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System Overview
ENTERING AN AGGREGATE RATE
When creating an aggregate configuration, you should always enter the aggregate rate before con-
figuring channels. Once an aggregate rate is entered, the selected and measured aggregate rates
appear below every channel parameter display:
SELECTED AGGREGATE RATE 2.048 MHZ
EST. REMAINING BANDWIDTH 1.54082 MHZ
MEASURED AGGREGATE RATE 2.048 MHz
Aggregate bandwidth is the number of bits, expressed in bits per seconds, that are transmitted
through the aggregate link. The aggregate bandwidth is equal to the aggregate data rate; the ag-
gregate bandwidth is composed as follows:
Aggregate Bandwidth = Sum of Channel Baud Rates + Overhead Bits
Overhead bits include the AUTO FRAME CHANNEL (the AUTO FRAMES at each node com-
municate by transmitting through a reserved channel 0 in the TDM system), overhead bits that
maintain synchronization and exchange status information between TDM nodes, and control bits
that continually report the status of each channel's control signals. In a T1 system, 192 kilobits
are reserved to meet overhead requirements for the link.
When you enter the aggregate rate through the supervisory port CRT, that rate is reported as the
SELECTED AGGREGATE RATE. The REMAIN-ING BANDWIDTH figure indicates the
amount of aggregate bandwidth that is not yet used by configured channels. Each time you spec-
ify the baud rate of a channel being configured, the baud rate is subtracted from the REMAINING
BANDWIDTH figure. The REMAINING BAND-WIDTH figure is already adjusted for the
overhead bandwidth required for system operation; any bandwidth reported there may be used in
con-figuring more channels.
Example
You are configuring a system with an aggregate rate of 1.544 MHz; the channel parameter display
reports remaining bandwidth of 50 kHz. This means that you can configure four channels at 9600
bits per second each, assuming that you have four data channels available.
If you attempt to configure a system with the sum of channel baud rates higher than the aggregate
rate, the REMAINING BANDWIDTH figure becomes a negative number. You will not be al-
lowed to save the configuration, or exit from the Modify Channel Parameters routine. The fol-
lowing message will be displayed:
ILLEGAL CONFIGURATION
Y ou m u st delete configured channels u ntil the R E M A IN IN G B A N D W ID T H figu re is a positive num ber.
Avoid system configurations that reduce the EST. REMAINING BAND-WIDTH figure to zero;
this can create configurations with very few overhead bits, and cause channels to be dropped.
The TDM measures the aggregate clock timing signal when power is applied to the node. The
frequency of the timing signal is reported as MEASURED AGGREGATE RATE. You cannot
change this aggregate rate of the TDM through the supervisory port; the Clock Generator Plus
module is programmed to supply a specific aggregate rate, and requires program plug rewiring to
change the rate. You are allowed to configure a system with a selected aggregate rate different
from the actual (measured) rate; this feature is useful if you want to configure a system in advance
of the required hardware changes, or experiment with configurations at different aggregate rates.
2-7
036R660-000, Issue 10
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