Owner manual

11
Switches SW1.1 SW1.2, SW1.3, SW 2.7 & SW2.8
These switches set the starting channel. The starting channel is
the first channel that carries valid data. This channel can be set to any
value between 1 and 24. If the starting channel is other than 1, then
the maximum possible bandwidth will be less than 1536 kbps. For
example, if the starting channel is set to be 12, then the maximum
bandwidth is limited to 13x64 kbps (channels 12~24), or 832 kbps. This
must be kept in mind when setting the starting channel. The Model
2711 will flash the ERR indicator LED if the switch setting is invalid.
Refer to section 5.1 for a more detailed explanation of the ERR LED
function.
T1 STARTING CHANNEL
T1 Starting Channel
SW1.3 SW1.2 SW1.1 SW2.8 SW2.7 (maximum value of n)
Off Off Off Off Off 1 (24)
Off Off Off Off On 2 (23)
Off Off Off On Off 3 (22)
Off Off Off On On 4 (21)
Off Off On Off Off 5 (20)
Off Off On Off On 6 (19)
Off Off On On Off 7 (18)
Off Off On On On 8 (17)
Off On Off Off Off 9 (16)
Off On Off Off On 10 (15)
Off On Off On Off 11 (14)
Off On Off On On 12 (13)
Off On On Off Off 13 (12)
Off On On Off On 14 (11)
Off On On On Off 15 (10)
Off On On On On 16 (9)
On Off Off Off Off 17 (8)
On Off Off Off On 18 (7)
On Off Off On Off 19 (6)
On Off Off On On 20 (5)
On Off On Off Off 21 (4)
On Off On Off On 22 (3)
On Off On On Off 23 (2)
On Off On On On 24 (1)
12
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 distance to the nearest
repeater. The telephone company providing the T1 service will advise
you of the required LBO setting.
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 network-is encoded. AMI reverses the polarity of consecu-
tive pulses. B8ZS is identical to AMI, except that, under certain circum-
stances, the alternate polarity rule is deliberately violated.
AMI: This stands for "Alternate Mark Inversion." The CSU/DSU
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.