Xiaofei Liao,
Basic:
- inter-overlay optimization, resources can join multiple overlays,
Goal：
- (1) improve global resource utilization and distribute traffic to all physical links evenly;
- (2) assign resources based on their locality and delay;
- (3) guarantee streaming service quality by using the nearest peers, even when such peers might belong to different overlays; and
- (4) balance the load among the group members.
Metrics:
- startup delay
- source-to-end delay
- playback continuity
Problem:
- still suffer from long delay and unplanned interruptions, especially when a large number of peers join the network simultaneously.
challenges:
- (1) how to find paths with low delays, including source-to-end delay and startup delay, in a global P2P network;
- (2) how to maintain the service continuity and stability (decreasing the impact of interruption caused by peers leaving);
- (3) how to determine the frequency of optimization operations; and
- (4) how to reduce the control overhead caused by the algorithm.
Component：
- inter-overlay optimization manager
- explores appropriate paths, builds backup links, and cuts off paths with low QoS for each end peer.
- key node manager
- allocates the limited resources: admission control policy
- buffer manager
- manages and schedules the transmission of media data.
Peer join or leave the topology
- LastDelay, which is the minimal of all source-to-end delays from the current node to the streaming source on different paths.
- Peers join or leave the topology according to LastDelay.
- Generally, each peer maintains one active streaming path set and one backup streaming path set.
- When the number of backup streaming paths is less than a threshold, the inter-overlay optimization algorithm is called to find appropriate streaming paths in the global P2P network with the help of the mesh-based overlay.
- a probing message named ProbM
- There are mainly two tasks for the inter-overlay optimization manager, including backup streaming path set management(reverse tracing) and active streaming path set management.
- When one active streaming path is cut off due to its poor QoS or peer’s leaving, a new streaming path is selected from the backup set.
Fetch algorithm:
- The playback deadline for each segment and the heterogeneous streaming bandwidth from partners.
topologies
- two types of topologies, physical topology and logical P2P topology.
- AnySee requires each peer maintain an INCD, from which each peer can have a position, named GID in the global network. The GID value of an end host is a 128-bits integer encoded by the 4-layer geometrical information corresponding to ISPs, cities, campuses, and buildings,
- height is always less than 7 even with a thousand peers included in one tree
Buffer size
- a small buffer space is enough, and indeed a small buffer often means a shorter startup delay.
- threshold DS is set to 25 seconds
- the necessary buffer size of AnySee is only 40 seconds, while Coolstreaming needs a 120-second buffer.
- layer-aware buffer management: Each peer computes its appropriate buffer space size according to the layer number.
Delay
- xx is the average disconnection times of one connection. T’ is the total transporting delay, ta denotes the total link delay,
- source-to-end delay is always less than 200 ms. the startup delay of most peers is less than 20s. the startup delay of Coolstreaming is around 60 seconds.
Problem
- too many users are leaving the overlay is the signal that the overlay is under heavy burden and needs to be optimized.
- “optimization index”, ADL= leaving percentage100 / average delay
Refer
- Simulation topology
- we use BRITE [3] generating three topologies, each with 5,000 nodes. The average number of neighbors of each node ranges from 4 to 10.
- a crawler based on Gnutella protocol [1] and the source codes are rewritten from Limewire open source client [2] forty-five independent threads, our crawler discovers over fifty thousands peers and their connections in one week.
- A location detector based algorithm is employed to match the overlay with the underlying physical topology [25].
- [25] Y. Liu, L. Xiao, X. Liu, L.M. Ni, and X. Zhang, "Location Awareness in Unstructured Peer-To-Peer Systems", IEEE Transactions on Parallel and Distributed Systems, 2005.
- LTM (Locationaware Topology Matching) technique [25] two major operations: flooding-based detection with limited TTL, and updating logical connections. dm(id, S, TTL)
- Simulation based on topologies from real P2P networks [1].
- NTP
- Current implementation of NTP version 4.1.1 in public domain can reach the synchronization accuracy down to 7.5 milliseconds [27].
- [27] NTP: The Network Time Protocol, .
- single tree protocols, such as ESM, NICE [19] and ZigZag [18]
- [13] Y. Chu, S. G. Rao, and H. Zhang, "A Case for End System Multicast," in Proceedings of ACM SIGMETRICS, 2000.
- [19] S. Banerjee, B. Bhattacharjee, and C. Kommareddy, "Scalable Application Layer Multicast", in Proceedings of ACM SIGCOMM, 2002.
- [18] D. Tran, K. Hua, and S. Sheu, "Zigzag: An Efficient Peer-To- Peer Scheme for Media Streaming", in Proceedings of IEEE INFOCOM, 2003.
- multiple tree protocols [14][15].
- Problem: the leaving or crash behavior of nodes in the upper layers often causes buffer underflow.
- mesh-based protocols: as Coolstreaming, PROMISE [17] and GNUStream [21].