Medium Access Control (MAC) and Physical Layer (PHY) - CISE

4-June-07 P1901_PRO_016_r0
The FMN must receive the resource reservations requests using the CAC protocol (See section 0) and must decide if
it has enough resources to assign to the incoming request or if it has to request more resources to the BPL master
node.
With this mechanism, we will have a complementary tool to limit the bandwidth. This information will be
interesting to known if a new traffic of a service class can be started and the requirements for that traffic and service
class can be assured.
8.2 SERVICE CLASS DEFINITION
Up to eight service classes can be defined within a BPL cell. Services classes are globally defined over a BPL
subcell. Four service parameters are necessary to fully describe a service class: priority, subcell_access_time,
resource reservation type and service reliability.
8.2.1 Priority
Service classes are directly mapped onto priorities. A priority uniquely identifies a service class. That is why all the
other service parameters are configured and mapped from this priority parameter. Priorities shall have values from
0 to 7, 0 being the lowest priority. If packets have to be dropped at the transmitter because of lack of resources, then
the lower priority packets shall be dropped before the higher priority packets. When there are data of different
priorities addressed to the same destination, higher priority data shall be transmitted earlier than lower priority data.
8.2.1.1 Configuration
Priority parameter is determined by the Classifier module operating at the bridging block level. The classifier
analyses all the frames received from a bridge port (BPL port, non-BPL port, management port) and assigns a
priority to each Ethernet frame transmitted to the convergence layer via the Eth.req primitive (see 6.3). The
Classifier operates according to some predetermined and/or configurable rules (see 11.4). Any frame received from
the management port shall be mapped to priority 7 (that is: service class 7).
Note: For each Eth.req primitives delivered by the bridging block, a priority is submitted as part of the OVLAN
word argument (PCP bits). The PCF bit of this OVLAN word might be set to 1 meaning that the priority is to be
seamlessly bridged through the intermediate nodes of the BPL cell. This priority information is summarized within
the Priority field of any Burst Header and the Frame Priority field of every upstream data token.
8.2.2 Max Subcell Access Time
The Max_Subcell_Access_Time corresponds to the max duration for a flow to access the channel on the subcell
level. It is a latency requirement for the scheduler to be configured within any master of a BPL cell.
Four Max_Subcell_Access_Time are defined at the master level. The minimum value of the
Max_Subcell_Access_Time is used as the reference step from which the three other Max_Subcell_Access_Time are
derived by multiplying by 2, 4 or 8 this reference step.
Submission page 179 UPA-OPERA