Comtech EF Data SLM-5650A Vipersat - Manual (Page 57)

Chapter 3 - Using the Web Server Interface (WSI) 3-17
Vipersat Configuration
method for remotes with low latency requirements to re-enter the network once
power is restored.
Refer to Appendix B “Automatic Switching” for additional information on how
each of the bandwidth allocation modes functions and the parameters used to
calculate the commands for each mode.
Acquisition Mode
The SLM-5650A modem/router offers two modes of choice for the Hub BC to
obtain acquisition of—detect and lock onto—the burst transmission from each
Remote in the group: Standard and Long.
Figure 3-15 Hub STDMA Acquisition Mode
Standard mode uses an uncoded preamble signature and results in a shorter
Preamble Time:
Data Rate = 64 to 447 kbps Preamble = 30 ms
Data Rate > 448 kbps Preamble = 20 ms
Long mode uses a combination of uncoded and coded portions of the signature
that provides additional reliability, but results in a longer Preamble Time, as is
illustrated with the following two examples:
Data Rate = 256 kbps Preamble = 26 + 79 = 105 ms
Data Rate = 3 Mbps Preamble = 2 + 38 = 40 ms
Note that, as a consequence of a longer preamble, the time period available for
data transmission is lessened. However, this trade-off is acceptable in those
applications where the priority is given to increased reliability.
Standard mode is appropriate, for instance, when Entry Channel is used as the
allocation method. Long mode is appropriate for a Hub controller whose
Remotes are allocated larger slot sizes, and thus would suffer greater data loss
per burst cycle with acquisition failure.
Group ID
The STDMA Group ID number defines a group of equipment (both Hub and
Remote units) that will respond to the output of a single STDMA burst control-
ler. This group is addressable within a network which, in turn, is defined by the
Network ID number assigned to the SLM-5650A.