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Line Coding: HDB3
(default)
Options: AMI, HDB3
HDB3: In this line coding, the transmitter substitutes a deliberate
bipolar violation when excessive zeros in the data stream are
detected. The receiver recognizes these special violations and
decodes them as zeros. This method enables the network to
meet minimum pulse density requirements. Unless AMI is
required in your application, HDB3 should be used whenever
possible.
AMI: Alternate Mark Inversion defines a pulse as a "mark,” a
binary one, as opposed to a zero. In a E1 network connection,
signals are transmitted as a sequence of ones and zeros.
Ones are sent as pulses, and zeros are sent as spaces, i.e.,
no pulse. Every other pulse is inverted from the previous
pulse in polarity, so that the signal can be effectively transmit-
ted. This means, however, that a long sequence of zeros in
the data stream will cause problems, since the NTU receiving
the signal relies on the signal to recover the 2.048 Mb/s clock.
If you must use AMI, you should ensure that the data terminal
equipment connected to the unit provides a minimally accept-
able pulse density. For this reason, there are advantages to
using HDB3 instead.
Clocking: Network
(default)
Options:
Network, Internal, External
Network: This is the most commonly used setting when connect-
ing to a carrier’s network. In this mode, the unit recovers the
clock from the received signal and uses it to transmit data. In
this way the unit remains synchronized to a master clock. In
campus applications, one of the units must be set to Internal
clock, and the other end is set to Network clock. At all times,
there must be only one clock source. Otherwise, clock slips
and framing errors and bit errors may occur.
Internal: This is commonly used in campus applications, where
the unit is not connected to the public telephone network
directly. In this mode, the unit uses the on-board oscillator as
the transmit clock source.
External: In this mode, the unit requires a clock signal from the
DTE via the external clock pin on the DTE interface connec-
tor. Most applications will use Network or Internal clock
modes.
Line Build Out: 120 Ohm
(default)
Options: 120 Ohm, 75 Ohm
120 Ohm: Use with 120 Ohm RJ-48C connector.
75 Ohm: Use with the 1001RCM11575 rear card. (Dual BNC
connectors)
CRC-4 Setting: Disabled
(default)
Options: Enabled, Disabled
CRC-4 Multiframe: CRC-4 Multiframe uses TS0 to carry CRC-4
information. It operates independently of CAS MF. When
CRC-4 is enabled, the unit monitors the incoming data stream
for CRC-4 errors. It transmits CRC-4 error counts to the trans-
mitting unit . Excessive errors may cause loss of frame or loss
of sync. If CRC-4 MF is used, both units must be set for CRC-
4 MF; otherwise, the one using CRC-4 MF will detect a loss of
sync.
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d
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