Comtech EF Data SLM-5650A Vipersat - Manual (Page 101)

Appendix B - Automatic Switching B-3
Load Switching
Load Switching
Overview
There are three primary functional components involved in the load switching
process.
• Hub STDMA Burst Controller(s)—These are the Hub units that provide
the load switching detection mechanism for Remotes that are operating
within the shared channel(s). Hub units that can serve as controllers
include CDM-570, CDD-56X, and SLM-5650A.
• Remote InBand Modem/Routers—The Remote modem units provide
the load switch detection mechanism when operating in dedicated SCPC
return channel. These modems include CDM-570 and SLM-5650A.
• VMS—The Vipersat Management System provides the switched capacity
and resource control for each request generated by the components
described above.
Load Switching is the mechanism by which the Vipersat network switches a
Remote terminal based on traffic levels at the Remote. This mechanism controls
both the switch from STDMA to SCPC mode as well as switches for SCPC
capacity changes. The main components of load switching in a Vipersat system:
are the VMS (network management) and the Comtech modem/router. The VMS
component receives switch requests from the modem/router, and based on
policy settings and available resources, either grants or denies the request.
Within the modem/router component, load switching is managed at either the
Hub or the Remote, based on the current mode of operation. When a Remote is
in STDMA mode, load switching requests for that Remote are managed by the
Hub STDMA Controller. After a Remote has been switched to SCPC mode, it
manages its own switching (or Step Up/Step Down) requests.
Note: For Hub STDMA Controllers operating in either GIR (Guaranteed Infor-
mation Rate) or Entry Channel Mode, typical load switching is not the
mechanism that performs the transition from STDMA to SCPC mode
due to traffic load. In GIR mode, the Remote is switched to SCPC as
soon as the GIR threshold is reached. In Entry Channel mode, the
Remote is switched to SCPC as soon as the Hub receives the first
transmission from the Remote.
For both GIR and ECM, the event of switching from STDMA to SCPC
can only occur if the SCPC Switch Rate parameter is set to a value
greater than 0 (zero).
The basic concept for all load switching is that a running average of current
utilization is maintained, and when that utilization exceeds a preset threshold, a
NOTE