Tellabs 251 Manual de usuario

7te11abs

technical

manual

76-81251

rev B

practice

section

81251

©Tellabs, Inc., 2

November

1982

all

ri9hts

reserved,

printed

USA

251

24-Channel Digital Echo Canceller System

figure

251 24-Channel Digital Echo Canceller System

(two Systems shown

same

Mounting Assembly)

for channel idle/busy status,

it can be controlled

from amanual control panel

from aremote control

and status interface

that

uses aserial data format

compatible with EIA standard RS-232-C.

1.02 This Practice section is revised

incorporate

the information formerly contained

the 251 Practice

Supplement dated 1June 1983 and also to provide

information on

two

optional modules that allow the 251

System

operate on circuitswith amaximum end-path

delay of

60ms

(instead of30ms).

1.03 The 251 System is intended for use near

the

end points

digital carrier facilities characterized

appreciable end-to-end propagation delays. Echoes

from the associated near-end voice-frequency chan-

nel circuits are effectively cancelled by the 251 Sys-

tem. These echoes are caused

signal reflections

at impedance discontinuities and interface points

such as 4wire-to-2wire interfaces.

1.04 Because it is asplit-type

echo

canceller sys-

tem, one 251 is required at each end of the com-

posite circuit, and each System protects

the

opposite

end of the circuit from echoes in return-path chan-

nels. The split-type configuration makes

the

251 Sys-

tem completely insensitive

transmission delays on

intermediate carrier links and therefore allows

the

System

operate effectively regardless of

the

dura-

tion of these delays. Thus,

the

251 System is well

suited for abroad range of digital-network applica-

tions, including single-hop and double-hop satellite

circuits (whose round-trip delays are approximately

600

and 1200ms, respectively) and terrestrial circuits

where the transmission characteristics of

echo

sup-

pressors

via-net-Ioss (VNL) designs may be un-

desirable.

page

page 17

page

page 20

page

page 20

page

page 22

page

page 4

page 5

page 6

page 7

page 8

page 9

page

page 9

page 10

page

general

description

application

section

contents

section

general

network

interface

system

control

remote

control/status

interface

automatic

self-test

alarms

tone disabler option

section

installation

inspection

mounting

251 Assembly

central

office

equalizers

installer connections (general)

input-power

connections

facility (signal) connections

alarm connections

facility(signal) connections via

optional

twinax

connector

panels

remote

control/status

interface

connections

(general)

remote

control/status

interface

connections for single 251 System

remote

control/status

interface

connection

multiple 251 Systems

module insertion

initial power-on sequence

self-test

checkout

section

local

system

control

system operating parameters

channel

operating parameters

section

remote

system

control

remote interface

protocol

remote

control

commands

command

examples

section

system

circuit

description

section

module

and

system

block

diagrams

specifications

testing

and

trOUbleshooting

general

description

1.01 The 251 24-Channel Digital Echo Canceller

System (figure

is an adaptive, split-type echo-

control system

that

directly interfaces 1.544-megabit-

per-second digital carrier facilities (commonly called

facilities) at the

DS-1

level. The 251 System pro-

vides individual echo control for all

facil- 1.05 Asignal

the receive path of

any

of the

ity's voice-frequency

(VF)

channel circuits and per- channels served by the 251 System, followed by

the

forms comprehensive self-tests on its cancellation signal's echo in the transmit

(I.e.,

return) path, causes

circuitry

when

channels are idle. The 251 can operate the System

begin an adaptation process known as

as astand-alone system by monitoring

the

signaling convergence. During convergence, adigital signal-

page 1

practice

section

81251

processing

circuit

called a

convolution

processor

(one of which is provided for each channel) constructs

and stores in memory amathematical model of

the

channel's near-end transmission path (terminating

set and

interconnecting

link), and uses this model

compute

echo

estimate

for

the

channel. This echo

estimate

is then subtracted from

the

transmit-path

signal

actually remove

the

echo

from

the

signal.

1.06 When

the

transmit-path signal consists of both

echo (from

the

far-end speaker) and near-end speech,

the

251 System removes only

the

echo

signal, leav-

ing

the

speech

signal

intact

for

transmission toward

the

distant

end. Thus, parties

both

ends

can

talk

simultaneously (this is known as futJ-duplex speech

doubletalk)

without

the

choppiness

lockout

prob-

lems characteristic of

echo

suppressors. When only

the

far-end

party

is talking (one party

talking

is known

single

talk),

the

transmit signal consists entirely of

echo, which

the

251 System removes by subtracting

the

echo

estimate from

the

echo

signal. Any residual

echo, which is normally avery small amount (typically,

less than

-40dBmO),

is removed by an integral resid-

ual suppressor.

1.07 Convergence, the process of initially adapting

anear-end

echo

path, usually

takes

less than

200ms

(about two

three

syllables of speech), de-

pending upon

the

receive-path (far-end speech) signal

level. The 251 System can

adapt

to any near-end

path

with

aminimum

echo

return loss (ERL)

6dB

and amaximum end-path echo delay of

either

30ms

60ms, depending upon module selection. After con-

vergence,

the

251 System

continues

monitor

the

echo-delayand ERL characteristics ofthe near-end path.

During periodsof singletalk,

the

convolution processor

repeatedly updates its mathematical model to match

theseobservedcharacteristics. Thus,

any

change in

the

near-end path, such as aline being switched, will result

in anew end-path model

accommodate

the

changed

echo characteristics.

aresult, after achieving con-

vergence,

the

251 System performs

echo

cancellation

continuously, keeping

the

transmit path free of

echo

for

the

duration of

the

call.

