Circuit priority and circuit preemption, Nominal call setup delay – Comtech EF Data MIDAS 4 System and Design User Manual
Page 58
System and Design Manual, Revision 2
3–16
Theory of Operation
Circuit Termination
The point-to-multipoint circuit termination could be initiated by:
• The MIDAS Controller, in response to operator action
• The traffic node, due to the following:
♦
User port command
♦
Traffic modem loses lock
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The point-to-multipoint circuit termination initiated by the MIDAS Controller
proceeds as follows:
1. The MIDAS Controller sends terminate messages to the Node Control
Modem at the transmitting traffic node and all the receiving traffic
nodes.
2. The Node Control Modem at the transmitting traffic node disables the
traffic modem transmit and acknowledges with a “path terminated”
message.
3. The Node Control Modems at the receiving traffic nodes disable the
traffic modem receive and acknowledge with “path terminated”
messages.
4. On receiving the acknowledgment to the terminate messages, the
MIDAS Controller releases the bandwidth and the traffic modems.
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Circuit priority and circuit preemption provide multiple grades of service to
the users.
The priority can be assigned on a per-circuit basis for pre-defined circuits
and/or per-traffic-channel basis. If both circuit-based and traffic channel-based
priorities are used, the higher of the two priorities is used to derive the priority
for a pre-defined circuit initiated from a traffic channel.
Based on priority, MIDAS supports:
High priority circuits,
Which can preempt normal-priority circuits if there is no
available bandwidth. Once established, they cannot be
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Only the modem losing lock will drop out. The circuit will only be terminated when
the last receiving modem reports loss of lock.