Routing and transport challenges in mobility assisted communication
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Routing and Transport challenges in mobility-assisted communication. Konstantinos Psounis Assistant Professor EE and CS departments, USC. The need for mobility-assisted communication. Intermittent connectivity  lack of contemporaneous end-to-end paths Disaster communication

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Routing and Transport challenges in mobility-assisted communication

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Routing and transport challenges in mobility assisted communication

Routing and Transport challenges in mobility-assisted communication

Konstantinos Psounis

Assistant Professor

EE and CS departments, USC


Routing and transport challenges in mobility assisted communication

The need for mobility-assisted communication

  • Intermittent connectivity  lack of contemporaneous end-to-end paths

    • Disaster communication

    • Vehicular ad hoc networks

    • Sensor networks for environmental monitoring and wildlife tracking

    • Ad hoc networks for low cost Internet provision to remote areas

    • Inter-planetary networks

    • Ad-hoc military networks

  • Routing: “store-carry-and-forward” model

  • Transport: message-oriented approach, link-layer retransmissions

  • Interoperability with “traditional” network segments also a goal


Example of store and forward routing

Example of store and forward routing

1

12

D

13

S

14

2

16

11

15

3

7

8

5

10

4

9

6


Routing

Routing

  • Redundant copies reduce delay

  • Too much redundancy is wasteful and induces a lot of interference

  • Middle ground:

    • spray a small number of copies to distinct nodes

    • use carefully chosen relay-nodes to route each copy towards the destination

  • Challenges

    • How many copies to use?

      • derive formal expressions that take into account real world limitations and compute number of copies that guarantee performance targets

    • How to optimally spray the copies

      • use stochastic optimization and portfolio theory to find optimal policy

    • How to optimally choose relays?

      • find a good utility function that indicates the goodness of a node as a relay


How well spraying based routing works

Tx Range K (connectivity: % of nodes in max cluster)

How well spraying-based routing works?

500x500 grid, 200 nodes, medium traffic load

  • Spraying schemes outperform flooding schemes in terms of both transmissions and delay

  • As connectivity increases

    • delay of spraying schemes decreases

    • delay of other schemes increases due to severe contention


How many copies to use

How many copies to use?

to be within some distance from optimal

  •  = expected delay of spraying schemes over the expected delay of an oracle-based optimal scheme

α = 2

Number of Copies L (M = 100)

α = 5

α = 10


How to spray the copies

How to spray the copies?

Optimal policy:

node A has l copies for node D

node A encounters node B

150x150 grid, 40 nodes, K=20

  • Practical heuristic:

    • if l  lth (a few copies)

      • the best node should keep/get all copies

    • else (a lot of copies)

      • do binary spraying (split copies in half)

B closer to D

A closer to D

lth


Transport

Transport

  • Message oriented transport

    • rather than stream-oriented (no concept of flow)

  • Link layer retransmissions

    • hard to support end-to-end feedback mechanisms

  • Congestion control:

    • short term relief: if a node is congested give it priority over other nodes that contend for the same medium

      • challenging to identify and coordinate these nodes in practice

    • medium term relief: use congestion information to dynamically adapt routing paths

      • e.g. lower utility of congested nodes

    • Of course, source rate adaptation should eventually occur if network is oversubscribed


Set of contending nodes

Set of contending nodes

  • Congestion control and fairness require coordination among contending nodes

  • Which are those nodes?

    • assume, for simplicity, a single disk model for the transmission and interference range

R

S


Interoperability

Interoperability

  • Future network:

    • Wired core

    • Wireless edge

      • single-hop wireless sub-networks (SWN)

      • multi-hop wireless sub-networks (MWN)

  • Use core-edge elements to break connections into sub-connections

    • mask differences

Delay/disruptive tolerant MWN

Sensor/Mesh MWN

WiMax SWN

A

Ac

Base station

WiFi SWN

Bc

Core-Edge

Element

B

Mobile Ad-Hoc MWN


Core edge element functionality examples

Core-edge element functionality examples

  • Transport connection management

    • Hide latencies and disconnections from the wired core

    • e.g. delay the start of successive sub connections until enough data are accumulated

  • Packet caching

    • Core-edge element acts as proxy of sender or receiver

    • e.g retransmit cached packets in case of loses

      • no requirement to contact (hard to locate) source


Experimentation and applications

Experimentation and applications

  • Human mote experiments

    • students carry motes within main campus and on its vicinity

  • USC testbed

    • hundreds of static nodes arranged in disconnected clusters (tutornet platform) and a handful of radio-capable robots (robomote project) to bridge the gaps between them

  • Applications

    • offer connectivity for delay tolerant applications to USC commuters

      • in collaboration with the university transportation office

    • customize protocols for VANET applications


Routing and transport challenges in mobility assisted communication

Selected Publications and funding sourcesmore infoavailable at http://ee.usc.edu/research/netpd/publications/

  • Publications:

  • Routing

    • Efficient Routing in Intermittently Connected Mobile Networks: The Multi-copy Case, T. Spyropoulos, K. Psounis, and C.Raghavendra, to appear in IEEE/ACM Transactions on Networking, February 2008.

    • Efficient Routing in Intermittently Connected Mobile Networks: The Single-copy Case, T. Spyropoulos, K. Psounis, and C. Raghavendra,to appear in IEEE/ACM Transactions on Networking, February 2008.

    • Performance Analysis of Mobility-Assisted Routing, T. Spyropoulos, K. Psounis, and C. Raghavendra, ACM MOBIHOC, Florence, Italy, May 2006.

  • Transport

    • Interference-aware fair rate control in wireless sensor networks S. Rangwala, R. Gummandi, R. Govindan, and K. Psounis, ACM SIGCOMM, Pisa, Italy, September 2006.

  • Mobility

    • Modeling Time-variant User Mobility in Wireless Mobile Networks, W.-j. Hsu, T. Spyropoulos, K.Psounis and A. Helmy, IEEE INFOCOM, May 2007.

  • Funding:

    • External: NSF Nets

    • Internal: Zumberge foundation, startup funds


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