1.08 Compact in size, an

entire

251 System com-

prisesonlysixTellabsType16 modules(five

modules

ifa

tone

disabler is

not

desired) and aprewired mounting

assembly, as shown in figure

Each of

these

System

components is described briefly below.

1.09 The

6953

Echo

Canceller

Power

Supply

and

Alarm

Module

derives regulated

power

for

all of

the

System's digital logic circuits from filtered, ground-

referenced

-44

-56Vdc

(nominal

-48Vdc)

input.

In addition,

the

6953

provides local minor alarm indi-

cations (via front-panel LED's) as well as relay opera-

tion

for

remote major

and

minor alarm indications

when faults of various types

(e.g.,

loss of power) occur.

These alarm indications can be manually

terminated

by depressing afront-panel

afarm

cutoff

pushbutton.

Fusing

for

the

System's input

power

is provided by a

13-ampere GMT-type fuse

conveniently

located

the

module's

front

panel.

1.10 The

6952

Echo

Canceller

Network

Interface

Module,

which is used in applications

where

maximum

end-path delays

not exceed 30ms, provides all re-

quired interfacingwith the

line(at

the

DS-1

level) and

performs all System timing functions (clock generation,

framing, and synchronization). If transmit synchroniza-

tion is lostdue

aproblem with

the

transmit-input PCM

line, ared

transmit

focaf LED on

the

front

panel lights. If

synchronization is lost at the channel bankwhose signals

are incoming

tothe

251 System(in whichcase

the

trans-

mit-input line indicates abit-2 alarm), ayellow

transmit

remote

LED lights. Asecond pair

front-panel LED's

providesidentical indications

forthe

receivechannel.

addition,

the

6952

contains

the

System's integral auto-

matic self-test subsystem

for

rapid

detection

and

iso-

lation of most System faults. With this subsystem, idle

channels

are

routinelysubjected

atest

sequence

that

on!! 251 SI/stem

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figure

Front detail

typical 251 System (Note:

Two

Systems, each containing the optional

6955

module, are

shown

the same

251

Assemby:)

page 2

practice section 81251

1.17 External connections

the

(DS-1) PCM

lines are normally made via wire-wrapping

terminal

blocks on the 251 Assembly's backplane. If desired,

however, the Assembly can be factory-equipped with

two

optional Tellabs 80-0121

Twinax

Connector

Panels

for concentric twinax connection of the

(DS-1) PCM lines

the Assembly. Each panel con-

tains four twinax connectors (Trompeter BJ77-type)

and serves one of the two Systems the Assembly can

accommodate. These panels are mounted on the

Assembly backplane via the same standoff posts

that

secure the CO equalizers; spacers provide the neces-

sary clearance between the panels and the equalizers.

means of aspecial printed-circuit backplane. As a

result,

neither

external

connections

individual

modules nor intermodule

connections

need be made.

Terminals on the backplane are provided

for

input

power and facility input and

output

connections. Two

versions of the 251 Assembly are available:

the

251A,

which mounts in a19-inch relay rack, and

the

251

which

mounts

in a23-inch relay rack. Each version

accommodates 12 modules (two complete 251 Sys-

tems)

and

occupies

four

mounting spaces

vertical

inches) in astandard relay rack.

1.16 The 251 Assembly is normally supplied with

four Tellabs

80-5078

Central

Office

Equalizer

sub-

assemblies

(two

per

251

System) factory-installed on

its backplane.These subassemblies provide the proper

amount

attenuation

limit

the

251 System's

transmit-output and receive-output signals (6 volts

peak)

no more than 3volts

peak

the

DX-1

cross-

connect

frame when

150

feet

(46

meters)

less of

cable

connects

the

251

System

the

cross-connect

frame. For

longer

cable runs,

two

direct-replacement

subassemblies that each provide less attenuation than

the 80-5078 are available. The Tellabs

9927

Equalizer

subassembly

is designed

for

cable runs of

150

450

feet

(46

137 meters), and

the

Tellabs

9928

Equalizer

sUbassembly

is designed for

cable runs of

450

650

feet

(137

198

meters).

1.13 The

6951

Echo

Canceller

Channel

Unit

Module

contains 12 independent convolution pro-

cessors and

their

associated timing-control circuitry.

Used in applications where maximum end-path delays 1.18 Although research indicates

that

voice-band

do not exceed 30ms, the 6951 performs the actual data can be transmitted

through

echo

cancellers

echo

cancellation for 12 of the

line's

channels.

without

degradation, the 251 System can, if desired,

Two 6951 modules are therefore required

every be equipped with an optional

6955

Echo

Canceller

251 System.

Tone

Disabler

Module.

This

module

is equivalent

tone

disablers used in

echo

suppressors and serves

1.14 The

6951A

Echo

Canceller

Channel

Unit

the entire

251

System, providing independent opera-

Module

is designed

for

use

place of the 6951 mod- tion

for

each

the

channels. Upon receipt of

ule in applications where maximum end-path delays nominal

2100Hz

digital disabling

tone

in any channel,

are as long as 60ms. While it is functionally similar to the

6955

causes all

echo

cancellation and residual-

the 6951, the

6951A

contains

convolution pro-

echo

suppression

cease

for

that

channel. Thus, the

cessors arranged

12 independent pal'rs, plus the,'r channel is rendered completely transparent; its trans-

associated timing and control circuitry. Each pair of

convolution processors serves 1of the

line's

mit-input PCM signals are not processed

but

simply

inserted into the correct time slots in the transmit-

channels, with 1processor of apair handling end-path output PCM bit stream. DIP

switches

the

6955's

delays of 0

30ms

and

the

other

handling end-path

delays of

60ms. Thus, as is

true

of the 6951 front panel allow each channel

be indiVidually

optioned so

that

echo

cancellation and residual-echo

module, one 6951Aserves 12 channels and, therefore, suppression

are

disabled only while

2100Hz

tone

two

6951A's are required

per

251 System. present

are disabled from the time

2100Hz

tone

1.15 The 251

Mounting

Assembly

is aTellabs received until the end

the

call (even if

tone

Type

Mounting

Shelf

that

is internally prewired by removed prior

the end of

the

call).

