T1/E1 Fiber Optic Modems

Models 78X & 278X - T1/E1 Fiber Optic Modems Reference Manual

Table of Contents

1.0 Introduction
2.0 Operating Modes
3.0 Theory of Operation
4.0 Specifications
5.0 Testing
6.0 Factory Default Settings
7.0 System Interconnection Diagrams
8.0 Power
9.0 Help
Warranty

1.0 Introduction

The Model 780, T1, and the Model 782, E1, 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 multimode fiber and support fiber distances of up to 3.5km. Alternatively, the Models 781 and 783 provide the same functional performance, but, are compatible with single-mode fiber cables and offer operation over distances of 14km.

Model No.	Description	Mode	Connectors
780	T1 to Fiber	Multi	ST
781	T1 to Fiber	Single	ST
782	E1 to Fiber	Multi	ST
783	E1 to Fiber	Single	ST

The above units are available with FC or ST connectors. FC performance is superior, due to the optics, see Specifications. The FC option requires special ordering.

All of the above units are available in a rack mount configuration as the Models 2780, 2781, 2782 and 2783 respectively. The basic card cage rack 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

2.0 Operating Modes

This section describes the various operating modes available from the Model's 780/81/82/83 T1/E1 fiber optic modems/converters. There are several switches that must be set properly to control the desired operation of the fiber optic modem. These switches and their function are described in the following section.

2.1 Line Length - Switch S1

Table 1 shows the various line length settings controlled by S1. The term short haul refers to copper line lengths to 655ft or less. Long haul identifies line lengths of 1500ft minimum to 6000ft maximum. Table 1 shows the appropriate switch settings to allow optimal transmission and reception signals. The T1 and E1 jumper format should be set as shown below:

T1 Jumper Settings

JP1	IN
JP2	2 & 3
JP3	1 & 2

E1 Jumper Settings

JP1	OUT
JP2	2 & 3
JP3	2 & 3

T1 modes are available on Models 780 and 781 only and E1 modes are used on Models 782 and 783. Model 780 and 782 utilize multimode fiber and Models 781 and 783 utilize single mode fiber.

Table 1 Line Length Settings T1 Mode Line Length Settings

Function	Rx Pulse	Rx Gain	S1-1	S1-2	S1-3	S1-4
Long Haul	0 dB pulse	36 dB	Off	Off	Off	Off
Long Haul	- 7.5 dB pulse	36 dB	Off	On	Off	Off
Long Haul	-15.0DB pulse	36 dB	Off	Off	On	Off
Long Haul	-22.5DB pulse	36 dB	Off	On	On	Off
Long Haul	0 dB pulse	26 dB	On	Off	Off	Off
Long Haul	- 7.5 dB pulse	26 dB	On	On	Off	Off
Long Haul	-15.0DB pulse	26 dB	On	Off	On	Off
Long Haul	-22.5DB pulse	26 dB	On	On	On	Off
Short Haul	0-133ft	12 dB	On	On	Off	On
Short Haul	133-266ft	12 dB	Off	Off	On	On
Short Haul	266-399ft	12 dB	On	Off	On	On
Short Haul	399-533ft	12 dB	Off	On	On	On
Short Haul	533-655ft	12 dB	On	On	On	On

The above table is for 100 Ohm twisted pair wire.

E1 Mode Line Length Settings, ITU G.703

Line Type	Rx Gain	JP2	JP3	JP4	S1-1	S1-2	S1-3	S1-4
75 Ohm Coax- Short Haul	12dB	5 to 6	1 to 2	1 to 2	Off	Off	Off	On
75 Ohm Coax- Long Haul	43dB	5 to 6	1 to 2	1 to 2	Off	On	Off	On
120 Ohm Twisted Pair-Short Haul	12dB	1 to 2	1 to 2	1 to 2	Off	Off	Off	On
120 Ohm Twisted Pair- Long Haul	43dB	1 to 2	2 to 3	2 to 3	Off	On	Off	On

2.2 Line Protection Switch

Protection requirements for T1 equipment are specified in FCC Part 68, ul 1459, Bell Core TR-TSY-000007, & 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 chart shown below identifies the different line conditioning necessary.

Line Protection Switch	T1 100 ohm Twisted Pair	E1 120 ohm Twisted Pair	E1 120 ohm Twisted Pair LH	E1 75 ohm Coax SH	E1 75 ohm Coax LH
S4-1	Open	Open	Closed	Open	Open
S4-2	Closed	Closed	Open	Closed	Closed
S4-3	Open	Open	Closed	Open	Open
S4-4	Closed	Closed	Open	Closed	Closed
S4-5	Open	Closed	Closed	Open	Open
S4-6	Closed	Open	Open	Open	Open
S4-7	Open	Open	Open	Closed	Closed

2.3 Operational and Diagnostic Settings

Table 2 - 7 shows the diagnostic and operational modes controlled by S2 as well as LED indicators.

Figure 1- 6 diagrams the various modes described herein.

