WildPackets recently hosted a webinar on the proliferation of wireless handheld devices, especially tablets and smart phones, during which we discussed how they put increased strain on today’s wireless networks. As technology continues to rapidly evolve, network engineers are in a race to keep up – both with system interoperability concerns and throughput, reliability, and security issues. New problems accompany new technologies, and voice over Wi-Fi, sometimes called VoFi, is no different.
So why do we need VoFi? Even in today’s technological environment with cell towers going up all around the country, phone call quality can still be quite spotty. Especially in office buildings, behind glass, aluminum and concrete, voice quality is reduced significantly.
VoFi enables organizations to utilize the 802.11 network rather than rely on a regular cellular network, improving quality of voice due to stronger signals and a well-controlled infrastructure. VoFi is available on most devices, and all new devices that support 802.11ac, making it much simpler to deploy, and offering organizations the convenience of not having to purchase new equipment. Lastly, because VoFi essentially relies on BYOD, organizations are no longer responsible for supplying the device, which decreases the total cost involved.
However, while organizations may consider VoFi for the quality, convenience and cost benefits, VoFi has very unique networking requirements as compared to typical data traffic on the network. Voice traffic is highly susceptible to packet loss, jitter and latency – resulting in dropped calls, interruptions and other issues. Below, we take a deeper dive into each of these issues and what organizations should look for to ensure they don’t occur.
- Latency: Most people think of latency as network propagation delay. But it often gets introduced in many other ways. With VoFi, latency occurs because packets must move from one handset to another, making their way through a number of switches and routers along the way. As a result, VoFi calls can experience halting conversations, echoing and overlapping sounds (noises, words). While latency is inherent in any network, the lower the latency, of course, the better the voice quality. Industry guidelines put the highest acceptable latency at 150 milliseconds (ms). Any higher and quality begins to degrade.
- Jitter: Jitter deals with the variance in the packet delivery interval and takes place when packet delivery suffers from variable delay. VoFi expects that packets are delivered at a very regular interval, but as soon as some variation in delivery occurs, the quality of conversations suffers. To help compensate for this, jitter buffering is often employed to smooth the variability and allow for reordering voice packets, which may arrive out of order, but adds some latency. In addition, severe jitter can lead to packet loss, as packets that are delayed too long are not allowed to enter the jitter buffer.
- Packet loss: Packet loss exists on every network and is caused by physical layer corruption, congestion without QoS provisions, and as we mentioned above, jitter buffer discards due to excessive latency. As a rule, packet loss in VoIP (and VoFi) should never exceed 1 percent, which essentially means one voice skip every three minutes. DSP algorithms may compensate for up to 30 ms of missing data; any more than this, and missing audio will be noticeable to listeners.
For much more information on VoFi, including the tools needed for securing your network and optimizing performance, and how you can identify and monitor the maximum threshold for voice and video over Wi-Fi capacity, please refer to our VoFi web seminar.