page 3

verifies

proper

operation of

their

convolution pro-

cessors and associated circuitry critical

echo can-

cellation. Any faults discovered result

local alarm in-

dications via an LED display on the System's control

interfacemodule.Thosefaultconditions

that

disablethe

System entirely, and

those

that do not disable the Sys-

tem but require immediate attention nonetheless, also

initiate relay operation in the

6953

module for remote

alarm indications.

1.11

The

6952A

Echo

Canceller

Network

Inter-

face

Module

is used in place of the

6952

module

applications where maximum end-path delays are as

long as 60ms. The

6952A

differsfrom the

6952

only

certain aspects of its EPROM software that allow the

6952A

operate in conjunction with

the

6951A

Channel Unit Module (see below).

New

system auto-

matic-self-test values

the 6952A's EPROM software,

for

example, ensure rapid detection and isolation of

6951A

channel failures.

1.12 The microprocessor-based

6954

Echo

Can-

celler

Control

Interface

Module

controls

and moni-

tors avariety of System functions. A

complement

six pushbuttons, seven

indicator

LED's, and an LED

window

display on

the

6954's

front

panel allows con-

trol

and

status information

for

the

System as awhole

and

for

its individual channels and subsystems

displayed

upon

demand; major and minor System

alarm indications are displayed automatically.

addi-

tion,

these

pushbuttons and LED's simplify

the

task

conditioning

the

251 System for aparticular applica-

tion

allowing both System and individual-channel

operating

modes

be programmed into memory

from

the

module's

front

panel. This memory is non-

volatile,

i.e.,

it retains all stored information in the

event of a

power

loss. Also available via

the

6954's

front

panel is manual override of most automatic Sys-

tem

control

functions. See paragraphs 2.05 through

2.13

for

details.

practice

section

81251

application

general

2.01 The 251 24-Channel Digital

Echo

Canceller

System is primarily intended

for

use on single-hop

and double-hop satellite circuits and long terrestrial

circuits with

(DS-1)

end

links. In such long-delay

circuits, the operating characteristics

conventional

echo suppressors may be objectionable,

thus

neces-

sitating the use of

echo

cancellers instead. Actually,

while the superior performance

the

251 System is

most noticeable on long-delay links, its insensitivity

total intermediate delay makes it suitable

for

nearly

all applications involving digital carrier. The 251 Sys-

tem cancels

echo

by adapting

each near-end

echo

path it encounters, and it can adapt

any near-end

path with an echo return loss (ERL)

greater

than

6dB

and amaximum round-trip delay (measured between

the System's receive-output and transmit-input ports)

of either

30ms

60ms, depending upon module

selection.

2.02 Atypical application of

the

251 System is

shown

figure 3. The primary cause

echoes

re-

ceived at

the

far

end

(B)

the

4wire-to-2wire voice-

frequency

(VF)

interface,

i.e.,

the

terminating

set, at

the near end

(A).

Signal reflections at

this

interface

are heard as

echoes

the

corresponding

far-end

channel. Because it is asplit-type

echo

canceller,

the

251

System at

the

near

end

actually

protects

the

far-

end receive channels from echo, and the far-end 251

System likewise protects

the

near-end receive chan-

nels from echo. This split-type configuration provides

effective

echo

control regardless of

the

total

delay

the intermediate transmission links.

6954

Echo

Canceller

Control

Interface

Mod-

ule

(one required

per

251 System).

6955

Echo

Canceller

Tone

Disabler

Module

(one

per

251 System is optional).

Issue

6900A

Blank

Type

Module

(one

per

251

System is optional when

6955

not

used).

network

interface

2.03 The 251 System interfaces

the

digital net-

work

directly

at the

(or DS-1) level and

thus

eliminates

the

need

for

per-channel echo-control

devices on

the

associated VF circuits. At

this

inter-

face level, both the transmit and

the

receive channel

of the 251 System accommodate multiplexed

input

signals

aserial stream at 1.544 megabits

per

second with segmented 1'-"255

companded

PCM

coding. (This is the

DS·1

bipolar alternate-mark-

inversion [AMI] signal format.)

2.04 The 251 System typically operates

con-

junction

with aD-type channel

bank

adigital toll

switch. In such applications,

the

251 System is nor-

mally located between a

DX-1

cross-connect frame

the

side toward

the

far

end

(i.e.,

the

satellite side)

and

another

DX-1

frame and

the

associated channel

bank

digital switch on the side toward

the

near

end

(i.e.,

the terrestrial side). An

arrangement

this

type

is shown in figure

Cabling

between

DX-1

cross-

connect

frame and aD-type channel

bank

must be

page

1.19 For any 251 System that does not require the

optional

6955

module, the Issue 2version of the

6900A

Blank

Type

Module

(Tellabs part number

826900A), which is also optional, can be used in place

of the

6955

to fill the empty module position

the

251 Assembly. The

6900A

helps

keep foreign mat-

ter

out

of the Assembly and also gives the System a

more attractive appearance.

addition, the Issue 2

version of the

6900A

can be used

silence external

alarms caused by removal of the System's

6953

mod-

ule from the Assembly. When the Issue 2

6900A

inserted into the module position from which a

6953

has been removed, aprojection at the end of the

6900A's

"pseudo

printed circuit board" opens the cut-

through module

connector

at that module position.

