Table of Contents
Advertisement
G e n e r a l
meet their QoS and cost requirements within their bandwidth allocation. The
result is a stable satellite network connection that automatically responds to the
customer's requirements while continuously monitoring and reacting to chang-
ing load, data type, and QoS requirements.
Bandwidth Allocation and Load Switching
Load Switching is the mechanism by which the Vipersat network switches a
Remote terminal from STDMA to SCPC mode based on traffic levels at the
Remote. There are two components of load switching in a Vipersat system: the
VMS (network management) and the CDM (Comtech Data Modem). The VMS
component receives switch requests from the CDM, and based on policy
settings and available resources, either grants or denies the request. Within the
CDM 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 for that Remote is 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.
The basic concept for all load switching is that a running average of current
utilization is maintained, and when that utilization exceeds a pre-set threshold, a
switch is initiated. The data rate for the switch is computed by determining the
current bandwidth requirement of the Remote, and adding some percentage of
excess margin. The main difference between switching from STDMA to SCPC
and adjusting within SCPC is that in STDMA mode, the current available band-
width is constantly changing, while in SCPC mode, it is constant between
switches. Furthermore, switches from STDMA to SCPC mode are always
caused by the traffic level exceeding the switch threshold. Within SCPC mode,
switches can be caused by traffic exceeding an upper threshold or dropping
below a lower threshold. However, in both cases the new data rate is based on
the actual traffic requirements adjusted up by the margin percentage. Also,
based on policies set in the VMS, if a Remote requests less than some threshold
amount of bandwidth, the Remote is put back into STDMA mode.
Note: If the Hub STDMA mode is GIR (Guaranteed Information Rate) or
NOTE
B-2
Entry Channel, normal load switching is automatically disabled.
In GIR mode, the Remote is switched to SCPC as soon as the
GIR threshold is reached, if there is a switch rate defined. In Entry
Channel mode, the Remote is switched to SCPC as soon as the
Hub receives the first transmission from the Remote.
V i p e r s a t C D D - 5 6 X S e r i e s U s e r G u i d e
Advertisement
Table of Contents
