effects of routing computations in content-based routing networks with mobile data sources vinod...

Effects of Routing Computations in Content-Based Routing Networks with Mobile Data Sources

Vinod Muthusamy, Milenko Petrovic, Hans-Arno Jacobsen

University of Toronto

August 30, 2005

Eleventh Annual International Conference on Mobile Computing and Networking

(MobiCom 2005)

Aug. 30, 2005 (MobiCom ’05) Mobile-ToPSS (University of Toronto) 2

Motivation Explosion in the number information producers

Blogs, wikis, podcasting, photo sharing

Mobility of users Cell phones, PDAs, sensors

Mobile information producers Fixed information producers are increasingly mobile New types of information producers

SMS, camera phones, location-based services

Publish/subscribe data dissemination Well suited to mobile clients

Decoupling, filtering

Effects of routing computations on pub/sub network with mobile information producers has not been studied Causes drastically different results and different conclusions


Publisher Mobility Scenarios Journalists with blogs

Update blogs on location Upload pictures from camera

phone

Police patrol car Status reports about

accidents, traffic, crime

Mail delivery Track delivery status,

location, broken parts

Information producer

1 2


Agenda

Publish/subscribe background Model and distributed protocol Routing operations

Publisher mobility Problem

Invalid assumptions cause excessive state maintenance Solution

New protocols to distinguish temporary disconnections

Evaluation Effects of routing computations on protocols


Publish/Subscribe Model

Publisher Publisher

Subscriber Subscriber

Subscriptions

Publications

NotificationNotification

Gridlock

Robbery AccidentNeed Backup

Snow

Fire

Congestion

Traffic Reports

Subscription:Name = “Bob”Report = “Accident”

BrokerNetwork

Subscription:Injury = TrueLocation = “Cologne”


Distributed Publish/Subscribe Advertisements

flooded Create ad tree

Subscriptions along reverse ad path Create

multicast tree

Publications along reverse sub path

PublisherSubscriber Subscriber

. . .. . .

Advertisements Subscriptions Publications


Generic Pub/Sub Router Operations Advertisement handling

Insert ad into AdsTable Find covering ads Find intersecting subs

Subscription handling Insert sub into SubsTable Find covering subs Find intersecting ads

Publication handling Find matching subs

Insertion

Covering

Intersection

Y

Y

N

N

e.g. “severity < 4”

“severity < 4”is covered by“severity < 6”

“severity < 4”intersects

“severity > 2”


Modeling Routing Computations Cannot ignore computations in distributed pub/sub protocols

Classes of algorithms FAST: tuple-based data (e.g., attribute-value pairs)

[Fabret et al., SIGMOD 2001] COMPLEX: tree or graph structured data (e.g., XML, RDF)

[Petrovic et al., WWW 2005]

Based on best reported results under most favorable workloads

Operation FAST COMPLEX

Matching O(1) O(n)

Covering O(matching)* O(matching)*

Intersection O(matching)* O(matching)*

Insertion O(matching)* O(matching)*

*Conservative estimates where no data available(Algorithms usually tuned for matching performance)


Publisher Mobility


Publisher Mobility Problem Ad and sub trees Moveout: both trees torn down Movein: both trees rebuilt Expensive

# ad messages > # sub messages No delivery until tree constructed

Distinguish temporary disconnections

t1

At Old Broker

t3

Disconnected At New Broker

t5t4

Can publishnew events

Connect(movein)

Disconnect(moveout)

t2

moveout

Publisher

1 2

. . . . . .


Publisher Mobility Problem Ad and sub trees Moveout: both trees torn down Movein: both trees rebuilt Expensive

# ad messages > # sub messages No delivery until tree constructed

Distinguish temporary disconnections

t1

At Old Broker

t3


t5t4


Connect(movein)

Disconnect(moveout)

t2

movein

Publisher

1 2

. . . . . .


