Model 78X/278X

Series

T1/E1
Fiber-Optic Modems
 
 

Reference Manual

Printed 06.07.01

Table of Contents

1.0 Introduction

2.0 Operating Modes
2.1     Line Length—Switch S1
2.2     Line Protection Switch
2.3     Operational and Diagnostic Settings
2.4     Special Testing Modes
2.5     Jitter Attenuator
2.6     LED Indicators

3.0 Theory  Of Operation
3.1     Fiber Optic Data Format
3.2     Remote Test

4.0 Specifications
5.0 Performing A Functional Test

6.0 Factory Default Settings
6.1     T1 Factory Default Settings
6.2     E1 Factory Default Settings

7.0 System Interconnection Diagrams And Additional Information
8.0 Power
9.0 Help

1.0 Introduction

The Telebyte Model 78X Series is a family of high performance, extremely reliable, stand-alone fiber-optic modems, with each model offering subtle differences designed to meet unique application requirements. The Telebyte Model 78X Series Fiber-Optic Modems are well suited for applications that include the extension of T1/E1 transmission distance for LAN or video conferencing, connecting distributed channel bank networks and providing error-free Internet service from a local ISP. The use of fiber optics as a cabling medium has several advantages, including data line security, total electrical isolation, lightning/surge protection and EMI/RFI immunity.

Note: Telebyte Model 78X/278X Series Definition
 
The Telebyte family of standalone Fiber Optic Modems—Models 780,  781, 782, 783, 784 and 785—are collectively referred to in this Reference Manual as the "78X Series."  Each of these units are available in a rack-mount configuration as Models 2780, 2781, 2782, 2783, 2784 and 2785, respectively. The Telebyte family of rack-mountable Fiber-Optic Modems are collectively referred to as the "278X Series."
 
Any given model and its counterpart (e.g., 780 and 2780) are similar in terms of general functionality, operation, settings and wiring. Therefore, this Reference Manual serves as a comprehensive reference source for the entire 78X and 278X Series. Differences within the 78X and 278X Series occur with respect to available modes, connector types and operational distances. Your specific application will help determine the Telebyte 78X or 278X Series Fiber-Optic Modem solution that meets your needs. 
 
Models 780 and 782 are high performance fiber-optic modems designed to extend the distance and transmission reliability of high speed T1 and E1 data traffic. These units are compatible with multi-mode fiber, and support fiber distances of up to 3.5km.

Models 781 and 783 provide the same functional performance, but are compatible with single-mode fiber cables and offer operation over distances of 14km.

Models 784 and 785 are fiber-optic modems designed with FC connectors. These units offer enhanced performance due to their optic technology, and support operation over distances up to 29km.

The chart that follows provides an overall view of the functionality and specifications of each model in the Telebyte Model 78X Series:
 

Note: All of these units are also available in a rack-mount configuration as Models 2780, 2781, 2782, 2783, 2784 and 2785, respectively. The basic card cage rack for the 278X Series is the Model 2200, and is available with either single or dual redundant power supplies for 110/220 Volt AC, 50/60 Hz, or _48 Volts DC. The chart below provides basic card cage specifications. Please consult the Telebyte catalog or speak with your Telebyte representative for additional information. (Refer to the Telebyte Model 78X/278X Series Definition, shown previously in this document).
 

2.0 Operating Modes

This section describes the various operating modes of the Model 78X/278X Series Fiber-Optic Modems. Each unit is equipped with several switches that must be set properly to control the desired operation of the fiber-optic modem. These switches and their functions are described in this section.

Typical Application Diagram

The following figure illustrates a typical application for the Telebyte 78X/278X units. This is a short-haul application which implies the lengths of the crossover cables are less than 133 feet. All units are shipped with short-haul default settings (see diagram for details).

Note: Please refer to section 6.0, "Factory Default Settings" to view default settings for E1. Refer to the remainder of this section for information concerning switch settings.
 

 
Typical Application System Interconnection Diagram  

2.1 Line Length—Switch S1

Tables 1 and 1A show the appropriate S1 switch settings that allow optimal transmission and reception signals. The T1 and E1 jumper formats should be set as shown below:
 

T1 modes are available only on Models 780 and 781. E1 modes are used on Models 782 and 783. Model 780 and 782 utilize multi-mode fiber, whereas Models 781 and 783 utilize single-mode fiber. (This same information applies to Model 278X counterparts.)