This causes both major-alarm and minor-alarm indica-

tions

cease. This feature is valuabie not only during

testing but also during installation of 251 Systems

prewired bays, in which case unwanted alarms can

result from module positions not yet equipped.

1.20 For reference purposes, the 251-System com-

ponents described above are summarized as follows:

251A

Mountin9

Assembly.

Twelve module posi-

tions, 19-inchrackmounting,equippedwith printed-

circuit backplane. Houses two complete 251 Sys-

temsand isfactory-equipped withfour

80-5078

Equalizer subassemblies(two per System).

*251 B

Mounting

Assembly.

Same as 251A except

23-inch rack mounting.

80-5078

Equalizer

subassembly

for

less

than

150

feet

(46 meters) of cable. Standard

equipment factory-installed on

251

Assembly

(four

80-5078's

per

Assembly).

9927

Equalizer

subassembly

for

150

450

feet (46

137 meters) of cable. Optional direct

replacement

for

80-5078.

9928

Equalizer

subassembly

for

450

650

feet

(137

198

meters) of cable. Optional direct

replacement

for

80-5078.

*80-0121

Twinax

Connector

Panels for concen-

tric

twinax connection of

(DS-1) PCM lines

251 Assembly. Optional, factory installed (two

per

Assembly).

*6951

Echo

Canceller

Channel

Unit

Module.

Serves 12 channels

applictions where max-

imum end-path delays do not exceed

30ms

(two

6951's required

per

251 System).

*6951A

Echo

Canceller

Channel

Unit

Module.

Takesthe place ofthe6951 andserves 12 channels

applications where maximum end-path delays

are as long as

60ms

(two 6951A's required

per

251 System).

6952

Echo

Canceller

Network

Interface

Mod-

ule. Used

applications where maximum end-

path delays do not exceed

30ms

(one required

per

251 System).

6952A

Echo

Canceller

Network

Interface

Mod-

ule. Takes the place of the

6952

applications

where maximum end-path delays are as long as

60ms

(one required per 251 System).

6953

Echo

Canceller

Power

Supply

and

Alarm

Module.

Operates from nominal

-48Vdc

input

(one

6953

required

per

251 System).

practice

section 81251

FAA

EHO(81

XMT XMT

OUT

251

XMTT1

LINE

24-CHAHNEil

ECHO

CANC:ELLEfIt

CHANNEL

SYSTEM

BANK

DlQITAL

SWITCH

RCVn

LINE B

SHORTiEND-PATH DIGITALCAARIER CIFlCUllS

NEAA·ENDVOICE·FREQUENCY

CIACUITS110F24CHANNEUit

\L-------------""DIG;;<;n

Al".nE1WO=ORvK

---'

130mB

MAXI"'UM)

2WtRE

TERM

@HO

XMT

SET

PAnt

4WIA£

F-1

XMTT1

LINE

2.,

24·C"AHHEL

ECHO

CANCELLeR

DIGITAL

SYSTEM

WITlI6951A'll

$WITCW

ANDIQS2A

DATER

2WIRE

TERM

@HO

4WI'RE

SET

PAnt

I~cv

i::c

RCVT1

LINE

OUT

LONG

END-PAlH A)

(8Oms

MAXIMU".

NEAR

END

(A)

figure

Typical application

251 System

ROM

END

UITS

XMT

OUT

DS-'

251

24-CHANNEL

ECHO

OX-,

CANCELLER

DX-'

SYSTEM OR

TO/F

DSX-' DSX-'

FAR-

X-CONN. X-CONN. CIRC

FRAME

RCVOUT

tRCV

DS-'

XMT

DS-' (

)

OOTYPE

CHANNEL

BANK

DIGITAL

SWITCH

TO/FROM

NEAR-END

CIRCUITS

2.06 The 251 System uses

the

basic

03-channel-

bank sequential channel-numbering scheme. With

this scheme,

the

channel

number

assigned

each of

the

T1-line (DS-1)

time

slots

the

same as

the

number of

the

time slot. Other types of channel banks,

however, use different channel-numbering schemes.

Table 1lists

the

channel-numbering

schemes

for

01 D

and

as well as

channel banks.

figure

Physical

connection

251 System

done

with

22-gauge

heavier

shielded

cable. With programmed via

the

6954

include

(1)

selection

the

22-gauge

cable, maximum

permissible

distance

be- data

transfer

rate (see paragraph 4.04)

for

the

remote

tween

the

DX-1

cross-connect

frame and

the

251

control/status

interface port,

(2)

automatic

blanking

System, including intraframe cabling in

the

DX-1

the

channel

display

after

a1-minute timeout, (3)

frame, is

650

feet

(198 meters). Where

this

distance

assignment of aSystem

unit

number

for

multiple

restriction

cannot

be met, heavier

cable

should

daisy-chained Systems, and (4) selection of one

six

used. In

extreme

cases, an intraoffice span

(Le.,

an in-

consecutive

self-test failures before

generation

of an

traoffice

repeater

line) can

used. In all applica- alarm.

tions,

separate

input and

output

cables must be used

between

DX-1

frames and

the

251 System.

system control

2.05 All

internal

System

control

functions

originate

in,

and all externally derived System

control

functions

are

handled through,

the

6954

Control Interface Mod-

ule.

