A Valuable Asset To Networking
Switches can be a valuable asset to networking. Overall, they can increase the capacity and speed of your network.
However, switching should not be seen as a cure-all for network issues. Switches occupy the same place in the network
as hubs. Unlike hubs, switches examine each packet and process it accordingly rather than simply repeating the signal
to all ports. Switches map the Ethernet addresses of the nodes residing on each network segment and then allow only
the necessary traffic to pass through the switch. When a packet is received by the switch, the switch examines the
destination and source hardware addresses and compares them to a table of network segments and addresses. If the
segments are the same, the packet is dropped or "filtered"; if the segments are different, then the packet is
"forwarded" to the proper segment. Additionally, switches prevent bad or misaligned packets from spreading by not
Easy to install, most switches are self learning. They determine the Ethernet addresses in use on each segment,
building a table as packets are passed through the switch. This "plug and play" element makes switches an attractive
alternative to hubs.
Switches can connect different network types (such as Ethernet and Fast Ethernet) or networks of the same type. Many
switches today offer high-speed links, like Fast Ethernet, which can be used to link the switches together or to give
added bandwidth to important servers that get a lot of traffic. A network composed of a number of switches linked
together via these fast uplinks is called a "collapsed backbone" network.
As more users are added to a shared network or as applications requiring more data are added, performance deteriorates.
This is because all users on a shared network are competitors for the Ethernet bus. A moderately loaded 10 Mbps
Ethernet network is able to sustain utilization of 35 percent and throughput in the neighborhood of 2.5 Mbps after
accounting for packet overhead, inter-packet gaps and collisions. A moderately loaded Fast Ethernet or Gigabit
Ethernet shares 25 Mbps or 250 Mbps of real data in the same circumstances. With shared Ethernet and Fast Ethernet,
the likelihood of collisions increases as more nodes and/or more traffic is added to the shared collision domain.
Benefits of Network Switching
The Factors Affecting Network Efficiency
Amount of traffic
Number of nodes
Size of packets
Measuring Network Efficiency
Average to peak load deviation
enough processing power
Switches replace hubs in networking designs, and they are more expensive. So why is the desktop switching market
doubling ever year with huge numbers sold? The price of switches is declining precipitously, while hubs are a mature
technology with small price declines. This means that there is far less difference between switch costs and hub costs
than there used to be, and the gap is narrowing. Since switches are self learning, they are as easy to install as a hub.
Just plug them in and go. And they operate on the same hardware layer as a hub, so there are no protocol issues.
There are two reasons for switches being included in network designs. First, a switch breaks one network into many
small networks so the distance and repeater limitations are restarted. Second, this same segmentation isolates traffic
and reduces collisions relieving network congestion. It is very easy to identify the need for distance and repeater
extension, and to understand this benefit of network switching. But the second benefit, relieving network congestion,
is hard to identify and harder to understand the degree by which switches will help performance. Since all switches
add small latency delays to packet processing, deploying switches unnecessarily can actually slow down network
performance. So the next section pertains to the factors affecting the impact of switching to congested networks.
Isolates traffic, relieving congestion
Separates collision domains, reducing collisions
Segments, restarting distance and repeater rules
Monitoring the network is more complicated
Packet processing time is longer than in a hub
Price: currently 3 to 5 times the price of a hub