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Document:	DEREP Ethernet Repeater Technical Manual
Order Number:	EK-DEREP-TM
Revision:	001
Pages:	100
Original Filename:

OCR Text

DEREP ETHERNET
REPEATER
Technical Manual
EK-DEREP-TM.001

EK-DEREP-TM-001

Networks ¢ COmmunication

DEREP
Ethernet Repeater
Technical Manual

Digital Equipment Corporation

Ist Edition, April 1984

The information in this document is subject to change without notice and should not be
construed as a commitment by Digital Equipment Corporation. Digital Equipment
Corporation assumes no responsibility for any errors that may appear in this document.

Printed in U.S.A.

This document was set on a DIGITAL DECset Integrated Publishing System.

The following are trademarks of Digital Equipment Corporation:

g;flflfl

DEC
DECmate
DECnet
DECUS
DECwriter
DELNI

DEREP

DEUNA

DIGITAL
ETHERJACK
LA
MASSBUS
PDP
P/OS
Professional

Rainbow

RSTS

RSX
UNIBUS
VAX
VMS
VT
Work Processor

PREFACE
INTRODUCTION
FUNCTIONAL DESCRIPTION..
Local Repeater ......................
Remote Repeater....................
Operator Interface.................
PHYSICAL DESCRIPTION .......
Local Repeater .......................
Remote Repeater....................
PHYSICAL SPECIFICATIONS..
EN\ IRONMENTAL SPECIFICATIONS
ELECTRICAL SPECIFICATIONS ...
PERFORMANCE SPECIFICATIONS......
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CHAPTER 1

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THEORY OF OPERATION

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INSTALLATION TESTING........
Internal Self-Test....................
External Self-Test...................
Executing the Repeater Self-Test
\DBY REPEATERS.
Standby Repeater Installation.................
Testmg the Standby Function of the Standb% Repeater.

Remote Repeater Installation.

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CHAPTER 2

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Standby Repeaters Reentering the Passive State

Internal Self-Test......ccoovvviiviiinriiirereeeeeeeeeeee
External l Self-Test for Local Repeaters............
External Self-Test for Remote Repeaters........

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XMT Data Encoder (Manchester Encoder)
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Control CirCuitS...oouueevvieeeeevieeeeeaaeeeenans
Master Oscillator and Clock Generator.
Input Synchronizer.............o......
State Machine ........oovvvvvveeeennnnn..
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GO COUNLET v
Display Indicators and Drivers.
Power-up Reset........................
Power Supply ....coevveeiiiiiiiiieeenn
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Slot-Time Counter ........oovvvevvennn.

Required Equipment .....................
Optional Equipment .........ccccoeeennn.

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A-3

A-2

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A-2

A-3
A-4

Title

1-1
1-2
2-1
2-2

Page

2-3
2-4
2-5
2-6
2-7
2-8
3-1
3-2
3-3
3-4

Local Ethernet Repeater ...................... e nateteteeeesannsseeaeansteeeisetteaeeanteeeeiiaeaeas 1-2
Remote Ethernet Repeater.......occveeviiiiieeeciiiiccecciieiececcn ISUUISUSUIUUSUURPURSRRIPRPRI X
Typical Repeater Installations ........cccooiiiiiiiinericiiicccc e 2-2
Unpacking the Ethernet Repeater........coooiiiiiiiiiiiiiin
e 2-4
Local Repeater Rear Panel ........cooooiviiiieeiieeeecceeceeeei
e 270
Typical Local Repeater Cabling........ccoccvviiiioienieeeeceeeeerceseeeeeeie
e neanias 271
Remote Repeater Rear Panel................oooeiil rvtreeererrernarrrssererarraaeeseesaannnreaeesassis 270
Typical Remote Repeater Cabling.........ccceece. eeeerrrrrerrrrerreesseseeinninrrasasenesenesesinnns 2210
LED Indications After a Successful SelfaTesz,,,_.,,mmm,,,. ,,,,,,,, e e e e einnnneeeeenens 2712
Typical Installation with a Standby Repeater.........c.ccocceeennn. i 2714
State Machine Flow Diagram........cccoooiiiiiiiiieiiiiiiiiieeecceieenns e eerer e e aaeeeinneees 373
Typical Installation with a Standby Répeater,mm,,,,.w,m,.‘m fffffff e creeireeenns 379
Internal Self-Test Flow Diagram............ v
3710
External Self-Test Flow Diagram................. TSSO
P U RRUSPPUSSR 3-15

5-3
5-4
5-5
5-6

Typical LED Status .. ..o ST 5-6
LE
D Do imitiONS ..o
e et e e 5-8
Repeater FRU LOCAUIONS. ... .viiiiiiiieeeie e 3-21
Opening and Closing the Repeater.........ooooviiiiiiiiiiiiiicie, i 5223

4-1
4.2
4-3
4-4
4-5
5-1
5-2

5-7
5-8
5-9
5-10
A-1
A-2

TYPICAl PACKET ... oottt
be
aa e n e 4-1
Repeater Functional Block Diagfam iiiiiiiiiiiiiiiiiiiiiiSUUTTR e
e e 4-3
Fiber-Optic Interface Block Diagram......................OO
PR
PPUPUPPPPRINP*21o
Manchester Encoded Data ........cocoeiiviiiiiiiiiiiiieciies e
47T
FIFO Block Diagram........ s ettt
a it t1aaaaase..4-9
Local Repeater Self-Test Dzagfam 5-3
Remote Repeater Self-Test Diagram.......ccoooieiiiiiiiiiiiiiiiiccieiccieiie
e, 94

Opening and Closing the Internal Metal CRASSIS o vvvovveererr oo . 3-25
Fiber-Optic Module Removal and Replacement...........cocooiiiiiiiiiiniiiiiiincn 5-27
Logic Module Removal and Replacement..........ccoooviieiciiiiiiiiiiiiiicicen. 3229
POWEr SUPPIY ChaSSIS .oueieeeiiieeiiee et .5-30
Typical FOTDR Trace Showing a Cf}figficté; USSP UUURRRUNSUPRPPON A-4
Typical FOTDR Trace Showing a Splice and CONNECLOT +vvverrvreerrereree crreeerinnnes A=S

TABLES
Title

1-1
2-1
2-2
5-1
5-2

Page

Performance SpecifiCations ..........ccoovveviiiiiineeniiecirie e, et
e e e e e e e e araes 1-5
Local Repeater Shipment List..........cccoceeene. ettt
e — e — e e n e e s e e ST 2»4
Remote Repeater Shipment LISt ..o sns 27
LEDs and TroubleShOOting . .......cvvviiriiiiiiiieieeieeeeciiie e crreerrinneeen 979
Self-Test Error LEDS.ottt eessnne
e snn s e asnneeees 910

This manual describes in detail the installation requirements, theory of operation, and servicing procedures
for the DEREP Ethernet Repeater.

Other publications that support the DEREP Ethernet Repeater are:
*

Ethernet Installation Guide

(EK-ETHER-IN)

DEREP-AA Local Ethernet Repeater
Installation/Owner's Manual

(EK-DEREP-IN;

DEREP-RA Remote Ethernet Repeater
Installation/Owner’'s Manual

(EK-DERRP-IN)

Ethernet Transceiver Tester
User's Manual

(EK-ETHTT-UG)

H4080 User's Manual

(EK-H4080-UQG)

INTRODUCTION

The Ethernet repeater (hereafter referred to as the repeater) provides a means of extending Ethernet
networks beyond the 500 m (1640 ft) limit of a single Ethernet coaxial cable segment. The repeater resides
between two Ethernet cable segments and is connected to them via transceiver cables and Ethernet
transceivers. The repeater’s main function is to transmit Ethernet signals from one cable segment to
another while maintaining synchronization across the network.
Two types of repeaters are presently available: the local repeater and the remote repeater. Both types of
repeater perform the same basic function. However, the applications of the two repeaters vary.

1.1.1
Local Repeater
The local repeater is designed to link Ethernet segments separated by not more than 100 m (328 ft). Two
50 m (164 ft) transceiver drop cable lengths make up this distance.

1.1.2 Remote Repeater
The remote repeater links segments separated by not more than 1100 m (3609 ft). This distance is
achieved through the use of a fiber-optic link and two 50 m (164 ft) transceiver cables. The fiber-optics
cable provides electrical 1solation between cable segments and is resistant to electrical interference.
1.1.3 Operator Interface
Operation of the repeater is fully automatic. Once the repeater has been installed and turned ON, no
further adjustments are required. The repeater is totally transparent to all Ethernet users.

This section describes the physical characteristics of the local repeater and the remote repeater.
1.2.1
Local Repeater
|
The local repeater (see Figure 1-1) 1s made up of a single ac-powered standalone package, and includes the
following components.

Two identical transceiver cable interfaces with each cable interface containing a 15-pin female
D-connector with slide latches for locking cables in place.
Four switches for controlling voltage selection, power ON/OFF, self-test, and standby mode

enable. The power ON/OFF switch is located on the front panel. The remaining switches are
located on the rear panel of the repeater.
e

Sixteen LED indicators that assist in diagnosing repeater and network malfunctions. The
indicators are located on the rear panel of the repeater.

1.2.2 Remote Repeater
The remote repeater (see Figure 1-2) is made up of two ac-powered standalone packages connected by up
to 1000 m (3281 ft) of duplex fiber-optic cable. Each standalone package is identical to that of the local

repeater except that a fiber-optic interface is installed inside the repeater unit. This fiber-optic interface
overrides the B transceiver cable interface.

TRANSCEIVER

CABLE INPUTS

PANEL

DEREP-AA

MKVE4-0049

Figure 1-1

Local Ethernet Repeater

FIBER-OPTIC CABLE

CONNECTORS\

TRANSCEIVER
CABLE INPUT B
(NOT USED ON

TRANSCEIVER

REMOTE REPEATERS)

CABLE INPUT A

DEREP-RA

MKVB4-0048

Figure 1-2

Remote Ethernet Repeater

1.3

PHYSICAL SPECIFICATIONS

Local Repeater

Size

Width
Depth
Height

45.72 cm (18 1n)
30.48 cm (12 1n)
10.16 cm (4 1in)

Weight

7.26 kg (16 1bs)

AC power cord length

1.83 m (6 ft)

Remote Repeater (each standalone package)
.

Size

Width
Depth

45.72 cm (18 in)
30.48 cm (12 1n)

Height

10.26 cm (4 in)

Weight

7.26 kg (16 Ibs)

AC power cord length

1.83 m (6 ft)

The local repeater and the remote repeater are designed to operate in a Class C environment as specified
by DEC STD 102.

1.5

Operating temperature

Relative humidity

5°C (41°F) to 50°C (122°F)
10% to 90% with a maximum wet bulb tempera-

ture of 28°C (82°F) and a minimum dewpoint of
2°C (36°F).

ELECTRICAL SPECIFICATIONS

The repeater requires the following line voltage for proper operation.
Local repeater

115 Vac @ 1 A (50/60 Hz)

%0 Vac @ 0.5 A (50/60 Hz)
Remote repeater (each standalone package)
115 Vac @ 2.5 A (50/60 Hz)

ggo Vac @ 1.25 A (50/60 Hz)
1.6 PERFORMANCE SPECIFICATIONS
Performance specifications are outlined in Table 1-1.

1-4

Table 1-1

Performance Specifications

Parameter

Minimum

Typical

Maximum

Transmitted preamble

2500

Transmit clock error
First transition in to first out
Collision propagation time
Data bit 1 in to bit 1 out delay

400
400
5

500
500
10*

01%
750
750
32%

Last bit in to last bit out delay

32%

Heartbeat detection windowi
Packet length

0
512

—_
—

32000
14144

*Dependent on preamble length.
t1f delay exceeds this value, data is invalid.
tMeasured from the end of data transitions on the “transmit to” side.

CHAPTER 2
INSTALLATION

This chapter provides the following information.
®
®
¢

Unpacking and installing both the local and remote repeaters
Procedures for testing the repeater
Installing and testing standby repeaters

Installation of the repeater is addressed in four basic procedures.
Preinstallation Considerations
Unpacking and Inspection
Installation
System Testing

2.2 TYPICAL INSTALLATIONS
Under most circumstances, a single local or remote repeater is used to join one Ethernet segment to
another. Figure 2-1 illustrates some typical Ethernet repeater installations.
When network reliability is critical, it may
be enhanced by installing a standby repeater. Information on

installing standby repeaters is included in Section 2.7.

2.3

PREINSTALLATION CONSIDERATIONS

The following should be considered prior to installing the repeater.

Position the repeater on a desk, shelf, or tabletop.

Verify access to ac power.

Determine which transceiver cables or which Etherjack connectors (if applicable) will be used.

Ensure that all cables (power, transceiver, Etherjack connector, and/or fiber-optics) can be
connected without straining the cables.

Ensure that the total cable length between the repeater and either transceiver does not exceed
50 m (164 ft).

