Acx2000 And Acx2100 System Architecture Overview; Packet Flow On Acx Series Routers; Figure 13: Acx Series Router Packet Forwarding And Data Flow - Juniper ACX2000 Hardware Manual

CHAPTER 3
ACX2000 and ACX2100 System
Architecture Overview

Packet Flow on ACX Series Routers

Copyright © 2015, Juniper Networks, Inc.
Packet Flow on ACX Series Routers on page 25
The class-of-service (CoS) architecture for ACX Series routers is in concept similar to
that of MX Series routers. The general architecture for ACX Series routers is shown in
Figure 13 on page 25.

Figure 13: ACX Series Router Packet Forwarding and Data Flow

Ingress classification
In order of
decreasing precedence:
Incoming packet
MF classification (DFW)
Fixed classification
BA classification
Based on the model, ACX routers contain a built-in Routing Engine and Packet Forwarding
Engine and can contain both T1/E1 and Gigabit Ethernet Ports.
The Packet Forwarding Engine has one or two "pseudo" Flexible PIC Concentrators.
Because there is no switching fabric, the single Packet Forwarding Engine takes care of
both ingress and egress packet forwarding.
Fixed classification places all packets in the same forwarding class, or the usual multifield
(MF) or behavior aggregate (BA) classifications can be used to treat packets differently.
BA classification with firewall filters can be used for classification based on IP precedence,
DSCP, IEEE, or other bits in the frame or packet header.
However, the ACX Series routers can also employ multiple BA classifiers on the same
physical interface. The physical interfaces do not have to employ the same type of BA
classifier. For example, a single physical interface can use classifiers based on IP
precedence as well as IEEE 802.1p. If the CoS bits of interest are on the inner VLAN tag
of a dual-tagged VLAN interface, the classifier can examine either the inner or outer bits.
(By default, the classification is done based on the outer VLAN tag.)
Eight queues per egress port support scheduling using the weighted deficit round- robin
(WDRR) mechanism, a form of round-robin queue servicing. The supported priority levels
Buffering Queuing Scheduling
Outgoing packet
Egress rewrite
25