User guide

Appendix F - Automatic Switching F-3
Load switching
Bandwidth Allocation and Load Switching by the STDMA
Controller:
As part of normal STDMA processing, the hub monitors the traffic levels from
each of the remotes for which it is allocating bandwidth. This is done using the
STDMA ACK management message (Table 1) which is transmitted at the
beginning of each burst from the remote. The STDMA ACK contains two
metrics that are used by the hub:
1. The number of bytes received for transmission (Queued Bytes) since the last
cycle.
2. The number of bytes currently waiting to be transmitted (Bytes In Queue).
These metrics are used by the hub for 3 purposes:
1. Determine the amount of STDMA bandwidth (slot size) to allocate in the
next cycle.
2. Provide statistics of the amount of activity at each remote (Average Bytes
Received).
3. Determine if a load switch is needed.
Table F-1STDMA ACK Message
If there is adequate upstream bandwidth available, the values of these two
metrics will be the same. However, if there is not enough bandwidth to satisfy
Data
Type
Size in
Bytes
Description
Unit of
Measure
Notes:
IP 4 IP address of
Remote
N/A Used by remote to
identify itself
Unsigned 4 Queued Bytes Bytes Total number of bytes
queued since last cycle
(includes possible buffer
overflow)
Unsigned 4 Bytes in Queue Bytes Number of bytes
currently queued
Unsigned 1 Group Number N/A
Unsigned 1 Dropped Buffers Packets Number of packets
dropped (due to limited
bandwidth)