Allow a minimum of 10.16 c¢cm (4 1n) clearance per side to ensure proper ventilation and to
prevent damage to any cables attached to the rear panel of the repeater.

Avoid locating the repeater in areas such as cable trenches or on the floor where dust or other

material is likely to interfere with proper fan ventilation.
NOTE

BNE3-** cables for connecting to transceivers or to
Etherjack connectors are not supplied.

2-1

TRANSCEIVER

l | l

| l COAXIAL SEGMENT

(

B \Es“1 - - JZ/ |.yyfff
J

L_QJ

—

TERMINATOR

LOCAL
1]

]

NODE”

TYPICAL SMALL-SCALE INSTALLATION

]
|

—

- e
EM

REPEATER

DUPLEX bt—rd

FIBER-OPTIC

CABLE

(1000 M MAX)

\LOCAL

REPEATER

\\.

'/
REMOTE
REPEATER

TYPICAL MEDIUM-SCALE INSTALLATION

Figure 2-1

Typical Repeater Installations (Sheet 1 of 2)

1
(

=
l

COAXIAL SEGMENTS

——
LOCAL
REPEATER

——
LJ

>
Z

v
O

1
L.J

]

‘]
| l"
-

DUPLEXOPTIC
FIBER-

CABLE

(1000 M MAX)

R
REMOTEERLlN

REPEAT

TYPICAL LARGE-SCALE INSTALLATION
TK-10809

Figure 2-1

Typical Repeater Installations (Sheet 2 of 2)

2-3

The Ethernet repeater i1s packaged according to commercial packing practices. When unpacking, remove

all packing material and check the equipment against the shipment list. Figure 2-2 illustrates the correct
unpacking procedure. The shipment list for the local repeater is provided in Table 2-1. The shipment list
for the remote repeater is provided in Table 2-2.
Inspect all parts for damage. Report damages or shortages to the shipper and notify the DIGITAL
representative.

POWER CORD*

INSTALLATION/OWNER'S
~ MANUAL®

ETHERNET
REPEATER

SHIPPING

CONTAINER

*IN NON-U.S. VERSIONS, THESE ITEMS MAY BE SHIPPED SEPARATELY
MKV84-0083

Figure 2-2

Table 2-1

Unpacking the Ethernet Repeater

Local Repeater Shipment List

Qty

Part No.

Description

DEREP-AA

Local repeater unit

EK-DEREP-IN

DEREP-AA Installation/Owner’'s Manual

AC power cord - 1.83 m (6 ft)

2-4

Table 2-2

Remote Repeater Shipment List

Qty

Part No.

Description

DEREP-RA

Remote repeater unit

EK-DERRP-IN

DEREP-RA Installation/Owner’s Manual

AC ‘pewfir cord - 1.83 m (6 ft)

2.5 INSTALLATION
This section provides detailed instructions for installing both the local and remote repeaters.
The instructions in this section assume that the following conditions are met.
®

An ac power outlet is within 1.83 m (6 ft) of the location where the repeater is to be installed.

All necessary cables can be connected to the repeater without straining the cables. Necessary
cables may include:
-

Power cord,
Transceiver cable(s), and
Fiber-optic cables (for remote repeaters only).

[f Etherjack connectors are being used, the total cable distance between the repeater and either
transceiver may not exceed 50 m (164 ft).

The network being configured with the repeater is within allowable limits.

A duplex fiber-optic cable (applicable to remote repeaters only) has been properly installed. If
installed by an external vendor, the cable should be certified (refer to Appendix A of this
manual). Also, the cable ends must be properly marked.

NOTE
Fiber-optic cable is not shipped with the remote
repeater.

2.5.1
Local Repeater Installation
This section describes the installation of a single local repeater.

The power switch i1s located on the front panel of the repeater. All other connectors, switches, and
indicators are on the rear panel (see Figure 2-3).

All cable connections to the local repeater are made on the rear panel of the repeater. Figure 2-4 shows the
final i cable connections.

2-5

Install the local repeater by performing the following steps.
1.

Verify that the power switch (on the front panel) is in the OFF position.

Verify that the standby mode enable switch is in the 0" (disabled) position.

Ensure that the voltage selector switch is set for the correct line voltage.

NOTE
Units are shipped with 115 Vac selected.
4.

Connect the transceiver cables (or cables from the Etherjack connection boxes) to the repeater

as shown in Figure 2-4.
5.

Lock the cables in place by sliding the connector latches to the locking position.

NOTE
Make sure that the transceiver or Etherjack connection box used serves the desired network segment.
Etherjack connection boxes may have appropriate
information located inside the cover.

Set the power switch to the ON position. Note that the four (4) green power indicator LEDs on
the rear panel (two labeled 2.0A and one each labeled 12V and 5V) are lit (refer to Figure 2-7).
Also make sure that the fan is running.

Proceed to the system test procedures outlined in Section 2.6.

TRANSCEIVER

CONNECTOR
AT

CONNECTOR
"B (NOT USED)

—~—

FUSE

STANDBY MODE

"B" LED

ENABLE SWITCH

Uo O 5883368

Eal

FUSE

US|

)

;

SELF-TEST
SWTICH

;
INDICATOR

"D CONNECTORS

AC POWER IN

LEDS

AC FUSE

»
VOLTAGE

SELECTION

SWITCH
TK-10930

Figure 2-3

Local Repeater Rear Panel

CABLES TO TRANSCEIVERS

OR ETHERJACK CONNECTION
BOXES.
NOTE

MAKE SURE THAT TRANSCEIVERS

OR ETHERJACK CONNECTION BOXES
USED SERVE DIFFERENT NETWORK
SEGMENTS.
TK-10929

Figure 2-4

Typical Local Repeater Cabling

2-7

2.5.2 Remote Repeater Installation
This section describes the installation of the remote repeater.

The power switch is located on the front panel of the repeater. All other connectors, switches, and
indicators are on the rear panel (see Figure 2-5).

All cable connections to the remote repeater are made on the rear panel of the repeater. Figure 2-6 shows
the final cable connections.

Install the remote repeater by performing the following steps.
NOTE

The remote repeater includes two identical units.
Each unit must be installed at opposite ends of a
duplex fiber-optic cable. The instructions in this section should be performed on both units of the remote
repeater.

Verify that the power switch (on the front panel) is in the OFF position.

Verify that the standby mode enable switch is in the “0" (disabled) position.

Connect the transceiver cable (or the cable from the Etherjack connector) to connector A as
shown in Figure 2-6.

Make sure that the transceiver or Etherjack connection box used serves the desired network segment.
Etherjack connection boxes may have appropriate
information located inside the cover.

Lock the cable from the transceiver or Etherjack connector in place by sliding the connector

latches to the locking position.

Connect the fiber-optic cables as shown in Figure 2-6. Do not reverse fiber-optic cable inputs

(—@) and outputs (@v)g

Repeat these steps to install the remaining repeater unit at the other end of the fiber-optic cable.

Set the power switch of both units to the ON position (the power switch is on the front panel).
Note that the four (4) green power indicator LEDs on the rear panel (two labeled 2.0A and one
each labeled 12V and 5V) are lit (refer to Figure 2-7). Also make sure that the fan is running.

Proceed to the system test procedures outlined in Section 2.6.

2-8

FIBER-OPTIC
ECTO

CONNECTORS

(RECEIVE])
'

FUSE

(TRANSMIT)

“B”

FUSE

STANDBY MODE

“B” LED

ENABLE SWITCH
\

AC POWER IN

| —

TRANSCEIVER
CONNECTOR
A

TRANSCEIVER
CONNECTOR
"B (NOT USED])
~

FUSE

“A” LED

SELF-TEST
SWTICH

“D” CONNECTORS

AC FUSE

INDICATOR

SELECTION

LEDS

SWITCH

TX-10830

Figure 2-5

Remote Repeater Rear Panel

Installation testing consists of running the repeater self-test.

NOTE
No special test equipment is required to verify
repeater operation.

The repeater self-test is made up of two separate tests.
¢
.

Internal self-test
External self-test

Internal self-test is automatically performed when the repeater is turned ON. The internal and external
self-tests are both performed when the self-test button is momentarily pressed and released.

NOTE
Normal repeater operations are suspended during

self-test. That is, packets are not repeated on the
network.

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2.6.1
Internal Self-Test
The internal self-test generates internal loopback of encoded data to both side A and B of the repeater*.
This test exercises the logic module up to, but not including, the transceiver cable interface and/or fiberoptic cable interface.

2.6.2 External Self-Test
»
The external self-test generates exrernal loopback of encoded data to both side A and B of the repeater*.
For local repeaters, signal turnaround occurs in the transceivers. In remote repeaters, signal turnaround
occurs in the local transceiver and in the remote half of the repeater.
For local repeaters, the external self-test exercises the following elements.

®
®
e

Logic module
Both transceiver interfaces (side A and side B)
Both transceiver cables and transceivers

For remote repeaters, the external self-test exercises the following elements.
Logic module
Transceiver cable interface and fiber-optic interface
Transceiver cable and transceiver (on side A)
Fiber-optic cable (on side B)

A detailed description of the self-test is provided in Chapter 5.
2.6.3 Executing the Repeater Self-Test
To initiate the repeater self-test, perform the following.

Torun internal self-test only, press the power switch to *0” (OFF). Wait five seconds and press
the power switch to *“1” (ON).

Observe the LEDs on the rear of the repeater. No error LEDs should remain lit (TST, FLT,
INT, or ERR). If any of these LEDs remain lit, follow the recommended procedures in Chapter
S

To run internal and external self-test, momentarily press and release the self-test button (see
Figure 2-7) on the rear of the repeater.

NOTES
All LEDs should light when the self-test button
is pressed and held down.
Remote repeaters do not pass external self-test
unless both repeater units are fully connected
and operating.

Side A of the repeater refers to the transceiver interface and circuitry associated with transceiver connector A on the rear of
the repeater.

For local repeaters, side B refers to the circuitry associated with transceiver connector B (on the rear of the repeater).
For remote repeaters, side B refers to the circuitry associated with the fiber-optic interface.

2-11

Observe the LEDs on the rear of the repeater unit being tested. A successful pass is indicated
when no self-test error LEDs (labeled TST, ERR, or INT) remain lit. Note that the self-test

LED (labeled TST) remains lit until the self-test has successfully executed (typically .3
seconds). Figure 2-7 illustrates a successful pass.

SE?.F~TEST BUTTON

2.0A

cD Sgg‘i??Tst Fit Err CPT

CcD Sag &V jnt Act Err CPT

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oo—o—opoo

SEE NOTE

THE "Act” LIGHT MAY
BE LIT IF THE
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FUSE B

INTHE “1” (STANDBY

MODE ENABLED)
POSITION.

—= = GREEN LED THAT IS NORMALLY ON
fi*
i

NOTE

THE “TST” LED LIGHTS WHEN THE SELF-TEST
SWITCH IS PRESSED AND STAYS ON UNTIL THE
SELF-TEST SUCCESSFULLY EXECUTES (TYPICALLY
.3 SECONDS). IF THE TST LED REMAINS STEADILY
LIT, A FAILURE IS INDICATED. CHAPTER 5
CONTAINS INFORMATION ON RECOMMENDED
PROCEDURES TO BE FOLLOWED IN THE EVENT A
FAILURE IS INDICATED.
MKVB4-0068

Figure 2-7

LED Indications After a Successful Self-Test

If the self-test LED remains steadily lit (typically for more than .5 seconds), a failure mode is indicated. In
this case, the specific failure mode may be determined by observing the conditions of the other LEDs.
Chapter 5 contains information on recommended procedures to be followed in the event that a failure
mode occurs.

If the repeater fails the self-test, remove it IMMEDIATELY from service in the network.

NOTE
|
|
When testing remote repeater installations, self-test
must be performed individually on each repeater
unit.
If no more repeaters are to be tested, the installation is now complete. If standby repeaters are to be
installed, proceed to Section 2.7.

This section provides instructions for installing local standby repeaters. Instructions for testing the standby
functions are also included.
CAUTION
Only local repeaters may be used in standby mode.
Do not attempt to use remote repeaters in standby
mode as network performance may be impaired.
When network availability is critical, it may be enhanced by installing a standby repeater. In most repeater

installations. one repeater is used to join two Ethernet segments. When two repeaters are used, one is
designated as the primary repeater and the other as the szandby. Figure 2-8 illustrates a typical installation using a standby repeater.

The standby repeater is typically installed in parallel with one primary repeater but has standby mode
enabled. In this mode, the standby repeater verifies the operation of the primary repeater by monitoring
the communications between segments. If the data on one segment is not repeated onto the other segment,
the standby repeater assumes that the primary unit has failed. The standby repeater automatically
switches to the active mode reestablishing communications between the segments.
NOTE
When installing a standby repeater in parallel with a

primary repeater, make sure that one and only one
standby mode enable switch is in the “1”’ (enabled)
position.

2.7.1 Standby Repeater Installation
This section contains general instructions for installing a local standby repeater.
&

Install the standby repeater by performing the following steps.
.

