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Compex PS2216 Switch

Review by Harry Lam on 02.12.03
Switch provided by Compex, MSRP: $89.95


Networking is becoming a more and more integral part of our society, as we shift more and more to a digital society.  As a result, network components are becoming cheaper and cheaper, and it's also more and more common for people to have their entire house networked together.  I personally remember back when a good quality 4-6 port switch would cost over $150, but now, you can get a generic 4 port switch for under $30, and a brand-name switch 4-6 port switch for under $60.  In this article, I'm going to take a look at the Compex PS2216 16-port 10/100Mbs switch.  This review won't just be one of those generic "I plugged it in and it works" type of "reviews," but rather, I'd like to explain a bit about networking and all of the features on the PS2216 switch (which actually isn't the run of the mill normal switch that consumers are used to).

A couple definitions of networking terms:

Collision - A collision is what happens when two nodes transmit at the same time.  The frames that are sent are both damaged; under Ethernet a random delay is inserted and the two devices re-send the frames.  Collisions can cause a significant impact on the speed of a network.

Collision Domain - Basically the area where frames can collide with each other (the more nodes in a collision domain, slower the network will act and the more collisions will occur)

Full Duplex -  The ability to transmit and receive packets simultaneously.  Full Duplex Ethernet is achieved by using two wire-pairs (inside Ethernet cable, which actually uses 4 wire-pairs) and a switched connection between the two "nodes."  A direct connection between the "transmit" and "receive" circuits of each node are established, which eliminates the entire possibility of collisions, as data is transmitted and received separately on two different circuits. 

Frame - A frame is basically a unit of data that operates at the second layer of networking; it contains a header and a footer, which contains a source and destination MAC address as well as error correction data.

Hubs vs Switches:

A hub basically is a multiple-port repeater.  If a hub is passive, it will just split a signal up into multiple versions.  If a hub is active, it will also repeat those signals split up (so that network cabling can exceed the 100m limit).  A hub functions at the lowest level of a network, basically just sending all the data it receives to every other node connected to it.

A switch intelligently forwards frames based on the destination address of every frame (basically in every frame, a source and destination MAC address is included, and a switch builds a switching table based on those datagrams).

Basically, a switch will send an incoming packet to only its destination rather than how a hub will forward any packet it receives to every node it is connected with.  Under a switched environment, a collision domain (the area where packets can collide and force re-transmission of packets -- slowing down the entire domain) is reduced to only the connection between the switch and the specific node the switch is communicating with.  With a hub, the collision domain is the entire network that isn't connected to a switch/bridge or a higher level device (like a router).  Not only will the amount of unnecessary information received by a node connected to a switch be greatly reduced (thereby speeding up transmission), but also collisions will be virtually eliminated (and entirely if both the switch and node are running in full-duplex).  A switch allows multiple simultaneous connections, resulting in a full 10/100Mbps (20/200Mbps if full-duplex is enabled) connection for each node (and the efficiency is much higher than a hub, which is just a 10/100 link shared between all of the nodes on the computer).


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