T1/E1 lines can be leased from TELCOs and can support data transmission at a rate of 1.544 MBPS. As applications require greater and greater transmission speeds there has been increasing use of T1 leased lines in corporate networks. However, TELCO responsibility for the line and its performance begins and ends at the wall of the building. The question then arises as to how you take T1/E1 to/from the line to the actual data equipment communicating e.g. the LAN Router or the PBX. A TELCO will do this for you, but at some not insignificant expense. An alternate possibility is to link the T1 line to the data equipment by fiber optic cable.

Along the same lines, increasingly high rate premises data communication devices such as Routers and Ethernet Switches are being ordered with T1 interfaces. This allows the traffic from them to go directly to Wide Area Networks (WANs) by way of a leased T1 line. A commonly used alternative is to connect these devices together with fiber optic cables and using the 78X connect the two WANs together.

Carrying out data communications using fiber optic cables in the premises environment presents several ready advantages. First, there is tremendous bandwidth potential. Not only can it deal with the T1 traffic it can handle much greater rates, easily, over premises distances. Applications which require very high data transmission rates can be easily accommodated. Secondly, there is the protection that fiber optic transmission provides against the variety of deleterious effects which plague transmission over copper cable. These include the resistance that fiber optic transmission has to Electromagnetic Interference (EMI), lightning induced current surges and ground loops. Finally, there is the protection that fiber optic transmission has with respect to 'tapping.' It is much more secure with no effective radiation of the communication occurring out of the cable.

In order to link traffic derived from a T1/E1 leased (copper) line to your data equipment you will need a T1/E1 Fiber Optic Modem. The Model 78X modems are ideal for this purpose as stand alone units. If you need versions appropriate for a card cage then the Model 278X modems can be employed. The 'X' denotes operating mode/wavelength/connector options. Respectively, these are: multi-mode/single-mode, 850nm/1300nm and ST/FC.

The employment of the Model 78X in a typical application is shown in the illustration above. On the left hand side and right hand side of the illustration are Routers. Each may be receiving traffic from a separate leased T1 line and want to forward it to a LAN station associated with the other Router. Each Router has a T1 interface. The Routers can be linked by employing a pair of Model 78Xs with fiber optic cable. As you can see, the distance that this Router-to-Router link can cover is quite large if the right mode option is chosen-up to 29 km.