Ensure that the primary repeater has been properly installed and tested following the proce-

dures in Section 2.5 and Section 2.6.
2.

Remove the primary repeater from network service by turning the repeater power OFF.

2-13

LOCAL
STANDBY

]

REPEATER

LOCAL
PRIMARY

1
J

]

s=0

]

[]
LJ

REPEATER

REMOTE

REPEATER

LOCAL
REPEATER

\_.

REMOTE

REPEATER

$=0 - STBY MODE ENABLE SWITCH SET TO “0” (DISABLED).

S=1 - STBY MODE ENABLE SWITCH SET TO “1” (ENABLED).

B
TK-10928

Figure 2-8

Typical Installation with a Standby Repeater
2-14

Install and test the standby repeater following the procedures in Section 2.5 and 2.6.

Set the standby mode enable switch of the standby repeater to ‘17" as shown in Figure 2-8
.

CAUTION
If the standby mode enable switch of both repeaters
(the primary and standby repeater) are set to the
same position, network performance may be seriously impaired.

Return the primary repeater to active service by turning the repeater power ON.
NOTE
A standby repeater is in the active standby mode (the
Act LED is lit) on power-up. The repeater returns to
the inactive state when the network is used.

2.7.2 Testing the Standby Function of the Standby Repeater
|
‘
|
Once the network is fully operational, test the standby function by removing the primary repeater from
service in the network. Turn the power switch of the primary repeater to the OFF position.

A standby repeater becomes active after eight full
packets have not been repeated by the primary
repeater.

Note that the active standby LED (labeled Act) on the rear of the standby repeater turns ON. Following
the particular network protocol, verify communication between nodes that normally communicate via the

primary repeater(s).

When the test is complete, return the primary repeater to active service in the network by turning the
primary repeater power ON. With the primary and standby repeaters both attempting transmission of

data. the unit with standby mode enabled returns to an inactive state. The active standby LED (labeled
Act) on the rear of the standby repeater should turn OFF.

CHAPTER 3
THEORY OF OPERATION

3.1 SCOPE
This chapter discusses the theory of operation of the Ethernet repeater. Included in this chapter are:
®
¢
¢

Special definitions,

Repeater states, and
Repeater operation.

The following terms have special definitions that should be understood before proceeding to the descriptions of repeater operation.
.

Carrier — Data transitions in the physical channel.
®

Coaxial cable - A shielded PVC or TeflonTM type constant-impedance (50 Q) cable used to make Ethernet
cable segments.
Collision - The result of simultaneous multiple transmissions overlapping in the physical channel resulting
in garbled data. This condition requires retransmission of the entire packet.
Collision enforcement — The transmission of a jam after a collision is detected. Collision enforcement
ensures that all transmitting nodes can detect the collision.

CPT (Collision Presence Test) - A signal sent by the transceiver via the collision presence pair of the
transceiver cable. The CPT signal duration is approximately 1 us (microsecond) in length and is sent
within 2 us of the carrier going away following a transmission. This signal is used by the repeater to verify
that the collision detect circuitry in the transceiver is functioning.
Interpacket gap - A time period of about 9.6 us that precedes packets. This gap is used for controller
recovery.

Jam - A series of transitions (32-bits minimum - 48-bits maximum) used to ensure that the duration of a
collision is sufficient to guarantee its detection by all transmitting nodes.

Manchester encoded data — A data stream that includes a self-synchronizing clock signal. The first half of

each bit cell contains inverse data while the second half contains true data. The clock signal and data are
recovered from the mid-bit transition of each bit cell.
Node - A network component having a network controller. The system and controller support networking
software. Nodes are connected to segments via transceivers.

Teflon is a trademark of Dupont de Nemours & Co., Inc.

Packet — The basic Ethernet network message unit that is made up of a preamble and data stream. The
data stream is preceded by the preamble. The minimum packet length is 512 bits. The maximum packet
length is 1708 bits. Packets must be separated by at least 9.6 us (the interpacket gap).
Ed

Physical channel - The transmission medium connecting all nodes in an Ethernet network. The transmission medium includes coaxial cable segments, repeaters, transceivers, and transceiver cables.
Preamble - A 64-bit series of alternating 1s and Os (ending in a 1 that precedes the actual message or data
string. The preamble is used by the repeater (and other Ethernet receiving devices) for stabilization and
synchronization of the decoder.

Runt packet — A packet that is less than 512 bits in length (512 bits is the minimum packet length). Runt
packets generally result when collisions cause the transmitting nodes to stop transmitting. Runt packets are

disregarded by receiving nodes.

Segment (coaxial segment) — A section of coaxial cable made up of one or more coaxial cable lengths and
coaxial connectors. The segment is terminated at each end in its characteristic impedance (50 Q). A
segment may contain up to 500 m (1640 ft) of coaxial cable. Transceivers and terminators are the only
devices allowed to physically attach to the segment. Other devices such as nodes, local network interconnects, and repeaters must connect through transceivers.

Slot time - The time required for data transitions to propagate from one end of a maximal (largest
allowable) Ethernet configuration to the other end, and for collision information to propagate back.
Specifically, the slot time for Ethernet networks is 51.2 us (round-trip propagation time + maximum jam
time).

Transceiver - A transceiver is the physical interface between Ethernet coaxial segments and other network
devices such as nodes, repeaters, and so on. Transceivers provide dc isolation, transmission and reception
impedance matching, and collision detection for those devices to which they are connected.
3.3

REPEATER STATES

The repeater responds to network conditions such as carrier or collision presence by implementing
specified machine states. When the repeater detects one of the specified conditions or a combination of
conditions, the repeater’s state machine responds by selecting the appropriate path to the next machine
state. Typically, the repeater must implement a series of states before returning to the initial (idle) state.
Figure 3-1 shows the state machine flow from one state to another.

The repeater can be in only one of nine operational states at any given time. The operational states are
described below. Inputs to the state machine determine the repeater’s operational state. The design of the
state machine ensures that the repeater is not in more than one state at any given time.
The following states make up the outputs of the state machine.
1.

RESET - This is the initial state of the repeater that is entered on power-up.
The RESET state exits immediately to the IDLE state.

IDLE - In this state the repeater is monitoring inputs from the fiber-optic or transceiver
interfaces. This state ends when carrier or collision is detected.

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TRANSMIT A - Entered when carrier has been detected on the B side of the repeater. This
state starts the slot-time counter and routes encoded transmit data to the A transceiver
interface.

This state ends when:

e
e

(Carrier B goes away and the FIFO is empty, and
Any collision 1s detected.

TRANSMIT B - Similar to TRANSMIT A.

JAM BOTH - In this state the repeater is transmitting a jam to both sides.
This state is entered when:

e
e

A collision occurs on the side which is being transmitted to, and
Simultaneous collisions or carriers occur when in the IDLE state.

This state ends when 128 jam bits have been sent (jam done) and a collision presence signal on
one side goes away.

LAST COLLISION B - The current (or most recent) collision is on the B side.
In this state the repeater is transmitting a jam to side A.
This state is entered from:

The TRANSMIT A state when a collision occurs on the receive side (side B),

The IDLE state when a collision occurs on the B side, and

The JAM BOTH state when 128 jam bits are sent to both sides and the collision presence
signal on side A has ended.

This state exits to:

¢
e

The JAM BOTH state if a new collision occurs on the A side while side A is being
&

jammed, and

The WAIT state when carrier B and collision B both end.

LAST COLLISION A - The current (or most recent) collision is on the A side.
In this state the repeater is transmitting a jam to side B.
This state is entered from:

The TRANSMIT B state when a collision occurs on the receive side (side A),

The IDLE state when a collision occurs on the A side, and

The JAM BOTH state when 128 jam bits are sent to both sides and the collision presence

signal on side B has ended.

This state exits to:

The JAM BOTH state if a new collision occurs on the B side while side B 1s being jammed,
and

The WAIT state when carrier A and collision A both end.

WAIT - There are no outputs during this state. The duration of the WAIT state varies
depending on the state of the repeater.

In normal operation, the duration of the WAIT state is 3.2 us. This allows time (called the
collision presence test jumpover period) for the cables to go idle before they are again monitored
for carrier and collision.
In self-test, the duration of the WAIT state defines an interpacket gap of 12.6 us.

FAKE CARRIER - This state causes one of the carrier inputs to the state machine to become
active for self-test.
This state is entered when the self-test i1s performed.
§

This state is exited to the WAIT state when there 1s a collision on side A or a collision on side B.
3.4

REPEATER OPERATION

The repeater utilizes a carrier-sense circuit to monitor the physical channel for traffic. When the repeater
detects carrier on one segment, the repeater automatically generates and transmits a new preamble to the
other segment. The remaining message is then retimed, amplified, and retransmitted to the other segment.
&

In addition, the repeater maintains network synchronization during collisions.
.

The repeater responds to the following network conditions.
Carrier on either side
Absence of CPT from either side
Collisions on either side
Excessive collisions on either side
Inactivity on one segment if in standby mode

3.4.1 Carrier
As soon as carrier is detected on the receive lines from a transceiver, the repeater begins generating and

sending a new preamble. The repeater continues to generate preamble until at least 63 bits have been
generated. Then the message portion of the packet is retimed, amplified, and transmitted to the other side
of the repeater.

3.4.2 CPT (Collision Presence Test)
After each transmission of data onto a coaxial segment by a transceiver, the transceiver generates a CPT
signal. CPT is a signal (about 1 s in length) that is coupled to the collision presence signal line pair of the

transceiver cable. The CPT signal is used by the repeater for verification of the collision detection circuitry

in the transceiver.

After transmission, when return data transitions have ceased on the repeater’s receive line pair, the
repeater looks for the CPT signal from the transceiver. If no CPT signal is detected within 3.2 us (32 bit
times) after data transitions have stopped, the repeater assumes that there is a fault in the transceiver’s
collision detection circuitry. The CPT LED is then latched ON to indicate the apparent fault.

3-5

3.4.3

Collisions

Collisions occur when two or more nodes transmit at the same time Their respective data packets run into
each other as they propagate throughout the network resulting in garbled data.

Once a node has begun to transmit, it takes a certain amount of time for the signal or carrier to propagate
to all parts of the network. As each node in turn senses carrier in the channel, it may defer (delay) its own
transmission until the carrier goes away and the interpacket gap (9.6 us) has expired.

It is possible for a node to transmit before the carrier of a currently transmitting node has been sensed.

This is the time during which collisions typically occur.

If the collision occurred at the opposite end of the network from the node which first transmitted, then the

first node must wait for the collision to propagate back to it. Once the slot time (round-trip propagation
time + minimum jam time) has passed with no collisions detected (51.2 us), the node is said to have

“acquired” the channel.

COLLISION HANDLING

The repeater’s role during a collision is to enforce the collisions between both network segments. The
repeater does this by transmitting jam bits to one or both sides of the repeater. Consider the following

examples.

Example 1 - Collisions on the “Transmit To”” Side
Assume the repeater is transmitting a packet to side B. A collision on side B is detected by all
transceivers and their respective nodes on that side. The remaining transmission is disregarded by
the receiving nodes on side B. The repeater stops sending data and begins transmitting jam bits to
side B.

At the same time, the nodes on side A must be made aware of the collision on side B. The repeater

forces a collision on side A by transmitting a jam to side A. This forces a collision on side A.

Example 2 - Collisions on the “Receive’” Side

Assume that the repeater is receiving data from side A and transmitting it to side B. A collision on
side A is detected by all transceivers and respective nodes on side A including the transmitting node
which then stops its own transmission.

As soon as the repeater detects the collision, it stops repeating data to side B and begins transmitting
jam bits. This transmission stops when side A goes idle.

Since collisions typically occur during the slot time, the packet never achieves the legal minimum
packet length of 512 bits. The result is a shortened or “runt” packet being transmitted to side B by
the repeater. Runt packets are disregarded by the receiving nodes.
Note that the repeater continues to transmit jam bits to side B until side A becomes idle. This
ensures that the network segments on both sides of the repeater go idle in relative synchronization.
3.5

SEGMENTATION

Segmentation is a process in which the repeater partially suspends communication between two network
segments. Segmentation results from an excessive number of collisions occurring on a particular segment
or from no data loopback during transmission.

3-6

3.5.1
Autosegmentation
In the segmented state, the repeater continues to transmit data to, and receive data from, that segment on
which the collisions are occurring. However, the received data will not be repeated to the “good” side.
Also, collisions on the “bad” side are not enforced on the *““goodTM side while in the segmented mode.

A coaxial segment is considered to be faulty if 64 consecutive collisions have occurred on transmission
attempts to a coaxial segment. Even with many active nodes on the network, it is unlikely that 64
consecutive collisions would occur except in cases of equipment failure. Thus, when the repeater counts 64
consecutive collisions on a coaxial segment, the repeater assumes that a failure has occurred and that
segment is then cut off or “segmented” from the remaining network.

