cisco CCNA - Understanding Ethernet routers and Ethernet switches

Understanding Ethernet Routers and Ethernet switches

When you go out to purchase a device that will access the Internet, you will be advised more towards a router. on most occasion, these routers will come with a built-in switch functionality so you can connect multiple Ethernet devices to just this one device. So at this point you should be asking yourself what is the difference between an router and an switch? The best answer to this type of question will requires an examination and understanding of the Open Systems Interconnection Model (OSI model), this model is used to explain how today's communication networks operate.


Within this seven layered OSI model, each of these layers provides a unique service. The process of communication between two end devices (personal computers Etc) would begins at layer 7 the Application layer with the sending device initiating a message to a receiving device via a common medium. With respect to the OSI model, Ethernet provides services at layer 1 Physical and layer 2 Data Link. An Ethernet switch is classified as a bridge and therefore operates at layer two data link layer while routers operate at Layer 3 the Network layer on the OSI model.


The lowest layer is Layer 1 the physical layer this defines the basic signal on the medium. Ethernet transmit symbols representing ones and zeros across the medium to another device that will then decode the symbols to extract the data. Ethernet can operate with coaxial cable as a medium, most modern Ethernet networks use twisted pair cabling. When the path of the network medium is too long, a repeater can be used to extend distance. If the preferred media is fibre optic cable, media converters could be used. If multiple devices need to share the connection, a repeating hub (hub for short) is used. These all reside at the physical layer because they do nothing more than process symbols on the medium.


The layer that's above the physical layer is called the data link layer. Ethernet is a local area network (LAN) technology the end devices are assigned unique 48-bit MAC addresses. These addresses are called media access control addresses or MAC address for short. When data is to be sent from one Ethernet station to another, the data is first arranged in frames. The destination and source addresses are appended so the intended station knows it is to receive the message and who sent it. Other parts of the frame include the Preamble, which alerts the receiving station a frame is coming, a Type or Length field that identifies either the type of data or length of the data field, the Data field itself, and the Frame Check Sequence used to verify the integrity of the frame. The payload of the frame is the actual data. Everything else is overhead.

Open Systems Interconnection Model 

Memorize The OSI model