From IPTV streaming to FaceTIme video, enterprise video applications are growing rapidly. Usually these videos are sent and received via mobile devices connected to the corporate wireless LAN. Now network administrators must implement a new WLAN design to optimize wireless video transmission and avoid performance degradation.
The challenges facing video WLAN design go far beyond the bandwidth limit
When building a wireless local area network (WLAN) that supports video applications, capacity is obviously a factor to consider, but capacity is not just a simple bandwidth issue. The bandwidth requirements of video applications are affected by resolution, frame rate and codec. For example, a 720p or 1080p surveillance camera that records 6-10 frames per second (FPS) and uses H.264 encoding requires 1 to 2 Mbps bandwidth. However, watching a 72-inch 120-240 FPS HD video may require up to 30 Mbps of bandwidth to achieve a satisfying viewing experience.
The codec can reduce throughput at the cost of quality, but it supports multiple Internet TV (IPTV) channels. And the mirrored data will also use up the available AP or RF capacity. The popularity of video in high-density environments (such as classrooms and dormitories) has increased competition for online time. To make matters worse, many video streams use multicast to reduce the load on the wired network, but through Wi-Fi, multicast reduces the data ratio to the weakest (the oldest and the most distant distance) clients. In a hall full of various consumer electronics devices, the problem of poor quality must still exist unless further measures are taken to optimize and prioritize video transmission.
Define capacity requirements for wireless video applications
The first step to ensure wireless video performance is to establish the required network capacity and performance requirements for video and multimedia applications in WLAN. Aruba Networks wireless network providers recommend that videos be divided into the following categories:
â—† Broadcast IPTV via Wi-Fi. This requires a single line of downward transmission of delay-insensitive traffic for each channel user on many high-bandwidth (1 to 4 Mbps SD or 6 to 10 Mbps HD) channels.
â—† Live event video streaming (webcast) via Wi-Fi. This requires unidirectional downstream delivery of delay-insensitive traffic, especially channels that all users watch over a single high-bandwidth (1-4 Mbps).
â—† IP surveillance recording via Wi-Fi. This requires uplink or downlink transmission delay-insensitive traffic, delivering many channels of video of different quality (500 Kbps to 2 Mbps) for a small audience.
â—† Interactive video conference. This is bidirectional delivery of traffic affected by traffic delay and jitter (up to 150 to 200 milliseconds), but both parties need low symmetric bandwidth (1 Mbps).
â—† Video on demand (training, pre-recorded programs). This requires unidirectional downlinks to deliver delay-insensitive traffic, with multiple users simultaneously consuming high-bandwidth channels (1 to 4 Mbps SD or 6 to 10 Mbps HD) per channel.
These examples illustrate the transformation of all video and multimedia WLAN deployments: directionality, throughput, delay and jitter tolerance, and the number of channels and users. Another key indicator is the error tolerance rate. Low packet error rates are usually available, but they can also cause problems for UDP multicast.
Design considerations: 802.11n wireless LAN for wireless video delivery
Fortunately, enterprise WLAN products are mature enough to provide a solid foundation for video and other multimedia applications. Video WLAN should use 802.11n to increase capacity, density and reliability. The key elements to be considered in the function and design of 802.11n include:
Channel bonding and spatial multiplexing through multiple input multiple output (MIMO) antennas, increasing the capacity of each radio to 450 Mbps (3X3) or 600 Mbps (4 & TImes; 4), enabling each AP to support more video users .
â—† The available throughput of each user will be limited by the capabilities of the Wi-Fi client, especially smartphones and tablets with 1x1 MIMO (up to 65 Mbps rate, which decreases with distance) technology. This may be sufficient for a single video stream, but keep in mind that slower clients may pull down the video performance of each user, and these lower data rates must be considered when designing a WLAN.
â—† Using 802.11n standard options, such as A-MPDU (MAC protocol data unit) and block confirmation, to further increase the data throughput of delay-insensitive unidirectional video streams.
â—† 802.11n devices can support 2.4 GHz and / or 5 GHz. When higher throughput is required, the 5 GHz channel should be fully utilized. For example, using predicted coverage areas designed by WLAN planners to replace APs to meet throughput, user density, and user rate uplink and downlink bandwidth requirements. But don't think that a strong signal will have high-quality video, you must always verify the performance.
â—† Using Wi-Fi Multimedia (WMM) priority allows video to have more online time than data, but will not consume all available bandwidth. The application of delay and jitter (such as VoIP, video conferencing, etc.) has higher priority than unidirectional data flow. WMM admission control may help avoid overloading an AP.
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