CHAPTER 1
CoS Overview
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CoS Overview on page 3
•
CoS Standards on page 4
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Understanding Packet Flow Across a Network on page 4
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Junos CoS Components on page 5
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Default CoS Settings on page 6
•
CoS Applications Overview on page 8
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Interface Types That Do Not Support CoS on page 9
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VPLS and Default CoS Classification on page 10
CoS Overview
When a network experiences congestion and delay, some packets must be dropped. The
Juniper Networks
®
Junos
®
operating system (Junos OS) class of service (CoS) enables
you to divide traffic into classes and offer various levels of throughput and packet loss
when congestion occurs. This allows packet loss to happen according to rules that you
configure.
For interfaces that carry IPv4, IPv6, and MPLS traffic, you can configure the Junos OS
CoS features to provide multiple classes of service for different applications. On the
routing device, you can configure multiple forwarding classes for transmitting packets,
define which packets are placed into each output queue, schedule the transmission
service level for each queue, and manage congestion using a random early detection
(RED) algorithm.
The Junos OS CoS features provide a set of mechanisms that you can use to provide
differentiated services when best-effort traffic delivery is insufficient. In designing CoS
applications, you must give careful consideration to your service needs, and you must
thoroughly plan and design your CoS configuration to ensure consistency across all
routing devices in a CoS domain. You must also consider all the routing devices and other
networking equipment in the CoS domain to ensure interoperability among all equipment.
Because Juniper Networks routing devices implement CoS in hardware rather than in
software, you can experiment with and deploy CoS features without adversely affecting
packet forwarding and routing performance.
3Copyright © 2013, Juniper Networks, Inc.
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