Data Format
The Model 78X can be configured to work with AMI data format or B8ZS/HDB3. Table 2 shows the switch settings.

Table 2 Mode

Function	S2-1
AMI	Off
B8ZS/HDB3	On

Test Functions

The Test Functions are described in the following paragraphs. They are controlled by front panel switch S2. Refer to figures 1-5.

1. Normal Mode-See Figure 1

Data is passed from the copper Rx side to the fiber Tx side and data from the fiber Rx side is passed to the Tx copper side. If enabled by S2, Network loopback can be activated.

2. Analog Loopback-See Figure 2

Data from the fiber Rx side is transferred to the copper Tx side and is also routed to the copper Rx side. Input data to the Rx copper side is disabled.

3. Remote Loopback-See Figure 3

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 S2.

4. Dual Loopback-See Figure 4

Data from the copper Rx side is transferred to the copper Tx side and data from the fiber Tx side is transferred to the fiber Rx side. No data is transferred between the copper and fiber side.

5. Remote Test-See Figure 5

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.

The above test functions are summarized in the following table.

Table 3 Test Functions

Function	S2-2	S2-3
Normal	Off	Off
Analog Loopback	Off	On
Remote Loopback	On	Off
Dual Loopback	On	On

Function	S2-7	S2-8
Remote Test	On	Off

In addition to the test functions described above the 78X/278X fiber optic modems have the ability to perform Special Functions as described below.

6. 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.

7. 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. Data internally generated is sent to the copper Tx side and data received on the copper Rx side is passed to the QRSS detector as well as to the fiber Tx side.

8. 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.

The above test functions are summarized in the following table.

Table 4 Special Functions

Special Functions Function	S2-4	S2-5
Normal	Off	Off
Tx All Ones (1)	On	Off
QRSS Mode (2)	Off	On
Normal - Net LP EN	On	On

(1) Normal or with Local Loopback only (2) Normal or with Analog Loopback only
2.4 Special Testing Modes
The special test modes are shown diagrammatically in the following figures. The switch settings for each mode are shown in Tables 3 & 4.

1. Bipolar Violation Insert.

Bipolar violation insert is available in all modes except when in Remote Loopback, or when Network Loopback is active.

2. Logic Error Insertion.

Forces an error in the QRSS mode in order to test error detection logic.

Insert Bipolar Violations

To insert bipolar violations for 20 microseconds, turn S2-6 on and then off.

2.5 Jitter Attenuator
The jitter attenuator control in the 78X/278X series of fiber optic modems offers the user control over the internal logic, which processes the data. As such the user can select from any of the three possibilities as shown in Table 5 below.

Table 5 Jitter Attenuator Settings

Jitter Attenuator	S2-7	S2-8
Disabled	Off	Off
In Tx Path	Off	On
In Rx Path	On	On

2.6 LED Indicators
The Model 78X has seven LED indicators on the front panel. The function of these indicators is shown in Table 6 below.

Table 6 Led Indicators

Power	On - power applied
Fiber Active	On - FO data present
Copper Active	On - RXD detected
Copper Diagnostic	On - Copper TXD driver failure
Network	On - Network Loopback activated
Internal	On - Elastic store over/under flow
Fiber Diagnostic	On - Remote test active
Internal + Network	On - QRSS Mode active

In addition, combinations of these indicators are used to display other status conditions. These are shown on the following chart.

Table 7 Status Indications

FO ACT	CU ACT	PWR	FI DIA	CU DIA	IN DIA	NT DIA	STATUS
							POWER
							FO RXD DETECTED
							CU RXD DETECTED
							REMOTE TEST MODE
							CU TX FAILURE
							BIPOLAR VIOLATION DETECT
							NETWORK LOOPBACK
							QRSS DETECT
							AIS DETECT
							STORE UNDER/OVERFLOW
							INVALID S1 OR S2 SETTINGS

= LED ON

= LED OFF
Note: CU ACT LED is always off in Dual Loopback mode.

3.0 Theory of Operation

3.1 Fiber Optic Data Format
Data encoding used on the Models 780/81/82/83 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 that 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 assures 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 and 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. Since the composite fiber data stream utilizes this pulse width 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.

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 limits 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 as well as initiating the transmission of this data pattern causing the local unit to also detect and light its FIBER DIAGNOSTIC LED.

4.0 Specifications

4.1 Electrical Interface, T1

^-9

4.2 Electrical Interface, E1

^-9

4.3 Optical Interface
4.3.1 Multi-Mode

4.3.2 Single-Mode

4.4 Diagnostic Capability

4.5 Special Functions

4.6 Alarm Functions

Power Failure:

Electrical Signal Loss:

Optical Signal Loss:

Relay Contact:

4.7 Size Standalone:

4.8 Environmental:

5.0 Testing

The Models 78X/278X T1/E1 to Fiber Optic Link can be tested according to the procedure described herein. The equipment required is one known working 78X/278X, a frequency counter with continuous count capability, 6000 ft of 22 AWG dual twisted pair or equivalent wire line simulator, a short fiber optic cable with appropriate connectors and a fiber optic variable attenuator.

