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FiberGateway User Manual
29
Technical Description
2.13 Policing/Rate Limiting
2.13.1
Downstream QoS
The OLT system supports traffic classification at the ingress ports (ETH, LAGs, PON, etc) based on P-
Bits, IP DSCP and IP.
The OLT system provides several QoS mechanisms, that can be targeted to the flow characterized by
one or two VLAN according with the type of service, or can be targeted to the packets priority, where
each p-bit/DSCP is mapped in one of eight queues of each port.
For each OLT ports are associated eight queues, for each of these queues is possible to configure the
p-bit mapping in one of the queues, the scheduler type (Strict Priority or Weighted Fair Queuing) and
the minimum and maximum bandwidth of each queue.
Figure 10: Dowstream QoS diagram
In the downstream direction, Figure 10, the ingress traffic can be firstly classified. It passes by a
policer and is configured to each ONT service, which is defined by one or two tags. It is remarked and
policed per-CoS rate (port profile).
After this, Network services (per VLAN) classification determine the PON port queue where packets
will wait for a transmission opportunity, and can remark the CoS (P-bits in VLAN PCP). The traffic is
put in a queue according with the p-bit/DSCP->Traffic Class mapping.
Each of these Traffic Classes is associated with a scheduler (WRR or SP) and a policer.
Queue congestion management is used to prevent the queue from overflowing and is performed
based on Tail Drop or WRED.
Each queue is served by either a priority or weighted scheduler and rate controlled.
Then Traffic Classes to P-bit remarking is done and the traffic flows to the GPON interface.
Destination ONU/ONT client service downstream profile defines traffic classless policing. The overall
PON port may be limited to a percentage of its capacity.
Traffic arriving to the ONU/ONT it will pass by a mapping block which will map the traffic in one of the
eight queues according with the p-bits; these queues have a Strict Priority scheduler in order to
guarantee that the most prioritized traffic passes first, Figure 10.
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