Once the network is segmented, the FLT (Fault) LED is lit. In addition, the appropriate SEG (A or B)
LED is latched ON as an indication that this condition has occurred on a particular segment.

3.5.2

Exit from Segmentation

The repeater exits the segmented mode when a packet of data is transmitted to the segmented side without

a collision. The repeater assumes this to indicate that the segment is functioning normally since no collision
occurred.
3.6

STANDBY MODE

When a repeater has standby mode enabled, the repeater monitors communications between the two

segments to which it is connected. In this configuration, it can monitor and verify the operation of the
primary repeater(s). Figure 3-2 illustrates a typical installation using a standby repeater.

3.6.1 Active Standby Repeaters
When the standby repeater detects data on one side that is not repeated on the other side for an entire slot
time, the standby repeater assumes that the primary unit has failed. The standby repeater then automatically switches from the passive to the active state.
When active, the standby repeater performs the same functions as a primary repeater except that the

segmentation process is slightly different. Primary repeaters enter a segmented mode after 64 consecutive
collisions. Active standby repeaters return to a passive state after 56 consecutive collisions.
3.6.2 Standby Repeaters Reentering the Passive State
The standby repeater reenters the passive state when:
e
e

56 consecutive collisions occur on a segment, and
A collision exists for a period that exceeds the slot time.

In most cases, these collisions are a result of the primary unit being returned to service in the network.
Note that the primary repeater must count 64 collisions before segmenting. Since the standby repeater
reenters the passive state after only 56 collisions, the collisions cease, letting the primary repeater assume
its original status in the network. The standby repeater also assumes its original status verifying operation
of the primary repeater.
«
3.7 SELF-TEST
Two levels of self-test are possible with the repeater.

Internal self-test

External self-test

The repeater automatically performs internal self-test when the system is powered up or when the self-test
button is pressed. External self-test is performed only when the self-test button is pressed.

3-7

The internal self-test for local and remote repeaters is identical. There are certain differences between the
external self-test for local and remote repeaters. These differences are described in Sections 3.7.2 and
3.7.3.

Figure 3-3 describes the internal self-test flow. Figure 3-4 describes the external self-test flow.
3.7.1 Internal Self-Test
During internal self-test, the repeater generates 256 preamble bits followed by a pack of 1792 ones. This
data stream is encoded, looped back through the decoder, and then clocked into the FIFO and checked.
This results in an extensive internal self-test of most counters and other internal circuitry.
NOTE
Normal repeater operation is interrupted during
internal self-test since outputs and inputs to the
transceivers on the A and B side are disabled.

3.7.2

External Self-Test for Local Repeaters

During external self-test, the repeater generates 256 preamble bits followed by a pack of 1792 zeros. This
data stream is encoded and transmitted to side A of the repeater. With the receive lines of the transceiver
active, the repeater monitors the transmission. Thus, a loopback is performed that verifies the operation
and connection of the transceiver. This same sequence is repeated for the B side of the repeater.
NOTE

The external self-test actually transmits a packet to
each side of the repeater. If carrier is present on the
Ethernet coaxial cable, the transmitted packets
result in a collision. If collisions do occur, the
repeater makes 64 attempts to complete self-test
and then segments if unsuccessful.
3.7.3

External Self-Test for Remote Repeaters

External self-test for remote repeaters is identical to that of local repeaters with the following exceptions.
e

The test packet comprises 2048 preamble bits (zeros).

The test packet to the B side loops back through the fiber-optic cable from the remote half of
the repeater.

The repeater only verifies the presence of data looped back from the B side. The data is not
clocked back through the FIFO.

3-8

LOCAL

]

STANDBY
REPEATER

LOCAL
PRIMARY

L-J

REPEATER

=
|

- REMOTE

(RY*

REPEATER

$S=0

= ]

FIBEROPTIC

CABLE

LOCAL

(1000 M MAX]

REPEATER
REMOTE

REPEATER

NODE

S§=0 - STBY MODE ENABLE SWITCH SET TO “0" (DISABLED).

S=1 - STBY MODE ENABLE SWITCH SET TO 1" (ENABLED).

||
TK-10825

Figure 3-2

Typical Installation with a Standby Repeater

3-9

SELF-TEST
EN?

Yves
|

WAIT

12.6 L 8

CINTERNAL
TEST?

| ‘%’ES
DISABLE INPUTS
AND QUTPUTS
ENABLE
INT MUX

CREATE FAKE
CARRIER A/B

O = MACHINE STATE OR

PROCESS THAT MAY

INCLUDE SEVERAL DISCRETE

SYNCHRONIZE

CARRIER A/B

STEPS IN THE FLOW DIAGRAM

= OFF PAGE MARKER

MKVB40100

Figure 3-3

Internal Self-Test Flow Diagram (Sheet | of 3)

TRANSMIT B/A l

SEND
PREAMBLE

BIT

COLLISION WAIT

16 BITS

SENT?

Tves

7256 BITS TM\

START RECEIVE

PREAMBLE

FIFO

N\\OoNE?
[ves
SEND 1782 ONES

COLLISION WAIT

MKV84-0101

Figure 3-3

Internal Self-Test Flow Diagram (Sheet 2 of 5)

3-11

START RECEIVE
FIFO

START RECEIVE

FIFO INPUT

START RECEIVE
FIFO OUTPUT

" END OF

PREAMBLE?

‘ SET ERROR LED !

YES |

SET INTERNAL
SELF-TEST

DATA BIT

~_NO

N=N-17

WAIT

FOR RESET

YES |

COLLISION WAIT

MKVB4-0102

Figure 3-3

Internal Self-Test Flow Diagram (Sheet 3 of 3)

COLLISION WAIT

N
D

—<\_ BITSSENT?

Yves
REMOVE FAKE
CARRIER

COLUSION?

Tves

NEVER

EXIT

SELF-TEST

ENABLE
JAM

INCREMENT

COLLISION A/B
COUNT

—<

JAMDONE?

MKVB84-0103

Figure 3-3

Internal Self-Test Flow Diagram
(Sheet 4 of 5)

STOP TRANSMIT

7 BOTH
TMS
COLLISION
\_ COUNT =

64 ? -

YES

RESET COLLISION l

COUNTS

+
SET EXTERNAL
TEST

MKV84.0104

Figure 3-3

Internal Self-Test Flow Diagram

(Sheet 5 of 5)

SELF-TEST
EN?

[ves
WAIT

12.6 (L s

" INTERNAL
TEST?

DISABLE
INPUT
AND

OUTPUT

= MACHINE STATE OR

PROCESS THAT MAY

INCLUDE SEVERAL DISCRETE

STEPS IN THE FLOW DIAGRAM

= OFF PAGE MARKER
MKVB4-0105

Figure 3-4

External Self-Test Flow Diagram (Sheet 1 of 6)

CREATE FAKE

ALLOW B/A

CARRIER A/B

SYNCHRONIZE

CARRIER A/B

‘

l
l

l TRANSMIT B/A '

COLLISION WAIT

MKVB4-0106

Figure 3-4

External Self-Test Flow Diagram

(Sheet 2 of 6)

SEND
PREAMBLE

BIT

16 BITS

SENT?

"YES

~ 256 BITS
"

" START RECEIVE

PREAMBLE

\ _ DONE?

FIFO

Tves

INSTALLED AND D
\_ XMTB _~

Tno
SEND 1792 ZEROS

COLLISION WAIT

MKV84.0107

Figure 3-4

External Self-Test Flow Diagram (Sheet 3 of 6)

3-17

START RECEIVE
EIFO

START RECEIVE
FIFO INPUT

SET
ERROR
LED
START RECEIVE

FIFO OUTPUT

SET INTERNAL

CEND OF

PREAMBLE?

YES

" DATA BIT

TM\

. N=N-17
_

SELF-TEST

'
WAIT
FOR RESET

YES

COLLISION WAIT

MKVB4-0108

Figure 3-4

External Self-Test Flow Diagram (Sheet 4 of 6)

COLLISION WAIT

~C_ BITS SENT?

Tves
INCREMENT

COLLISION A/B

REMOVE FAKE

COUNT

CARRIER

COLUSION?

< JAMDONE? >
YES

NEVER
EXIT

SELF-TEST

STOP TRANSMIT

ENABLE

JAM

TM
“BOTH
" COLLISION

\_ COUNT
=

YES

SEGMENT

WAIT FOR

RESET

MKVB4-0109

Figure 3-4

External Self-Test Flow Diagram (Sheet 5 of 6)

YEST
SET PACKET B

soTx4?

> NO

YES

< DATA ERROR? >

ves]

PACKET TO NNO

~_AANDB?

YES|

RESET

SELF-TEST

MKV84-0110

Figure 3-4

External Self-Test Flow Diagram (Sheet 6 of 6)

3-20

CHAPTER 4

TECHNICAL DESCRIPTION

4.1 SCOPE
This chapter provides a technical description of the Ethernet repeater. Included in this chapter are
discussions on:
e
®

The data structure,
The functional block diagram, and

The circuit descriptions.

Only the local repeater and the fiber-optics interface are discussed.

The repeater is largely controlled by the received data transitions. Thus, an understanding of the nature of
valid transitions is helpful in understanding the operation of the repeater.

The repeater is designed to distinguish valid data from non-data and to respond accordingly. A valid data
frame or “‘packet” has certain characteristics such as bit rate, signal level, and duration that set it apart
from other transitions. The incoming data must possess these characteristics before it can be processed by
the repeater.

From the standpoint of a repeater, a packet is made up of two main parts: a preamble and a data stream
(see Figure 4-1). Note that the packet is preceded by the interpacket gap of 9.6 us. This ensures that the
nodes are ready to process the incoming transitions.
EOP

TPACKET
?55U-SECS

9.6

DATA STREAM

Zz FAMBLE

5§12 BITS TO 14144 BITS

BITS

TK-10822

Figure 4-1

Typical Packet

The preamble is a 64-bit series of alternating Is and Os (ending in a 1) that precedes the actual message or
data string. The preamble is used by the repeater (and other Ethernet receiving devices) for stabilization
and synchronization of the decoder. The pattern is:
10101010 10101010 10101010 10101010 10101010 10101010 10101010 10101011

The preamble is transmitted from left to right. Notice that the last bit pair is identical (two Is instead of a
] and a 0). This bit pair is used to signal the end-of-preamble (EOP). The repeater recognizes this bit pair
and all successive bits are treated as the data string.

4-1

The data string 1s the actual message being transmitted. The data string includes different data fields.

However, the repeater treats the data string solely as a bit stream and does not recognize the different
fields.

This section describes a typical data flow as a packet is processed by the repeater.
4.3.1
Assumptions
This discussion of functional blocks assumes the following conditions.
®

The data flow is from receive B to transmit A. Signals coming from or going to a specific side
are typically identified as A or B. For example, B DATA is data from the B side.
&

The repeater is a local repeater (the operation of the fiber-optic interface is described in Section
4.4.1.2).
®

The “packetTM is made up of a 64-bit preamble (including the EOP) and the data string.

All signals from the transceiver must pass through the transceiver interface before they may be processed
by the repeater.
The outputs of the transceiver interface are used to control the repeater’s state machine. They are:
L

CAR B (carrier B) - The CAR B signal is a steady voltage level (high or low) indicating the
presence or absence of data on the receive pair of the transceiver cable. The active (high) level

begins as soon as carrier is detected and ends when data transitions cease. Carrier B informs the
state machine that there are data transitions on B.
COL B (collision B) - COL B is a steady voltage level (high or low) indicating the presence or
absence of the collision presence signal. The active (high) level begins as soon as the collision
presence signal 1s detected on the collision pair of the transceiver cable. The active level ends
when collision presence transitions cease.

CPT B (collision presence test B) -~ A CPT signal is sent by the transceiver via the collision
presence pair of the transceiver cable and should occur within 2 us after the carrier goes away.

B DATA - B DATA includes all buffered transitions from transceiver B. When CAR B (from
the carrier detect circuit) is active, the transitions are treated as valid data unless COL B is also
active. When CAR B is inactive, any transitions are ignored bythe repeater.

NOTE
Similar signals are generated when transitions enter
the transceiver interface on the A side of the
repeater.

4.3.2 Typical Data Flow
This section describes a typical data flow. Refer to the repeater block diagram in Figure 4-2 as you read

through this section.
All signals from the B transceiver interface and fiber-optic interface pass through the select multiplexer.
The multiplexer selects data from the fiber-optic interface or transceiver connector B to be processed by
the repeater. In this example, no fiber-optic board is present, so the multiplexer selects data from
transceiver connector B.

