1. Effectiveness of the 2-hop Routing Strategy in MANETS
Michele Garetto – Università di Torino, Italy
Paolo Giaccone - Politecnico di Torino, Italy
Emilio Leonardi – Politecnico di Torino, Italy
Tuesday, 15 January 2019

2. Outline Introduction and motivation Experimental traces
Analysis of the Two-Hops forwarding scheme

3. Introduction The sad Gupta-Kumar result:
In static ad hoc wireless networks with n nodes, the per-node throughput behaves as
P. Gupta, P.R. Kumar, The capacity of wireless networks, IEEE Trans. on Information Theory, March 2000   

4. Introduction The happy Grossglauser-Tse result:
In mobile ad hoc wireless networks with n nodes, the per-node throughput remains constant
M. Grossglauser and D. Tse, Mobility Increases the Capacity of Ad Hoc Wireless Networks, IEEE/ACM Trans. on Networking, August 2002

5. Introduction
Node mobility can be exploited to carry data across the network
Store-carry-forward communication scheme S R D
Drawback: large delays (minutes/hours)
Delay-tolerant networking

6. Mobile Ad Hoc (Delay Tolerant) Networks
Have recently attracted a lot of attention
Examples
pocket switched networks (e.g., iMotes)
vehicular networks (e.g., buses, taxi)
sensor networks (e.g., disaster-relief networks, wildlife tracking)
Internet access to remote villages (e.g., IP over usb over motorbike)

7. The impact of mobility
In their original paper, Grossglauser and Tse assume that the mobility pattern of each node produces a uniform distribution of node presence over the network area
results have later been extended to a restricted mobility model in which each node moves over a random great circle on the sphere
Per-node throughput is still !
S. Diggavi, M. Grossglauser, and D. Tse, Even One-Dimensional Mobility Increases Ad Hoc Wireless Capacity, IEEE Trans. on Information Theory, November 2005

8. Outline Introduction and motivation Experimental traces
Analysis of the Two-Hops forwarding scheme

9. DieselNet-Umass experiment
30 buses running the campus transport service in Spring 2005 (60 days)
traces provide the amount of data transferred through TCP connections using WLAN MAC access
mij measured in bytes

10. Infocom2005-iMotes experiment
iMotes carried by 41 volunteers attending the conference (5 days)
traces provide the radio contact duration between any two iMotes using Bluetooth MAC access
mij measured in seconds

11. Experimental traces
Virtual capacities are directly measured for each pair of nodes (i,j)
contact graph: a capacitated graph in which
each vertex corresponds to a mobile node
edge (i,j) is weighted by
The maximum throughput is computed by solving a standard multi-commodity flow problem (for a given flow assignment)

12. Experimental contact graphs
“minDC”
flow assignment
“MaxDC”
flow assignment
class 1
class 2
class 3
class 4
capacity x
10x
100x
significant asymmetries and inhomogeneous capacities
few edges contribute most of the capacity: class 3-4 contribute for 80% (Umass) and 60% (iMotes) of the overall transport capacity

13. Theoretical performance of experimental networks
Traffic scenario
Maximum aggregate capacity
Average number of hops
Umass mDC
Gbytes
2.31
Umass MDC
Gbytes
1.85
iMotes mDC
1.756 Msec
2.60
iMotes MDC
3.008 Msec
1.69
Probability
Number of hops

14. Outline Introduction and motivation Experimental traces
Analysis of the Two-Hops forwarding scheme

15. Analysis in Heterogeneous Nets.
Consider a MANET whose contact graph is a full mesh topology with capacities inhomogeneous capacity
Capacity of the archs are i.i.d random variables μij with distribiution g(x)

16. Maximum Throughput Consider a source destination pair (s,d)
The maximum throughput can be easily evaluated appling the famous max-flow min-cut theorem
Being μ= (n-1)E[μij]

17. 2 Hops throughput
The througput provided by 2-hops forwarding strategy:
Being μmin=(n-1)E[min(μsi μid)}]

18. Comparison
g(x) ≈exp (1) the efficiency of two-hops forwarding scheme is ½
g(x) ≈pareto(a,b) the efficiency of two-hops forwarding scheme is 2(b-1)(2b-1)
Going to 0 for b →1.

19. ...the end...