Comtech EF Data Vipersat CDM-570 User Manual page 107

3. The STDMA Hub Controller compares the remote CDM-570/570L's pre-
4. If the buffer status continues to exceed the preselected limits, the STDMA
5. The VMS processes the switch request by checking for available resources
• Determining if there is a free demodulator.
• Determining the channel space (bandwidth) requirements to accommodate
6. If the VMS finds available resources it processes the switch request and
The ideal condition being looked for is that about 90% utilization of the
channel be achieved striving to optimize the use of available bandwidth.
In the case where the remote CDM-570/570L continues to report buffer
overflow, the STDMA Hub Controller will send a request to the VMS which
in turn will attempt to double the carrier bandwidth for that channel.
The ability to actually accomplish this is limited by the currently available
carrier bandwidth, and ultimately the power output and antenna size available
at the transmitting remote site.
If the STDMA Hub Controller cannot make the increase in bandwidth, it will
continue to receive buffer status reports from the remote CDM-570/570L
indicating that buffer flow is continuing and the STDMA Hub Controller
will, in turn, continue to request additional bandwidth from the VMS. If at
any time another service drops making bandwidth available, the next time the
STDMA Hub Controller requests additional bandwidth the VMS will grant
the request.
If the video data stream is completed before the switch in bandwidth is done,
the channel is closed, the bandwidth which had been used is made available
again to the pool, and no further action is taken.
A p p e n d i x A u t o m a t i c S w i t c hi n g
B -
selected buffer limits with its buffer status and if the buffer status exceeds
the preselected limits the STDMA Hub Controller increases the time-slot
allocated to that channel. If this brings the buffer status within established
limits no further changes are made.
Controller sends an Automatic Switch Request (ASR) to the VMS.
by:
the data flow requested by the STDMA Hub Controller.
sends tuning commands which switches the remote CDM-570/570L out of
STDMA into SCPC mode.
L o a d S w i t c h E x a m p l e
B-9