|
The most
modern implementations of Ethernet use switching technology, which
replaces the traditional shared hub with a switch. A switch creates a
direct internal connection between any two nodes attached to it when
they need to communicate, which effectively eliminates collisions.
With 10Mbps shared Ethernet, a hub with 24 ports created a collision
domain of 24 nodes. All 24 workstations or servers would be competing
for a share of the 10Mbps total bandwidth. If you replace the 24-port
hub with a 24-port 10Mbps switch, you will provide a full 10 Mbps
bandwidth between any two nodes. The size of the collision
domain with a switch is always two nodes, regardless of the number of
ports.
With a shared Ethernet hub only one
data packet could be on the cable at a time. A switch can handle
multiple packets simultaneously so multiple workstations can
communicate with each other at the same time. Traditional shared
Ethernet hubs can also be connected to a switch to reduce the size of
collision domains. Ethernet switches are compatible with Ethernet
hubs.
The first Ethernet switches were
10Mbps, but since they did not have to contend with collisions, they
provided a dedicated 10Mbps between any two nodes that needed to
communicate. This was a vast improvement over the shared collision
domain approach.
By using switching technology, this
bandwidth can be increased to 20 Mbps with full-duplex transmission.
Since the receive circuit of the NIC does not have to listen for
collisions, the NIC can transmit and receive at the same time. This
results in a full 20 Mbps dedicated bandwidth to a workstation or
server.
Switched Ethernet has become
increasingly popular in recent years and is the dominant LAN
technology being implemented today. Ethernet switches and NICs are
available in 10Mbps, 100Mbps (fast Ethernet) and 1000Mbps (Gigabit
Ethernet) speeds. Since these are switched technologies, these numbers
can all be doubled by using full-duplex data transmission if the NICs
in the workstations and servers can support it. The Figure shows the use of a switch to connect workstations.
|