SWITCH SW2-1 LINE CODING: HDB3
(DEFAULT)
Use Switch SW2-1 to control the Network Line Coding options.
Set these options to be the same as the Line Coding given to you by
your Service Provider. If you are using two Model 2701s together as
short range modems, set both units to HDB3.
SW2-1
Line Encoding
OFF
HDB3
ON
AMI
OPTIONS: HDB3, AMI
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 an E1 network connec-
tion, 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
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equipment connected to the unit provides a minimally accept-
able pulse density. For this reason, there are advantages to
using HDB3 instead. AMI coding does not inherently account
for ones density. To meet this requirement, the user should
ensure that the data inherently meets pulse density require-
ments.
SWITCH SW2-2: CRC-4 MULTIFRAME
In framed mode, SW2-2 is used for CRC-4 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 transmitting unit.. When using
timeslot zero (TS0), excessive errors may cause loss of frame or loss
of sync. If CRC-4 MF is used, both units must be set for set for CRC-4
MF. Otherwise, the one using CRC-4 MF will detect loss of sync.
SW2-2
Option
Off
CRC-4 Disabled
On
CRC-4 Enabled
NOTE: When the data rate is set to 2.048Mb/s, then the unit is
forced into G.703 mode, and it transmits user data on all 32 time-
lots. There is no framing information; therefore, the CRC4 MF
(SW2-2) switch is ignored. In all other rate settings, the unit
employs G.704 framing; TS0 is reserved for signaling.
SWITCH SW2-3 DATA INVERSION
Set Switch S2-3 to determine whether or not the data stream from the
local DTE is inverted within the Model 2701 before being passed to the
G.703/G.704 network. An inverted data stream may be required when
you use the Model 2701 to communicate with a G.703 device (that
inverts the data) on the remote end. In typical installations, data inver-
sion is not necessary.
SW2-3
Option
Off
Data not inverted
On
Data inverted
SWITCH SW2-4: REMOTE DIGITAL LOOPBACK TYPE
The user can set this switch to select the type of remote loop that
will be initiated by the Model 2701. If set to V.54, the Model 2701 will
initiate a V.54 loop when Remote Loop is selected by the front panel
switches. If set to CSU, the Model 2701 will initiate a CSU loop when
Remote Loop is selected by the front panel switches.
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SWITCH SET 2 SUMMARY TABLE
Position Function Factory Default Selected Option
SW2-1
Line Coding
OFF
HDB3
SW2-2
CRC-4 multiframe
OFF
Disabled
SW2-3
Data Inversion
OFF
Data Not Inverted
SW2-4
V.54/CSU select
OFF
V.54 RDL loop
SW2-5
FPS enabled
OFF
Enabled
SW2-6
V.54 Response
OFF
Enabled
SW2-7
Not Used
N/A
N/A
SW2-8
Not Used
N/A
N/A
