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Optimizing Voice over IP (VoIP) using Quality of Service (QoS)

This article assumes knowledge of the VoIP Proxy and Quaility of Service features on the Ecessa appliance. To learn more, please visit the Quality of Service (Bandwidth Throttling) and Voice over IP (VoIP) sections of the online Ecessa manual.

 Quality of Service allows traffic prioritization and bandwidth allocation for VoIP traffic or other services on each WAN line. For VoIP, this can reduce or eliminate conversations experiencing poor (“choppy”) voice quality. Quality of Service can also limit the bandwidth other applications can use, allowing the required bandwidth to be available by more time-sensitive data, such as VoIP.

 This article will provide an example for how VoIP and QoS can be configured to optimize performance.

 Typically, a single phone call uses 64 kbps of bandwidth so the following equation can provide a baseline for how much bandwidth should be reserved for VoIP use:

 (64 kbps) * (# of concurrent phone calls) = VoIP bandwidth

 However, if unsure how much VoIP traffic is or will be generated, it is recommended to start with 50% of the bandwidth on a WAN line reserved for VoIP. If bandwidth is available due to lack of VoIP traffic, other services can utilize up to 100% of the bandwidth; however VoIP will be guaranteed 50% if there is an increase in call volume (and thus, VoIP traffic). The bandwidth allocation can be adjusted at any time if it is determined that more or less bandwidth is required.

 When configuring QoS for VoIP, the RTP protocol (Real-Time Protocol) will be used to identify the traffic for prioritization as it contains the voice data. RTP is included as a protocol in the drop-down list when configuring the QoS classifier on the ClariLink platform.

 RTP.png

 

If RTP is not included in the drop down list, the classifier will need to be defined by destination port number(s). In this example, the port range used for RTP is 7000-7999.

RTP_manual.png

QoS includes the default classifier which acts as a catch-all for traffic that is not identified in other classifiers. This traffic will typically have the lowest priority. In this example, classifiers were created for VoIP (called rtp) and ICMP (called EcessaTesting). It is important to reserve a small amount of bandwidth for WAN testing to prevent disrupting the testing the Ecessa appliance performs to determine WAN status.

 Classifiers.png

 

After creating classifiers to identify the traffic, classes are added to the link to prioritize the traffic and allocate bandwidth. Please note, that there are outbound and inbound classes and each will need to be configured and activated.

 RulesinQoS.png

QoS is configured for VoIP and is reflected on the Configure VoIP page.

QoS_enabled.png

 

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    tziemann

    Very helpful!

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