FUNCTIONAL TEST

Connect one known working 78X/278X of the same type to the unit under test using two short twisted pairs. Connect a short fiber optic cable between the FO TX and FO RX on the unit under test. On the test fixture unit, connect a frequency counter with continuous count capability to the test point connected to U1-12.

1. Before applying power, set S1 and S2 switches to OFF on the unit under test.

2. Upon applying power to the unit under test only, observe the LED's light one at a time for about 0.75 seconds with the PWR LED lit continuously.

3. On the test fixture unit set all switches on S1 to OFF and set S2-5 to ON only. After applying power to the test fixture unit, observe that PWR, CU ACT, IN IA and NT DIA are lit (QRSS detected) on the test fixture unit and that PWR, FO ACT, CU ACT are lit on the unit under test.

4. Reset the frequency counter and observe that there is no count (QRSS errors) for at least 2 minutes. Note the frequency counter must be set to continuous count mode, not frequency and must be properly triggered for a positive TTL counting edge. This may be verified by backing out the FO RX connector until counting starts.

5. On the test fixture unit set S2-5 OFF and set S2-6 ON then OFF, on the unit under test, observe PWR, FO ACT, CU ACT and IN DIA (Bipolar violation detect) to light for about 1 second with every S2-6 ON/OFF on the test fixture unit.

6. On the test fixture unit set S2-4 ON. On the test fixture unit observe PWR, CU ACT, CU DIA, IN DIA (AIS detect) to be lit. On the unit under test, observe PWR, FO ACT, CU ACT, CU DIA, IN DIA (AIS detect) to be lit.

7. On the unit under test set S2-1 ON only. Observe PWR, FO ACT, CU ACT, FI DIA (Remote test mode detected) on only.

8. On unit under test, set S2-1 and S2-2 ON only. Observe all LED's are lit. (Invalid switch setting)

9. Repeat step 3 with S1-1 ON, on both unit under test and test fixture unit.

PERFORMANCE TEST

Connect the test fixture and the unit under test as described above.

1. On the test fixture unit, set S2-5 ON only. On the unit under test, set all switches to OFF. On the test fixture unit observe PWR, CU ACT, IN DIA, NT ACT (QRSS detect) to be lit and on the unit under test, PWR, FO ACT, CU ACT to be lit only.

2. Extend the copper connection to 6,000 feet of 22 AWG or wire line simulator equivalent. Observe no changes in the LED's from the above.

3. Reset the frequency counter and observe that there is no count (QRSS errors) for at least 2 minutes. Note the frequency counter must be set to continuous count mode, not frequency and must be properly triggered for a positive TTL counting edge. This may be verified by backing out the FO RX connector until counting starts.

4. Reconnect the short twisted pair cable between the two units and install a FO attenuator. Set the attenuation to 15DB (1/30 of the voltage at U7-4 input).

5. Observe the same indications as in step 1 and 3 above.

6. On the unit under test set S2-1 ON only. Observe PWR, FO ACT, CU ACT, FI DIA (Remote test mode detected) on only.

6.0 Factory Default Settings

6.1 T1 Factory Default Settings

JP1	IN	S2-1	ON	S4-1	OPEN
JP2	2 + 3	S2-2	OFF	S4-2	CLOSED
JP3	1 + 2	S2-3	OFF	S4-3	OPEN
		S2-4	OFF	S4-4	CLOSED
S1-1	ON	S2-5	OFF	S4-5	OPEN
S1-2	ON	S2-6	OFF	S4-6	CLOSED
S1-3	OFF	S2-7	ON	S4-7	OPEN
S1-4	ON	S2-8	ON

6.2 E1 Factory Default Settings

JP1	OUT	S2-1	ON	S4-1	OPEN
JP2	2 & 3	S2-2	OFF	S4-2	CLOSED
JP3	2 & 3	S2-3	OFF	S4-3	OPEN
		S2-4	OFF	S4-4	CLOSED
S1-1	OFF	S2-5	OFF	S4-5	CLOSED
S1-2	OFF	S2-6	OFF	S4-6	OPEN
S1-3	OFF	S2-7	ON	S4-7	OPEN
S1-4	ON	S2-8	ON

7.0 System Interconnection Diagrams

Figure 6: 75 Ohm Coax Cable Hook Up

Figure 7: Crossover cable for unkeyed RJ48C connectors

Figure 8: System Interconnection Diagram

8.0 Power

The Model 78X is powered by a small, wall mounted power cube that supplies 12 VDC @ 500 ma. NOTE: The power supply must be connected to the Model 78X, through the 1.3mm connector located on the rear of the unit, prior to plugging the power supply into the wall.

9.0 Help

If any assistance is required please visit 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 number (RMA) and can be obtained by visiting our Technical Support Center. Reference RMA number on the outside container.

Document No. 0315-0280/Rev. B

Model	Product Info
78X
278X