A Cross-layer Decentralized BitTorrent for Mobile Ad Hoc Networks
Rajagopalan and Shen
bittorrent p2p sharing manet cross-layer
@inproceedings{rajagopalan:mobiquitous-2006,
title={A Cross-layer Decentralized BitTorrent for
Mobile Ad Hoc Networks},
author={Rajagopalan, S. and Shen, C.C.},
booktitle={Workshops of the 3rd International Conference on
Mobile and Ubiquitous Systems ({MobiQuitous})},
year={2006},
organization={{IEEE}}
}
Wired P2P protocols expect stable routes, high bandwidth, high uptime
MANET nodes have frequent link breakages, topology changes, network partitions, and node outages
BitTorrent not directly applicable to MANET
- Centralized control & point of failure in the tracker, torrent sharing
- If all seeds disappear or are partitioned, file is lost
But has some nice features
- On-demand overlay construction
- Cost of download split across multiple peers rather than one assuming all
- Clients can begin sharing files as soon as they have some pieces
Many P2P protocols proactively maintain the overlay, which is costly on a MANET due to high rates of change
Since every node may be involved in routing, every node has some topology information it may use in selecting peers
- Doesn't this depend greatly on selected routing protocol?
Basic protocol
- Initial seed broadcasts torrent file
- Torrents maintained by probabilistic gossip
- When torrent is requested
- Local cache consulted
- Expanding ring search broadcast if not locally stored
- Search for peers
- Local cache consulted
- Expanding ring search to find peers
- Exchange peer information, select peers with some input from topology information
- Peer search redone periodically to update peer list during download
Protocol additions
- Nodes which match a hash function of the torrent become proxy seeds
- Immediately download file from initial seed (using BitTorrent scheme, not straight download)
- Serve up that file
- Helps mitigate partitions
- Nodes share downloaded files for probabilistic period of time
Of note: