Dipanjan Chakraborty

Anupam Joshi

CSEEUniversity of

Maryland Baltimore County

Anamika:

Distributed Service Discovery and Composition Architecture for Pervasive

Environments

Printing to the Nearest Printer

Wireless Sync between PDAs

Composition of Multiple Services

Wireless Office

Discover and Compose Information from robots on the fly

Service

• “Service”– Hardware or software entity residing on any device or

platform• Has distinct functional description

• Can be utilized by other services/clients

Service

I am Wireless LAN enabled!!Blender!!

I have GPS service!!

Do you have MP3 songs?

Service Discovery

I am looking fora printer!!

Are you a Toaster ??

MANET

MANET

MANET

MANET

MANET

MANET

MANETMANET

MANETMANET

MANETMANET

MANETMANET

MANETMANET

MANETMANET

MANETMANET

MANETMANET

Issues of Discovery and Composition in Ad hoc Environments

• Service Discovery needs to be distributed– Network-wide reachability– Efficient utilization of underlying network bandwidth

• Composition needs to be done in a de-centralized manner

• Fault tolerance and graceful recovery

• Solution should efficiently utilize node/service topology

General Architecture

Network Layer (DSDV/AODV/CSGR, GSR)

Service IntegrationLayer

Application Layer

Broker Arbitration and Delegation

Service ExecutionLayer

Fault Recovery Module

Service Discovery Layer (GSD)

Planner

Group-Based Service Discovery (GSD)

• GSD= Group-based Service Discovery

• Peer-to-peer caching of service advertisements– No global advertisements– No global request broadcast

• Describe services semantically in DARPA Agent Markup Language (DAML)– Enhance service matching mechanism based on

semantic description

GSD Protocol Summary• Class/subClass hierarchy of DAML used to classify

services to different groups based on functionality• Intelligently forward requests to appropriate nodes

– Prevent request flooding• Efficient in terms of bandwidth usage and discovering a

service in a MANET

Request Routing in GSD

S1 (G1)

S4,G1,G2,G3

N4: S1 (G1)

N1: S4

N5: S2 (G2)

N3: S3 (G3)

N2

Source

Advertisement

Service Request

N6: S6 (G2)

Combining Routing with Discovery

• Service Invocation requires data streaming– Usually underlying ad hoc routing protocol (AODV,

DSR, TORA etc) used

• Disadvantages of using standard routing protocols– Repeats a few steps performed during discovery– Node-address centric packet delivery– Routing Layer is not service-aware

Advantages of Integrating Routing with Discovery

• Reduced network load– Steps performed during routing is combined with

discovery

• Usage of available routes (formed during discovery) to stream service data

• Service-based route redirection

• Resilience to node failure

Features of Integrated Discovery and Routing Protocol (GSR)

• Uses path traversed by a service request and a service advertisement to form a data path– Data path used to stream service data

• Service-based route redirection in case of service/node failure

• End-to-end state-based session maintenance – Handles node and link failure– Session-based packet buffering and retransmission

upon session reconnection

Service Composition Techniques

• “Request Processor” uses DAML-S to model Composition Knowledge

• Dynamic Broker Selection Technique– No assumption about the platform of the broker/central

entity– Broker Arbitration and Delegation

• Source of the request starts a process which decides the broker platform

– Parameters based on current processor usage, memory capability, longevity, services available in its vicinity etc

Dynamic Broker Selection Technique (contd.)– Broker discovers *all* the required services– Fault tolerance

• Source-monitored fault-tolerance– Assumption: Source remains ‘alive’ all the time

• Periodic ‘checkpoints’ being sent to the source

• Source issues a new composition request in case of failure

Service Composition Techniques• Distributed Brokering Technique

– Broker Arbitration and Delegation• Requester is responsible to determine the ‘first’ broker

– Parameters to select a broker are similar to the ‘dynamic Broker selection’ mechanism

» More emphasis on services that are needed ‘immediately’

– ‘first’ broker not responsible for the whole composition

• Composes only ‘as much’ as it can• ‘radius’ of composition is small

– ‘first’ broker selects another broker when it has completed the ‘partial’ composition

Distributed Brokering Technique (contd.)– Fault Recovery

• Similar to the one used in ‘dynamic entity selection’ mechanism

– Each broker keeps the client informed about the partial state of composition and execution

– Client issues a new composition request with the subset that is remaining

Practical Implementation

• proof-of-concept level implementation using Bluetooth – IBM Bluedrekar driver – Ericsson Development Kits

• Laptops (Dell, IBM T series) used for hosting services

Anamika: Network Manager

• Communication between Bluetooth peers done over RFCOMM

• Connect-transmit-disconnect mode of operation

• Segmentation and reassembly of Anamika messages

Anamika: Service Discovery

• Peer-to-peer service discovery (Group-based Service Discovery)

• Dynamic caching of discovered services in peers

• Semantic description based service matching (using DAML-S and DReggie Ontology)

