Motorola BSR 2000, Руководство по настройке и управлению

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Release 1.0 Configuring the CMTS
526360-001-00 Rev. B MGBI 6-97
Service Classes
The concept of service classes implies assigning service flows to a service class and
providing all flows belonging to that class with a defined quality of service. DOCSIS
1.1 has defined a set of QoS parameters, including maximum sustained and minimum
reserved traffic rates, and a way for associating specific QoS parameter values to
service flows. DOCSIS 1.1 has further incorporated the concept of a service class
name so that service flows, when being created, may be assigned their QoS
parameters by referencing a service class name. The Service Level Classes with
Maximum Assigned Bandwidth feature has extended the DOCSIS definition of a
service class by introducing additional service class parameters for maximum
assigned bandwidth, over-booking, and class-based scheduling priority. Service
classes are supported for both downstream and upstream directions.
Maximum Assigned Bandwidth
Maximum Assigned Bandwidth (MAB) specifies the amount of bandwidth a service
class is permitted to consume on an interface. It is expressed as a percent of the total
interface bandwidth capacity. The MAB of a service class is applied during admission
control to determine whether to admit a new service flow and again by the scheduling
algorithms to provide a class-based weighting to the scheduler. Any unused portion of
a class’ bandwidth may be used ‘on demand’ by other classes which have a traffic
load in excess of their own MAB.
Overbooking
Since not all service flows are active simultaneously the service level classes feature
permits customers to overbook service classes. Overbooking means admitting service
flows to a service class such that the sum of their guaranteed minimum reserved rates
are in excess of the configured MAB for the service class. A configurable
overbooking factor is provided by the service levels classes feature to control the
amount of overbooking. This parameter is called the Configured Active Percent
(CAP). The CAP is an estimate of how many service flows, expressed in percent, are
likely to be active simultaneously. For example, if the CAP for a service class is set to
20 percent then it is estimated that only 20 percent of the service flows belonging to
that class will be active simultaneously. Therefore, 5x (1 / 0.2) overbooking would be
allowed. A CAP of 100 percent means that no overbooking will be allowed. A CAP of
zero percent means that unlimited overbooking is allowed.