1. Plethora: Infrastructure and System Design

2. Introduction Key features: Peer-to-Peer (P2P) networks: Key problems:
Self-organizing distributed systems
Nodes receive and provide services cooperatively
No predetermined client/server roles
Key features:
Scalable
Adaptive and reconfigurable
Leverage technology trends (network/processor/memory)
Key problems:
Locating and routing objects efficiently
Consistency management
Fault-Tolerance

3. Location and Routing - DHT
Apply structure to the network:
Inputs hashed to a key
Each node responsible for a subset of keys
Nodes maintain small routing tables
Queries routed to neighboring nodes that ensure progress towards the ultimate destination.

4. Location and Routing - DHT
0XXX
1XXX
2XXX
3XXX
0112
2321
START
0112 routes a message to key 2000.
2032
First hop fixes first digit (2)
2001
Second hop fixes second digit (20)
END
2001 closest live node to 2000.

5. Motivation Virtualization destroys locality.
Query responses do not contain locality information.
Recent studies show that queries for multiple keys in P2P networks follow a Zipf-like distribution.
Exploit geographic locality.
Build highly-distributed collaborative environments and applications:
information lifecycle
distributed file systems
software distribution
archival storage and disaster recover

6. IP Addresses as Virtual IDs
Incorporate locality into overlay networks:
Explore addressing scheme of the underlying network.
In most cases, nodes with IP addresses that are numerically close are also physically close.
Organization of the Internet in ASs. By correcting a few bits in each hop, the last hops would be inside an AS.
Issues:
IP space is not uniformly populated by peers.
Load imbalance at the peers.
The upper bound of O(log n) can no longer be guaranteed.

7. IP Addresses as Virtual IDs

8. IP Addresses as Virtual IDs

9. IP Addresses as Virtual IDs
2,420 nodes. 20 keys per node.

10. Plethora Two-level overlay
One global overlay
Several local overlays
Global overlay is the main repository of data.
Global overlay helps nodes organize themselves into local overlays.
Local overlays exploit the organization of the Internet in ASs.
Size of the local overlay is controlled by an overlay leader.
Uses efficient distributed algorithms for merging and splitting local overlays.

11. Cache Organization

12. Simulation Setup
Internet topology generated using GT-ITM topology generator.
10,000 overlay nodes selected randomly from the hosts.
NLANR web proxy trace with 500,254 objects.
Zipf distribution parameters: {0.75, 0.80, 0.85, 0.90, 0.95}
Local cache size: 5MB (LRU replacement policy).

13. IP Addresses as Virtual IDs

14. Simulation Results Zipf-parameter Cache Hit Ratio Gain 0.75 76% 31.0%
0.80
79%
33.5%
0.85
81%
36.0%
0.90
83%
38.7%
0.95
86%
41.3%

15. Summary IP addresses as virtual IDs: Plethora Routing Core:
Overlays with good locality properties.
Non-uniform realworld distribution:
severe load imbalance
no bounded latency
Plethora Routing Core:
Two-level overlay architecture.
Local overlays are created to cluster nodes that are close in the underlying network.
Significant performance gains
Low maintenance overhead

16. Latency Hiding
For large-scale collaborative and distributed applications:
latency effects are still an issue.
need resliency in the presence of network failures.
Record updates using a transactional versioning system:
Aggregate updates
Distributed conflict resolution

17. Versioning and Transaction Model
Local Home
Global home T2 T3
commit Tk
Tk+1
Tk+2

18. Open Issues Implementation of versioning trees
Efficient update and commit protocols
Dealing with failures (node, network)
Object structure of the repository to exploit versioning semantics
What guarantees can the system provide on object access and consistency of updates?