When information is delivered over a Wifi network, sometimes data can get delayed or lost in transmission. When this happens, these packets are corrected or resent for many types of data. This process normally takes a very short time (milliseconds) and has no perceptible negative consequences on normal app activities such as web browsing or transferring files. VoWLAN (Voice over Wireless Local Area Network) carries voice traffic as data over the Wifi network making voice traffic vulnerable to the same issues as any other data transmission. When data loss, delays or corruption happen to a VoWLAN call, the effect can be much more dramatic, resulting in poor call quality with effects such as reduced call clarity as well as popping and crackling sounds, or even causing the call to drop entirely. QoS (Quality of Service) can help with voice across the network but not the connection from the smartphone to the AP (Access Point). QoS is a standard that will prioritise voice data over other types of data which will allow voice data through to its destination more quickly.
Voice over a network has a very low tolerance for network errors and delays and loss of information of only a few hundred milliseconds can severely deteriorate voice quality. The industry standard is to use a 50 ms buffer for voice calls. After that, it is too late thus call quality deteriorates or the call is lost depending on the severity. Data traffic is often delivered in bursts and quite sporadic. This is acceptable in most cases because most apps can tolerate network congestion with slow downs and higher response times but not voice traffic.
One of the greatest challenges for smartphones in an work environment is delivering acceptable voice quality when using an organisation’s Wifi network. Smartphones are primarily designed and enhanced for cellular voice calls and data. Most smartphones Wifi functionality is optimised for data, not voice. Smartphones have much more limited coverage and performance due to their lower transmitter power and minimal antennas. Voice traffic requires very little bandwidth but cannot tolerate unpredictable delays and depends on bandwidth that is much more constant and consistent. Another factor to consider when determining the coverage area is device usage. Wireless telephone users tend to walk around as they talk, while data users are usually stationary or periodically move around. Users move from hallway to offices to meeting room, roaming from one access point to another during the transition and require no loss of packets and expect no degradation of audio quality. This is where a proper hand-off is required and is not just an AP or Wifi controller issue but a device issue. Most smartphones will wait until the signal from the AP they are attached to is very weak, before looking for a new AP. This is often because switching APs is battery intensive compared to staying connected to a weak signal and manufactures are trying to lower battery usage with their power hungry devices. AP controller software can be set to notify a device to switch to another AP but unfortunately the device is not forced to comply.
Also, AP to device signal strength is impacted by how and where the users hold their phones compared to other devices. Users often hold the phone close to their head and this may attenuate the signal. This factor may result in reduced range for Wifi phone app service compared to a data app service. Therefore the Wifi network layout should account for some reduction of radio signal. To provide seamless connectivity for VoWLAN applications, the APs must be positioned with sufficient overlapping coverage of handsets to ensure there are no gaps, or dead spots, amongst them.
In addition to the layout and configuration of the network’s APs, network capacity requirements are a factor in the number and type of APs required. Busy areas such as meeting rooms and common areas, where it’s normal for data and voice to compete for limited bandwidth, are problematic for voice on smartphones over Wifi. This is in part due to the AP’s connected active clients. The more clients connected to an AP the less ‘air time’ per client and thus reduced effective data throughput. Using multiple APs with lower power and HD (High Density/Wave 2) APs in congested areas may help.
There is no single solution. Every business has different requirements and a different office or work environment. If you want to use your smartphone as a Wifi phone or have good Wifi coverage in general then good Wifi equipment, a heat map (diagram of signal strength in a Wifi network), proper design and implementation testing are a necessity but not a guarantee.
For assistance with a Wifi solution please contact the TELECO sales team either by phone at 807-346-7264 or using our Contact Us form.