Figure 3: Multipoint Queue Behavior With Shared Queuing Enabled - Alcatel-Lucent 7750 SR OS Service Manual

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Introduction

Figure 3: Multipoint Queue Behavior with Shared Queuing Enabled

Ingress Multipoint Shared Queuing

Ingress multipoint shared queuing is a variation to the unicast shared queuing defined in

Shared Queuing on page

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 predominate 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 disadvantage of enabling multipoint shared queuing is that multipoint packets are no longer

managed per service (although the unicast forwarding queues may provide limited benefit in this

Multipoint Service Queue is Represented

by a Single Hardware Queue (Single Pass)

Unicast Service Queue is Represented by a Single Hardware

Queue But Dual Pass through the Forwarding Plane

30. Ingress unicast service queues are mapped one-for-one with hardware

7750 SR OS Services Guide

Switch Fabric