Table 1
 

 
The receiver equalizer processes the signal received at the RTIP and RRING Ports. The switch settings of S1 determine the maximum gain applied at the equalizer:  

· For "S1-1 Off" up to 36 dB of gain may be applied. 
· For "S1-1 On" 26 dB is the gain limit which provides an increased noise margin in shorter loop operations.

*For use with 100-Ohm #24 AWG twisted-pair wire.

 
The distances listed in Table 1 were obtained from the graph shown below:
 

2.2 Line Protection Switch

Protection requirements for T1 equipment are specified in FCC Part 68, UL 1459, Bell Core TR-TSY-000007 and AT&T publication 62411. Similar protection circuitry is suggested for E1 applications in ETS 300 046-3 and ITU K17-K20. Switch S4 implements the appropriate protection circuit for the 78X/278X Series. The following chart identifies the different line conditioning settings necessary for proper operation.

2.3 Operational and Diagnostic Settings

Table 2 shows the diagnostic and operational modes controlled by Switch S2, as well as LED indicator illumination. With respect to data format, Model 78X/278X Series Fiber-Optic Modems can be configured to work with either the AMI data format or B8ZS/HDB3. Table 2 shows the switch settings.

Table 2
 

 
Test Functions

The Model 78X/278X Series test functions are described in the following paragraphs. They are controlled by Switch S2 on the front panel. Refer to Figures 1 through 5 for illustrations and descriptions of each mode.

Normal Mode

Data is passed from the copper RX side to the fiber TX side. Data from the fiber RX side is passed to the TX copper side. If enabled by S2, Network Loopback can be activated.

Analog Loopback

Data from the fiber RX side is transferred to the copper TX side, and is then routed to the copper RX side. Input data to the RX copper side is disabled.

Remote Loopback (Network Loopback)

Data from the copper RX side is transferred to the copper TX side, as well as to the fiber TX side. Input data from the fiber RX side is disabled. This mode may also be activated by a Network Loopback command if enabled by Switch S2.

Dual Loopback

Data from the copper RX side is transferred to the copper TX side. Data from the fiber TX side is transferred to the fiber RX side. No data is transferred between the copper and fiber sides.

Remote Test Mode

Activates the internal remote test generator, which transmits a unique pattern on the fiber TX side that initiates the Remote Test Mode on the far-side unit. Upon successful operation, both the local and remote units light the "Fiber Diagnostic" LED. These test functions are summarized in Table 3:

Table 3
 

 
In addition to the test functions described above, Model 78X/278X Series Fiber-Optic Modems have the ability to perform special functions as described below:

· Transmit "All Ones:" An "all-ones" pattern is sent from the copper TX side. Data from the fiber RX side is disabled. Copper RX data is passed to the fiber TX side. 
 
· QRSS Mode: Quasi-Random Signal Source testing (as defined in Bellcore Pub 62411 for T1 and ITU G.703 for E1) is performed in this mode. Internally-generated data is sent to the copper TX side. Data received on the copper RX side is passed to the QRSS detector as well as to the fiber TX side. 
 
· Normal-Net LP EN (Network Loopback Enabled): Allows the Network Loopback feature to be disabled. When this is done, the copper Network Loopback command will be passed through the fiber system.

These test functions are summarized in Table 4:

Table 4
 

 
(1) Normal or with Local Loopback only
(2) Normal or with Analog Loopback only

2.4 Special Testing Modes

The Model 78X/278X Fiber-Optic Modems are capable of performing specialized test functions. This is accomplished by manipulating Switch S2 to insert Bipolar Violations and Logic Errors. Please refer to Tables 3 and 4 for the switch settings for each testing mode.

Bipolar Violation Insert: Bipolar violation insert is available in all modes except when in Remote Loopback, or when Network Loopback is active. To insert bipolar violations for 20 microseconds, turn Switch S2-6 ON and then OFF.

Logic Error Insertion: Forces an error in the QRSS mode in order to test error detection logic. To induce a logic error, back out the FO RX connector until counting starts.

Please refer to the section 5.0, "Performing a Functional Test" for step-by-step instructions on how to execute the special testing modes.

2.5 Jitter Attenuator

The Jitter Attenuator control in the Model 78X/278X Series of Fiber-Optic Modems offers users control over the internal logic, which impacts how the modem processes data. The user can select from any of the three setting combinations shown in Table 5:

Table 5
 

2.6 LED Indicators

The Model 78X/278X Series Fiber-Optic Modems have seven LED indicators on the front panel. The function of these indicators is shown in Table 6:

Table 6
 

 
In addition, combinations of these indicators are used to display other status conditions. These are shown on Table 7:

Table 7
 

l = LED ON
O = LED OFF 

 
The interface to the Model 78X/278X Series is provided by three connectors mounted in the back of the unit. They are an RJ48C, a DB15 male and a four-position terminal block. Each Model 278X is shipped with a DB25-to-DB15 adapter cable. Tables 8 and 9 describe the DB15 and Terminal Block connections.

