Focus on Distributed Hash Tables

Distributed hash tables (DHT) provide resource locating
and routing in peer-to-peer networks
– But, more than object locating and routing
– Basically, a routing network

Outline
– Three papers
• Mobile Grid
• Broadcast
• An architecture based on DHT for grid resource location and
allocation for massively distributed applications
– One implementation
• Grid resource location and allocation
Wireless Grid

Vision: provide a easy way to access resource in the
grid
– PUT and GET: put/get a resource from/into the grid
– Fundamental service: routing!

Comprise of stationary Internet hosts and wireless
devices
– Wireless devices can change their network attachment points

A potential application: NCHC’s EcoGrid
– Internet severs + sensors in the wild

Our solution to provide a wireless grid
– Based on distributed hash tables (DHT)
Wireless Grid (cont’d)

Nodes can change their network addresses
 Research problem
– Given the network bandwidth budget (Bi) of each node i to
maintain the DHT
– How to efficiently utilize Bi of each node i to provide efficient
routing
• By efficiency, the route takes nearly zero timeouts
An example of DHT
Failed route from 1 to 12
Successful route
Wireless Grid (cont’d)

Preliminary results
– PHT: percentage of hop counts due to timeouts
– PBT: percentage of maintenance bandwidth due to timeouts

Manuscripts in preparation
– Mobility churn in DHTs
– Nearly, optimal peer state supervision for mobile DHTs
Our sol.
Broadcast in Dynamic P2P Networks

Broadcast is a basic building block for many P2P
applications
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
Message broadcast
Query routing in unstructured P2P networks
Diagnostics for overlay network structure
…
Broadcast in P2P networks
– Each message has a TTL value
– TTL decreases when the message is forwarded every time
– A message is not forwarded if TTL = 0
Broadcast … (cont’d)

Research problem
– Given a TTL value
– How to maximize the broadcast scope while to minimize the
maintenance bandwidth?

Intuition behind: to maximize the broadcast scope
requires the overlay network being maintained robustly!
Broadcast … (cont’d)

There is no easy way to maximize the broadcast scope and
meanwhile to minimize the maintenance bandwidth
– We investigate several scalable failure detection and recovery
mechanisms in the context of DHT
– Paper under reviewed: scoped broadcast in dynamic peer-to-peer
networks
P2P Mechanism for Grid Resource
Location and Allocation

Overview
P2P Mechanism for Grid Resource
Location and Allocation (cont’d)

Organizes the allocated resources as a tree-like overlay

Submit tasks using Armada agents
– Send the agents to the tree root
– The tree root helps distribute the agent codes to its children
Implementation

Targeted environment: NCHC UniGrid

Status:
– A DHT Prototype for a cluster environment is
available
– P2P mechanism for Grid resource location and
allocation
– Hopefully, can be tested in UniGrid