Pushbutton

switches and LED's on

the

6954's

front

panel (see figure 2) provide

the

means

for

pro-

gramming

both

System and individual-channel oper-

ating

parameters

(in effect, optioning

the

System for 2.07 For each of

the

251 System's

channels, a

its

particular

application). These

codes

are

stored in a

number

control

inputs can be

entered

externally

special nonvolatile memory

that

retains all stored in-

(Le.,

via

the

6954's

front panel

via aremote

control!

formation

even if

power

the

251 System fails. After

status

interface [see paragraphs 2.11 and 2.12])

the

desired operating parameters are programmed, override certain internal

control

functions

normally

the

6954's

push

buttons

and LED's can be used to performed by

the

6954

in response

information

display

the

status

these

parameters

any time. contained in

the

transmit-input bit stream. As is

true

Specifically,

the

channe'

LED

window

and advance of all user-programmed System parameters, the status

pushbutton

are used

select

and display

the

chan- of each externally

inputted

control

function

can be

nel number, and the five control

and

two status

LED's

displayed at any time after the function

initiated.

indicate

the

selected

channel's status. The five push- The external control inputs

that

can be

entered

for

buttons

associated

with

the

control

LED's are used

each channel individually

override internal

control

the

indicated

functions.

Options

that

can be functions are as follows:

page

practice

section

81251

to hold its current contents. The

channel's

echo-

cancellation circuitry

and

residual

suppressor

still

operate normally, but the channel's convolution

processor(s) is prevented from adapting

changes in the end path.

Note:

self-testing is taking

place

the time the

Hhold

input

is entered, self-test failure

occurs

and

the 6954's

test

fail LED

lights

because adap-

tation is disabled

the Hhold input.

remote

control/status

interface

2.11 The 251 System can, if desired, be

controlled

from aremote location via a

remote

control/status

interface that uses aserial data

format

compatible

with EtA standard RS-232-C. The 251 System itself is

data terminal equipment (DTE), and

the

signals it pro-

vides are suitable

for

serial interface

with

either

data

communication equipment (DGE) or,

anull-modem

adapter is provided, with other

DTE.

All channel-related

control functions and status indications available via

the

6954

module's front-panel

switches

and LED dis-

plays are also available via

the

remote

control/status

interface.

2.10 For details on local configuration and status-

monitoring via the

6954

module's

controls

and indica-

tors, refer

section 4

this

Practice,

local

system

control.

2.08 For each channel, additional status informa-

tion derived from the

6954

module's internal control

circuits can also be displayed at any time via the

6954's

status LED's. This information consists of the

follOWing:

Channel's failure of self-test and subsequent re-

moval of the channel from service (status test fail

LED lighted).

Channel's

echo

cancellation disabled

for

any

the following reasons (status bypass LED lighted):

(1)

The channel is bypassed.

(2) The Hreset control input is activated

for

the

channel.

(3)

The channel is idle (on-hook) and therefore

has been automatically placed in

the

self-test

mode.

(4)

Atone-generated data-disable condition is

detected by the

6955

module,thuscausing

the

6954

module

automatically

generate

an H

reset control input for the channel.

2.09 When operating as astand-alone unit,

the

251

System monitors the channel-associated signal-

ing in

the

frame-6 and frame-12 signaling bits of both

the transmit and receive digital lines

determine

the

busy/idle

status of each channel. If desired (or if

channel-associated signaling is not present),

the

channel busy/idle status can be provided

externally

through the remote

control/status

interface, typically

from aprocessor-controlled toll switch (see para-

graphs

2.11

through 2.13).

251-System and

basic

03-bank

sequential

THine

channel-number

010

channel-

(08-11 assignments number number

time

slot (preferred) assignment assignment

11 1

2 2 13

3 3 2 1

,,14

5535

6615

7 7 ,9

8 8 16 15

9 9 53

10 10 17 19

11 11

12 12 18 23

"14 19 14

15 15

8 2

20 18

17 96

18 18

19 10

20 22 16

23 23

24 24 24

table

Channel-number assignments for T1-line

(OS-I) time slots

Bypass.

When

the

bypass

input

is entered, can-

cellation is disabled; the channel is routed around

the processing circuits and placed

the

self-test

mode. Self-test failures cause the

6953's

minor-

alarm relay

operate and

minor

alarm LED

light and also cause the

6954's

test

fail LED

light. The bypass input also lights

the

6954's

control

bypass and status bypass LED's.

Off

Hook.

When the

011

hook

input

is entered,

the

channel is placed in a

permanent

busy condi-

tion.

Continuous

echo cancellation takes place,

and self-testing is inhibited. Also, any existing test

fail and

minor

alarm indications

for

the channel

are cleared.

Bypass

plus

Off

Hook.

When abypass and an

011

hook

input are entered simultaneously, the

channel is completely removed from service. It is

routed around

the

processing circuits,

and

the

test fail and

minor

alarm indications

for

the

channel are cleared and inhibited.

Canceller

Only. When the canceller

only

input is

entered, the channel's residual suppressor is dis-

abled but its cancellation circuitry remains active.

Note:

self-testing is taking place

the time the

canceller

only

input

is entered, self-test failure

occurs

and

the 6954's test fail LED lights because

the residual

suppressor

checked

self-test.

HReset. When the Hreset input is entered, the H

the end-path impluse response) is zeroed, effec-

tively disabling echo cancellation

for

the channel.

The

Hreset input also lights the

6954's

status by-

pass LED.

Note:

self-testing is taking

place

the time the

Hreset

input

is entered, self-test failure

occurs

and

the 6954's test fail LED lights because can- 2.12 Figure 5shows

four

possible

remote

control/

cellation is

disabled

the Hreset input. status interface configurations.

configuration a,

Hold.

