User's Manual

XGS-PON FGW User Manual
26
Technical Description
Q_PPS_DM_018_V1.3
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 PON 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 FGW 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 PON interface.
Destination FGW 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 FGW 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.