WaveRider LMS4000, User Manual

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3 Detailed Description
APCD-LM043-4.0 39
Grade of Service (GOS)
In the Polling MAC, the grade of service (GOS) determines how often, and when, an
associated EUM is polled. Since the EUM can only send one packet each time it is polled, the
data rate is related to the polling rate.
Operational objectives that are factored into the determination of the basic polling rate include
the following:
• Maximize overall user capacity and minimize the overhead related to empty polls.
• Accommodate different types of data; for example, short, bursty data, such as email
and browsing, and large file transfers.
• Support differentiation of user classes in terms of committed information and
maximum burst rate throughput levels.
• Control packet latency to support interactive services such as VoIP and chat.
• Support both symmetrical and asymmetrical data applications.
• Control unauthorized web hosting or gaming applications.
• Support multi-user network applications at a single EUM
To accommodate these often-conflicting operational objectives, WaveRider has designed a
patented Polling MAC layer that incorporates an integrated GOS management algorithm.
Within this algorithm, a total of 11 GOS parameters (GOS parameter set) are controlled to
achieve specific performance objectives.
To maximize the performance of the GOS algorithm, and therefore Polling MAC, control of the
following factors is key:
• Delay between packets transmitted to (or from) an EUM
• Relative weighting of different GOS classes
• Determination of when an EUM is active or inactive.
Manipulating these factors through the GOS parameter set can provide
• differentiated levels of service to end-users, which are defined in terms of average
committed and maximum burst throughput rates, and
• other special service classes.
The polling algorithm controls packet rates and timing, which in turn provide varying data
throughput in kbps, depending on the packet sizes for a given application.
GOS classes are defined based on particular combinations of the GOS parameter set. The
system operator assigns a GOS class to each EUM, and the CCU gets the EUM's polling
parameters from that class.