Transcript ppt
How to meet QoS requirements for video applications over IEEE 802.11 wireless LANs Project by Jeonghun Noh and Frederic Sarrat May 31, 03 How to meet QoS requirements for video applications over IEEE 802.11 wireless LANs EE384B project presentation Sarrat, Frederic – Noh, Jeonghun Outline • Motivation : A technical challenge – Video Service – IEEE 802.11 WLANs • Previous Solutions – Efforts at each layer of network systems – Limitation of previous solutions • Proposed System – QoS definition over a wireless link – Preliminary Analysis : decision making – Operations of the system • Concluding remark & future work How to meet QoS requirements for video applications over IEEE 802.11 wireless LANs EE384B project presentation Sarrat, Frederic – Noh, Jeonghun Motivation : A Technical Challenge INTERNET • Video Applications – high bitrate – Low latency – Bi-directionnal – Sensitive to bursty errors – Error propagation • Wireless LAN – Limited bandwidth – Bursty errors – Time-varying channel – Shared medium How to meet QoS requirements for video applications over IEEE 802.11 wireless LANs EE384B project presentation Sarrat, Frederic – Noh, Jeonghun Previous Solutions • Breaking the work into smaller pieces – Efforts at each layer of network systems – Limitation of previous solutions How to meet QoS requirements for video applications over IEEE 802.11 wireless LANs EE384B project presentation Sarrat, Frederic – Noh, Jeonghun Application Layer Frame reordering Reference Picture Selection Adaptive coding Layered coding Multiple Description Feedback needed No Yes Yes No No Decoding delay Yes No No No No Redundancy controlled by Encoding parameters Encoding parameters Error rates Encoding Parameters Improvement on bandwidth Improvement on delay No Reduced Adapted Encoding parameters, number of layers Adapted Maximum delay reduced Yes No No No No No No Yes Yes No Yes No No Yes Suitable for multicast Error robustness No How to meet QoS requirements for video applications over IEEE 802.11 wireless LANs EE384B project presentation Sarrat, Frederic – Noh, Jeonghun Network Layer • QoS Support at Network Layer – Ad hoc mode in IEEE 802.11 standard – Mesh network between STAs • Requirements for QoS Support – Bandwidth reservation – QoS Routing – Congestion Control • Potentials & Limitations How to meet QoS requirements for video applications over IEEE 802.11 wireless LANs EE384B project presentation Sarrat, Frederic – Noh, Jeonghun MAC layer(I): IEEE 802.11 • Media Access Scheme : CSMA/CA – Avoidance by RTS/CTS – ACK mechanism – Exponential Backoff • MAC protocol : DCF(CP) / PCF(CFP) How to meet QoS requirements for video applications over IEEE 802.11 wireless LANs EE384B project presentation Sarrat, Frederic – Noh, Jeonghun MAC Layer(II): IEEE 802.11e for QoS Enhancing efficiency of medium • Extension of 802.11 to support QoS – Polling by HCF / Packet Bursting • EDCF – Enhanced DCF. Supports statistical QoS • HCF – Hybrid Mode. Supports QoS guarantee How to meet QoS requirements for video applications over IEEE 802.11 wireless LANs EE384B project presentation Sarrat, Frederic – Noh, Jeonghun MAC Layer(III): Retransmission • ARQ(Automatic Repeat Request) – Stop & Wait – Go back N – Selective Repeat • Problems – Error-free retransmisson – No delay bound under bad link How to meet QoS requirements for video applications over IEEE 802.11 wireless LANs EE384B project presentation Sarrat, Frederic – Noh, Jeonghun Physical Layer(I) • FEC(Forward Error Correction) – Robust channel coding – Requires extra bandwidth for added codes – Avoids retransmissions – Weak against bursty errors How to meet QoS requirements for video applications over IEEE 802.11 wireless LANs EE384B project presentation Sarrat, Frederic – Noh, Jeonghun Physical Layer(II) – Adaptive Modulation • Symbol rate / modulation level – Strong against bursty errors – Strong against fast fading channel – Precise channel estimation – SNR feedback loop How to meet QoS requirements for video applications over IEEE 802.11 wireless LANs EE384B project presentation Sarrat, Frederic – Noh, Jeonghun Limitations • Suboptimal solutions – Optimal in a restricted manner – Could do better • Rigid QoS requirements – Hard to solve problems • End-to-end feedback – Resource fluctuation due to wireless medium – Delay for adaptation. How to meet QoS requirements for