Prefetching Protocol

Exploits knowledge of future mobility patterns

Concurrent Construction at new broker Teardown at old broker

Tree construction time hidden from user

t1

At Old Broker

t3


t5t4


Connect(movein)

Disconnect(moveout)

t2

moveout

Publisher

1 2

. . . . . .


Prefetching Protocol

Exploits knowledge of future mobility patterns

Concurrent Construction at new broker Teardown at old broker

Tree construction time hidden from user

t1

At Old Broker

t3


t5t4


Connect(movein)

Disconnect(moveout)

t2

movein

Publisher

1 2

. . . . . .


Proxy Protocol

Maintain trees from several brokers

Advantageous if restricted mobility region

t1

At Old Broker

t3


t5t4


Connect(movein)

Disconnect(moveout)

t2

moveout

Publisher

1 2

. . . . . .

movein

Publisher


Delayed Protocol

Maintain trees at old broker for some time

Allow new tree to graft onto old tree

Remove extraneous portions of old tree

t1

At Old Broker

t3


t5t4


Connect(movein)

Disconnect(moveout)

t2

moveout

Publisher

1 2

. . . . . .

movein

Publisher


Prefetch-Delayed Protocol Combine advantages of

Prefetching Tree construction time hidden

from user Delayed

Cheap tree construction cost

t1

At Old Broker

t3


t5t4


Connect(movein)

Disconnect(moveout)

t2

moveout

Publisher

1 2

. . . . . .

movein

Publisher


Evaluation


Evaluation Setup Simulation Environment

ns-2 network simulator Implemented mobility protocol optimizations

Parameters Topology

Metropolitan Area Network 4 levels of degree 4 64 leaf brokers

Subscribers: 500 Publishers: 50 Mobility

Static subscribers, mobile publishers Random speeds (5km/h, 50km/h, 100km/h)

Metrics Tree rebuild load Tree rebuild time

• • •

64• • •

1


Routing Computation Model Based on conservative estimates or best published

results of four pub/sub router operations For COMPLEX: assume n = 100 000 subscriptions

at each broker

Ignore other processing delay sources Network protocol stack, operating system, etc.

Operation FAST COMPLEX

Matching 2 ms n / 1000 + 40 ms

Covering 2 ms n / 1000 + 40 ms

Intersection 2 ms n / 1000 + 40 ms

Insertion 2 ms n / 1000 + 40 ms

n = number of subscriptions


Publisher Scalability – No Routing Computations Standard is much worse than Proxy which is worse than Delayed,

Prefetch-Delayed For both tree reconstruction message load and time

Tree reconstruction time seems independent of number of publishers Incorrect conclusion

No algorithm No algorithm


Publisher Scalability – With RC With FAST algorithm

Scale: approx. 5X worse Trend: varies with number of publishers (no longer independent)

With COMPLEX algorithm Standard protocol collapses after 150 publishers 60s tree rebuilding time with 250 publishers!

Routing computations can alter the apparent scalability of protocols Network is not necessarily the bottleneck

FAST algorithm COMPLEX algorithm


Implications of Slow Tree Rebuilding

Publications sent during tree rebuilding may not be delivered

100% delivery with no routing computation False

impression of protocol’s performance

STANDARD protocol


Proxy Locality – With RC

No change in the trends Change in point where Proxy outperforms Prefetch-

Delayed The relative negative impact of overshoot on Proxy

increases with more expressive subscription languages

No algorithm FAST algorithm COMPLEX algorithm


Conclusions The publish/subscribe model is well suited to

mobile applications No evaluation of mobility with routing computations

Routing computations cannot be ignored in pub/sub protocols Not a lower order effect Affect the scale, trend, tradeoff points of results Alter the conclusions of protocols’ performance

Future Work Refine computation models

Expect greater impact of routing computations Other scenarios: realistic traces, mobile subscribers

effects of routing computations in content-based routing networks with mobile data sources vinod...

Documents

mobile computing

mobile clients

networking mobicom

cologne slide

modeling routing computations

tuplebased data

ad tree subscriptions

contentbased routing