When the H

hold

input is entered, up- the control

center

is close enough

the

251 System

dates are inhibited so that the Hregister is forced to allow a

direct

RS-232-C connection. The maximum

page 6

practice

section

81251

OCE

da'sy-chain

...--

~b-Ie

(see flgure

251

SYSTEM

TERMINAL

COMPUTER

IOTEI

OTE

d,aisyot::h8in

+---c",ble

('See

figure-

r-------,

I I

TERMINAL

OR I

ICOMPUTER I

IOTEI

i--------l

I I

TERMINAL

ICOMPUTER I

IOTE)

I I

L_~TROL~~_~

+--..null modem

adapter

lsee figure til

standard

~S232C

eable

1------1

I I

TERMINAL

ICOMPUTER I

(OTEI

I I

L_~~CENTER_

251

Sy$lem

data

RS-232-C

nuU-modem Wiring

terminal

interface equipment

(OTE) (OTEf

25D 25D

signal connector connl;l!ctOf

s~gnal

FRAME

FRAM

GND GND

Jlrome

TXD

2ground 2

TXD

RXD

RTS

t:J

RTS

CTS

GND

OCD

ls.gna,

DCD

'='

ground

DTR

figure

Four

remote

control/status

interface configurations

data

link

are used

link

the

251 System

acontrol

center

located beyond the range of adirect RS-232-C

connection.

configuration c, four

251

Systems are

interfaced

with

the

control

center

via a

OTE

daisy-

chain cable (figure

7).

in configuration

the

range of

the

direct daisy-chained

connection

feet. In configuration d, the 251 Systems are inter-

faced

with

the

control

center

via a

OCE

daisy-chain

cable

(figure

8),

two

modems, and aprivate data link.

Contact

Tellabs' Applications Engineering Group

our

U.S.

Canadian headquarters

your

Tellabs

Regional Office

for

details on

other

special

interface

configurations.

2.13 For details on

the

remote

control/status

inter-

face protocol and on remote configuration and status-

monitoring procedures, refer

section

5of this Prac-

tice, remote system control.

automatic

self-test

2.14 The 251 System's self-test subsystem auto-

matically verifies proper operation of each channel's

convolution processor (and associated

support

cir-

cuits),

doubletalk

detector, and

update

control ci

figure

Null-modem wiring for connection to DTE cuits. The self-test

sequence

initiated

the

6954

recommended

range

for

direct

RS-232-C connec- Control Interface Module, which scans each channel

tion

50 feet. Anull-modem adapter, the wiring

regular 36ms intervals for on-hook/off-hook status.

which is shown in figure

interfaces

the

251 Sys- On-hook (idle) channels are marked available

for

test,

tern

(OlE)

with

the

control-center

terminal or com- and this information is passed to

the

6952

6952A

puter.

configuration b, two modems and aprivate Network Interface Module, which contains

the

self-

page 7

practice

section

81251

251 System 1RTS

251

System 2

RTS

CTS CTS

Rxe

TXD

GND

oeD

OTR

Rxe

TXD

GNP

oeD

OTR 5

1 3 278

remote control male

center

(PTE)

-connectors -

pin no

.•

FRAME

GROUND

TXQ

Rxe 3

RTS 4:J

CTS 5

GNP

OeD 8

DTR

tfemale

251

System N(up

32) RTS 0

CTS

AXe

TXD

GND DCD OTR 5

13 2 78

connector

figure

Daisy-chain

connection

multiple

251

Systems

DTE

251

System 1RTS

t:)

251

SyS1lml

2RTS

CTS CTS

Rxe

TXD

GND OCD OTR

Rxe

TXD GND DCD

OTR

1 3 278

modem

(DeE)

••

connectors-

pinno.~

FRAME

GROUND

TXO

t><:

Rxe

RTS 4

eSR 6

I--

GND

oeD

PTR

20 L.

251

System

(up

32)

RTS

CTS

RXO

TXD

GND

oCD

DTR

1327820

figure

Daisy-chain connection

multiple

251

Sysfems to

DeE

test

circuitry

and performs the actual testing. The test-

ing sequence, which takes approximately

750

milli-

seconds

per

channel, is halted

for

any channel that

goes off-hook during testing, while on-hook channels

continue

under

test until

the

end of the test sequence.

Test results are reported

for

only those channels that

have undergone

the

entire test sequence. Any chan-

nel that repeatedly fails aself-test activates aminor

alarm (see paragraphs 2.15 and 2.16) and causes a

channel alarm code

appear

the LED display on

the

6954

module.

alarms

2.15 When fault conditions are

detected

the

251 System, they are automatically classified as

minor

major, depending upon

their

effect

the

System. Both classes of alarms result in similar alarm

indications: lighting

the sysfem alarms

minor

major

LED on

the

front panel

the

6953

Power Sup-

ply and Alarm Module and lighting of

the

channel

LED display (indicating

the

affected

channel) and ap-

propriate

status

LED's on

the

front

panel of

the

6954

Control

Interface

Module. In addition,

each

the

two

alarm classes has

two

dedicated

pairs

form-C relay

contacts, both

which provide aclosure

for

an ex-

ternal indication (audible, visible,

both) when an

alarm occurs.

2.16

Minor

alarms are

generated

upon failures

single channels.

addition

initiating

the

afore-

mentioned LED indications and minor-alarm relay-

contact operation, failure

asingle channel causes

the

251 System

bypass

that

channel

that trans-

mission can still take place over

the

channel, albeit

with possible echo.

page 8

2.17 Major alarms comprise

the

following:

Loss of remote transmit or receive frame syn-

chronization (yellow transmit remote

receive

6952

6952A

module lighted). If frame syn-

chronization cannot be achieved in

3ms

less,

the aforementioned LED indications on the

6953

and

6954

modules are provided and major-alarm

relay-contact closure takes place. Also, the entire

251 System is bypassed so that transmission can

still take place over all

channels, albeit with

possible echo.

