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.
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