Lucent Technologies MERLIN LEGEND Release 7.0 Feature Reference page 585

MERLIN LEGEND Communications System Release 7.0
Feature Reference 555-670-110
Features
Primary Rate Interface (PRI) and T1
ZCS line coding monitors each DS0 channel and prevents strings of eight or more
zeros. Upon detecting eight consecutive zeros in a channel octet, ZCS line coding
forcibly changes the seventh zero (the second least significant bit) to a one. The
factory-set line coding is ZCS.
B8ZS line coding matches the ones-density requirement by using a special
sequence with a bipolar violation in bit positions 4 and 7. Normally, for bipolar
transmission, ones are encoded alternately as a positive then negative, or
negative then positive, pulse. If two positive or two negative pulses are received in
succession, a bipolar violation occurs. Bipolar violations are normally caused by
noise hits to the signal; however, B8ZS uses a specific binary sequence with
bipolar violations as a code for an all-zero channel octet.
B8ZS line coding is preferred over ZCS because it provides no possibility of
corrupting data transmissions.
B8ZS violations are passed by the ACCULINK™ 3150 and 3160/3164, and
ESF T1 channel service units (CSUs) but not by other CSUs.
Channel Service Unit
The channel service unit (CSU) is the interface between the 100D module and the
DS1 facility provided by the telephone company. This facility contains 24 channels
on one 4-pair wire.
The CSU is a hardware component needed when two endpoints are located in
different buildings or when the distance between the two endpoints makes office
or line repeaters necessary. The CSU is located on the customer's premises and
is used to connect the system to DS1 network facilities. The CSU has the
following functions:
It terminates an outside DS1 facility on the 100D module.
It ensures that the signals entering the public network comply with the
requirements of the DS1 facility as specified by the FCC.
It includes maintenance, diagnostic, and testing capabilities.
NOTE:
Verify that any CSU on the DS1 circuit between the MERLIN LEGEND
Communications System and the PSTN is programmed for the same
framing as the DS1 slot on the MERLIN LEGEND Communications
System.
There are several channel service units: ACCULINK 3150 and 3160/3164 ESF T1
CSUs, ESF T1 CSU (no longer available but still supported), and 551 T1 L1 CSU
(no longer available but still supported). The ACCULINK 3150 or 3160/3164
CSUs are recommended for this system because they allow maintenance without
Issue 1
April 1999
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