Table 8
 

 
Table 9
 

  
Table 10
 

 
Table 11
 

   
3.0 Theory Of Operation

3.1 Fiber-Optic Data Format

Data encoded and used on the Model 78X/278X Series Fiber-Optic Modems consists of converting incoming AMI, B8ZS or HDB3 data into a format suitable for fiber-optic communication. A proprietary coding scheme is used to combine the input clock and data into a composite signal that is then transmitted over the fiber. At the receiver, this composite signal is then separated back into its respective signals and formats.

This coding technique provides a composite data pulse for each incoming data bit. This ensures 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." Each incoming logic-one data bit produces a pulse having a fixed width of approximately 2/3 the bit rate. A logic-zero data bit produces a pulse width of approximately 1/3 the bit rate. The leading edge of all data bits is synchronous to the input and output data clock. Therefore, because the composite-fiber data stream utilizes this pulse width scheme, no synchronizing headers are required, resulting in faster recovery from loss of signal-data errors, as well as guaranteeing true data and timing transparency.

3.2 Remote Test

The composite fiber-optic data stream also allows for the transmission of a unique pattern which is used to activate the Remote Test Mode. Since the incoming data coding specifications limit the number of consecutive zeros, a pattern or frequency can be sent which does not meet this criteria, but is used to activate the Remote Test Mode. This test mode is detected by the remote unit, which lights its "Fiber Diagnostic" LED while initiating the transmission of this data pattern. This causes the local unit to also detect and light its "Fiber Diagnostic" LED.

4.0 Specifications

Electrical Interface, T1:  
     Transmission Rate: 1,544 Kbps 
     Line Code: Supports both AMI and B8ZS 
     DS-1 Output Signal: Conforms to ITU-T G.703 
     Line Build-out: Switch selectable from 0 dB to _22.5 dB BER<10^-9  

Electrical Interface, E1:  
     Transmission Rate: 2,048 Kbps 
     Line Code: HDB3 
     Line Impedance: Supports 120-Ohm balanced and 75-Ohm Coax (customer supplied)
     I/O Ports: Conforms to ITU-T G.703 
     Line Build-out: Switch selectable, four settings, 12 dB to 43 dB BER<10^-9  

Optical Interface:  

     Multi-Mode:  
          Connectors: ST 
          Cable: 62.5/125 um multi-mode 
          Wavelength: 850 nm 
          Power Budget: 15 dB 
          Fiber Distance: 3.5 Km 

     Single-Mode:  
          Connectors: ST 
          Cable: 9/125 um single-mode 
          Wavelength: 1300 nm 
          Power Budget: 10 dB 
          Fiber Distance: 16 Km 

          Connectors: FC Cable: 9/125 um single-mode 
          Wavelength: 1300 nm 
          Power Budget: 14.8 dB 
          Fiber Distance: 29 Km 

Diagnostic Capability:  
     Analog Loopback: Switch selectable for electrical interface 
     Remote Loopback: Switch selectable, includes total fiber path 
     Remote Test: Switch selectable, test entire communications channel 

     Dual Loopback: Switch selectable 
     Insert Bipolar Violations: Switch selectable, inserts 20 usec. violation 

Special Functions:  
     Transmit All Ones (1s) 
     QRSS Mode 
     Normal-net LP EN 
     Jitter Settings: Switch selectable for Transmit and Receive

Alarm Functions:

Power Failure: The card cage provides both visual and audible alarms in the event of a power failure. The power supply for both the AC and DC power supplies consist of dual units. Therefore, a supply failure in a single power supply version of the card cage will still be detectable. The standalone unit has a "Power On" LED.

Electrical Signal Loss: "Copper Active" LED goes off in an alarm condition. Also activates visual and audible alarms in the card cage.

Optical Signal Loss: "Fiber Active" LED goes off in an alarm condition. Also activates visual and audible alarms in the card cage.

Relay Contact: Card cage provides a dry contact closure, Form A, when an alarm condition is present.

