SatLink VSAT User Guide
Publication no. 101557
Copyright © 2009 – STM Group, Inc.
Page 69 (160)
12. Bandwidth on Demand
The STM 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 STM SatLink 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 STM SatLink 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 log-on sequence and, thus, override the default settings.
The capacity requested by the VSAT and the capacity granted by the NCC to the STM SatLink 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 capacity and was granted by the Hub NCC a total of 156 kbps.
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