User guide

1-10 Packet Over SONET Module Installation and User Guide
Overview
MPLS labeled packets can also be encapsulated in Ethernet headers and transported
across a PPP link using BCP.
Jumbo Frames
The PoS module ports provide jumbo frame support that is similar to that provided by
Ethernet ports on a BlackDiamond 6800 series switch.
Jumbo frames are Ethernet frames that are larger than 1522 bytes, including four bytes
used for the cyclic redundancy check (CRC). Extreme products that use the “i” chipset
support switching and routing of jumbo frames at wire-speed on all ports.
Jumbo frames are used between endstations that support larger frame sizes for more
efficient transfers of bulk data. Both endstations involved in the transfer must be
capable of supporting jumbo frames.
QoS and Differentiated Services
The PoS modules support eight ingress queues and eight egress queues per port. The
scheduling parameters for these queues (minimum bandwidth, maximum bandwidth,
priority level, etc.) are controlled by QoS profiles that you can customize for individual
ingress or egress queues on a specific PoS port.
You can assign frames to queues based on IEEE 802.1p priorities, MPLS EXP values,
Differentiated Services Code Points (DSCPs), or by configuring a QoS profile for the
port or VLAN. You can tailor the DSCP-to-queue mapping for ingress or egress
directions on a per-port basis. Most of the existing ingress classification functions, along
with the DiffServ replacement functions, are also supported for PoS ports.
The supported DiffServ functions maximize user flexibility while providing all of the
features needed to support the standard per-hop behaviors (PHBs), including:
• Default
• Class Selector
• Assured Forwarding
• Expedited Forwarding
The PoS modules also provide flexible support for the well-known Weighted RED
(WRED) congestion avoidance algorithm.