C-DOCSIS Service Flows
A Service Flow is a MAC-layer transport service that provides unidirectional transport of packets either to upstream
packets transmitted by the CM or to downstream packets transmitted by the CMTS.
A Service Flow is characterized by a set of QoS Parameters such as latency, jitter, and throughput assurances. In order to standardize
operation between the CM and CMTS, these attributes include details of how the CM requests upstream mini-slotsand the expected behavior of the CMTS upstream scheduler.
ServiceFlowID: exists for all service flows
SID Cluster Group: defines the set of SID Clusters assigned to a service flow. It only exists for admitted or active
upstream service flows.
ProvisionedQosParamSet: defines a set of QoS Parameters which appears in the configuration file and is presented
during registration. This may define the initial AuthorizedQoSParamSet allowed by the authorization module. The
ProvisionedQosParamSet is defined once when the Service Flow is created via registration.199
AuthorizedQoSParamSet: defines a set of QoS Parameters which define the maximum collection of resources that
a particular flow is authorized to use. Any subsequent flow requests will be compared against the
AuthorizedQoSParamSet. The AuthorizedQoSParamSet is communicated to the CMTS through a means other than
the configuration file.
AdmittedQosParamSet: defines a set of QoS parameters for which the CMTS (and possibly the CM) are reserving
resources. The principal resource to be reserved is bandwidth, but this also includes any other memory or timebased
resource required to subsequently activate the flow.
ActiveQosParamSet: defines set of QoS parameters defining the service actually being provided to the Service
Flow. Only an Active Service Flow may forward packets.
A Service Flow exists when the CMTS assigns a Service Flow ID (SFID) to it. The SFID serves as the principal
identifier in the CM and CMTS for the Service Flow. A Service Flow which exists has at least an SFID, and anassociated Direction.
Parameters and Classifiers associated with a Service Flow. As such it defines an "envelope" that limits the possible
values of the AdmittedQoSParameterSet and ActiveQoSParameterSet.
The ActiveQoSParameterSet is always a subset of the AdmittedQoSParameterSet which is always a subset of the
AuthorizedQoSParamSet.
To say that QoS Parameter Set A is a subset of QoS Parameter Set B, the following
MUST be true for all QoS Parameters in A and B:
• If a smaller QoS parameter value indicates fewer resources (e.g., Maximum Traffic Rate), A is a subset of B if
the parameter in A is less than or equal to the same parameter in B.
• If a larger QoS parameter value indicates fewer resources (e.g., Tolerated Grant Jitter), A is a subset of B if the
parameter in A is greater than or equal to the same parameter in B.
• If the QoS parameter specifies a periodic interval (e.g., Nominal Grant Interval), A is a subset of B if the
parameter in A is an integer multiple of the same parameter in B.
• If the QoS parameter is not quantitative (e.g., Service Flow Scheduling Type), A is a subset of B if the
parameter in A is equal to the same parameter in B.
In the dynamic authorization model, the authorized envelope (the AuthQosParamSet) is determined by the
Authorization Module. In the provisioned authorization model, the authorized envelope is determined by the
ProvisionedQoSParameterSet.
It is useful to think of four states of Service Flows:
Provisioned: A Service Flow in this state is known via provisioning through the configuration file, its
AdmittedQoSParamSet and ActiveQoSParamSet are both null.
Authorized: A Service Flow in this state is known to the CMTS via an outside communication mechanism, its
AdmittedQoSParamSet and ActiveQoSParamSet are both null. Authorized service flows are not normally
communicated to the CM.
Admitted: A Service Flow in this state has resources reserved by the CMTS for its AdmittedQoSParamSet, but
these parameters are not active (its ActiveQoSParamSet is null). Admitted Service Flows may have been
provisioned or may have been signaled by some other mechanism. Generally, Admitted Service Flows have
associated Classifiers, however, it is possible for Admitted Service Flows to use policy-based classification.
Active: A Service Flow in this state has resources committed by the CMTS for its QoS Parameter Set, (e.g., is
actively sending MAPs containing unsolicited grants for a UGS-based service flow). Its ActiveQoSParamSet is nonnull.
Generally, Active Service Flows have associated Classifiers, however, it is possible for Active Service Flows
to use policy-based classification. Primary Service Flows may have associated Classifiers(s), but in addition to any
packets matching such Classifiers, all packets that fail to match any Classifier will be sent on the Primary Service
Flow for that direction.
An inactive service flow may or may not have associated Classifiers. If an inactive service flow has associated
Classifiers, the Classifiers MUST NOT be used by a CM or CMTS to classify packets onto the flow, regardless of
Classifier Activation State.