Maintaining voice quality in Skype for Business telephony

Managing and maintaining high call quality for Skype for Business telephony requires understanding the elements of PSTN quality requirements, including which metrics to watch and manage.

Editor's note: As Microsoft brings advanced capabilities to Skype for Business telephony, organizations must pay...

close attention to the network requirements for high-quality voice calls, from latency to performance metrics. In this podcast, ZK Research principal analyst Zeus Kerravala explains how organizations can maintain voice quality in Skype for Business telephony.

Skype for Business has obviously been around for quite a while, and Microsoft recently added PSTN calling add-on. It's important to understand that Skype for Business real-time media travels through many different devices, including client apps, servers, software and across different networks. Provisioning quality is actually a multifaceted problem.

The end-to-end latency of real-time media is the total amount of latency introduced across all these components and network segments. The quality of the end-to-end connection is determined by the network segment with the worst quality. This segment acts as a bottleneck for traffic. If you think about it, the quality is determined by the least common denominator, and that needs to be dealt with. For example, in a conferencing scenario, the media path consists of a number of different network segments. The media path connects from the user to the edge of the Microsoft network. This normally includes a network connection such as Wi-Fi or Ethernet, the WAN connection, the connection from the user to the Internet ingress point where your network edge is, and then over to the other user. There's also a connection within the Microsoft network itself if you're using their cloud service. All those things have to be factored in. 

Skype for Business telephony metrics

For optimal Skype for Business media quality, there are a number of network performance metrics, targets, or thresholds that are required for your connection from your company's network to the Microsoft network edge. This segment of the network includes your internal network and includes all Wi-Fi and Ethernet connections, any company or site-to-site traffic over a WAN connection, such as MPLS, as well as internet or express route partner connections into the edge of the network. A number of the metrics are latency. Microsoft recommends that one-way latency needs to be less than 50 milliseconds. Round trip latency needs to be less than 100 milliseconds. Burst packet loss has to be less than 10% during any 200-millisecond interval. Packet loss has to be less than 1%. Packet interval arrival jitter should be less than 30 milliseconds and packet re-order has to be less than 0.05% out-of-order packets.

There are a few other performance target requirements. For instance, the Microsoft network has over 160 edge locations worldwide and they work with all the major Internet service providers throughout those edge sites. The latency metric target assumes that your company's sites or single site and the Microsoft edge are on the same continent. Your company's site or sites connect to the Microsoft edge network and that connection includes first-hop network access, which can be Wi-Fi or other wireless technology. The network performance target assumes that proper bandwidth or a quality of service plan has been implemented. In other words, these metrics apply directly to Skype for Business real-time media traffic when the network connection is under a peak load.

All those things together comprise what are the PSTN quality requirements for Skype PSTN calling. It does not take an inordinate amount of work to do. You have to gather all of those different metrics and make sure that each of those metrics has been hit. You have to look at them from a network router hop-by-hop basis to have a very successful Skype for Business deployment.

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