Airheads scottsdale 2010 broadcast quality video over 11n
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This document discusses delivering broadcast-quality video over 802.11n wireless networks. It describes various types of video content and challenges with using multicast for video delivery over 802.11. It proposes using unicast delivery of multicast packets as a solution and describes Aruba's Dynamic Multicast Optimization which dynamically switches between unicast and multicast delivery. Validation testing showed unicast delivery significantly reduced packet error rates compared to multicast. The document outlines considerations for network planning and areas for further optimization.
Airheads scottsdale 2010 broadcast quality video over 11n
- 1. Aruba Networks CONFIDENTIAL. © 2010 All Rights Reserved. Scottsdale 2010! Broadcast-Quality Video over 802.11n Partha Narasimhan Aruba Networks [email protected]
- 2. Aruba Networks CONFIDENTIAL. © 2010 All Rights Reserved. • Stored video content – On-demand video, Youtube, etc. – Typically Unicast to interested user – UDP or TCP • Live Video Content – IPTV, Video stream of live events (for example, company meeting) – Typically Multicast/UDP • Video surveillance – Live content, but typically headed to central monitoring station – Mostly unicast, but multicast is sometimes used • Video coding means not all video packets are equal Video Basics
- 3. Aruba Networks CONFIDENTIAL. © 2010 All Rights Reserved. • Reliability – No feedback mechanism from stations to AP – No ACKs, so no retransmissions – Packet loss is unavoidable • Capacity – Typically sent at lowest PHY rate – PHY rate optimizations provide marginal gain – 802.11n PHY rate gains do not apply • QoS – Multicast packets do not use WMM – Sent in best-effort • Power-save – Buffering of packets due to PS clients can cause latency and jitter – PS clients may not be interested in any multicast streams Multicast Video over 802.11
- 4. Aruba Networks CONFIDENTIAL. © 2010 All Rights Reserved. • Disable use of multicast for video delivery on 802.11 – Causes video server scalability problems – May require rewriting video applications – Not very promising • Limit number of available multicast streams/channels – Not desirable, which channels should be made available? – Reliability problems still persisit • Use a wire – Not an option • 802.11 unicast delivery of multicast packets – Solves 802.11 multicast delivery problems – Buys reliability in exchange for capacity, but when do we choose one over the other? Possible solutions
- 5. Aruba Networks CONFIDENTIAL. © 2010 All Rights Reserved. • Unicast delivery at 802.11 MAC – No changes at L3 and above required – No modifications required at servers and applications • Unicast delivery only to users subscribed to that multicast stream – Unicast delivery is derived from IGMP state at the controller • Dynamic switching between unicast and multicast delivery – Unicast/multicast mode selection is independent for each multicast stream on each VAP – Switching between modes is determined by user-configurable thresholds Dynamic Multicast Optimization
- 6. Aruba Networks CONFIDENTIAL. © 2010 All Rights Reserved. • Additional load on the controller – Currently DMO is supported only on the 3000 series and M3 controllers – Network design should factor in multicast video usage • Additional load on the intermediate network – May not be that much of a factor on most campus networks – Presence of slow links between controller and AP impacts performance • Additional load on wireless channel – Different load factors for 11n vs 11abg clients • Video server tuning – Video bit rate, IP fragmentation Network Planning considerations Video Server Controller AP1 AP2 User1
- 7. Aruba Networks CONFIDENTIAL. © 2010 All Rights Reserved. • Video servers – Video Furnace – Microsoft Media Server – VideoLAN server • Multiple video streams/channels – Different video bit rates – Most tests were with SD videos, not much HD testing yet • Mix of 11n and 11abg clients – 20 clients on a single AP tested with multiple 2 Mbps video streams • Packet error rate with multicast delivery is around 1-3% – Significant impact on user experience • Unicast delivery can get PER very close to 0 – User experience is superior at all video rates Validation
- 8. Aruba Networks CONFIDENTIAL. © 2010 All Rights Reserved. • Current DMO thresholds are based on user count – All users are not identical – 3:1 load ratio between 11abg and 11n is too simple • Migrate DMO thresholds to use channel time – More accurate measure of channel load – Load due to different PHY rates can be measured accurately – Works across client types, do not need a ratio – DMO threshold planning becomes simpler • Expand DMO decisions to both controllers and APs – Controllers switch between delivery modes today – DMO switching at AP may simplify network planning for DMO – Provides finer coupling between airtime accounting and DMO decisions The Road Ahead
- 9. Aruba Networks CONFIDENTIAL. © 2010 All Rights Reserved. • Not all video frames are equal – Video coding results in uneven distribution of information across video frames – Losing or delaying some video frames can cause a higher impact on user experience – Look deeper into IP packets in a video session to enable differentiated handling of video frames • Load balancing and DMO – Move clients between APs to increase the probability of unicast delivery to more clients across more APs • Optimize multicast flows within wired network The Road Ahead