Loss

remote transmit

receive frame syn-

chronization (yellow transmit remote

receive

remote LED on

6952

6952A

module lighted). If

remote frame synchronization cannot be achieved

in the amount of time allotted,

i.e.,

if abit-2 aiarm

from

the

channel

bank

on the transmit-input or

receive-input line is detected, the aforementioned

LED indications on the

6953

and

6954

modules

are provided and major-alarm relay-contact closure

takes place. Also, the entire 251 System is

by-

passed

that

transmission can still take

ace

over all

channels, albeit with possibie echo.

Failure of 251-Assembly

input

power, faiiure of

the

6953's

power supply,

biowing of the 6953's

input-power fuse. If input power

the

251

Assem-

bly fails, if the 6953's power supply fails entirely or

cannot maintain System power within its regulated

limits,

the

6953's

front-panel 1V3-ampere fuse

blows,

the

power

LED on

the

6953

goes

off and

major-alarm relay-contact ciosure takes place.

(No

other

LED indications are provided.)

Failure of

the

6954's

microprocessor system. If

the

6954's

microprocessor system fails, the afore-

mentioned LED indications on the

6953

and

6954

modules are provided and major-alarm relay-con-

tact

closure takes place. Also, the entire 251 Sys-

tem is bypassed

that transmission can still

take place over all

channels, albeit with pos-

sible echo.

2.18 When

either

aminor

major alarm

not

caused

power

failure,

blown

fuse,

re-

moval

the

6953

from

its

module

position

occurs,

momentarily depressing the alarm

cutotf

pushbutton

the

6953's

front panel restores

the

corresponding

alarm relay

its normal state,

thereby

causing the

external alarm indications

cease. Aithough de-

pressing

the

6953's

alarm

cutoff

pushbutton clears

all external alarm indications, local alarm indications

(the lighted system alarms

major

minor

LED on the

6953

and

the

lighted LED display on

the

6954)

remain until the fault is cleared.

2.19 When

alarm caused by failure of input

power

the

251 Assembly, failure of the

6953's

power

supply, blowing of

the

6953's

input-powerfuse,

removal of the

6953

from its module position

occurs, the aiarm indications can only be cleared by

locating and correcting

the

problem.

tone

disabler

option

2.20 Should disabling of any of

the

251

System's

channels during voice-band data transmission be

deemed

necessary, the System can be equipped withpage 9

practice section 81251

an optional

6955

Echo Canceller Tone Disabler Mod-

ule. This single module serves

the

entire System, pro-

viding independent operation

for

each channel. Upon

detection in achannel of digital

2010

2240Hz

dis-

abling

tone

(at alevel greater than

-36dBmO)

either

both d'"ections of transmission, the module

disables that channel's echo-cancellation circuitry

and residual suppressor

that

the channel is com-

pletely transparent

all transmission. Aguard band

is used

prevent false operation of

the

6955

mod-

ule by

speech

signals. Three 8-position DIP switches

on the

6955's

front panel allow each channel

individually optioned so that disabling occurs only

while

tone

is present or so that disabling lasts from

the time

tone

detected

until the end

the call

(even if

tone

is removed

prior

the

end

of the call).

installation

inspection

3.01 Each component of the 251 24-Channel Echo

CancellerSystem,

i.e.,

all five modules(six ifthe

6955

used) and the

251

Mounting Assembly, should bevisu-

ally inspected upon arrival

find possible damage in-

curred during shipment. If damage is noted, aclaim

should immediately be filed with

the

carrier. If stored,

both the modulesandthe assemblyshou

beinspected

again prior

installation.

mounting

251

Assembly

3.02 The 251 AMountingAssemblymounts

astan-

dard 19-inchrelayrack, andthe251 B

Mounting

Assem-

bly mounts

astandard23-inchrelayrack. Each version

the

251 Assembly occupies 7inches of vertical rack

space. Ensure thatthe

251

Assembly is securelymount-

ed before proceeding to

central

office

equalizers and

installer connections below.

central

office

equalizers

3.03 The

251

Assembly is normallyshippedwith four

Tellabs80-5078Central OfficeEqualizersubassemblies

(one

for

the transmit

output

line and

one

for

the re-

ceive

output

line of each of the two Systemsthat the

Assembly can house) factory-installed on the Assem-

bly's backplane.

replace any of

these

equalizers

(e.g.,

if aTellabs

9927

CO Equalizer subassembly [for

150

450

feet

of cable between the System and the

DX-1

cross-connect frame) or aTellabs

9928

CO Equal-

izer subassembly [for more than

450

feet

of cable be-

tween the System and the

DX-1

cross-connect frame)

is to be used

place of an

80-5078

subassembly),

proceed as follows:

Remove and save the two Phillips-head screws

that secure the subassembly to its standoff posts

on the backplane. (If your

251

Assembly is

equipped with optional Tellabs 80-0121 Twinax

Connector Panels, remove and save the

four

Phillips-head screws that secure the twinax con-

nector panel covering the subassembly to be

replaced. Then remove and save not only the

panel itself but also the four spacers between the

panel and the subassemblies below

it.)

Unplug the subassembly

be replaced from its

five-pin

connector

(P4,

P5,

PIG, or

I).

Plug the new subassembly into the five-pin con-

nector.

practice

section

81251

and

two

25-pin

female

RS-232-C

connectors.

