This topic describes how to set up QoS on branch gateways to shape inbound and outbound traffic. It includes these sections:

QoS for branch gateways is a per-uplink traffic shaper for inbound and outbound traffic.

SteelConnect provides an easy-to-use queue management system for inbound and outbound traffic. With QoS for branch gateways:

SteelConnect looks for the differentiated services code point (DSCP) marking on traffic as it comes into the SteelConnect gateway. This marking can be the DSCP value that you set in the traffic rules using SCM or the DSCP value that you set using another device, such as a SteelHead appliance, LAN switch, VoIP phone, or router.

For details on setting the DSCP value in traffic rules using SCM, see QoS priority. SteelConnect uses this DSCP value to enforce QoS classification and shaping.

QoS for gateways uses the common applications kept enhanced (CAKE) scheduler. CAKE uses an advanced fair queue mechanism that distributes bandwidth while considering packet delays. CAKE is a connection-based system that tracks latency on each connection or traffic flow rather than bandwidth per class.

CAKE is not a typical traffic shaper or policer: it tries to give each traffic flow a fair share of the traffic. It does not allow fat flows to take up the whole circuit. CAKE is purposely built for internet-based uplinks so it is ideal for dynamic WAN throughput. CAKE automatically adjusts to traffic changes throughout the day, providing increased bandwidth when a traffic flow requires it and less bandwidth if the traffic flow slows down. CAKE also avoids excessive buffering, which can lead to a bad user experience.

For details on CAKE, go to https://www.bufferbloat.net/projects/codel/wiki/Cake/.

The CAKE scheduler dynamically places traffic flows in these traffic class queues for mapping enforcement:

According to Bufferbloat.net, “CAKE implements soft admission control, making it robust against starvation attacks relying on strict priority that otherwise would be easy to trigger by accident. If a traffic class (including all traffic in higher classes than itself) exceeds its bandwidth threshold, it is demoted in priority until it falls below the threshold again. Thus, if there is no competing traffic, any traffic class can use the full link bandwidth, but it is always possible for new traffic in a different class to start up.”

For more information, go to https://www.bufferbloat.net/projects/codel/wiki/CakeTechnical/.

Only DSCP marked traffic is placed in the QoS priority queues. Traffic must have a DSCP marking value for QoS traffic to be classified and shaped.

You can mark traffic with a DSCP value using: