Fully Decentralized Information System
Last updated
Last updated
Global scale application.
Example: Gnutella.
40.000 nodes, 3 Mio files.
3M nodes (Jan 2006).
Good response time, scalable.
No infrastructure, no administration.
No single point of failure.
High network traffic.
No structured search.
Free-riding.
| Type | Description | Contained Information |
|---|---|---|
Ping | Announce availability and probe for other servents. | None. |
Pong | Response to a ping. | IP address and port# of responding servent; number and total kb of files shared. |
Query | Search request | Minimum network bandwidth of responding servent; search criteria. |
QueryHit | Returned by servents that have the requested file | IP address, port# and network bandwidth of responding servent; number of results and result set. |
Push | File download requests for servents behind a firewall | Servent identifier; index of requested file; IP address and port to send file to. |
(Query/QueryHit/GET)
Queries are flooded to neighbors, have a TTL, and are forwarded only once.
A query may obtain several responses indicating which peers provide the requested file. Among those, it selects one and is directly contacted in order to download the file.
Can we search using fewer packets?
Expanding Ring.
Start the search with small TTL (e.g. TTL = 1).
If no success iteratively increases TTL (e.g. TTL = TTL +2).
k-Random Walkers.
Forward the query to one randomly chosen neighbor only, with large TTL.
Start k random walkers.
Random walker periodically checks with the requester whether to continue.
Ultrapeers can be installed (KaZaA) or self-promoted (Gnutella v.2).
Popular open-source file-sharing network.
~450,000 users as of 2003.
~2,000,000 today.
Ultrapeer-based Topology.
Queries flooded among ultrapeers.
Leaf nodes are shielded from query traffic.
Based on multiple crawlers.
