Comtech EF Data CDM-570/570L Vipersat - Manual (Page 47)

Chapter 3 - Using the Command Line Interface (CLI) 3-11
Vipersat Configuration
1 – Fixed
In the Fixed mode, all remotes have the same data slot size regardless of type of
traffic or load. This mode minimizes the amount of jitter between remote trans-
mission times, and is useful for tuning STDMA as well as for troubleshooting
purposes.
2 – Dynamic Slot
In the Dynamic Slot mode, slot size is adjusted each cycle depending on the
activity during the previous cycle. The slot size for each remote is computed
based on the time (at the current data rate) needed to transmit all the bytes in
queue. If the result is less than the minimum slot size or more than the maxi-
mum slot size, the slot is adjusted accordingly. This mode allows the burst
controller to provide additional slot time in the cycle to remotes with higher
traffic demands, increasing throughput and alleviating congestion.
3 – Dynamic Cycle
In the Dynamic Cycle mode, available bandwidth is allocated to remotes
proportionally based on their current bandwidth needs. The bandwidth require-
ments are determined by the number of bytes in queue for each remote divided
by the total number of bytes in queue for all remotes, and results in the percent-
age of bandwidth to allocate for each remote. This mode provides improved
efficiency of STDMA due to faster cycle times during periods of light traffic
demands, thus providing minimum latency for the current load.
4 – GIR
In the GIR mode, the initial computed slot size value is the same as in the
Dynamic Cycle mode except there is no maximum limit. After all remotes have
been assigned slots, the burst map is checked to see if the total cycle length
exceeds one second. If not, then all requirements are satisfied and the burst map
is complete. However, if the cycle is greater than one second, then the slots are
adjusted proportionally so that all remotes receive at least their guaranteed rate
plus whatever excess is still available.
GIR mode allows guaranteed information rates to be set for each remote in the
group. When the one second restriction is exceeded, remotes without a specified
GIR are reduced to the global minimum slot size and the remaining bandwidth
is distributed to remotes that have been assigned a GIR rate, thus ensuring addi-
tional bandwidth for these units when needed.
Note: GIR allocations are restricted so that assigned GIR totals cannot exceed
the available bandwidth. This ensures proper bandwidth allocation when
the network is overloaded.
NOTE