Comtech EF Data VMS v3.12.x Vipersat - Manual (Page 171)

Chapter 3 - VMS Configuration 3-71
MN/22156, rev 12 Network Manager Configuration
As a switch request is processed, it is compared to the Advanced Switching
table. If the requested data rate crosses a threshold where the higher-order
modulation actually becomes more bandwidth efficient, the switch request will
go up to the higher-order modulation at the lowest bit rate that exceeds the
request. Thus, it is possible that a higher bit rate can be granted while actually
utilizing less bandwidth resources.
For example, a site currently operating at QPSK 3/4 that generates a switch
request for 192 kbps will be switched up to 256 kbps at 8PSK 7/8, provided this
modulation and code rate was specified in the Advanced Switching table entry
for this switch point.
The following equations illustrate this scenario:
QPSK 3/4 @192 kbps @1.3 spacing:
Allocated Bandwidth = 192 x (1/2) x (1/.75) x 1.3 = 166.4 kHz
8PSK 7/8 @256 kbps @1.3 spacing:
Allocated Bandwidth = 256 x (1/3) x (1/.875) x 1.3 = 126.781 kHz
Roaming with Advanced Switching
A roaming remote (SOTM) can take advantage of the Advanced Switching
function when transitioning from one satellite beam to another. Switching tables
for a remote can be configured on a per satellite region basis and, upon entering
into a new service area, the remote forwards the designated table for that area to
the VMS. This dynamically updates the modulator transmission settings on each
transition.
Refer to the ROSS User Guide for additional details on the configuration and
use of the Advanced Switching feature in a roaming application.
Note: Site link power budgets must be in compliance to operate higher-order
modulation/code rates.
When using Guaranteed Bandwidth in conjunction with Advanced Switching,
there are important considerations which should be taken into account when
performing the configuration of these features. Refer to the section “Consider-
ations for Using Guaranteed Bandwidth with Advanced Switching” on
page 3-69.
NOTE