A Method for P2P Streaming System Join Latency Reduction Using Preferred Peer Lists Jeonghun Noh Sachin Deshpande* Information Systems Laboratory Stanford University * Sharp Laboratories of America

Toward Low Latency P2P Video Streaming Real-time video streaming is time-sensitive. Users prefer quick video play-back. Channel surfing benefits from a short join latency. Join latency in P2P systems During join procedure, new peers connect to peers in the system to receive video. Existing P2P networks: new peers blindly probe for parents at random. Rapid channel switching, channel surfing. GOAL: Design a P2P network that provides a small join latency

Overview Preferred Peers List System Experimental Results Conclusions Preferred Peer Cache/List Parent switching Soft Handover Experimental Results Conclusions

Overview: Preferred Peer List System Preferred Peer Cache (PPC) Caches information about available peers (preferred peers) in the overlay. Maintained by the source peer Preferred peers have a high probability of being available to other peers Using PPC for peer recommendations New incoming peers contact the source peer. The source peer sends a Preferred Peer List (PPL) containing preferred peers. The new peers directly contact the preferred peers to connect to.

Partial Learning of the Overlay Source peer partially learns about the overlay from the peer’s join / leave reports S PX PY X Y JOIN Report LEAVE Report

Using the Knowledge about the Overlay A list of peers, PPL, is created when a recommendation is requested from new peers. Among the most recently updated peers, peers recommended less often are chosen. Peer address | Use-count | Update time (in secs) 3 24.0 12 2 23.0 7 20.0 PPC (at the source) Selected peers

Join Procedure Using PPL Initial join request Contact video source Receive number of trees, video rate Receive flat list, preferred peer list (PPL) … Video stream Direct connection and peer probe Contact preferred peers on PPL Probe peers on flat list Use probe replies; if preferred peer attempt fails. Selects best parent from probe replies Parent selection factor Available bandwidth Minimize tree height Combine the prev slide to this. Instead, Note that on probing, send upstream hosts list to avoid loop. Over provisioning 1.11 for Salesman, 1.5 for Foreman

Parent Switching Preferred peer recommendations do not guarantee the best parents One method to choose better parents Utilize collected probe replies Perform the probe-based join process

Distribution Tree at time 71s No Parent Switch : video source : peer in the session : peer that left the session Can we allign slides? Also, get some values for tree height. Average Tree Height : 3.76 Average PSNR : 39.71dB

Distribution Tree at time 71s Parent Switch : video source : peer in the session : peer that left the session Can we allign slides? Also, get some values for tree height. Average Tree Height : 2.67 Average PSNR : 40.13dB

Soft Handover Parent switching may cause video discontinuity. Using Soft Handover Keep old and new parents simultaneously so that both parents forward video packets. As soon as duplicate packets are detected, send leave message to old parent.

Experimental Setup Network simulation in ns-2 Video streaming 75 / 300 active peers Random peer arrival/departure average: ON (90 sec) / OFF (10 sec) Peer uplink: typical access bandwidth / uniform bandwidth Video streaming Mother & Daughter sequence encoded with H.264/AVC @ 281 Kb/s (CIF quality) 15-minute live multicast System constructs 4 complimentary multicast trees.

Distribution of Join Latency Comparison of join time distribution PPL system versus a probe-based system Influence of peer uplink bandwidth: heterogeneous / uniform distributions Legend is blocking the curves. One plot on one slide. First tree join time Full connection time

Effects of Parent Switching Probe- based PPL PPL with Parent Switch PSNR (dB) 40.67 40.33 40.85 Average play-out latency (sec) 1.97 1.40 1.38 Bar graph. PSNR difference is so insignificant Simulation setup: 500 secs, uniform bandwidth distribution for peer uplink PSNR averaged over 10 simulations and 75 peers

Effects of Soft Handover Observations (+) Up to 55% of redundant packet forwarding is reduced (-) Slight PSNR drop may occur Ignorant Handover Soft Number of duplicate packets 7,677 3,448 Average video quality (dB) 39.89 39.72 3448/7677 => 55% reduction , 278/618 => same. 55% reduction 75peers. Session time : 200secs

Conclusions PPC keeps partial information about the P2P overlay system. Preferred peers are selected from incomplete PPC. One step closer to low-latency P2P video streaming: New peers can join faster. By switching parent after PPL-based direct attach, overlay quality is improved. By Soft Handover, up to 55% of redundant video packet transmission can be avoided.