What Is A Network Switch & How It Works

What Is A Switch ?

Switch is a networking device which filters and forward packets through the network. It is a Layer 2 device. It is more advanced than a hub but not as advanced as a router.Switch connects separate LAN segment. It allows multiple system to transmit simultaneously.

Now a days Switch is mostly used in LAN due to their superior performance higher density lower per port cast and greater flexibility. The cast of Switch depends on the number of ports. As the number of Ports increases cost increases. Switch available in 4, 8, 16, 24 and 48 port.  

Working of A Switch

When switch receives data from one of the connected device, it forwards data only to the port on the which destination system is connected. It uses the media access control (MAC) address of the device to determine the correct port.

Consider a device A wants to send data to device B. A prepares the frame and sends to the switch. Switch receives the frame and check the MAC address of the destination system in the frame. It then transfer data to device B only instead of broadcasting to all the devices. By forwarding data only to the system to which the data is address, switch decreases the amount of traffic on each network link. 

A MAC frame is divided into four parts. The first part contains the MAC address of the recipient. This address is followed by the MAC address of the sander's machine. In the third part, the data that is to be transmitted is placed. A maximum of 1500 bytes of data can be sent in a frame. This may differ depending on a network. The NIC forwards the data to the correct recipient. If the size of the data is larger than the NIC's capacity, then the data must be broken down into frame sizes chunks and then send to the NIC. The fourth part of a frame is especially bit called CRC (cyclic redundancy check) which is used to verify that data is received without any errors. CRC is only 4 bytes long. The CRC value is calculated by the sender's NIC.

Connecting Ethernet Segments

Multiple switches are useful in the network for redundancy and network expansion. The maximum number of ports available on switch are 48. This restrict the number of users that can be connected to the switch. To include more users than the available port on the switch, another switch is required. This Switch should be connected to the previous switch for the data transfer between two segments. if one of this which stops functioning, it affects only this segment to which is it connected and the rest will work fine. A crossover cable is required to connect two switches. Few switches are available with crossover ports for connecting with other switches. 

Crossover port also known as up-link, input or output.

 Two switches are never connected by their crossover port while connecting this switch using regular cable, one end of the cable is connected to the crossover port on one switch and other end to any regular port on other switch or backbone switch which normally operates at a higher speed as compare to distributed switch. Crossover cable allows you to connect two computers together using their NIC's without a switch in between.

Multi-Speed Switches. 

The multi-speed switches provides multiple speed. These switches are two types. One type of which has some number of ports operates at 100 Mbps and one or two gigabit ports. It is possible for the users to install gigabit Ethernet card into the server and then connect to the service directly to the gigabit ports. 

Each ports on the other type of multi speed switch has the capacity of running at the more than one Speed. For example, a 10/100/1000 switch will run at either 10 Mbps or 100 Mbps or 1000 Mbps. When the user connects the cable to the port, the port will detect the speed of the NIC on the other end of the cable and run at that speed. This is called auto-sensing. The auto-sensing port that runs at 10 Mbps or 1000 Mbps is referred as a 10/100 ports. If both that runs at 10, 100 or Gigabit is referred as a 10/100/1000 Port.

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