Tellabs 251 Manual

7te11abs
technical manual
76-81251
rev B
practice section 81251
©Tellabs, Inc., 2 November 1982
all ri9hts reserved, printed in USA
251 24-Channel Digital Echo Canceller System
figure 1. 251 24-Channel Digital Echo Canceller System
(two Systems shown in same Mounting Assembly)
for channel idle/busy status, or it can be controlled
from a manual control panel or from a remote control
and status interface that uses a serial data format
compatible with EIA standard RS-232-C.
1.02 This Practice section is revised to incorporate
the information formerly contained in the 251 Practice
Supplement dated 1 June 1983 and also to provide
information on two optional modules that allow the 251
System to operate on circuits with a maximum end-path
delay of 60ms (instead of 30ms).
1.03 The 251 System is intended for use near the
end points of digital carrier facilities characterized by
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 by signal reflections
at impedance discontinuities and interface points
such as 4wire-to-2wire interfaces.
1.04 Because it is a split-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 to transmission delays on
intermediate carrier links and therefore allows the
System to operate effectively regardless of the dura-
tion of these delays. Thus, the 251 System is well
suited for a broad 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 or via-net-Ioss (VNL) designs may be un-
desirable.
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general description
application
section 8
section 9
contents
section 1
section 2
general
network interface
system control
remote control/status interface
automatic self-test
alarms
tone disabler option
section 3 installation
inspection
mounting of 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 of multiple 251 Systems
module insertion
initial power-on sequence
self-test checkout
section 4 local system control
system operating parameters
channel operating parameters
section 5 remote system control
remote interface protocol
remote control commands
command examples
section 6 system circuit description
section 7 module and system
block diagrams
specifications
testing and
trOUbleshooting
1. general description
1.01 The 251 24-Channel Digital Echo Canceller
System (figure 1) is an adaptive, split-type echo-
control system that directly interfaces 1.544-megabit-
per-second digital carrier facilities (commonly called
TI facilities) at the DS-1 level. The 251 System pro-
vides individual echo control for all 24 of a T1 facil- 1.05 A signal in the receive path of any of the 24
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 to begin an adaptation process known as
as a stand-alone system by monitoring the signaling convergence. During convergence, a digital signal-
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