In which layer of the OSI model would you find network switches?
- Network
- Physical
- Transport
- Data Link
EXPLANATION
The Application layer, layer 7, is the closest to the user. Hubs, switches, and routers operate at the lowest three layers of the OSI network model: the physical layer, data link layer and network layer.Hubs work at the first or Physical layer. It links all the devices connected to it and forms a single network. Each device that directly connects to the hub uses a port on the hub. When one device sends out a message to another device, the hub does not decide where the message goes. It just repeats the message to all the ports. Each device needs to decide whether this message is for itself or for others. One problem with hubs is that they share bandwidth among everyone. A telephone party line is like a hub. Each person decides by the ring if it is their phone call or someone else’s call, BUT, everyone can listen in on the call.
Switches operate at the Data Link or second layer. Switches are “intelligent” hubs. Switches can remember which ports are connected to which devices. When a switch receives a packet (data), it resends that packet directly to the correct port. For example, host A sends out a message through port A. The switch records into its switch table that host A is on port A. When host B decides to send a packet to host A, the switch first checks its switch table. If port A is registered in the switch table, it will resend the packet directly to port A instead of sending it to all the ports. This also means that switching gives dedicated bandwidth. A private phone call is like a switch. The phone number that is entered is looked up in the table and the correct telephone rings at the other end.
Routers are on the third layer, the Network layer. They are used to connect networks together. The Internet consists of many interconnected routers. Using a network protocol, like TCP/IP, a router can intelligently move data from one network to another. For example, when a user sends a request for a server, the router in the local network will check its routing table and decide where to resend the data. So, a router needs to have a better understanding of the whole network structure than does a switch. A long distance phone call uses a router like device. The initial one plus area code tells the system that the call is not local but needs to be routed to a distant phone network. The “phone router” then connects the call to the correct distant phone network.
