1. A Parameter-Based Service Discovery Protocol
for Mobile Ad-Hoc Networks
´ ˜
Unai Aguilera and Diego Lopez-de-Ipina
unai.aguilera@deusto.es
DeustoTech - Deusto Institute of Technology, University of Deusto
Bilbao, Spain
http://www.morelab.deusto.es
July 10, 2012

2. Outline
Introduction
Overview
Taxonomy usage
Search
Conclusions
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3. Motivation
MANET of devices providing services.
Devices connect/disconnect
No central information manager
Service Oriented Applications ⇒ Service Discovery
Current solutions
Search using service identifiers or service type
Not suitable when searching for functional properties
Service Composition
Create service work-flows to provide new functionalities to the
users.
Discover compatible services (Input/Output).
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4. Parameter-based Service Discovery
Services are located using their input/output parameters
I/O parameters are classified
Taxonomy of concepts
Parameter dissemination
Service search and route management
Other elements
Neighbour detection ⇒ using periodic beacon messages.
Reliable broadcast ⇒ ACK messages
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5. Parameter dissemination
Each node mantains a Parameter table
The higher the value ⇒ the closer a parameter of that type.
Local parameters Dd (max. dissemination value).
Real distance (hops) = Dd - value.
Decremented with each hop until it reaches 0.
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6. Parameter table
Defined as a table of {P, L} pairs.
P ⇒ parameter type.
L ⇒ list of elements (D, N). Multiple Paths
D ⇒ disseminated distance value.
N ⇒ neighbour (e.g network address) which supplied the
information. Avoid back-propagation.
Proactive algorithm
Dissemination starts on nodes with services.
New neighbour detection ⇒ broadcast parameter table.
Neighbour disappears ⇒ remove entries received from that
node.
Updates are propagated across the network.
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7. Updates propagation
Changes are propagated to neighbours using UpdateTable
messages.
Deletions ⇒ list of entries which must be removed from
receiver’s tables.
Additions ⇒ contains new information to be added.
Nodes apply received updates
Changes are incremental. Reliable broadcast needed.
If changes occur in a node parameter table ⇒ continue prop
agation. Except
Maximum dissemination distance reached.
No more values to delete.
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8. Taxonomy and parameter grouping
Pre-shared taxonomy relates the types of disseminated
service’s parameters
Expressed in XMLSchema, RDF or OWL.
Let A and B be two different parameters
Equality occurs when their type is equal.
Subsumption means that A has a more general type than B.
Not-related if none of previous conditions occurs.
Parameter grouping
A group represents all those parameters related through
equality or subsumption relationships.
Parameter tables are grouped during dissemination.
Reduce the number of broadcasted messages.
Most general concept. (A and B as A)
Highest value.
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9. Neighbour detection
Protocol is proactive.
Disseminates and maintains parameter information.
Searches are hold until explictly cancelled.
Reaction to network mobility needed.
Usage of periodic beacon messages.
Table of known neighbours.
Nodes send beacons with a period Tb
Expiration time T ≥ 2 ∗ Tb
Any message acts as beacon message.
Neighbour updates are notified with an small delay.
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10. Reliable broadcast
IEEE802.11 does not avoid hidden terminal/collisions.
Proposed dissemination uses incremental changes.
Reliable broadcast
List of expected destinations.
1-hop neighbours reply with an ACK message.
Messages will be repeated until correctly received.
Random time for rebroadcast.
To reduce number of broadcasted messages.
Multiple messages ⇒ one single broadcast.
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11. Taxonomy propagation
A subsumes B
New nodes appear
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12. Taxonomy propagation
A subsumes B
Network breaks
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13. Experiments configuration
Simulated with NS-2 + AgentJ (Java 1.6 implementation).
100 nodes.
700x700 area.
Transmission range 100 m.
IEEE802.11 as MAC protocol.
11 Mb/s and MTU 1500 bytes.
Maximum dissemination distance 10 hops.
Random Waypoint
Speed 0-5 m/s. Pause time: 50, 100 s.
This scenario has1
Average Network Partition ≤ 5%
Average Shortest Path = 4.15 hops
1
Kurkowski, S., Navidi, W., Camp, T.: Constructing MANET simulation
scenarios that meet standards. In: IEEE Intl. Conf. on Mobile Adhoc and
Sensor Systems. pp. 1–9 (2007)
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14. Dissemination experiment
2 to 20 services deployed with and without replication.
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15. Service search
Service search is started by sending a SearchMessage
Types of service’s parameters to locate.
Propagation controlled using a TTL.
Flooded ⇒ Unique search ID.
Active until explicitly cancelled.
Two search types:
Exact: I/O parameters of the same exact type are located.
Generic: exact and subsumed types are located.
Node accepts a search message ⇒ SearchResponse
message is sent to searching node.
Using unicast routes created during the propagation of search
messages.
Response message also create unicast routes.
Route tables are updated during mobility.
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16. Search pruning
Search is propagated only if:
TTL ≥ (Dd − v ).
v is obtained from the parameter table
Meaning that:
Near compatible parameters exist.
Can be reached with the current search message TTL.
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17. Search experiment
30 services randomly distributed with 6 parameters each one.
Searches performed each 5 seconds. Groups of 5 nodes.
10 seconds until search cancelled.
a) b)
c) d)
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18. Conclusions
Protocol for service discovery proposed and tested.
Situations where a functional search is required (e.g service
composition).
Two parts:
Dissemination
Disseminates service I/O parameters instead of service type or
id.
Uses taxonomy information to group paramaters and decrease
the number of messages.
Service search
Performs pruning based on disseminated information to reduce
message overhead.
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19. Future work
Generalize proposed protocol to propagate and search any
kind of information, not only service parameters.
Propagation of taxonomies through ad hoc network avoiding
a pre-shared one.
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20. Questions?
Thank you!
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