What are the most common QoS settings for VoIP in LAN switching?

1 QoS Classification

The first step in QoS configuration is to classify the network traffic into different classes or categories, based on the type, source, destination, or application of the traffic. For example, you can classify VoIP traffic as a high-priority class, while web browsing traffic as a low-priority class. By doing so, you can assign different QoS policies and actions to each class, depending on your network needs and objectives. There are several methods to classify traffic on LAN switches, such as using VLANs (Virtual Local Area Networks), CoS (Class of Service) values, DSCP (Differentiated Services Code Point) values, or ACLs (Access Control Lists).

2 QoS Marking

The next step in QoS configuration is to mark the network traffic with QoS values, which indicate the priority and treatment of the traffic. Marking is done at the ingress (incoming) interface of the switch, where the traffic enters the network. Marking allows the switch to identify and differentiate the traffic classes and apply the appropriate QoS policies and actions along the network path. There are two main types of QoS marking: Layer 2 marking and Layer 3 marking. Layer 2 marking uses CoS values, which are embedded in the Ethernet header of the frame. Layer 3 marking uses DSCP values, which are embedded in the IP header of the packet. For VoIP traffic, it is recommended to use both Layer 2 and Layer 3 marking, as some switches may only support one type of marking.

3 QoS Queuing

The third step in QoS configuration is to queue the network traffic according to the QoS values, which determine the order and frequency of the traffic being transmitted. Queuing is done at the egress (outgoing) interface of the switch, where the traffic leaves the network. Queuing prevents congestion and ensures that high-priority traffic, such as VoIP, gets enough bandwidth and low latency. There are several types of queuing algorithms that can be used on LAN switches, such as FIFO (First In First Out), PQ (Priority Queuing), WFQ (Weighted Fair Queuing), or CBWFQ (Class-Based Weighted Fair Queuing). For VoIP traffic, it is recommended to use PQ or CBWFQ, as they can guarantee a minimum amount of bandwidth and a maximum delay for each traffic class.

5 QoS Trust Boundaries

The fifth step in QoS configuration is to define the QoS trust boundaries, which determine where and how the QoS values are trusted or verified. Trust boundaries are important to ensure that the QoS values are consistent and accurate across the network, and that the QoS policies and actions are applied correctly and effectively. There are two main types of QoS trust boundaries: trust and untrust. Trust means that the switch accepts and forwards the QoS values that are already marked by the previous device, such as a phone or a router. Untrust means that the switch ignores or overwrites the QoS values that are already marked by the previous device, and applies its own QoS classification and marking. For VoIP traffic, it is recommended to trust the QoS values at the edge of the network, where the phones are connected, and untrust the QoS values at the core of the network, where the switches are connected.

6 QoS Verification and Monitoring

The final step in QoS configuration is to verify and monitor the QoS settings and performance, which ensure that the QoS objectives are met and that the VoIP quality is satisfactory. Verification and monitoring can be done using various tools and methods, such as show commands, debug commands, ping, traceroute, SNMP (Simple Network Management Protocol), or IP SLA (IP Service Level Agreement). These tools and methods can help you check the QoS values, statistics, status, and behavior of the network traffic, and identify and troubleshoot any QoS issues or problems. For VoIP traffic, it is recommended to monitor the key QoS metrics, such as bandwidth utilization, delay, jitter, and packet loss, and compare them with the baseline and threshold values.

7 Here’s what else to consider

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