Ad-hoc Storage Overlay System (ASOS): A Delay-Tolerant Approach in MANETs

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Ad-hoc Storage Overlay System (ASOS) A
Delay-Tolerant Approach in MANETs

• Guang Yang1, Ling-Jyh Chen2,
• Tony Sun1, Biao Zhou1, Mario Gerla1

1 University of California, Los Angeles 2
Academia Sinica, Taiwan
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Motivation

• MANETs often deployed in adverse environment that
  are less reliable.
• Nodes in MANETs can crash, lose power, be
  blocked, or move out of communication range.
• Difficult to guarantee continuous end-to-end
  connectivity in MANETs.

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Background What is DTN?

• A new network architecture for challenged
  scenarios of intermittent connectivity
• Space communications,
• Messages to remote villages,
• Wildlife monitoring,
• etc.
• DTN highlights
• Mimics the post office model,
• Data are aggregated into bundles,
• Bundles are sent hop-by-hop to the destination
  (compared to end-to-end in the Internet).

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Why DTN is needed in MANETs

• In MANETs, connectivity is highly susceptible to
  mobility, interference, failures, etc.
• As a result, e2e connections break frequently.
• Many solutions aim to add new nodes to bridge the
  gaps.
• We introduce the DTN concept into MANETs.
• ASOS Ad-hoc Storage Overlay System
• Deploy on existing MANET nodes
• Data is stored in a distributed and redundant way
  among participating ASOS peers.
• Opportunistic data delivery relies on node
  mobility.
• Follows DTN semantics and complements end-to-end
  transport.

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ASOS Example
D
4 ASOS data delivery
2 Network partitioning
ASOS overlay
3 Data temporarily stored in nearby ASOS peers
1 Conventional end-to-end transport
S
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Basic Architecture
When the destination node is at location 1 and
disconnected from the source node, undeliverable
data is submitted to ASOS for storage (1).
Stored data is delivered to the destination node
(2) after it is reconnected to the network at
location 2.
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Interaction with Routing
Two methods to activate ASOS. The first is
initiated by the source node after receiving a
route error message. The second is initiated by
an intermediate ASOS peer node.
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Distributed Storage
Distributed storage of a file in ASOS. The first
200 data units of File 1 have been delivered
end-to-end to the destination. The next 150 units
have been submitted for storage at an earlier
ASOS agent A. The current ASOS agent is B with 50
units already submitted.
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Data Replication
Probabilistic replication of data. Node B has a
lower but non-zero probability of holding a copy.
Nodes C and D have comparable probabilities
though neither of them deterministically hold a
copy.
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Evaluation Mobility Model
Key concepts Switch stations Tracks
Mobile/static nodes Groups Split/merge
The Virtual Track mobility model. One group is
split into three subgroups at the center switch
station, while two groups merge at the
bottom-right switch station.
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Evaluation Scenario
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Evaluation Instantaneous Throughput
ASOS instantaneous throughput may temporarily go
above the input rate. Reason stored fresh data.
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Evaluation Delivery Ratio
Cumulative amount of data delivered to the
destination. ASOS delivers both fresh and stored
data overall delivery ratio is higher.
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Summary

• DTN concept is very useful in MANETs where
  continuous connectivity cannot be guaranteed,
• ASOS is designed for native DTN support in
  MANETs.
• Available immediately after network is deployed,
• ASOS stores data safely during connectivity
  disruptions.
• Opportunistic data delivery in ASOS eventually
  increases the delivery ratio compared to pure
  end-to-end transport.

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Q As

• Thank you!