Author:Minsu Shin, Seongik Hong, Injong Rhee
Publication:CHANTS
Year:2008
In this paper, we apply Levy walk patterns to routing in delay tolerant networks(DTN).Using the optimality property of Levy walks, we devise two styles of routing strategies.One is an active strategy using message ferries(MF) where the movement of MFs can be controlled to have a Levy walk pattern in order for them to maximize the opportunity of meeting the destiniations and the other is a passive strategy(Scale Free Routing,SFR) in which the movement of nodes cannot be controlled, but messages are forwarded in such a manner that their forwarding patterns mimic the Levy walk patterns.
Levy Walk Mobility Model:
A variety of mobility models have been proposed.Random Way Point(RWP) and Brownian Motion(BM) are well known models.We proposed a Levy walk mobility model called Truncated Levy Walks(TLW) in which flight length and pause time distributions follow truncated power laws.We show based on the analysis of GPS recorded human walk traces that these heavy tailed flight length and pause time distribution in TLW statistically resembles human mobility.
[Reference this paper for more detail on Truncated Levy Walk]
Scale-Free Routing:
If utility is lower than certain threshold, SFR chooses ballistic nodes as relays until nodes move into an area where utility is high.Otherwise, it switches to gradient schemes.The definition of utility can vary depending on gradient schemes and SFR can be applied to any gradient schemes.
Under low density, the long-jump routing and SFR have smaller delivery delays compared to utility and seek and focus. Hower , long-jump routing suffers from much higher delays when the node density is getting higher.In contrast ,SFR achieves similar performance as utility routing.
It shows that position information is not useful for choosing ballistic relays.This shows that SFR can be practically adapted while achieving better performance.
Levy Message Ferries[Mobility patterns follow TLW]:
Assume that msgs are delivered only by one MF node and other nodes just generate or receive message.
In simulation run, all nodes excepts MF (target nodes)move according to TWL with a.MF also uses TLW but uses different diffusivity of node mobility.As a becomes smaller, the occurrences oflong flights get more.It induces higher diffusivity.If the parameter is larger than 2, the long flight probability diminishes rapidly and the motion approaches to BM.
Fixed Transmission Range:
Varying Transmission Range:
In reality, when nodes move faster their transmission ranges get smaller.
The speed of humans has high correlation with flight lengths.
The more the target nodes are mobile, the less mobile MF should be to achieve the best performance,suggesting that adjusting the statistical mobility patterns of MF according to the statistical mobility patterns of target nodes yield good performance.
Related Work:
Message Ferries:M.M.B.Tariq,M.Ammar, and E.Zegura.Message ferry route design for sparse ad hoc networks with mobile nodes.In ACM MobiHoc,pages 37-48,2006.
Throw Boxes:W.Zhao, Y.Chen, M.Ammar, M.D.Corner, B.N.Levine, and E.Zegura. Capacity enhancement using throwboxes in dtns. In IEEE MASS, October 2006
The main difference between MF and throwbox is that MF is moving while throwboxes are stationary.
Examples of multi-copy routing:Epidemic routing, Spray and Wait, RAPID
Examples of Single copy routing:
- Direct transmission,
- Two hop relay
- Randomized Routing
- Utility based routing
- Mobispace
- Seek and Focus
Conclusions:
Ballistic nodes mimic long flights in Levy walks while utility-based gradient routing can be viewed as short flights.
The levy walk search patterns can also be used for other applications such as content distribution in DTN enviroments.
My Questions:
1,How to judge that a node is high diffusive?