Table of Contents
Advertisement
Shared Queue QoS Policies
Ingress Multipoint Shared Queuing
Ingress multipoint shared queuing is a variation to the unicast shared queuing defined in
Ingress
Shared Queuing on page
568. Ingress unicast service queues are mapped one-for-one with
hardware queues and unicast packets traverse the ingress forwarding plane twice. In addition to the
above, the multipoint queues defined in the ingress SAP QoS policy are not created. Instead,
multipoint packets (broadcast, multicast and unknown unicast destined) are treated to the same
dual pass ingress forwarding plane processing as unicast packets. In the first pass, the forwarding
plane uses the unicast queue mappings for each forwarding plane. The second pass uses the
multipoint shared queues to forward the packet to the switch fabric for special replication to all
egress forwarding planes that need to process the packet.
The benefit of defining multipoint shared queuing is the savings of the multipoint queues per
service. By using the unicast queues in the first pass and then the aggregate shared queues in the
second pass, per service multipoint queues are not required. The predominant scenario where
multipoint shared queuing may be required is with subscriber managed QoS environments using a
subscriber per SAP model. Usually, ingress multipoint traffic is minimal per subscriber and the
extra multipoint queues for each subscriber reduces the overall subscriber density on the ingress
forwarding plane. Multipoint shared queuing eliminates the multipoint queues sparing hardware
queues for better subscriber density. Figure 2.3 demonstrates multipoint shared queuing.
One caveat of enabling multipoint shared queuing is that multipoint packets are no longer
managed per service (although the unicast forwarding queues may provide limit benefit in this
area). Multipoint packets in a multipoint service (VPLS, IES and VPRN) use significant resources
in the system, consuming ingress forwarding plane multicast bandwidth and egress replication
bandwidth. Usually, the per service unicast forwarding queues are not rate limited to a degree that
allows adequate management of multipoint packets traversing them when multipoint shared
queuing is enabled. It is possible to minimize the amount of aggregate multipoint bandwidth by
setting restrictions on the multipoint queue parameters in the QoS nodes Shared Queue policy.
Aggregate multipoint traffic can be managed per forwarding class for each of the three forwarding
types (broadcast, multicast or unknown unicast – broadcast and unknown unicast are only used by
VPLS).
Another caveat for multipoint shared queuing is that multipoint traffic now consumes double the
ingress forwarding plane bandwidth due to dual pass ingress processing.
7450 ESS OS Quality of Service Configuration Guide
Page 571
Advertisement
Table of Contents