4-2

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The CAR B signal goes to the state machine via the input synchronizer. The synchronizer synchronizes
inputs to the state machine. When the state machine detects CAR B, XMT A EN (transmit A enable)
goes active. This enables transceiver interface A to transmit encoded data. The slot-time counter begins
generating a new preamble that is sent to the transmit multiplexer. The preamble is then encoded and sent
to the cable drivers of the A transceiver interface.
COL B results from CPT on the collision pair of the transceiver cable. COL B is channeled to the collision
counter and CPT detect circuits. The collision counter and CPT detect circuits are gated at the proper
times to look for a signal on the collision presence pair.
B DATA passes to the receive multiplexer that selects the incoming data stream or ENCODED XMT
DATA (from self-test) to be decoded and loaded into the FIFO.
The Manchester decoder recovers the clock and the data from the incoming data stream. The data is then
clocked into the 32-bit circular FIFO.
After a delay that allows the decoder to stabilize, the FIFO begins clocking decoded data through itself to
the transmit multiplexer. Note that the first data from the FIFO is the old preamble. The transmit
multiplexer ignors the old preamble from the FIFO and selects the new preamble being generated by the
slot-time counter. The new preamble is then Manchester encoded.
When the EOP (end-of-preamble) is detected by the EOP detect circuit, and a minimum of 63 new
preamble bits have been generated, the transmit multiplexer begins selecting data from the FIFO. If
necessary, an EOP bit is also added. Thus, a new preamble is generated which precedes a retimed data
string. All transitions from the transmit multiplexer are then Manchester encoded and gated to the
transmit connector.
4.4

CIRCUIT DESCRIPTIONS
This section describes individual circuits of the Ethernet repeater. For clarity, this section is divided into
the following subsections.

Data path circuits

(Control circuits

4.4.1
Data Path Circuits
The following sections describe individual circuits in the data path.

4.4.1.1 Transceiver Interfaces - The repeater has two identical transceiver interfaces. One interface is
for the transceiver connected to the A side of the repeater, and the other interface is for the transceiver
connected to the B side of the repeater.

®»

Each transceiver interface is made up of:

A transceiver connector,
A carrier detect circuit,
A receive data preamplifier, and
A collision detect circuit.

TRANSCEIVER CONNECTOR
The transceiver connector is a 15-pin female D-connector with a slide latch for connecting and locking to a
transceiver cable. The transceiver connectors are physically located on the rear of the repeater.

4-4

CARRIER DETECT
Input to the carrier detect circuit is from the receive pair (+ receive and —
receive) of the transceiver. The
input is through pins 5 and 12 of the transceiver connector. Signals on these lines
are typically 1.2 V data
transitions from the transceiver.

The output of carrier detect is a steady voltage level (high or low) indicating the presence
or absence of
valid data. This output is used to drive the state machine.
RECEIVE DATA PREAMPLIFIER
Input to the preamplifier is from the receive pair of the transceiver cable (pins 5 and 12 of
the transceiver

connector). The receive preamplifier buffers incoming data levels for processing by

the repeater.

When a collision occurs, it should be detected by each transceiver installed on the
segment on which the
collision occurs. Each transceiver then generates a 10 MHz collision presence signal that is coupled
to the
collision presence (+) and collision presence (—) signal line pair of the transceiver cable.
Input to the repeater’s collision detection circuit is the 10 MHz collision presence
signal from the
transceiver. The collision signal is generated by the transceiver when:
¢

A collision is occurring, and
A CPT signal is sent (see Section 4.4.1.4).

The collision presence signal enters the repeater via pins 2 and 9 of the transceiver connector.

The colhision

presence pair of the transceiver cable is normally inactive except during the above conditions.

The output of the collision detection circuits is a steady voltage level (high or low)
indicating the presence
or absence of collision.
This output, called collision A (or collision B if from transceiver connector B). 1s

machine and to increment the collision counter.

4.4.1.2

used to drive the state

Fiber-Optic Interface - The fiber-optic interface is included only in remote repeaters
using a
fiber-optic cable.
&

The fiber-optic interface converts ECL data levels to optical signals for transmission via
a fiber-optic
cable. Conversely, the fiber-optic transceiver receives optical signals from a fiber-optic cable
and converts
them to ECL data levels. The ECL levels can be used by the repeater.
A block diagram of the fiber-optic interface is shown in Figure 4-3.

4.4.1.3

Collision Counters - Each side (A and B) of the repeater has its own collision counter.

The collision counter (for side A) increments when the collision presence pair on side A goes active
while a
packet is being transmitted to side A.
The collision counter (for side A) resets to 0 when 512 consecutive bits have been transmitted
to side A
with no collision presence being detected (512 bits = 51.2 us = slot time).

The collision counter for side B behaves in a like manner when similar conditions occur on

side B.

set.
When the repeater has the “Standby” switch in the 1" (enabled) position, the STANDBY H signal1.1sThis
of
instead
8
from
counting
start
to
The presence of this signal causes both the A and B counters
means that SEGMENT B (or A) is set after 56 consecutive collisions. When a standby repeater is active,

SEGMENT B (or A) results in the repeater reentering the passive standby mode.

RECEIVER

OPTICAL

RCV DATA

BUFFER

F.O.DATA
DETECT

o—+

ECL F.O. DATA

ECL F.O. RCV ENABLE

ECL XMT ENABLE

OPTICAL

ECL XMT DATA

TRANSMITTER
+5V

e
_I_

ECL F.O. BOARD PRESENT

O—~t——— TTL F.O. BOARD PRESENT
O

GROUND

TK-10815

Figure 4-3

Fiber-Optic Interface Block Diagram

4.4.1.4 CPT Detect - A CPT signal is sent by the transceiver via the collision pair of the transceiver
cable. The signal is sent within 2 pus after the receive pair of the transceiver cable goes idle (after
transmission by the repeater).

The CPT signal is a collision signal typically about 1 us in duration. CPT is used to verify the operation of
the collision detect circuitry of the transceiver.

The repeater has two CPT detect circuits; one for each side (A and B) of the repeater.

Be aware that side B of local and remote repeaters has an identical circuit. However, in remote repeaters,

the side B CPT detect circuit is disabled.

Input to the CPT detect circuit on side A is a synchronized collision presence signal from the collision
detect circuit on side A. The CPT detect circuit is gated to look for the collision presence signal ina 3.2 us
search window. The search window begins after a valid packet has been sent to side A with no collisions
being detected.

If no CPT signal is detected, COLLISION ERROR (A or
B) H is set signaling a malfunction in the
collision detect circuitry. The appropriate rear panel
LED(s) is latched ON indicating that a failure
occurred. This latch is reset by any collision (or CPT) signal
from the transceiver.

The CPT search window is terminated by RESET HOLDO
FF which goes inactive 32 bit times (3.2 us)
after carrier goes away.
4.4.1.5 B Interface Select Multiplexer - The select multipl
exer is a quad 2 line-to-1 line multiplexer.
This device selects data from the B transceiver connector or the
fiber-optic interface if one is present.

Inputs to the select multiplexer are from the following

sources.

Transceiver interface B and its associated carrier detect,
collision detect, and preamplifier
circuits.

The fiber-optic interface.

When no fiber-optic interface is present, the FO BOARD
PRESENT line is inactive. This causes the
multiplexer to select inputs from transceiver interface B for
processing by the repeater.
When a fiber-optic interface is present, the FO BOARD
PRESENT line is active. This causes the

multiplexer to select inputs from the fiber-optic interfac
e for processing by the repeater. FO BOARD

PRESENT

also disables the B transceiver interface.

The outputs of the select multiplexer are CAR B, REC DATA

B, and COL B.

4.4.1.6

Receive Multiplexer - The receive multipl
] exer acts as a 3 line-to-1 line multiplexer. The
multiplexer is used to transfer one of three inputs to the
Manchester decoder. The three inputs are:

®
®

Encoded data from the B side of the repeater,
Encoded data from transceiver connector A, and

Encoded transmit data (for internal self-test loopback).

The receive multiplexer is controlled by the state machine

and self-test circuit.

4.4.1.7 Manchester Data Decoder - Manchester encoded
data from the recejve multiplexer is decoded
and the 10 MHz clock is recovered from the data stream.
Manchester encoded data includes a selfsynchronizing clock signal. Since the first half of each bit cell
contains inverse data, and the second half
contains true data, a clock signal can be recovered from the mid-bit
transition of each bit cell. Figure 4-4
illustrates data that has been Manchester encoded.

TYPICAL DATA STREAM

HIGH LEVEL

ENCODED SIGNAL PATTERN

LOW LEVEL

TK-10813

Figure 4-4

Manchester Encoded Data

4-7

been delayed 75 ns
The flip-flop that reads the incoming data is clocked by mid-cell transitions that have
(nanoseconds) by a delay line. Thus, the output of the flip-flop 1s always 25 ns into the next sequential bit
cell and. therefore, always contains inverse data.

The clock signal is recovered by the same decoder.

(REC CLK) from ECL to
Translators are used to convert decoded serial data (REC DATA) and clock
clock.

TTL levels. The decoded TTL data levels are sent to the FIFO with the

8-bit latches and four 8-to-1 line
4.4.1.8 FIFO - The FIFO is a 32-bit circular register made up of four turn,
to load and latch its outputs
multiplexers. A decoder, driven by counters, enables each 8-bit latch, in
with eight consecutive data bits.

by a binary
The multiplexers act as parallel-to-serial converters. Each multiplexer in succession is enabled
counter and decoder to serially select each of its eight lines for transfer to the common output. The output
is sent to the transmit multiplexer.

A block diagram of the FIFO register is shown in Figure 4-5.

up of a 74LS8&S5
4.4.1.9 FIFO 1/0 Address Comparator - The FIFO address comparator is made
register. The
FIFO
the
from
address
output
the
to
address
comparator. This device compares the input
when the
machine
state
the
signal
to
and
control
FIFO
for
comparator output (input = output) is used
FIFO is empty.

counters. The slot
4.4.1.10 Slot-Time Counter — The slot-time counter is made up of three 4-bit binary
The slot-time
occur.
legally
can
s
collision
which
in
time is 51.2 us (512 bit times) and is the window
MHz clock.
10
the
with
ts
incremen
and
state
IDLE
counter begins as soon as the state machine exits the
n.
generatio
preamble
and
control,
self-test
control,
Outputs of the slot-time counter are used for FIFO
counter. As
4.4.1.11 Preamble Generator — The preamble generator uses the first bit of the slot-time
generated
The
.
counting
begins
counter
soon as carrier is detected by the state machine, the slot-time
preamble is used as an input to the transmit multiplexer.

When 63 positive
The preamble count is incremented by each positive transition of the 10 MHz clock.
signal is used as
DONE
BITS
63
The
clock transitions have occurred, the 63 BITS DONE signal is set.
one of several steering inputs to the transmit multiplexer.

4.4.1.12 EOP (End-of-Preamble) Detect - The EOP detect circuit is made up of an EXCLUSIVE OR
gate and a D flip-flop. Inputs to the EXCLUSIVE OR gate are:
e

FIFO DATA, and

DELAYED FIFO DATA (this is FIFO data that has been delayed one bit time).

gate. The EOP is made up of
Thus, two consecutive bits become the two inputs to the EXCLUSIVE ORIVE
OR gate output goes low
two consecutive like bits at the end of the preamble. Thus the EXCLUS
because both inputs are momentarily the same.

The output of the OR gate drives a D flip-flop that latches in the low state. The flip-flop output, EOP L,
and EOP H are used as steering inputs to the transmit multiplexer.

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4.4.1.13 Transmit Multiplexer - The transmit multiplexer selects retimed FIFO DATA or new PREAMBLE DATA (from the slot-time counter) for encoding and transmission. When the 63 BITS DONE
signal from the preamble generator goes active, the multiplexer deselects PREAMBLE DATA and selects
FIFO DATA. The transmit multiplexer ensures that the last two bits of the preamble are like bits;
changing the last bit if needed.

The output of the transmit multiplexer is XMT DATA H which is Manchester encoded and transmitted.
4.4.1.14 XMT Data Encoder (Manchester Encoder) - The XMT (transmit) data encoder circuit 1s
made up of four D flip-flops and an EXCLUSIVE OR gate. As XMT DATA H is clocked through the
flip-flops, the leading edge of a 20 MHz clock causes the outputs to change states in the middle of each bit
cell. This causes the first half of the output bit cell to contain inverse data.

4.4.1.15 XMT (Transmit) Enable - The XMT enable circuit routes encoded XMT data to the proper
transceiver interface.

4.4.2

Control Circuits

The following sections describe individual repeater control circuits.

4.4.2.1 Master Oscillator and Clock Generator - The master oscillator is a 40 MHz crystal oscillator.
Clock outputs of 20 MHz, 10 MHz, 5 MHz, and 2.5 MHz are tapped from a binary counter to control the
repeater. Translated clocks are also provided to run the ECL encoder.

4.4.2.2 Input Synchronizer - The input synchronizer is a dual-ranked flip-flop. This flip-flop synchronizes asynchronous inputs (COL A, COL B, CAR A, and CAR B) with the repeater’s 10 MHz clock.

Synchronized inputs are used to run the repeater state machine.

4.4.2.3 State Machine - The state machine is a 16R8 PAL (programmed array logic). Synchronized
inputs from the transceiver interfaces and inputs from the FIFO, go counter, and power-up reset circuits
control the state machine.

