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Model 375 Application Notes

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When Local Area Networks (LANs) are implemented, there always seem to be one or more stations which are isolated from where the 'action is,' one or more stations which are far from the Ethernet hub. These isolated stations may be in a separate building from the Ethernet hub or they may even be across an industrial campus. Including these isolated stations in the LAN presents a real 'headache' when it is implemented using, the newer, higher speed, Fast Ethernet, 100Base-T, twisted pair, copper cable, technology. The maximum distance, which really is set by the CSMA cable sharing protocol, is only 100 meters. This hardly allows including isolated stations in the LAN.

The Model 375 is just the right 'pain killer' to end this 'headache.' It will allow you to connect an isolated station to the LAN using low cost, multi-mode, fiber optic cable. While meeting the CSMA requirements the low cost, multi-mode, fiber optic cable allows the isolated stations to be extended a full 2 km from the hub. Of course, you will need a Model 375 at the isolated station end to convert the electrical signal to/from copper to light for fiber optic transmission. You will need another Model 375 at the hub end to do the same conversion-unless the hub has this already built-in. This is just like the illustration shows. Using the Model 375 allows you to get significant range extension with your LAN.

The Model 375 has some important features. Firstly, it is that it is 100Base-F compatible and fully 100Base-FX compliant. This allows it to communicate with LAN equipment from other vendors that conforms to these standards. Secondly, it operates both full duplex and half duplex thereby getting higher throughput. Finally, it supports far end fault detect. This is a convenience for network managers in responding to outages.

But, let's get back to the basic issue of LAN extension. You will get some additional side benefits from using fiber optic cable to do the LAN extension. You will become immune to interference caused by lightning strikes- a real problem when you are transmitting LAN signals between buildings. You will also have total electrical isolation with the fiber optic cable and not have to worry about grounding problems. This is still another 'headache' when you have different elements of a network connected to different physical grounds- as often happens when you go between buildings.

The illustration above shows the Model 375 in an application. Here we have 2 LANs, one on the right and one on the left. The distance between them is of the order of 1 km.

Let's be specific. On the right hand side of the illustration we have a Fast Ethernet, 100Base-T, LAN. It is networking a group of PC's all located within a relatively short distance of the 100Base-T Hub- 50 meters. The PC's are connected to this Hub by copper UTP cabling.

On the left hand side of the illustration we have a more complicated situation. Here we have the usual 10Base-T LAN. It is networking a group of PC's all located within a relatively short distance of the 10Base-T Hub- 50 meters. Again the PC's are connected this Hub by copper UTP cabling. However, also tied into this second LAN is a Server. More to the point the Server is tied into this second LAN through its relatively low speed 10 MBPS port.

However, this same Server, as shown, has a relatively high speed 100 MBPS port. This same server would also like to be tied into the Fast Ethernet, 100Base-T LAN on the right hand side through this port. The speeds are compatible. The only problem is the Server is relatively far from the Fast Ethernet LAN.

As indicated in the illustration the Model 375 in conjunction with signaling by fiber optic cable solves this problem. The low attenuation of multi-mode fiber optic cable can link the Server on the left to the LAN on the right. However, first the Server's 100 MBPS output must be put in a form suitable for transmission on fiber optic cable. The Model 375 performs this function. On the right hand end this optical signal must be put in an electrical form suitable for the Fast Ethernet LAN operating with copper UTP cabling. The Model 375 performs the conversion back. It also performs the conversion in the left-to-right direction.
  

 

Model Product Info
375 Product Page   Specifications   Manual
For more information, contact:
Metrotek
Phone: (727) 547-8307
Fax: (727) 547-0687

E-mail: fiberoptics@metrotek.com

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