In which layer of the OSI model would you find network switches?
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Network
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Physical
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Transport
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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.
