12. Bandwidth on Demand
The SatLink System supports Bandwidth on Demand (BoD) based on the following modes:
Rate-based BoD using low jitter assignments
Volume-based BoD using immediate assignments, aiming at achieving good satellite resource
efficiency
A combination of the above two BoD modes, targeting a balance between good performance and
good efficiency
These BoD modes use the DVB-RCS capacity request categories on the Return Link:
Rate based (RBDC)
Volume based (VBDC) / Absolute Volume Based (AVBDC)
Please refer to [5] for a detailed description of the Return Link capacity request categories.
As mentioned in section 11 the VSAT supports four PHB / PHB groups:
Best Effort (BE) PHB
Critical Data (CD) PHB
Real Time Video Conferencing (RT-ViC) PHB group
Real Time Voice over IP (RT-VoIP) PHB group
Default factory configuration of the VSAT is to use the Best Effort PHB for all Return Link traffic and
utilize the Rate-based BoD mode. That is, the VSAT is pre-configured to request capacity from the
NCC/Hub using the RBDC request category. Normally, the Hub or ISP will issue new Service Level
Agreement parameters during the logon sequence and thus override the default settings.
The capacity requested by the VSAT and the capacity granted by the NCC to the VSAT on the Return
Link can be viewed using the CLI command dvb tx show –capacity.
Example:
# dvb tx show –capacity
Capacity parameters per channel:
Channel CRA[kbps] Allocated[kbps]
0 0 156
Requested capacity per QoS class:
Channel CRClass MaxRBDC[kbps] MaxVBDC[kB] RateReq[kbps] VolReq[octs] Description
0 0 512 1000 138 0 Best Effort
0 1 128 0 0 0 VoiP
0 2 400 55 0 0 ViC
0 3 50 0 0 0 Critical Data
In the example above, the NCC has not assigned any continuous rate capacity (CRA) to the VSAT. The
VSAT is authorized to request up to a maximum of 512 kbps Rate Based Dynamic capacity and to have a
maximum of 977 Kbytes of outstanding not yet granted Volume/Absolute Volume Based Dynamic
Capacity requested for the Best Effort PHB. Additionally, the VSAT is authorized to request Rate Based
Dynamic Capacity for the VoIP PHB Group, a combination of Rate and Volume Based Dynamic
Capacity for the ViC PHB group, and Rate Based Dynamic Capacity for the Critical Data PHB. In this
example the VSAT requested 138 kbps of capacity and was granted by the Hub NCC a total of 156 kbps.
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