airheads scottsdale 2010 broadcast quality video over 11n
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Aruba Networks CONFIDENTIAL. © 2010 All Rights Reserved.
Scottsdale 2010!
Broadcast-Quality Video over 802.11n Partha Narasimhan Aruba Networks partha@arubanetworks.com
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
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
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
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
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
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
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
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
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