As 802.11n-based wireless LANs become more pervasive throughout enterprises, users will start using video over Wi-Fi. Unified communications (UC) managers will need to collaborate with wireless network engineers to ensure a good enterprise video user experience.
Unlike the typical data traffic on the enterprise wireless network, the real-time nature of video is particularly sensitive to packet loss, latency and jitter. Since 802.11n technology operates within an unlicensed wireless spectrum, video over Wi-Fi must also contend with interference from an untold number of wireless devices that may not always play by the rules.
Users will take their video over Wi-Fi complaints to the UC team at the first sign of trouble, even if the wireless LAN is the real source of trouble. UC managers should work with network engineers to optimize the network for video over Wi-Fi and collaborate with the engineering team on troubleshooting.
Video over Wi-Fi success starts with good WLAN design
When tasked with supporting video over Wi-Fi, UC managers should work with network engineers to ensure the wireless LAN is designed to support such real-time media and communications, according to Paul Debeasi, research vice president for Gartner.
Access point coverage should not only be ubiquitous throughout a corporate facility. UC managers must also ensure that engineers deploy access points in larger numbers within areas where video over Wi-Fi users congregate in large numbers, such as conference rooms or lecture halls.
UC managers must have a good understanding of the enterprise wireless LAN when troubleshooting video over Wi-Fi problems. By knowing how many users are in a given area or how far away a client device is from the nearest access point, UC teams and networking engineers know whether the coverage and density of a wireless LAN is affecting video over Wi-Fi performance. “Even a well designed WLAN is susceptible to issues that could affect video performance. For video, the help desk will need to up their game and be ready with the tools for rapid troubleshooting,” Debeasi said.
Standard 802.11n tools for support of video over Wi-Fi
Wi-Fi -certified infrastructure and clients have standardized provisions for support of video. Wi-Fi Multimedia (WMM), a subset of 802.11e, enables Quality of Service (QoS) and prioritization for real-time applications on the wireless LAN. Before supporting video over Wi-Fi, UC managers should verify that network engineers have enabled these WMM features on the network.
“802.11n and its high throughput rates certainly gives plenty of headroom for videos,” said Manju Mahishi, director of product strategy at Motorola Solutions, “The MIMO and channel bonding capabilities native to the standard can only help to enhance video performance over the air.”
Multiple In Multiple Out (MIMO) antenna technology, unique to 802.11n access points, reduces errors between clients and access points by transmitting a data stream on multiple antennas. This MIMO technique improves the chances that the client receives packets on the first try and reduces video over Wi-Fi killers like packet loss and jitter.
Wireless interference can affect any data transfer on the wireless LAN, but can be particularly painful on real-time video. Microwaves, cordless phones and other transmitters share airspace with the wireless LAN. UC managers must ensure that network engineers have the right tools to identify sources of interference and remediate them. UC managers should also ask the network team if the video over Wi-Fi can be configured for exclusive transmission in the 5 GHz spectrum, which has less competition from interferers. Many enterprises operate a wireless LAN on both the 2.4 GHz and 5 GHz spectra simultaneously because many legacy client devices can only transmit on the 2.4 GHz spectrum.
Managing multicast and unicast with video over Wi-Fi
The challenges of pushing video over Wi-Fi vary with the type of video transmitting across the wireless LAN. Unicast video is a simple point-to-point transmission from one device to another device on the IP network. Unicast video includes video chat applications and on demand video services. Multicast video is a point- to- multipoint model where video streams from a single source to multiple receivers. Many enterprise video applications such as telepresence and video training services use multicast. On wired IP networks, multicast video is efficient because a single stream is pushed to the network with requesting client devices listening for it.
Multicast services like video conferencing and video surveillance applications often suffer performance issues across the wireless LAN unless the infrastructure is configured properly. Multicast video will automatically transmit at the data rate of the slowest client it communicates with. This issue slows down video performance for all other clients on the wireless LAN.
Wireless LAN infrastructure vendors take several approaches to dealing with the challenges of multicast video. Most vendors convert multicast streams into unicast video, but their techniques vary. Cisco Systems and Motorola collect multicast streams at each access point and convert them to individual unicasts for individual client requests at the highest data rates they require. Other vendors split the multicast into unicast streams at the wireless controller and pass them to the access points at the edge.
Vendors will argue over which approach to multicast-to-unicast conversion is best, but UC managers should focus on the potential downside of both approaches. While this conversion to unicast resolves multicast's lowest common denominator issue, it can also create a new bottleneck. As controllers and access points manage multiple unicasts for clients that operate at different data rates, the wireless network can get bogged down by all the traffic generated.
Ultimately, video over Wi-Fi is a balancing act. An organization’s UC and network teams will need to rely on each other’s skillset to ensure a quality video experience for their end users.
This was first published in March 2011