These

items

are

shown

figure

and

all

mandatory

and

optional

connections

asingle 251 System

are

sum-

marized

table

Detailed

wiring

instructions

and

complete

wiring

table

for

both

systems

in a251

Assembly

not

equ

ipped

with

twinax

connector

pan-

els

paragraphs

3.07

through

3.09. If

your

251

Assembly is

equipped

with

twinax

connector

panels,

make

all

connections

except

facility

(signai)

connec-

tions

and cable-shield

connections

directed

paragraphs 3.07

through

3.09;

then

proceed

para-

graph

3.10.

Note:

Before

making

any

connections

the

251

Mounting

Assembly,

ensure

that

power

off

and

modutes are

removed.

Modules

shoutd

inserted

into

their

Assembly

positions

onty

after

all

wiring is

completed. For easy reference

during

the wiring

pro-

cedure, table 3lists each

individual

connection

(both

mandatory

and

optional)

for

each

the

two

251 Sys-

tems

that

can

housed

in a251 Assembly. Acheck-

list

in the table's

rightmost

column

can

be filled

out

mandatory

connections:

power

inputs:

-BAT

(-44

to -56Vdc, filtered,

positive

ground

referenced)

+GND (input ground

[OVdc))

lines

(05-1

message

signals}(see

note

1):

ReV

IN T&R (receive input from far end)

ReV

OUT

T&R (receive

output

to near end)

XMT

IN T&R (transmit input from near

end)

XMT

OUT

T&R

(processed transmit output to far

end)

optional

connections:

power

inputs:

FRAME

GROUND

lines

(05-1

message

signals)

(see note

1):

RCV

(receive input cable shield)

ReV

OUT

(receive output cable shield)

XMT

(transmit input cable shield)

XMT

OUT

(transmit output cable shield)

alarm

outputs:

MINOR ALARM (Two form-C sets

minor-alarm relay

contacts

are

available)

MAJOR ALARM (Two form-C sets

major-alarm relay

contacts

are

available.)

remote

control/status

interface

connections

(made

via

25-pin

o-subminiature

RS-232-CIV.24 connector)

(see

note

2):

FRAME

GROUND

TXD

(transmit data output)

RXD

(receive data input)

RTS

(request to

send)

CTS

(clear to

send)

GND

(signal ground)

DCD (data

carrier

detect)

DTR

(data terminal ready)

Note

1: These

connections

can be made

either

directly

to the

251-Assembly

backplane

via wire-wrapping or to an

optional

Teflabs 80-0121 Twinax

Connector

Panel via

appropriate

cables.

Note

2: The

251

System's

remote

control/status

interface sig-

nals are

compatible

with EIA

standard

RS-232-C

electrical

characteristicS

and

are thus suitable

for

serial

interface

with

data

communication

equipment.

Secure

the

new

subassembly

its

standoff

posts

with

the

two

Phillips-head screws. (If

your

251

Assembly

equipped

with

twinax

connector

pan-

els,

replace

the

four

spacers

between

the

two

subassemblies

and

the

twinax

connector

panel

that

was

removed, reinstall

the

panel

over

the

subassemblies, and

secure

the

panel and sub-

assemblies

with

the

four

Phillips-head screws.)

installer

connections

(general)

3.04

Because

the

251

Assembly

prewired and

equipped

with aprinted-circuit backplane,

neither

ex-

ternal

connections

individual

modules

nor

intermod-

ule

connections

need

be made.

The

only

mandatory

external

connections

each 251

System

in a251

Assembly

are

follows:

Eight

facility

(signal)

connections,

consisting

one

tip

and

one

ring

connection

for

each

the

four

inpul/output

cables

accessing

the

System.

Unless

the

251

Assembly

equipped

with op-

tional

twinax

connector

panels (see paragraph

3.10),

these

connections

are

made

via wire-

wrapping

four

clearly

labeled

three-pin

terminal

blocks

the

Assembly's backplane.

Input

battery

and

ground

connections,

which

are

made

with

16AWG

heavier

wire

screw-type

terminals

on a

three-position

barrier

strip

the

Assembly's backplane.

3.05

Optional

external

connections

each 251

System

in a251

Assembly

comprise

the

following:

One

cable-shield

connection

for

each

the

four

facility

(signal)

inpul/output

cables. Unless

the

251

Assembly

equipped

with

optional

twinax

connector

panels

(see

paragraph

3.10),

these

are

made

via

wire-wrapping

the

same

three-pin

ter-

minal

blocks

used

for

facility

(signal) connections.

Input-power

frame

ground.

This

connection

made

with

16AWG

heavier

wire

the

same

three-position

barrier

strip

used

for

input

battery

and

ground

connections.

Connections

for

external

minor-alarm indications.

These

connections

are

made

via

wire-wrapping

asix-pin

terminal

block

the

251 Assembly's

backplane.

(Two

sets

minor-alarm relay con-

tacts

are

provided,

and

three

pins

are

used

for

each

set.)

Connections

for

external

major-alarm indications.

These

connections

are

made

via

wire-wrapping

asix-pin

terminal

block

the

251 Assembly's

backplane.

(Two

sets

major-alarm relay

con-

tacts

are

provided,

and

three

pins

are

used

for

each

set.)

Remote

controllstatus

interface

connections.

These

connections

are

made

via a

25-pin

female

D-subminiature

connector

arranged

for

RS-232-C

serial

interface

and

located

the

251 Assem-

bly's backplane.

3.06

Because

the

251

Assembly

can

house

two

separate

and

independent

251 Systems,

the

Assem-

bly's

backplane

contains

two

input-power

barrier strips,

two

sets

wire-wrapping

terminal

blocks

for

facility

(signal), minor-alarm,

and

major-alarm

connections,

page

table

Summary

mandatory

and

optional external

connections

251

System (made via

251-Assembly backplane)

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