Clear Voice Over Wi-Fi in the Enterprise

Clear Voice Over
Wi-Fi in the Enterprise
Ruckus Wireless | White Paper Delivering high-quality VoIP over Smart
Enterprise Wireless LANs.
Executive summaryWireless LANs (WLANs) are becoming pervasive in the Quality of service must be maintained, so that voice packets enterprise. Businesses are turning to WLANs to give employees get priority over data. The system must allow for the voice immediate access to business applications and communication client to conserve power, so that battery life is high. As voice tools. By adding voice to their to their wireless networks, clients roam from AP to AP, resulting in re-association and re-businesses can improve collaboration and responsiveness, authentication, the system must ensure a high level of security, and save money by being more ef? cient. The increasing use of while roaming with the least amount of delay so as to not affect Voice over Wi-Fi (VoFi) phones and dual-mode phones offering voice quality or cause dropped calls. In addition, roaming services like Unlicensed Mobile Access (UMA), offer new needs to work in a Layer 2 or Layer 3 environment, allowing the opportunities to increase productivity in the workplace. enterprise to choose the right architecture, without impacting voice quality.However, Voice over Wi-Fi places some unique requirements on the WLAN that are vastly different from data. The effect The following sections provide further details on the issues of signal degradation due to interference and obstructions in and challenges facing Voice over Wi-Fi technology, and how to an enterprise can play havoc with voice, whilst not affecting overcome these challenges.data traf? c quite so much. Transmission paths must be chosen between the access point (AP) and voice client that maximizes By maximizing transmit signal strength and receiver sensitivity, the signal, while at the same time attenuating any interference voice handsets can send the same information in shorter or noise. Page 2
Delivering High-Quality VoIP over Smart Enterprise Wireless LANs
timeframes, using less power. This can be accomplished by (channel) can reduce noise. But with only three non-overlapping using Smart Wi-Fi antennas to narrowly direct signal towards channels available for use by 802.11b/g/n (when 802.11n is in 2.4 each voice handset, reducing retransmissions, extending battery GHz mode), most Wi-Fi networks end up coexisting with several life, and improving user satisfaction. interfering devices.
Wi-Fi signals degrade not only due to noise, but because of RF interference and its effects on Wi-Fi distance and intervening objects. A laptop and AP in the same performance of? ce, with nothing but air between them, can experience The 2.4 and 5 GHz bands used by 802.11 WLANs are shared by relatively high data rates up to 54 Mbps for 802.11g/a, or even Ūmany other devices, including cordless telephones, Bluetooth higher for 802.11n. But put that laptop in the next of? ce, and peripherals, satellite services, and neighboring Wi-Fi networks. radio waves will be partially absorbed (attenuated) by the These common sources of interference make it harder for intervening wall (see Figure 1). Place the AP beneath a metal Wi-Fi devices to differentiate between legitimate transmissions bookcase and waves will bounce (re? ect) off that surface. and background noise. Tuning an AP to a different frequency Waves passing through walls, furniture, and even people become slightly bent (refracted). This is why radio waves sent Figure 1 through open air can be received 300 feet away, yet indoor Wi-Fi Signal Degradation transmissions are often too faint to span even a small of? ce.
When signal strength drops, Wi-Fi devices Refractiontry to compensate by reducing data rate (i.e., less RF energy is needed to deliver fewer bits without error). This only worsens the user experience, because now it takes longer to send the same packets, so more Attenuationinterference and collisions result. While re-transmissions can somewhat mitigate this issue for data frames, voice is very sensitive Interferenceto re-transmissions and the resulting delay that is introduced.ReflectionMultipath and 802.11nWi-Fi networks are also impacted by RF phenomena like hidden nodes and multipath. Multipath occurs because radio waves are re? ected to some degree by every object encountered between transmitter and receiver, especially concrete or metal surfac... [download for more]