These signals include:

CAR A from transceiver interface A,
COL A from transceiver interface A,

CAR B from transceiver connector B or fiber-optic interface,
COL B from transceiver interface B,
FIFO EMPTY from the FIFO I/O comparator,
JAM DONE from the jam counter,
GO from the go counter, and
SYNCH RESET H from power-up reset.

The outputs of the state machine perform the following functions:
Start the slot-time counter,

Route encoded XMT data to the proper transceiver interface,

Control the jam counter,

Control the go counter, and

Control the self-test process.

4.4.2.4 Jam Counter — The jam counter is made up of two cascaded binary counters. The counter is
controlled by JAM WAIT from the state machine and increments with each positive transition of the 10
MHz clock. When the jam counter reaches 128, JAM DONE H signals the state machine.
4-10

4.4.2.5

Go Counter - The go counter is an 8-bit binary counter

that is enabled by the state machine.

During normal operation, the go counter defines a CPT detectio

n window of 3.2 uUs.

During self-test, the go counter defines an interpacket gap of

12.6 us.

4.4.2.6

Display Indicators and Drivers - Power indicators for +5
V, +12 V, transceiver fuse A, and
transceiver fuse B are LEDs that are visible from the rear of
the repeater unit. These indicators are turned

ON when the associated voltage levels are present at the LED.

Remaining indicator LEDs are turned ON when the appropriate

associated gate.

error or status conditions enable the

4.4.2.7

Power-up Reset — After power-up, two pulses (RESET L and RESET
H) are generated. These
pulses perform the following repeater functions.
®

Initiates the internal self-test (after synchronizing with the internal

flip flop).

clock through a dual-ranked

Generates SYNCH RESET L that resets the collision counters

Turns ON (momentarily) all LEDs and then resets latched error LED

to 0.

indications.

RESET L and RESET H are also generated when the self-test button
is pressed. In this case, RESET L
and RESET H work in conjunction with SELF TEST L and
EXTERNAL TEST L to initiate the external
self-test.
4.4.2.8

Power Supply - The power supply can operate from either 115
Vac or 230 Vac (50 Hz - 60 Hz).
A switch on the repeater’s rear panel must be set for the appropriate
input voltage.

The following output voltages are available.
®

+5volts

+12 volts (for transceiver power)

(Ground

Separate +12 volt supply lead for the fan

4-11

CHAPTER 5

5.1 SCOPE
This chapter provides information for maintaining the local repeater and the remote repeater. Included
in
this chapter are:
Maintenance philosophy,
Preventive maintenance,
Corrective maintenance, and
Repeater disassembly.

5.2 MAINTENANCE PHILOSOPHY
Maintenance of the Ethernet repeater consists of preventive and corrective maintenance procedures.
Instructions for replacing faulty FRUs are provided as part of the corrective maintenance procedures.
The local repeater FRUs are:

®
®
e

]ogic module,
Power supply chassis, and
AC power cable.

The remote repeater FRUs are:
¢
¢

Logic module,
Power supply chassis,

Fiber-optic interface, and
AC power cable.

5.2.1
Required Equipment
For local repeaters, fault isolation to the FRU may be achieved by using the state indicator LEDs on the
rear of the repeater. No special equipment is required to isolate faults to this level.
For remote repeaters, a fiber-optic turnaround test connector may be required for some fault isolation
procedures.

The fiber-optic turnaround test connector is a 19.05 cm (7.5 in) fiber-optic cable loop. This test connector
replaces the fiber-optic cable for off-line testing of a remote repeater.
5.2.2 Optional Equipment
|
|
The following two test devices may be helpful in performing some corrective maintenance procedures.
Note that the test devices are not supplied.

H40R0 turnaround test connector

This connector is a modified transceiver. The H4080 test connector can replace an on-line
transceiver for off-line self-testing of the repeater. For more information, consult the H4080
User's Manual.

H4000-TA (or TB) Ethernet transceiver tester

This tester transmits a packet onto an Ethernet coaxial segment (via a transceiver). The tester
then monitors the transmission via a second transceiver and verifies network operation. For
further information consult the Ethernet Transceiver Tester User’s Manual.
5.3

PREVENTIVE MAINTENANCE (PM)

Preventive maintenance involves a periodic exercise of the repeater self-test. There is no specific PM
schedule. however, the self-test should be exercised when network PM is performed.

PM is especially important in installations that use primary and backup repeaters. In these cases, it is
possible for a repeater failure to go unnoticed until either both repeaters fail or until the failure is detected

during PM.

The repeater self-test is performed on two levels.

Internal loopback is automatically performed when the repeater is turned ON. See Figures 5-1

and 5-2 for diagrams of the internal loopback tests.

Internal and external loopback are both performed when the self-test button is momentarily

pressed and released. See Figures 5-1 and 5-2 for diagrams of the loopback tests.
Repeater operations are suspended during the time
that the self-test button is depressed, and while the
self-test is executing. Normal repeater operations
are resumed after the self test successfully
completes.

5.3.1

Internal Self-Test

The internal self-test generates an internal loopback of encoded data to side A and to side B of the
repeater*. This test exercises the logic module only. The transceiver cable interface and/or fiber-optic
cable interface are not exercised. See Figures 5-1 and 5-2 for block diagrams of the internal self-test.
The internal self-test for the local and remote repeaters is identical.
5.3.2

External Self-Test

The external self-test generates external loopback of encoded data to side A and then to side B of the
repeater”®.

* Side A of the repeater refers to the transceiver interface and circuitry associated with transceiver connector A on the rear of
the repeater.

Side B of the repeater (for local repeaters) refers to the transceiver interface and circuitry associated with transceiver
connector B on the rear of the repeater.

Side B of the repeater (for remote repeaters) refers to the circuitry associated with the fiber-optic interface on the rear of the
repeater.

5-2

In local repeaters, signal turnaround occurs in the transceivers (see
Figure 5-1). In remote repeaters, signal
turnaround occurs in the local transceiver and in the remote half
of the repeater (see Figure 5-2).

To test the entire remote repeater, the self-test must be executed from both of

the repeater units.

Test results are observed by noting the conditions of the state indicator LEDs
on the rear of the repeater
being tested.
&

{

ETHERNET

r——-t_ TRANSCEIVER l |

[}

EXTERNAL

SELF-TEST

TRANSCEIVER INTERFACE

——

oo s s e oo e ‘e i

LOGIC

MODULE

INTERNAL

SEL!ITES?

TRANSCEIVER INTERFACE

EXTERNAL

SELF-TEST

Y
-agf

[ ETRERNET

TRANSCEIVER

__r——J
|

o
TK-10811

Figure 5-1

Local Repeater Self-Test Diagram

5-3

—

ETHERNET

TRANSCEIVER t"

EXTERNAL

SE%ES?

TRANSCEIVER INTERFACE
i

LOGIC

EXTERNAL

FIBER-OPTIC

MODULE

INTERNAL

ss;.Tssz

INTERFACE

SELF-TEST
-

EXTERNAL

FIBER-OPTIC
INTERFACE

SELF-TEST
g

LOGIC

MODULE

INTERNAL

SELF-TEST

A
TRANSCEIVER INTERFACE
l

;

ETHERNET

TRANSCEIVER

EXTERNAL
SELF-TEST
A

TX-10812

Figure 5-2 Remote Repeater Self-Test Diagram

5.3.3 Executing the Repeater Self-Test
To initiate the repeater self-test, perform the following.
I.

Torun internal self-test only, press the power switch to “0TM (OFF). Wait five seconds and press

the power switch to 1" (ON).

Observe the LEDs on the rear of the repeater. No error LEDs should remain lit (TST, FLT,
INT, or ERR). If any of these LEDs remain lit, follow the recommended proceduresin this
chapter.
2.

Torun internal and external self-test, momentarily press and release the self-test button on the
rear of the repeater. All LEDs should light while the self-test button is pressed and held down.

NOTES
1.

Normal repeater operations are suspended dur-

ing the self-test.

All LEDs should light when the “TST” button
is held in.

Remote repeaters do not pass external self-test
uniess both repeater units are fully connected
and turned ON.

Observe the LEDs on the rear of the repeater being tested. A successful pass is indicated when
no self-test error LEDs remain lit. Figure 5-3 shows a typical LED status after self-test has
successfully completed.

If the self-test LED remains steadily lit (typically for more than .5 seconds), a failure mode is indicated. In

this case, the specific failure mode may be determined by observing the conditions of the other LED:s.
Specific failure modes are identified in Section 5.4.

Corrective maintenance should be performed once it has been determined that a faulty repeater exists.
Corrective maintenance comprises fault isolation to, and replacement of, the faulty FRU. Fault isolation is
accomplished by running the self-test and analyzing the results indicated by the LEDs on the rear of the
repeater.

It is possible that a fault will exist in the transceiver or other equipment electrically close to the repeater. In
some cases, this type of fault may initially appear to be in the repeater. However, careful exercise of the
troubleshooting proceduresin this section should isolate the f‘atfit to the repeater FRU or point to other
possible sources of malfunction.

5-5

SELF-TEST BUTTON

CD Seg ‘%?’vTst Fit Err CPT

CQ S

- OCRO000

jnt Act Err CPT |

QOO:

;/
THE “Act” LIGHT MAY

FUSE A

BE LIT IF THE

FUSE B

"STANDBY"” SWITCH IS
INTHE "1 (STANDBY
MODE ENABLED)

5 i .

(

POSITION.

Y—- = GREEN LED THAT IS NORMALLY ON
%

MKVB4-0068

Figure 5-3

Typical LED Status

S.4.1 Troubleshooting Tips
The following tips are suggested as aids to troubleshooting.
®

When problems are suspected, always ensure that the repeater is receiving the correct voltage

and that all cables are properly connected.
®

When interchanging local repeater inputs:

Note that the A and B inputs to local repeaters are identical, and reversing the transceiver cable
inputs should have no effect on the functions of the repeater. Intentionally reversing transceiver
cable inputs is a routine troubleshooting procedure for local repeaters.
,
For example, when transceiver cables are reversed, malfunctions existing outside the repeater

appear to move to the repeater’s other side (from side A to side B or vice-versa). In contrast,

malfunctions existing within the repeater generally remain with the repeater’s same side even

when transceiver cables are reversed.

5.4.2 Repeater LED Indications |
This section describes each of the LEDs on the repeater rear panel and suggests procedures to be followed
in the event that an abnormal indication is present.

When a repeater is suspected of a malfunction, first examine the LEDs to determine if the repeater

functioning.

The following chart provides a quick reference to normal LED conditions. Numbers in parentheses reflect
non-U.S. LED designations.

Occasionally
Flickering (see note)
5V (12)

12V (5)

OFF

CD A (3)
CD B (10)

All others

FUSE B
NOTE
These lights turn ON indicating when activity on the
associated coaxial segment has been transmitted to

the repeater’s other side. During heavy network traffic, these LEDs may appear to be steadily ON.
Figure 5-4 shows the repeater LEDs and associated definitions.

Table 5-1 contains a more complete description of LEDs and recommended corrective procedures.

5.4.3 Self-Test Errors and Troubleshooting
Table 5-2 describes self-test error indications and outlines recommended procedures to be followed when
self-test errors occur.

5-7

i
A

CD Seg 12V Tst Fit Err CPT

CD Seg 5V int Act Err CPT

O000000O

OO0O0O0O

LED =

LED NAME

COLOR

DEFINITION

2.0A

GREEN

FUSE A FUNCTIONING

2.0A

GREEN

FUSE B FUNCTIONING

CcD

GREEN

CARRIER RECEIVED ON B AND TRANSMITTED TO A

SEG

YELLOW

REPEATER WAS SEGMENTED ON SIDE A

12V

GREEN

+12 VOLT SUPPLY FUNCTIONING

T8T

RED

EXECUTING SELF-TEST

FLT

RED

CURRENTLY SEGMENTED

ERR

RED

EXTERNAL SELF-TEST ERROR ON SIDE A

CPT

RED

CPT ERROR ON SIDE A

CcD

GREEN

CARRIER RECEIVED ON A AND TRANSMITTED TO B

SEG

YELLOW

REPEATER WAS SEGMENTED ON SIDE B

GREEN

+5 VOLT SUPPLY FUNCTIONING

INT

RED

EXECUTING INTERNAL SELF-TEST

ACT

RED

STANDBY ACTIVE

ERR

RED

EXTERNAL SELF-TEST ERROR ON SIDE B

CPT

RED

CPT ERROR ON SIDE B
MKVB4-0050

Figure 5-4

LED Definitions
5-8

Table 5-1

LED
Name

LED
Definition

Normal
State

2.0A

FUSE A

LEDs and Troubleshooting

Indications/ Corrective Action
This (green) LED indicates that the +12 V transceiver
power fuse on side A is good.

When OFF, this indicates that either the fuse is blown

or that +12 V is not reaching the fuseholder.
1.

