Network Switch Roundupby Jason Clark & Greg Hanna on June 14, 2000 10:49 PM EST
- Posted in
In addition to reducing traffic on each port, switches that conform to the IEEE 802.3 specification (which is all of the ones we tested) are able to further reduce the number of collisions by using CSMA/CD (Carrier Sensing Multiple Access/Collision Detection). This feature is a media-access method which allows the switch to, among other things, check the line for traffic before it sends data. If it senses that there is traffic on the line, it waits for the line to clear before sending data. CSMA/CD also enables the switch to listen to each packet that comes across it, and discard damaged or fragmented packets, thus reducing traffic even further.
One final note about switching technology: All of the products featured in this round-up are 'store-and-forward' type switches, as are virtually all new switches today. Store-and-forward switches take in each packet completely before sending it out to the destination. This allows the switch to analyze the packet (to see if it might be a fragment from a collision, for instance) and decide if it should be sent or dropped. The other predominant type of switching technology is called 'cross-point' switching. A cross-point switch begins to send the packet out before it even receives the entire thing. The cross-point switch used to be the choice for expensive, enterprise switching due to it's lower latency (doesn't wait for the whole packet) and overhead (doesn't analyze packet size, etc). Today, however, store-and-forward switching technology has evolved to the point where it is so fast that the benefits of entirely taking in and analyzing the packet before sending actually outweigh the detriments. That is, the dropping of packets determined to be bad by the analysis reduce traffic enough to more than offset the minor gain in speed of using a cross-point switch.
Now that you know all you ever wanted to know about switch technology, let's take a look at the switches themselves. First off, we should go over the things these products have in common, in order to get a baseline from which to start the comparison. One of the most important things to note is that all the products in this round-up come with unlimited, free technical support. Although switches are extremely simple to set up and get running, the free tech support could become very important if you do encounter any issues. All the switches here are able to auto-sense and auto-adjust for speed (10 or 100 Mbps) and duplexing.
The mention of duplexing brings up an interesting point: you will see notices by some of the manufacturers, most notably the huge ad on the Linksys box, that the switch is capable of "Blazing Speeds" of 200 Mbps per port. This is a bit of a marketing spin, in that the 200 Mbps is really 100 Mbps each direction (as in full-duplex). Don't be fooled into thinking that you will be able to transfer files at 200 Mbps…it's not gonna happen.
Each switch also carries a MAC address table for storing addresses for the purposes mentioned above in the tech brief. While the space for possible entries varies, from 1000 to an impressive 12288 in the case of the Linksys, but all have plenty of space considering the intended use of the switches. If you have more than 1000 MAC addresses to deal with, the table limits will be the least of your worries J. Finally, all of these switches are able to daisy-chain to other switches for expansion via an "uplink" port. The uplink ports are, without exception, shared with one of the regular ports, so that you lose the functionality of one port on each switch when expanding them. That is to say that two of the 8-port switches together will give you 14 available ports rather than 16.
Post Your CommentPlease log in or sign up to comment.
View All Comments