Hcc Configuration - Comtec CDM-840 Installation And Operation Manual

CDM-840 Remote Router
Appendix G
G.3.2.2.1 Tap Message
The TAP message is a standard UDP/IP multicast forward over the outbound channel with a
payload containing the following sections:
• Standard Vipersat Header (distinguishes TAP from other Vipersat messages)
•
Timestamp field (set by CDM-840 [at WAN interface] when TAP is received)
•
Aloha Channel Frequency Plan (Frequency, Data Rate, Modulation, and Coding)
•
Slot and Timing Control
•
Lists of CDM-840s with Assigned Slots (previous transmission succeeded / failed)
•
List of CDM-840s that have completed their handshake in the last cycle
As noted previously, receipt of a TAP causes all listening CDM-840s to synchronize internal
transmit timing clock in order to minimize collisions in the Aloha channel.
G.3.2.2.2

HCC Configuration

The TAP IP Address specifies the multicast address that all CDM-840s in the group use to receive
the TAP:
•
Timing as exposed to the user is message interval;
•
Total slot count that derives the Cycle Length is set in milliseconds;
• All other parameters are calculated based on current rate;
•
The Date Slot Size is fixed at 6, and VersaFEC Blocks and Preamble is computed in
milliseconds based on the specified data rate;
•
Guard Band is determined during terminal commissioning.
G.3.2.2.3 Hub Operation
After configuration and initialization, the HCC broadcasts the TAP message on cycle intervals
waiting for Aloha channel RID messages. Successful reception of the RID places the indicated
CDM-840 IP Address along with its ECM state flag (i.e., Online, Wait, or Offline) into the first
queued list. The controller checks the flag to determine next operation. If the ECM state is
Online, an SRS is assigned for next TAP processing.
•
The CDM-840 receives the TAP with its IP Address in the SRS list and, based on where its
place is in the sequential order, determines the slot assignment. By design convention,
assigned slots are at the end of the cycle and whatever remains is used for contention at the
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MN-CDM840
Revision 3