---

Product Description

The 278X Series of fiber optic modems provide an extremely reliable, high performance alternative for extending T1 or E1 circuits over fiber cables. The series also includes both multimode and singlemode versions. Advanced silicon circuits provide comprehensive error checking and diagnostics. The model number assignments for the rack mount versions are as follows.

Model No.	Description	Mode	Wavelength nm	Connectors	Link Budget dB
2780	T1 to Fiber	Multi	850	ST	15
2781	T1 to Fiber	Single	1300	ST	10
2782	E1 to Fiber	Multi	850	ST	15
2783	E1 to Fiber	Single	1300	ST	10
2784	T1 to Fiber	Single	1300	FC	14.8
2785	E1 to Fiber	Single	1300	FC	14.8

The multimode units are compatible with multimode fiber and support fiber distances of up to 3.5km. The singlemode units, the Models 2781 and 2783, provide the same functional performance, but, are compatible with single-mode fiber cables and offer operation over distances of 15km.

The Models 2784 and 2785 are available with FC connectors and enhanced performance due to the optics, and offers operation over distances of 29km. The FC option requires special ordering.

All of the above units are available in a standalone configuration as the Models 780, 781, 782, 783, 784 and 785 respectively. The card cage rack for the 278X modules is the Model 2200 and it is available with either single or dual redundant power supplies for 110/220 Volt Ac, 50/60 Hz, or -48 Volts DC. The arrangement of model numbers is shown below.

Model No.	Description	Input Power	Redundant
2201	Card Cage-16 Modules	110/220, 50/60 Hz	No
2202	Card Cage-16 Modules	110/220, 50/60 Hz	Yes
2203	Card Cage-16 Modules	-48 Volts, DC	No
2204	Card Cage-16 Modules	-48 Volts, DC	Yes

Data encoding used on the 278X Series consists of converting the incoming AMI, B8ZS or HDB3 to a format suitable for fiber optic communication. A proprietary coding scheme is used which combines the input clock and data into a composite signal which is then transmitted over the fiber. At the receiver this composite signal is then separated the respective signals and back into their respective formats.

This coding technique provides a composite data pulse for each incoming data bit. This insures that the original timing information for each bit is transferred and can be recovered. Decoding long zero runs in the AMI code does not rely on timing interpolation between the transfer of AMI ones. The leading edge of all data bits is synchronous to the input and output data clock. Since the composite fiber data stream utilizes this scheme, no synchronizing headers are required which results in faster recovery from loss of signal data errors as well as guaranteeing true data and timing transparency.

Applications

Applications for the Series 278X modems include extending T1/E1 transmission distance for LAN or video conferencing connecting distributed channel bank networks or providing error free Internet service from a local ISP. The attributes of the fiber transmission line are data security, total electrical isolation, lightning/surge protection and EMI/RFI immunity. These attributes, in addition to the continuous reduction in fiber cable and connectors are compelling reasons to employ fiber transmission links.

---