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Switches SW2.6 & SW2.5 Line Build Out
These switches are used to set the line build out (LBO). The LBO
controls the pulse shape and attenuation of the signal sent to the net-
work. The amount of LBO depends on the length of cable used on the
T1 side.
SW2.6
SW2.5
LBO
Off
Off
0 dB, 0-133 ft
Off
On
-7.5 dB
On
Off
-15.0 dB
On
On
-22.5 dB
Switch SW2.4 Line Coding
This switch is used to set the line code. There are two line coding
options available through the DIP switches: B8ZS and AMI. The line
code refers to the way that the signal-the sequence of ones and zeros
sent to the T1 equipment-is encoded. AMI reverses the polarity of con-
secutive pulses. B8ZS is identical to AMI, except that, under certain cir-
cumstances, the alternate polarity rule is deliberately violated.
AMI:
This stands for "Alternate Mark Inversion." The 2090
transmits data as a sequence of ones and zeros. Ones are
usually sent as pulses, and zeros as spaces (no pulse). In
order to maximize transmission range, every pulse is of the
opposite polarity of the preceding pulse. AMI does nothing
else. Maintaining network integrity requires a minimum pulse
density (ones desity) of the signal being transmitted on the
network. AMI does not inherently provide for this feature.
Thus, if a long sequence of zeros happen to be sent, the net-
work may suffer. To meet this requirement using AMI requires
one of two methods: Reduce the rate of each time slot (DS0)
to 56 kbps, so that the last bit can be used to guarantee the
minimum ones density. Or, make sure that the DTE sends
data in such a way that ones density is always maintained.
For this reason, B8ZS may be preferred over AMI.
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B8ZS:
This stands for "Bipolar 8 Zero Substitution." This line code
ensures minimum ones density. Long sequences of zeros are
specially encoded. This line code allows any data pattern to
be transmiited without causing ones density problems. Thus,
it allows the use of 64 kbps timeslots.
SW2.4
Line Code
Off
B8ZS
On
AMI
Switch SW2.3 Line Framing
This switch is used to set the frame. There are three framing
modes available in the Model 2090 Series: ESF, D4 and Unframed.
When SW1.8~SW1.4 are turned off, the unit is set to unframed opera-
tion, and SW2.3 is ignored. Otherwise, SW2.3 is used to set the frame
to either ESF or D4.
SW2.3
Frame
Off
ESF
On
D4
Line Framing Options
D4/Superframe: The D4 framing format, as specified in AT&T
TR62411 is the standard in which twelve frames make up a super-
frame. All signaling and synchronization is done in-band.
Extended Superframe: Extended Superframe, as specified in AT&T
TR 54016, consists of twenty-four (24) T1 frames. The framing bits are
now used for framing, CRC and the Facility Data Link (FDL). The FDL
allows maintenance messages and information to be passed between
the 2090 and the Central Office.
Note:
1. For unframed operation, 1544 kbps, set SW1.8,
SW1.7, SW1.6, SW1.5 & SW1.4 to OFF.
2. For unframed operation, SW2.3 is ignored.
