Rec. ITU-T G.987.3 (10/2010) – Prepublished version 18
CRR
i
i
A
i
F
≤+
(7-3)
where the summation is over the set of all upstream or downstream traffic flows on the PON, and C
is the capacity of the upstream or downstream interface, respectively.
The specified general form of traffic descriptor allows support of both rate-based service disciplines
and priority-based service disciplines. By setting certain descriptor components to zero (rate
parameters) or identical values (priority and weight parameters), the system operator can effectively
specify the required service discipline. The upstream and downstream traffic flows may be specified
with different subsets of descriptor components. In particular, the fixed bandwidth parameter is
important in a distributed scheduling environment, where it serves to mitigate the communication
latency between the network elements hosting, respectively, the scheduler and the traffic queues,
and may not be applicable in the downstream direction where scheduling is centralized.
If necessary, two or more traffic flows may be considered as a single aggregate flow. The traffic
descriptor of the aggregate flow is constructed by the system from the individual traffic descriptors
of the constituent traffic flows. The rate parameters of the aggregate flow traffic descriptor (denoted
by an asterisk) are expected to satisfy:
()
≤≤
+=+
j
j
MM
j
M
j
j
j
A
j
FAF
RRR
RRRR
*
**
max
(7-4)
where the superscript j denotes a parameter of the j-th constituent traffic descriptor. Determination
of the parameter values of the aggregate flow traffic descriptor from its constituent traffic
descriptors is beyond the scope of this recommendation.
In the downstream direction, it is the responsibility of the OLT to provide QoS-aware traffic
management (including, as applicable, buffer management, traffic scheduling and shaping) of
XGEM Port-ID traffic flows based on the respective traffic descriptors, availability of memory and
bandwidth resources, and dynamic traffic conditions. Because this function is internal to the OLT, it
is beyond the scope of this recommendation.
In the upstream direction, an aggregate traffic descriptor is constructed for each T-CONT based on
the service specifications of the XGEM Port-ID flows multiplexed onto that T-CONT. It is the
responsibility of the OLT to provide QoS-aware traffic management of the aggregate traffic flows
associated with the T-CONTs based on the respective aggregate service specifications, the upstream
bandwidth availability and, possibly, the information obtained through upstream traffic monitoring
and/or ONU status reporting. For each individual T-CONT, it is the responsibility of the ONU to
which the T-CONT belongs to provide QoS-aware traffic management of the constituent XGEM
Port-ID traffic flows based on the respective XGEM Port-ID service specifications, resource
availability, and dynamic traffic conditions.
The ONU upstream traffic management facilities supporting resource allocation and QoS may
include ingress traffic policing, traffic shaping, XGEM Port-ID flow scheduling within a T-CONT.
The specification of these functions is beyond the scope of this Recommendation.
The remainder of this clause is concerned specifically with the upstream traffic management, and
any reference to provisioned traffic parameters pertains to aggregate traffic descriptors associated
with Alloc-IDs.