video applications over IEEE 802.11 wireless LANs EE384B project presentation Sarrat, Frederic – Noh, Jeonghun New System architecture • Motivation – Limitation of layer specific techniques – New QoS concepts over wireless links – network congestion vs. wireless link deterioration • New System proposed – Preliminary Analysis : decision making – proposed System architecture – Operations of the system How to meet QoS requirements for video applications over IEEE 802.11 wireless LANs EE384B project presentation Sarrat, Frederic – Noh, Jeonghun New QoS Concepts Required • Bandwidth Utility 1 0.9 0.8 0.7 User's 0.6 0.5 utility 0.4 0.3 0.2 0.1 0 User A • Delay Distribution – Depends on MAC, retransmission method – Has long tails User B • Statistical QoS support – Loss toleration & rigid delay bound 64 kb/s 128 kb/s 256 kb/s 512 kb/s 1024 kb/s Possible video data rates • Soft QoS concept – Loss differentiation – Bandwidth range How to meet QoS requirements for video applications over IEEE 802.11 wireless LANs EE384B project presentation Sarrat, Frederic – Noh, Jeonghun Preliminary Analysis • Diffserv/Intserv – Wireline part – packet differentiation over wireless links • end-to-end / Local – Adaptation vs. Localization at wireless part • Distributed / Centralized – Independent adaptation at each layer vs. – Centralized control • New architecture / modification – Compensation between performance and realization How to meet QoS requirements for video applications over IEEE 802.11 wireless LANs EE384B project presentation Sarrat, Frederic – Noh, Jeonghun Proposed System architecture WLAN Access Point Sender Application Application QoS Layer Layer requirements RTP/UDP RTP/UDP IP LLC Layer IP Ethernet LLC Layer MAC Layer MAC Layer Physical Layer Physical Layer Receiver Application Layer RTP/UDP - Type of traffic - Packet lifetime - QoS requirements Central Control Unit IP 802.11e LLC Layer MAC Layer - State of Link SNR Physical Layer Video Transmission How to meet QoS requirements for video applications over IEEE 802.11 wireless LANs EE384B project presentation Sarrat, Frederic – Noh, Jeonghun The Central Control Unit Packet CCU Packet - Data type - Lifetime PER Packet Scheduler / Dropper QoS require -ments for each flow Prioritized Queues Packet transmission parameters derivation DROP If NACK TRANSMISSION Parameters : - Amount of redundancy - Priority - Modulation scheme - Routing How to meet QoS requirements for video applications over IEEE 802.11 wireless LANs EE384B project presentation Sarrat, Frederic – Noh, Jeonghun Optimization (I) max U i Bi i N • • • where Bi B i N - Bi is the bandwidth affected to user i. - B is the total bandwidth currently available on the channel (on average, calculated using the SNR estimate) - Ui(Bi) is the utility that user i associates with bandwidth Bi. - N is the number of users 1 Pr iority TypePk PLi Ti lifetimePk 2 • - i is the priority associated with each queue (8 total). • - Pk is the current packet • - Li is the length of the queue (time to arrive in front) • - Ti is the average transmission time when it is served (including possible retransmissions) • - P() is the probability of the event in parenthesis. How to meet QoS requirements for video applications over IEEE 802.11 wireless LANs EE384B project presentation Sarrat, Frederic – Noh, Jeonghun Optimization (II) • Fairness Delay bound (large) • Efficient utilization of the bandwidth No FEC + ARQ + high rate modulation No FEC + low rate modulation (Small) light FEC + high rate modulation Drop the packet low high • Uses adaptive QoS • end-to-end feedback – Limit of local effort Channel condition – Based on channel state (PER) – Application specific/RTCP CCU decision for low priority packets How to meet QoS requirements for video applications over IEEE 802.11 wireless LANs EE384B project presentation Sarrat, Frederic – Noh, Jeonghun Conclusion & Future work • Wireless Video is challenging • Analysis of QoS support techniques at each level • New definition of QoS over wireless link • New system for application specific wireless LAN • Future work – Optimal combination of input signals – Unicast to multicast – QoS support vs fairness – Many potential research & implementations How to meet QoS requirements for video applications over IEEE 802.11 wireless LANs EE384B project presentation Sarrat, Frederic – Noh, Jeonghun