Check the fuse. If blown, replace it with correct
Sfuse

(2 A - Digital Equipment Corporation part
number 90-07215-00).

If the fuse continues to blow, try connecting to
a different transceiver or transceiver cable.
Check other indicators (5V and 12V LEDs) to

determine that the repeater is properly powered.
4.

Verify that the power switch is ON, and that

the power cord is connected to the proper voli-

age source. Check the line fuse (refer to Note |

at the end of this table).
2.0A

FUSE B

Similar to 2.0A (side A)

+5 volts

This (green) LED indicates that the +5 V circuit of the
power supply is functioning.

When OFF, this may indicate that the +5 V circuit is
not functioning.
1.

Check the 12V LED to determine whether the
power supply is functioning.

Check the FUSE A and FUSE B LEDs. These
LEDs indicate that +12 V is being supplied to

the transceivers.
3.

Verify that the power switch is ON and that the

power cord is connected 1o the proper voltage

source. Check the line fuse (refer to Note | at

the end of this table).

5-9

Table 5-1

LED

Name

LED

Definition

Normal

State

LEDs and Troubleshooting (Cont)

Indications/Corrective Action
4.

Press the self-test button. All LEDs should
light while the button is pressed. If all LEDs
(with the exception of the 5V LED) turn ON,
the 5V LED is defective. Replace the logic

module.

12V

+12 volts

If the above procedures do not correct the problem, replace the power supply.

This (green) LED indicates that the +12 V circuit of
the power supply is functioning.

When OFF, this indicates that the +12 V circuit 1s not
functioning.
1.

Check the 5V LED to determine that ac power
is reaching the power supply.

Check the FUSE A and FUSE B LEDs. These
LEDs indicate that +12 V is being supplied 1o
the transceivers.

Verify that the power switch is ON and that the
power cord is connected to the proper voltage
source. Check the line fuse (refer to Note | at
the end of this table).

Note whether the fan is running. The fan operates on +12 V and indicates that part of the
+12 V section of the power supply is

functioning.

Press the self-test button. All LEDs should

light while the button is pressed. If all LEDs
(with the exception of the 12V LED) turn ON,
the 12V LED is defective. Replace the logic
module.

If the above procedures do not correct the problem, replace the power supply.

Table 5-1
LED
Name

CD (A)

LED
Definition

Normal
State

Carrier
Detect A

Should
Flicker

LEDs and Troubleshooting (Cont)

Indications/Corrective Action

This (green) LED flickers when data packets are
received from side B AND transmitted to side A. During heavy network traffic, this LED may appear to be
steadily Iit.
When continuously OFF, this may indicate that:
&

There is no traffic on side B.

The transceiver on side B is not functioning.
The carrier detect circuit on side B is not
functioning.

The carrier A LED is not functioning.

Check other indicators (FUSE A, FUSE B, 5V,
and 12V LEDs) to determine that the repeater

is properly powered and whether the transceiver

IS getting power.

Press the self-test bution. All LEDs should
light while the button is pressed. If the Carrier
A LED fails to turn ON, the LED is defective.
Replace the logic module. If the LED lights,
note the results of the self-test (see Table 5-2).
For local repeaters, interchange transceiver
cable inputs.
a.

Try swapping transceiver cable inputs 1o
see If the inactive indications shift 1o side

B of the repeater (refer to Note 2 at the
end of this table).

If the indication does shift to the other
side of the repeater, suspect inactivity on
that segment, or a problem with the

transceiver and/or transceiver cable.

If the indication stays with side A, check

FUSE B. If FUSE B is good, change the
logic module.

Table 5-1
LED

Name

LED

Definition

Normal

State

LEDs and Troubleshooting (Cont)

Indications/Corrective Action
4.

For remote repeaters, try using a different
transceiver or transceiver cable (refer to Note 2
at the end of this table).
a.

If the CD indication improves, suspect a
problem in the transceiver or transceiver
cable.

If the CD indication does not improve,
suspect inactivity (no traffic) on side B or
a faulty logic module.

CD (B)

Carrier

Should

Similar to CD (A)

CPT
Error
A

Collision
Presence
Test Error

OFF

This (red) LED latches ON to indicate that a CPT signal was not detected on side A following a previous
data transmission to side A. The CPT signal is sent

Detect B

(Side A)

Flicker

from the transceiver via the collision pair to indicate

that the collision detect circuitry is functional.
The absence of CPT suggests:
®

A malfunction in the collision detect circuitry.
A malfunction in the transceiver or transceiver
cable.

Excessive transceiver cable length (over 50 m

[164 ft]).

Press the self-test button to reset the error indication. Note that CPT detect is turned OFF
during self-test. Monitor the LED for reoccurrence of CPT error.

For local repeaters, interchange transceiver

cable inputs.

Try swapping transceiver cable inputs to
see if the CPT error indication shifts to
side B of the repeater (refer to Note 2 at
the end of this table).

If the indication does shift to the other

side of the repeater, suspect a problem

with the transceiver and/or transceiver
cable.

Table 5-1

LED
Name

LED
Definition

Normal
State

LEDs and Troubleshooting (Cont)

Indications/Corrective Action

If the indication stays with side A, suspect a problem in the CPT detect circuitry. Replace the logic module.

For remote repeaters, try using a different
transceiver or transceiver cable (refer to Note 2

at the end of this table).
a.

If the CPT error indication goes away,
suspect a problem in the transceiver or
transceiver cable.
If the CPT error indication remains, suspect inactivity (no traffic) on side B or a

faulty logic module.

CPT

Collision

Error

Presence

Test Error
(Side B)

OFF

For local repeaters this indication is similar to CPT

Error A.

|
For remote repeaters, the CPT circuit on side B is

disabled.

FLT

Fault

OFF

When ON, this (red) LED indicates that one of the
transceivers and its associated coaxial segments is currently segmented or faulty (refer to Note 3 at the end
of this table).
1.

Observe the SEG A and SEG B LEDs. At least

one of these should be latched ON to indicare
which side is segmented.

Be aware that the conditions which resulted in
segmentation could cease to exist appearing

possibly as an intermittent malfunction.

Run the self-test and note the results (refer to

Table 5-2).

For local repeaters only, interchange transceiver
cable inputs (refer to Note 2 at the end of this
table).
a.

Swap transceiver cable inputs to see if the
segmented indication shifts to side B of
the repeater.

Table 5-1
LED
Name

LED
Definition

Normal
State

LEDs and Troubleshooting (Cont)

Indications/Corrective Action
b.

If the indication does shift to the other
side of the repeater, suspect a problem
outside the repeater such as a transceiver,
transceiver cable, or coaxial segment.
If the indication stays with side A, suspect a problem in the collision detect circuitry. Replace the logic module.

Standby
Active

OFF

When ON, this (red) LED indicates that the repeater
is in the active standby mode. The standby mode

becomes active when the primary repeater has failed or

when no primary repeater exists.

Check the LEDs on the rear of the primary repeater.
Follow the suggested corrective procedures.
SEG

Segmented A

OFF

This (vellow) LED indicates that side A was segmented at least once since the last self-test or power-up
was performed (refer to Note 3 at the end of this
table).
L.

Note whether side A is currently segmented (the
FLT LED would be ON|. Press the self-test
button to reset the segmented LEDs and to run
the self-test. Note the self-test results in Table
For local repeaters, try interchanging transceiv-

er cable inpuis:
a.

Swap transceiver cable inputs to see if the
segmented indication shifts to side B of
the repeater (refer to Note 2 at the end of
this table).

If the indication does shift to the other
side of the repeater, suspect a problem
outside the repeater such as a transceiver,
transceiver cable, or coaxial segment.

If the indication stays with side A, suspect a problem in the collision detect circuitry. Replace the logic module.

Table 5-1

LED
Name

LED
Definition

Normal
State

LEDs and Troubleshooting (Cont)

Indications/Corrective Action
3.

For remote repeaters:
a.

If side A is not currently segmented (the
FLT LED is OFF), press the self-test buiton to reset the SEG LED and 1o run the
self-test. Note the self-test results in
Table 5-2.
If side A is currently segmented (the FLT
LED is ON), try using a different transceiver or transceiver cable (refer to Note 2
at the end of this table).
If the segmented condition ends, suspect a
Sfaulry transceiver or transceiver cable.

If the condition persists, suspect the coaxial cable or its associated equipment.
SEG

Segmented B

OFF

Similar to SEG (A)

(B)

NOTES
Turn OFF the repeater and unplug the power
cord before checking the line fuse.

Turn the repeater OFF before unplugging any
cables.
Segmentation is an unusual condition resulting
from loss of data loopback or from 64 consecutive unsuccessful attempts to transmit a packet.

If the A or B segmented indicator is frequently
found “ONTM, it may indicate intermittent
problems on the coaxial segment or its associated equipment.

Table 5-2

LED
Name

Self-Test Error LEDs

LED
Definition

Normal
State

Indications/ Corrective Action

Self-Test
Executing

OFF

This (red) LED lights briefl} (typically .3 seconds) on

power-up and on pressing the “TST” (seif*tefii) button.
This indicates that the repeater self-test is executing.

If the “TST” LED remains lit, the self-test has failed

(the repeater never exits self-test).

A remote repeater unit which is failing self-test
(the “TST” LED is ON) causes the remaining

unit to fail (external) self-test. This problem

can be minimized by resetting both units.

Turn each unit OFF for five seconds and

then back ON.

Observe the LEDs at this point.

Run self-test on the “good” unit to verify
its operation.

[

ernal

-3

5.’

INT

If-Test

OFF

Note the condition of the other self-test LEDs
(for both local and remote repeaters):

“INT” (internal self-test)

“ERR’” (self-test error A)

“ERR’ (self-test error B)

When ON, this (red) LED indicates that the repeater

is in the internal self-test state. If a data error is found
during internal or external self-test, the repeater locks

itself into the internal self-test state. This state is maintained until the repeater is reset (turned OFF for five
seconds and then turned back ON).

Turn the repeater OFF, wait five seconds, and

turn the repeater ON. Only the internal test is
performed on power-up (the internal test exe-

cutes with or without transceiver cables and/or

fiber-optic cables being connected).

If the “INT” LED still remains lit, a malfunc-

tion exists in the logic module.

Table 5-2

LED
Name

LED
Definition

Normal
State

Self-Test Error LEDs (Cont)

Indications /Corrective Action

If the “INT"" LED does not remain lit after
power-up, press and release the “TST" button.
The transceiver cable and/or fiber-optic cable
must be connected (for remote repeaters both
units must be ON). This runs both the internal
and external self-test. Note the conditions of
the “ERR” LEDs for the A and B sides.

ERR

Self-Test

(A)

Error A

OFF

This (red) LED lights when the self-test has detected
an internal or external data loopback error on side A.
If the ERR (A) LED remains ON after the internal
test, a malfunction exists in the logic module of the
repeater.

If this LED remains ON after the external self-test
only, a malfunction may exist in:

The transceiver cable interface.

The transceiver cable.
The transceiver connected to side A.
The coaxial segment on side A.

For local repeaters:
a.

Try swapping transceiver cable inputs to
see if the error indication shifts to side B
of the repeater. Refer to the note at the
end of this table.

If the indication does shift to side B, suspect a problem outside the repeater. Typically, such a problem might be the
transceiver, transceiver cable, or other
equipment on the associated coaxial
segment.

5-17

If the problem remains on side A after
swapping transceiver cable inputs, the logic module should be changed.

Table 5-2

LED
Name

LED
Definition

Normal
State

Self-Test Error LEDS (Cont)

|
Indications/Corrective Action
2.

For remote repeaters:

Try using a different transceiver or transceiver cable (see the note at the end of
this table).

Turn the repeater power ON and rerun
the external self-test (press and release
the “TST" button).

If the "ERR" (A) indication goes away,
suspect a problem in the transceiver
cable, the transceiver, or associated coaxial segment.

If the "ERR" (A) indication remains,
replace the logic module.
ERR

(B)

Self-Test
Error B

OFF

This (red) LED lights when the self-test has detected
an internal or external data loopback error on side B.
1.

For local repeaters, indications and procedures
are similar to "ERR" (A).

For remote repeaters, use the following procedures when the "ERR" (B) LED remains lit following the external self-test.
a.

Turn the repeater OFF.

Table 5-2

LED
Name

LED
Definition

Normal
State

Self-Test Error LEDs (Cont)

Indications/Corrective Action
b.

Disconnect the fiber-optic cable and
install a fiber-optic turnaround connector
in its place (see the note at the end of this
table).

Press and release the “TST" button.

If the "ERR"” (B) indication remains, suspect the fiber-optic interface or the logic
module.

If the “ERR" (B) indication goes away,
suspect the remote repeater unit or the
fiber-optic cable. Perform the self-test on
the remote unit.
&

CAUTION: Fiber-optic turnaround connectors cause
collisions while they are connected. ALWAYS remove a
fiber-optic turnaround connector after testing is
completed.

