Q-Flex Satellite Modem Installation and Operating Handbook
7-23
7.8.9 Traffic Shaping
Traffic shaping provides greater control over the management of data within the modem.
Specifically it provides a guaranteed quality of service for defined IP data streams. It is
aligned with all of the major quality of service schemes and can be used to extend
terrestrial services over satellite to create fully provisioned end-to-end services, thereby
providing direct support for the implementation of customer service level agreements. Key
time-based performance metrics are gathered continuously by the modem and can be
extracted in order to be assimilated into customer quality of service reports.
A satellite modem in general normally acts as a transparent pipe for data, so the data that
is finally received at the destination on the terrestrial network at the far end of the link is
identical to that which has been supplied to the local modem for transmission over satellite.
This is not necessarily true for IP data. Being packet based, IP naturally supports
multiplexing of different data streams. These streams often have different inherent priority
levels and competing demands for bandwidth. What is transmitted over satellite often
requires careful management, both in terms of what is actually sent (versus what is filtered
out) and in relation to the order in which packets from different streams are sent (i.e. the
relative priority levels of packets from different streams and the effect this has on packet
jitter).
Traffic shaping essentially controls these two key aspects of traffic management, namely,
access to satellite bandwidth and the level of delay and jitter that is experienced.
The Paradise traffic shaping feature is controlled via the modem web user interface under
Edit->Unit->Advanced->QoS
.
7.8.9.1 Guaranteed Bandwidth
The allocation of bandwidth to a classified data stream can be controlled via the
Edit->Unit-
>Advanced->QoS
tab of the web user interface.
The
Commited Information Rate
(CIR)
is the guaranteed bandwidth, in bits per second
(bps) that will be allocated to the specified data stream. This is the level of bandwidth that
is guaranteed under all normal circumstances where the equipment is operating correctly.
The sum of all CIRs for all classified data streams cannot be more that the transmission
data rate of the modem.
7.8.9.2 Maximum Bandwidth
If excess bandwidth becomes available at any point (i.e. one or more streams do not
require their allocated bandwidth), or some of the overall bandwidth has not been allocated
to any particular stream, then it is not wasted and it can be allocated in a controlled manner
between potentially competing streams.
This setting is called the
Burst Information Rate
(BIR)
specified in bits per second (bps).
It defines the maximum amount of bandwidth, beyond the guaranteed bandwidth, that a
stream should be allocated, should spare bandwidth become available. Each BIR should
not be greater than the transmission data rate of the modem.