• Service Discovery also provides invocation information

Group-based Service Discovery Results

• Simulation carried in Glomosim simulator

• 25 to 100 nodes

• Movement pattern=random way-point– A(b,c) => pause for A seconds and then move to the

next location with speed varying from b to c m/s

• Radio Range of each node=31 meters

Group-based Service Discovery Results

• Simulation carried in Glomosim simulator

• 25 to 100 nodes

• Movement pattern=random way-point

• Radio Range of each node=31 meters

Increase in Nodes Receiving Advertisements with Increase in Adv. Diameter

0

10

20

30

40

50

60

1 2 3 4 5 6 7 8

Advertisement Diameter

Av

era

ge

Nu

mb

er

of

No

de

s R

ec

eiv

ing

Ad

ve

rtis

em

en

ts

Nodes=25,Radio Range=40m

Nodes=100, Radio Range=40m

Nodes=900, Radio Range=40m

Explanation

• In static topology– Number of nodes receiving advertisements increase

quadratically with adv. Radius

• In mobile topology increase in number of nodes receiving advertisements is approximately linear– Significantly affects the scalability– Important result for mobile application architecture

development

Message Statistics comparing GSD with Broadcast

Static Topology

0

10

20

30

40

50

60

1 2 3 4

Advertisement Diameter

Avg

. Nu

mb

er o

f M

essa

ges Avg. Number of Broadcasts per Node (GSD)

Avg. Number of Selective Forwards per Node(GSD)Avg. Number of Requests processed per Node(GSD)Avg. Number of Broadcasts per Node (SBS)

Avg. Number of Requests processed per Node(SBS)

Mobility=30(1,4)

0

10

20

30

40

50

60

70

80

1 2 3 4

Advertisement Diameter

Avg

. N

um

ber

of

Mes

sag

es

Avg. Number of Selective Forwards per Node (SBS)

Avg. Number of Requests processed per Node(GSD)Avg. Number of Broadcasts per Node (SBS)

Avg. Number of Requests processed per Node(SBS)

Message Statistics comparing GSD with Broadcast

Message Statistics comparing GSD with Broadcast

Mobility=3(1,4)

0

10

20

30

40

50

60

70

80

1 2 3 4

Advertisement Diameter

Av

g. N

um

be

r o

f M

es

sa

ge

s

Avg. Selective Forwardings per Node in GSD

Avg. Requests processed per Node in GSD

Avg. Number of Broadcasts per Node in SBS

Avg. Requests processed per Node in SBS

Explanation

• Average number of messages exchanged is lower in GSD

• Mobility affects the number of messages but GSD in general performs better

• Broadcasts are very much reduced in GSD leading to the improvement in the total traffic

More GSD Results

Effect of Advertisement Diameter on Request Diameter

0

1

2

3

4

5

6

7

1 2 3 4 5 6

Advertisement Diameter

Avg

. R

equ

est

Dia

met

er

Avg. Request Diameter

GSD Results

Group-based Selective Forwarding vs. Broadcasting w.r.t No. of Requests (Static Topology)

0

10

20

30

40

50

60

1 2 3 4

Number of Advertisement Hops

Av

g. S

erv

ice

Re

qu

es

ts P

roc

es

se

d b

y a

No

de

Broadcasting Requests to all Neighbors

Selective Service group-based Forwarding

GSD Results

Group-based Selective Forwarding vs. Broadcasting w.r.t No. of Requests (Mobility=30(1,4))

0

10

20

30

40

50

60

70

80

1 2 3 4

Advertisement Diameter

Avg

. N

o.

of

Req

ues

ts P

roce

ssed

/N

od

e

AbsoluteForwarding ofRequestsGroup-basedSelectiveForwarding

GSD ResultsGroup-based Selective Forwarding vs. Broadcasting w.r.t No. of Requests (Mobility=3(1,4))

0

10

20

30

40

50

60

70

80

1 2 3 4

Advertisement Diameter

Av

g. N

o. o

f B

roa

dc

as

ts p

er

No

de

Complete Broadcasting

Group-based Selective Forwarding

Group-based Service Routing (GSR) Results

• Comparison with AODV – GSD used for service discovery– AODV used for data transmission (refered to as

GSD+AODV)– Benefits of end-to-end session studied

• Simulation on Glomosim

Avg. Packet Delivery Ratio

Avg. Packet Delay

Observations

• Packet Delivery Rate is very high for session-based service routing

• GSR (without session) performs better than AODV in general

• Packet Delay is more in GSR-S (GSR with session) – Due to buffering and retransmission

Avg. Packet Hop Count

Avg. Response Time for Discovery Requests

Avg. Response Hops Comparison

Composition Results

Effect of Response Time on Number of Services needed for a Composite Process

0

5

10

15

20

25

30

35

40

45

1 2 3 4 5

Number of Services

Ave

rag

e R

esp

on

se T

ime

(Sec

on

ds)

Average Response Time to Discover allservices

Observations

• AODV has more packet hop count than GSR/GSR-S

• Response Time for Request is low in GSR-S when compared to GSD+AODV– Mainly because GSR-S does not have the overhead of

route discovery

• In Composition, execution time increases with increasing number of services– However, the increase is very slow

Future Work

• Simulation of the whole composition architecture

• Implementation of a pro-active service discovery and composition architecture

• Mathematical modeling of the discovery and composition process