Draytek 2750 manual Port Rate Control, QoS Control List

3.5.3 Port Rate Control

A policer can limit the bandwidth of received frames. It is located in front of the ingress queue. And a shaper can limit the bandwidth of transmitted frames. It is located after the ingress queues. This page allows you to configure the switch port rate limit for Policers and Shapers.

Port	Represent DSL interface.
Policer Enabled	Check this box to enable policer function.
Policer Rate(Rx)	Type the number for policer function. The default value is 500.
	It is restricted to 500-1000000 when the Policer Unit is set in
	kbps, and it is restricted to 1-1000 when the Policer Unit is set
	in Mbps.
Policer Unit	Determine the unit (kbps/Mbps) for policer.
Shaper Enabled	Check this box to enable shaper function.
Shaper Rate (Tx)	Type the number for shaper function. The default value is 500.
	It is restricted to 500-1000000 when the Shaper Unit is set in
	kbps, and it is restricted to 1-1000 when the Shaper Unit is set
	in Mbps.
Shaper Unit	Determine the unit (kbps/Mbps) for shaper function.

3.5.4 QoS Control List

Deploying QoS (Quality of Service) management to guarantee that all applications receive the service levels required and sufficient bandwidth to meet performance expectations is indeed one important aspect of modern enterprise network.

One reason for QoS is that numerous TCP-based applications tend to continually increase their transmission rate and consume all available bandwidth, which is called TCP slow start. If other applications are not protected by QoS, it will detract much from their performance in the overcrowded network. This is especially essential to those are low tolerant of loss, delay or jitter (delay variation).

Another reason is due to congestions at network intersections where speeds of interconnected circuits mismatch or traffic aggregates, packets will queue up and traffic can be throttled back to a lower speed. If there’s no defined priority to specify which packets should be discarded (or in another term “dropped”) from an overflowing queue, packets of sensitive applications mentioned above might be the ones to drop off. How this will affect application performance?

There are two components within Primary configuration of QoS deployment:

zClassification: Identifying low-latency or crucial applications and marking them for high-priority service level enforcement throughout the network.

62 Vigor2750 Series User’s Guide