Comtech EF Data MIDAS 4 System and Design - Manual (Page 53)

System and Design Manual, Revision 2
Theory of Operation 3–11
Circuit Setup
A full duplex data circuit setup could be initiated by:
• The MIDAS Controller, due to
♦ Permanent circuit establishment by the MIDAS operator
♦ Activation of a pre-defined circuit by the MIDAS operator
♦ The passing of the start time for a scheduled circuit
• The traffic node, due to
♦ User port command
♦ RTS/DTR going active
♦ IP packet destination address matches CiM Modem route entry
A user
3
could request a data circuit via the user port by providing all the
required parameters, or it can request a pre-defined circuit by indicating the
pre-defined circuit identifier. A typical user-initiated circuit, where both the
traffic nodes have dedicated Node Control Modems, proceeds as follows:
1. The user requests a data circuit by specifying the destination, data rate,
encoding and modulation scheme, or a pre-defined circuit by specifying
the circuit ID through the user port.
2. The Node Control Modem formats a request message and forwards this to
the MIDAS Controller on the inbound control channel.
3. The request is validated by the MIDAS Controller. If the required
resources are available, the MIDAS Controller allocates bandwidth and
sends an assignment message to both the Node Control Modems.
4. Both the Node Control Modems configure the traffic modems and enable
the transmit and receive. They also respond with a status message
indicating the current traffic modem status. (If either Node Control
Modem reports a bad status, the MIDAS Controller terminates the
sequence.)
5. The data circuit is established when the traffic modems lock.
6. The user is informed of the progress of the data circuit setup through the
user port.
3 In this section, the term “user” excludes the NMS operator.