Chapter 1 General Information
MX-2100/2104
Installation and Operation Manual
1-38 Application Considerations
When it is necessary to report an alarm condition, MX-2100 initiates the call set
up. After the destination answers, MX-2100 sends the complete contents of the
alarm buffer. Following the transmission of the alarm buffer contents, MX-2100
disconnects automatically.
To increase reporting reliability, MX-2100 enables the user to define the number
of dialing retries, and an alternate number, to be called in case the primary
number cannot be reached. If the call cannot be established, the full contents of
the buffer is sent the next time a call is set up.
System Timing Considerations
One of the critical requirements of data communications networks is timing
accuracy. The basic requirement is that all the equipment in the network must
operate at exactly the same clock rate or at an integer sub-multiple of the clock
rate. If this condition is not met, then from time to time bits transmitted between
two equipment units that operate at even slightly different clock rates will be lost,
or the same bit may be read twice. Such occurrences, that lead to the loss of bit
count integrity, are highly undesirable and may cause severe and periodic
disruptions in network operation.
Many networks use very accurate timing sources, such as atomic clocks, to provide
the primary timing signals to the main network nodes, e.g., telephone switching
offices, digital switches, etc. From the nodes, the timing is disseminated via the
communication links.
Since very accurate timing sources are often free-running, communication
equipment usually includes "elastic" buffers that absorb small timing differences. An
elastic buffer is a first-in first-out (FIFO) memory with separate write (input) and
read (output) clocks. For example, such buffers are inserted in the receive path of
the MX-2100 KML modules operating in the DTE or external DCE modes.
MX-2100 is designed to support reliable propagation of the timing information, by
allowing the selection of the appropriate timing mode in accordance with system
requirements and the type of main link interface module installed in the unit. The
following are the different main link interfaces with the available types of timing
modes:
•
With KML.1, KML.2, KML.3 and KML.4 modules, three main link timing
modes are available:
−
DTE
−
External DCE
−
DCE.
•
When operating in the DCE or external DCE modes, the timing of the main
link transmit clock can be locked to an external source (the external clock
signal supplied to one of the data channels), or derived from an internal
oscillator.
•
With KML.5 and KML.6 modules, two main link timing modes are available:
−
Internal
−
Loopback.
