Compex DynaStack DSR2216 16-Port Switch

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The Compex DynaStack DSR2216 16Port Switch - Page 2

The Compex DynaStack DSR2216 16-Port Switch
It's Time for a "Switch"

By Jeff Bouton
5/12/2002

 
 

 

Hubs, Switches, They're All The Same...Right?
Not Really...

Before we head on over to the test bench, we'd like to take a small detour for our less network savvy readers.  I'm sure there are a few of our readers who have heard us use some terminology that left them scratching their heads a little.  So we thought we'd try to cover a couple of key concepts about networking to help clarify the basics, as well as demonstrating the functions of a switch versus a hub.  Don't worry, this is not going to be rocket science, just a very basic description to help you understand some key terms and concepts.

When a computer sends a request, it is comprised of a series of "packets" which contains the basic details of the request.  In general, the packet contains the sending computers MAC address, the data itself, and the receiving computers MAC address.  A MAC address is a unique identifier common to all network cards that acts much like a finger print, meaning no two networks cards have the same address.  This helps to insure that the request is received by the intended recipient.  A "request" can be a simple print command, e-mail, file transfer or any other action that requires that data be sent across the network.  On a fundamental level, all requests are the same, since they all involve the sending and receiving of "packets."

On a hub-based network, the packets sent between devices are "broadcast" to all of the devices connected to the network until it is received by the intended recipients.  A device can be anything that is connected to the network, whether it be a printer, computer or other network ready component.  Once the message is received, the recipient sends a confirmation packet back to the original sender confirming that the message has been received and that it is waiting for the next request.

Below is a basic diagram of how a hub-based network handles a single request.  In this example, Computer "A" is sending a request to Computer "C."  As the request travels across the network, it is 'broadcast" to all of the devices on the networks, in this case computer "B" and the Printer.  Since computer "B" and the printer recognize that the request is not for them, the packet is rejected, while Computer "C" recognizes the request and accepts it.
 

The Hub-Based Network

 

This is a fairly rudimentary explanation, but nonetheless, this has been the norm for many years.  The main disadvantage of a hub-based network, however, is a condition called "collisions."  Collisions occur when two or more devices send a request at the same time.  As the "packets" from each device are "broadcast" across the network, they can collide, corrupting the packet, requiring that it be retransmitted.  In general, this is a common occurrence that has little noticeable effects on the performance of a small network.  Nevertheless, as a network grows, adding more devices and making an increasing amount of requests, these collisions can bring a network to a crawl.  In fact, if enough devices are added to the network, a "broadcast storm" can occur where the hub-based network is saturated with enough requests that nothing can reach its intended recipient.  This is where the advantage of switching technology can help.

A "switch" has one distinct advantage over a hub which can have a tremendous effect on how well a network performs.  While a hub can only "broadcast" a request for all devices to hear, a switch has the added ability to direct the request to the intended device.  A switch can analyze a packet, determining who to direct the request to by scanning the packet for the MAC address of the desired recipient.  Once the switch determines the destination machine, the packet is sent directly to the port that machine is connected to, while leaving the other ports on the switch free for other traffic.

The Switch-Based Network

In the diagram above, computer A is sending a command to computer C, while computer B is sending a print job to the printer.  Both requests pass through the switch, reaching their destination at the same time.  Once again, this is only a very basic demonstration, but hopefully it helped some of our readers gain a better understanding of the basic concept of networking.

Next we'll hook up the DynaStack DSR2216 16-Port Switch and transfer a few files... 

Some Benchmarks and The Rating...

 

 
Tags:  NAS, Enterprise, DS, ITC, switch, SR2, port, RT, AC, COM, K

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