Network Switch Roundupby Jason Clark & Greg Hanna on June 14, 2000 10:49 PM EST
- Posted in
As the cost of networking equipment drops further and further, the accessibility of such equipment to the consumer increases inversely. That is, where only a few years ago, 100Mbit network cards and hubs were all but out-of-reach for the average Joe, today they are common. In fact, the old stalwart of the home network, the hub, is gradually disappearing from business and home networks alike, as it gets replaced by switches offering far better performance at very attractive prices. And, as always, increased demand has created increased supply: There are now a variety of very good, low-cost fast Ethernet switches coming out on the market. We figured that it was time we found out just how good this new breed of switches is, so we took five of them from four popular manufacturers and put them through their paces.
Before we get to the comparisons, though, you might be wondering what the difference is between a hub and a switch, and what makes one better than the other. Simply put, a hub is much like a cable splitter. It takes in signals from each port and feeds them to all the other ports. This means that the signal from each node (computer, printer, etc) connected to the hub goes to every other node connected to the hub. That ensures that the node that the message is intended for will get it. Unfortunately, it means that all the nodes the message isn't intended for get it too. This makes for a lot of unnecessary traffic across the hub, and on the network. That, in turn, means that the network gets more and more congested as more nodes are added. Since there is no way for the hub to manage the traffic it receives, packets run into each other fairly often (collisions). These collisions fragment the packets involved, so they have to be re-sent, increasing delivery times and thereby lowering the effective speed of the network.
While hubs merely pass packets along the wire, switches are intelligent enough to manage the packets they receive in a number of ways. Without going into OSI model specifics, let's say that switches are able to "look inside" each packet to a certain degree. Inside each packet is the MAC address of the sender and intended receiver of the packet. The MAC (Media Access Control) address is a unique identifying number borne by each node on the network.
By keeping track of these MAC addresses, the switch is able to tell on what port each network node resides. For example, a packet comes in on port 2 with destination address X and source address Y. The switch immediately knows that the address Y is on port 2 as the packet has come in to that port. In the meantime, a packet comes in to port 5 with the destination address Z and the source address X. The switch now knows that X resides on port 5, and thus has the destination port of the original packet from port 2 (MAC address Y). Theoretically, this chain of events only needs to happen once for each MAC address, because each switch has an address table built into it which holds the information for future reference.