Adapt QoS modes

Link Aggregation is supported on the access side with access or hybrid ports. Similarly to LAG on the network side, LAG on access aggregates Ethernet ports into all active or active-standby LAG. The difference with LAG on networks lies in how the QoS or H-QoS is handled. Based on hashing configured, a SAP’s traffic can be sprayed on egress over multiple LAG ports or can always use a single port of a LAG. There are three user-selectable modes that allow operator to best adapt QoS configured to a LAG the SAPs are using:

1. adapt-qos distributed (default)

   In a distributed mode the SLA is divided among all line cards proportionally to the number of ports that exist on that line card for a specific LAG. For example a 100 Mb/s PIR with 2 LAG links on IOM A and 3 LAG links on IOM B would result in IOM A getting 40 Mb/s PIR and IOM B getting 60 Mb/s PIR. Because of this distribution, SLA can be enforced. The disadvantage is that a single flow is limited to IOM’s share of the SLA. This mode of operation may also result in underrun because of hashing imbalance (traffic not sprayed equally over each link). This mode is best suited for services that spray traffic over all links of a LAG.

2. adapt-qos link

   In a link mode the SLA is given to each and every port of a LAG. With the example above, each port would get 100 Mb/s PIR. The advantage of this method is that a single flow can now achieve the full SLA. The disadvantage is that the overall SLA can be exceeded, if the flows span multiple ports. This mode is best suited for services that are guaranteed to hash to a single egress port.

3. adapt-qos port-fair

   Port-fair distributes the SLA across multiple line cards relative to the number of active LAG ports per card (in a similar way to distribute mode) with all LAG QoS objects parented to scheduler instances at the physical port level (in a similar way to link mode). This provides a fair distribution of bandwidth between cards and ports whilst ensuring that the port bandwidth is not exceeded. Optimal LAG utilization relies on an even hash spraying of traffic to maximize the use of the schedulers' and ports' bandwidth. With the example above, enabling port-fair would result in all five ports getting 20 Mb/s.

   When port-fair mode is enabled, per-Vport hashing is automatically disabled for subscriber traffic such that traffic sent to the Vport no longer uses the Vport as part of the hashing algorithm. Any QoS object for subscribers, and any QoS object for SAPs with explicitly configured hashing to a single egress LAG port, are given the full bandwidth configured for each object (in a similar way to link mode). A Vport used together with an egress port scheduler is supported with a LAG in port-fair mode, whereas it is not supported with a distribute mode LAG.

4. adapt-qos distributed include-egr-hash-cfg

   This mode can be considered a mix of link and distributed mode. The mode uses the configured hashing for LAG/SAP/service to choose either link or distributed adapt-qos modes. The mode allows:

   • SLA enforcement for SAPs that through configuration are guaranteed to hash to a single egress link using full QoS per port (as per link mode)

   • SLA enforcement for SAPs that hash to all LAG links proportional distribution of QoS SLA amongst the line cards (as per distributed mode)

   • SLA enforcement for multi service sites (MSS) that contain any SAPs regardless of their hash configuration using proportional distribution of QoS SLA amongst the line cards (as per distributed mode)

The following restrictions apply to adapt-qos distributed include-egr-hash-cfg:

• LAG mode must be access or hybrid.

• The operator cannot change from adapt-qos distribute include-egr-hash-cfg to adapt-qos distribute when link-map-profiles or per-link-hash is configured.

• The operator cannot change from adapt-qos link to adapt-qos distribute include-egr-hash-cfg on a LAG with any configuration.

Table 1 shows examples of rate/BW distributions based on the adapt-qos mode used.