NOTE
Turn repeater power OFF before disconnecting any
cables. Turning the power OFF resets error
indications.

5.5

REPEATER DISASSEMBLY

It is necessary to disassemble the repeater to repair or replace a defective FRU. Figure 5-5 shows the

location of all FRUs in the repeater.

To prevent electrical shock and damage to compo-

nents, turn OFF power and disconnect all cables
attached to the repeater before opening the chassis.

The instructions in this section assume that all external cables to the repeater have been removed. When
removing cables, be sure that they are properly marked so that they are reconnected in the same locations.

5-20

TOP COVER

POWER SUPPLY MODULE -

§§§§ CHASSIS

POWER SUPPLY
INTERCONNECT

CABLE

ift

gfig

it;

POWER SUPPLY

. POWER SUPPLY
~ COVER

FIBER-OPTIC MODULE
]

CHASSIS®
CHASSIS INCLUDES:

METAL CHASSIS

COVER

« POWER SUPPLY
MODULE

POWER SUPPLY

COVER
«

POWER SUPPLY

INTERCONNECT

LOWER METAL
CHASSIS

CABLE
¢«

—_

LOGIC
MODULE *

FILLER PANEL

N BOTTOM COVER

* = FRU

** = SUPPLIED WITH REMOTE REPEATERS ONLY
MEKVBL-0041

Figure 5-5

Repeater FRU Locations

FAN

5.5.1

Opening and Closing the Repeater

Perform the following steps to open the repeater (refer to Figure 5-6).
E

Lift the front of the top cover up.

Remove the two slotted screws from the bottom of the repeater.

Completely remove the top cover and set aside.

Perform the following steps to close the repeater.

Align the top and bottom covers holding the front of the top cover in the open position.
-

Carefully close the cover making sure that the tabs on the rear of the top cover fit into the
o

catches in the rear of the bottom cover.

Insert the two slotted screws into the two holes in the bottom cover and tighten.

3-22

TM~

TOP COVER

METAL CHASSIS COVER

TK-10928

Figure 5-6

Opening and Closing the Repeater

5-23

5.5.2
@

Opening and Closing the Internal Metal Chassis

Perform the following steps to open the internal metal chassis (refer to Figure 5-7).

—

Pull up on the plunger of each plastic fastener (the fasteners are located at the front of the

metal chassis).

—

Lift the front of the top chassis cover up.

Disconnect the power supply interconnect cable from the logic module.

Slide the top chassis cover forward about 1 cm (.394 in). The four metal tabs of the top

chassis cover should slide out of the holes in the rear of the bottom chassis cover.

Perform the following steps to close the internal metal chassis.

—

Fit the four tabs at the rear of the top chassis cover into the slots at the rear of the bottom

chassis cover.

Connect the power interconnect cable from the power supply to the logic module.

Close the top chassis cover.

Press the plunger of both fasteners down firmly until they latch, locking the top and bottom

chassis covers together.

5-24

@ REMOVE PLASTIC
FASTENERS

OPEN CHASSIS

TOP METAL

CHASSIS COVER

PULL UP

METAL

CHASSIS COVER

TK-10926

Figure 5-7

Opening and Closing the Internal Metal Chassis

5-25

5.5.3

Fiber-Optic Module Removal and Replacement

The fiber-optic module is located at the right-rear section of the logic module (see Figure 5-8). The fiberoptic module is mounted on four standoffs (two standoffs with screws and two standoffs that are plastic
fasteners).

Perform the following steps to remove the fiber-optic module.
-

Remove the two screws from the rear standoffs.

Gently pull the locking clip of the remaining standoffs away from the module as shown in

Figure 5-8.

Remove the module by lifting the module up from each standoff and off of the electrical
connector.

Perform the following steps to replace the fiber-optic module.

Align the fiber-optic module with the electrical connector and the standoffs at the right-rear
section of the logic module (the components should be facing down and the fiber-optic
connectors aligned with the hole in the rear panel).

Gently push down on the module making sure that the electrical connector is properly

-~
-

connected.

Push down on each corner of the module ensuring that the locking clip of each standoff

locks the module in place.

Replace the two screws in the rear holes of the fiber-optic module.

5-26

SCRE

FIBER-OPTIC MODULE ~—

LOGIC MODULE _

FIBER-OPTIC MODULE

— CONNECTOR

TK-10831

Figure 5-8

Fiber-Optic Module Removal and Replacement

5-27

5.5.4

Logic Module Removal and Replacement

The logic module is held in place by three plastic fasteners. See Figure 5-9 for the locations of these
fasteners.

Perform the following steps to remove the logic module.
—

Pull up the plungers of the three plastic fasteners.

Carefully lift the logic module out of the metal chassis.

Perform the following steps to replace the logic module.

Fit the module into the chassis. Make sure that the D-shaped transceiver connectors and
other hardware are properly aligned with the access holes in the rear panel of the repeater.

Align the three holes in the module with the corresponding holes in the metal chassis.

Push down on the plunger of the three plastic fasteners to lock the module in place.

5-28

PULL UP

TO UNFASTEN

PUSH DOWN
, TO FASTEN

PLASTIC

FASTENERS

LOGIC MODULE
T ———————

N\ LOGIC MODULE

TK-10524

Figure 5-9

Logic Module Removal and Replacement

5-29

5.5.5

Power Supply/Fan Removal and Replacement

The power supply and fan are located in the top cover of the internal metal chassis as shown in Figure 510.

When a power supply or fan is malfunctioning, the entire assembly (the fan, power supply, and metal
cover) should be replaced.

POWER SUPPLY COVER

POWER SUPPLY
MODULE

POWER SUPPLY
INTERCONNECT

RO
Ve R
o SR . S

i NGB, o S

}

‘

CABLE

CONNECTOR

“TOP COVER
GROUND

LUG
TK-10827

Figure 5-10

Power Supply Chassis

5-30

APPENDIX A

FIBER-OPTIC

LINK CERTIFICATION

A.1 INTRODUCTION
This appendix contains the necessary procedures for certifying fiber-optic link installations for the Remote
Ethernet Repeater. The certification should be performed before the Remote Ethernet Repeater is
installed.
|

Link certification ensures the following.
®

The correct cable type is used.

The fiber-optic connectors are properly installed.

The link (installed cable) is within the specifications required by the repeater.

A.2 FIBER-OPTIC LINK CERTIFICATION
The link certification must be performed by a person skilled in the appropriate equipment and fiber-optic
cable testing techniques.

A certified link:
®
®

Is capable of transmitting the optical signals between remote repeater units, and
¥

Has topology documentation that is accurate and accessible. Topology documentation must

include:

—~

Link routing,
Cable splice locations, and
Connector locations.

A certified fiber-optic link must meet the following parameters.
e

e
A.3

Signal attenuation
Link length

REQUIREMENTS

This section describes cable and equipment requirements for certifying fiber-optic cable.

Cable Requirements

A.3.1

The fiber-optic cable and connectors used must meet the following constraints.
®

The fiber used should be a Corning 1508TM type fiber or equivalent. For any questions regarding
specific parameters, refer to the DIGITAL Fiber-Optic Cable Specification (number 1700333).

Connectors used on these cables must be Amphenol 906TM type SMA style or equivalent.
Attenuation per connector must remain under 1.5 dB.

Required Equipment

A.3.2

To perform the fiber-optic link certification, either of the following fiber-optic time domain reflectometers

(FOTDR) are required.

NOTE

The FOTDR needs special instruction in its operation and handling.

Photodyne 5500TM FOTDR or equivalent with Amphenol 906 type SMA style connector.

The Photodyne 5500 FOTDR is a district-level tool that requires the following additional
®

equipment.

~
-

Oscilloscope (Tektronics 564TM type or equivalent), and
Oscilloscope camera (Tektronics C-5CTM type or equivalent).

Tektronics OF-150TM model FOTDR or equivalent with Amphenol 906 type SMA connector.
An oscilloscope and chart recorder are included with the Tektronics OF-150 model FOTDR.
The Tektronics OF-150 model FOTDR is a regional-level tool.
The FOTDR must have been calibrated to manufacturer’s specifications within the recommended calibration period.

The FOTDR measures the following parameters of fiber-optic cable.
®

Length
Attenuation

NOTE

It is possible to calculate the fiber propagation delay

using length and attenuation parameters.

Corning 1508 is a trademark of Corning Glass Works.

Amphenol 906 is a trademark of Amphenol North America, Division of Bunker Ramo Corp.
Photodyne 5500 is a trademark of Photodyne, Inc.

Tektronics 564, C-5C, and OF-150 are trademarks of Tektronix, Inc.

A-2

A.4 CERTIFICATION PROCEDURE
The certification procedure is made up of the following.
1.

Visual inspection of the fiber-optic link (cable, connectors, and all splices). Any damage must be

repaired and any stress bends must be removed.
2.

Precalculation of expected cable, connector, and splice losses.

FOTDR measurement of the fiber-optic link. Discrepencies between the calculated and measured losses should be investigated.

A.4.1

Loss Calculation Formula

Calculate what the cable, connector, and splice losses should be (the total loss for the system must be less
than 10.0 dB).
L X .006 dB =
C X 1.50 dB =
S X 0.50dB =

(L = the length in meters)
(C = the number of barrel connectors)
(S = the number of mechanical fiber-optic splices.)

Total dB loss =
A.4.2 FOTDR Procedure
Measure the fiber-optic link with the FOTDR. Look for indications of breaks or areas of severe attenuation (>.5 dB for splices and >1.5 dB for connectors).

Do not look into a fiber-optic connector while the
cable is connected to an FOTDR. Laser light may
cause damage to eyes.

NOTE
It is important to perform the FOTDR measurement
from each end of both fibers that make up the link.
This assures that a broken fiber at the far end of the
link is not missed (mistaken for the end of the fiber).
A.4.2.1

Equipment Setup - Use the Photodyne 5500 FOTDR and an oscilloscope (or an equivalent

FOTDR). Follow the directions given in the equipment manual for setup and use.
NOTE
Be sure that all equipment is disconnected from the
fiber-optic link prior to measuring the link.
When using the Photodyne 5500 FOTDR, select the following settings.

PULSE WIDTH:
-

—

20 ns (for lengths less than 100 m [328 ft])
100 ns (for lengths greater than 100 m [328 ft])

UNITS IN METERS? = Yes

CORE INDEX = 1.47

A-3

A.4.2.2

Cable Measurement -

Connect the oscilloscope to the Photodyne 5500 FOTDR as follows.

TRIGGER-OUT from FOTDR to TRIGGER-IN on oscilloscope

LOG-OUT from FOTDR to oscilloscope input with a 50 terminator in the same line.

Measure each fiber separately. Look for abnormalities in the slope of the oscilloscope readout
(see Figure A-1). Compare the oscilloscope information with the redundant information displayed by the Photodyne 5500 FOTDR unit.

CONNECTOR
BEGINNING

OF FIBER

END OF
FIBER

0.0d8 b L;

-1.0 dB |

-2.0d8B |

0.7 dB LQSS{ _

~3.0 dB |
—4.0 dB

—5.0 dB

—

E i

600 METERS

200
METERS

MKVB84-0116

Figure A-1

Typical FOTDR Trace Showing
a Connector

Measure the length of each channel of the fiber-optic link in accordance to the procedures
outlined in the FOTDR manual. The link length must not exceed 1000 m (3281 ft).

Measure the attenuation of each channel of the fiber-optic link. The attenuation for each fiber
should be less than 6 dB per km. Total loss including splices, connectors, and cable attenuation
must be less than 10 dB.

The attenuation is the distance between the upper portion of the slope to the lower portion of
the slope (refer to Figure A-1).
5.

Note the connector losses. Individual connectors should not have more than 1.5 dB of loss (see
Figure A-1).

Note loss through cable splices. Individual splices should not have more than 0.5 dB of loss
(see
Figure A-2).

CONNECTOR
END OF
FIBER

=1.0 dB

—-2.0 dB

-3.0 dB
-4.0 dB

~5.0 dB

600 METERS

—! 200

METERS

MKVB84-0117

Figure A-2

Typical FOTDR Trace Showing a Splice
and Connector

A.S POSSIBLE PROBLEM SOURCES
If losses recorded exceed 10 dB, check the following.
®

Verify all connectors and connections.

Make sure that the connector ends are clean before remating.

Remove any stress bends found in the cable.

A-5

If the attenuation remains greater than 10 dB, the fiber-optic link cannot be certified. The installer (or
customer) should be informed of the problem. Appropriate repairs or modifications must be completed
and the link retested before it can be certified.

Once all the measurements have been made, be sure to record the results in the network site guide. It is
preferred that the recorded results be placed near the fiber-optic connectors if possible. The following must

Date of certification
Attenuation of each fiber

Installer’s company name and address

Installer’s name

be recorded.

Length of link measured by the FOTDR
Name of the person(s) recording data
Equipment used to certify the link

If a strip graph recording is taken, it should be included with the above records.

A-6