Dimensions (Stand-alone):
     Model 78X Series: 7" W x 1.5" H x 5.5" D 
                                  178mm x 38mm x 140mm

     Card Cage:          19" W x 7" H x 18" D
                                 482mm x 178mm x 457mm

Environmental:
     Temperature:        All models operate over the range of 0^oC to +50^oC
     Humidity:              0% to 95 % Relative Humidity, no condensation
 

5.0 Performing A Functional Test

Telebyte Model 78X/278X Series Fiber-Optic Modems can be tested according to the procedure described below. The following equipment is required:

· One fully-operational Model 78X/278X Fiber-Optic Modem 
· One short-fiber optic cable (minimum two meters in length) with appropriate connectors

Test Procedure

1. Connect a fully-operational Model 78X/278X Series Fiber-Optic Modem (referred to as "the Reference Unit") of the same type as the unit to be tested (referred to as "the Unit Under Test") with the appropriate connector cable type. 

2. Set the Reference Unit for unframed "all ones" (S2-4 ON and S2-5 OFF). 

3. Set the Unit Under Test in the Remote Loopback Mode (S2-2 ON and S2-3 OFF). Do not connect a fiber jumper cable between the Fiber-Optic TX and RX ports at this time. 

4. Observe that on the Reference Unit, the "Power," "Copper Active," "Copper Loopback" and "QRSS" indicators are lit. Observe that on the Unit Under Test, the "Power," "Copper Active" and "Network Loopback" indicators are lit. 

5. Next, change the settings on the Unit Under Test to the default positions and connect a fiber jumper cable between the Fiber-Optic TX and RX ports. 

6. Observe that on the Reference Unit, the "Power," "Copper Active," "Copper Loopback" and "QRSS" indicators are lit. Observe that on the Unit Under Test, the "Power," "Copper Active" and "Fiber Active" indicators are lit. 

7. Next, set the Reference Unit for the QRSS Generator Mode (S2-4 OFF and S2-5 ON). The Unit Under Test should still be in its default positions and the fiber jumper cable connected as before. 

8. Observe that on the Reference Unit, the "Power," "Copper Active," "QRSS" and "Network Loopback" indicators are lit. Observe that on the Unit Under Test, the "Power," "Fiber Active" and "Copper Active" indicators are lit.

6.0 Factory Default Settings

Your Telebyte Model 78X/278X Series Fiber-Optic Modem ships with the following T1 and E1 Factory Default Settings:

6.1 T1 Factory Default Settings

6.2 E1 Factory Default Settings

7.0 System Interconnection Diagrams
And Additional Information

The following illustrations show system interconnection diagrams, PC board assembly and the front and rear panels of Telebyte Model 78X/278X Series Fiber-Optic Modems. Use these figures as a reference source and to familiarize yourself with connection schemes.
 

 
Note: For units equipped with a four-section Terminal Block that is not labeled as shown previously, please refer to the diagram below for the correct terminal pins.

 
8.0 Power

Telebyte Model 78X Series Fiber-Optic Modems are powered by a small, wall-mounted power cube that supplies 12 Volts DC @ 500 ma.

Note: The power supply must be connected to a Model 78X Series unit through the 1.3mm connector located on the rear of the unit. This must be done prior to plugging the power supply into the wall.

9.0 Help

Assistance can be obtained by visiting our Technical Support Center.
 

Warranty

Telebyte warrants the equipment to be free from defects in material and workmanship, under normal and proper use and in its unmodified condition, for 12 months, starting on the date it is delivered for use. TELEBYTE's sole obligation under this warranty shall be to furnish parts and labor for the repair or replacement of products found by TELEBYTE to be defective in material or workmanship during the warranty period. Warranty repairs will be performed at the point of manufacture. Equipment approved for return for warranty service shall be returned F.O.B. TELEBYTE factory and will be redelivered by TELEBYTE freight prepaid, except for non- continental U.S.A. locations. These deliveries will be sent COD freight and import/export charges. 
 
The above warranty is in lieu of all other warranties, expressed or implied, statutory or otherwise, including any implied warranty of merchantability or fitness for a particular purpose. Telebyte shall not be liable for any damages sustained by reseller or any other party arising from or relating to any equipment failure, including, but not limited to consequential damages nor shall telebyte have any liability for delays in replacement or repair of equipment.  
 
Out of warranty equipment may be returned to the Greenlawn, NY customer service facility prepaid as described above. Return shipping charges will be billed to the customer. The repaired unit will have a 90 day warranty. In those cases where "NO TROUBLE" is found, a reduced charge will be billed to cover handling, testing and packaging. Whether in or out of warranty, a Return Material Authorization (RMA) number is necessary. Assistance can be obtained by visiting our Technical Support Center.

 
Document No. 0315-0280/Rev. D