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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
Aug. 30, 2005 (MobiCom ’05) Mobile-ToPSS (University of Toronto) 3
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
Aug. 30, 2005 (MobiCom ’05) Mobile-ToPSS (University of Toronto) 4
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
Aug. 30, 2005 (MobiCom ’05) Mobile-ToPSS (University of Toronto) 5
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”
Aug. 30, 2005 (MobiCom ’05) Mobile-ToPSS (University of Toronto) 6
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
Aug. 30, 2005 (MobiCom ’05) Mobile-ToPSS (University of Toronto) 7
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”
Aug. 30, 2005 (MobiCom ’05) Mobile-ToPSS (University of Toronto) 8
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)
Aug. 30, 2005 (MobiCom ’05) Mobile-ToPSS (University of Toronto) 9
Publisher Mobility
Aug. 30, 2005 (MobiCom ’05) Mobile-ToPSS (University of Toronto) 10
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
. . . . . .
Aug. 30, 2005 (MobiCom ’05) Mobile-ToPSS (University of Toronto) 11
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
movein
Publisher
1 2
. . . . . .
Aug. 30, 2005 (MobiCom ’05) Mobile-ToPSS (University of Toronto) 12
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
Disconnected At New Broker
t5t4
Can publishnew events
Connect(movein)
Disconnect(moveout)
t2
moveout
Publisher
1 2
. . . . . .
Aug. 30, 2005 (MobiCom ’05) Mobile-ToPSS (University of Toronto) 13
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
Disconnected At New Broker
t5t4
Can publishnew events
Connect(movein)
Disconnect(moveout)
t2
movein
Publisher
1 2
. . . . . .
Aug. 30, 2005 (MobiCom ’05) Mobile-ToPSS (University of Toronto) 14
Proxy Protocol
Maintain trees from several brokers
Advantageous if restricted mobility region
t1
At Old Broker
t3
Disconnected At New Broker
t5t4
Can publishnew events
Connect(movein)
Disconnect(moveout)
t2
moveout
Publisher
1 2
. . . . . .
movein
Publisher
Aug. 30, 2005 (MobiCom ’05) Mobile-ToPSS (University of Toronto) 15
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
Disconnected At New Broker
t5t4
Can publishnew events
Connect(movein)
Disconnect(moveout)
t2
moveout
Publisher
1 2
. . . . . .
movein
Publisher
Aug. 30, 2005 (MobiCom ’05) Mobile-ToPSS (University of Toronto) 16
Prefetch-Delayed Protocol Combine advantages of
Prefetching Tree construction time hidden
from user Delayed
Cheap tree construction cost
t1
At Old Broker
t3
Disconnected At New Broker
t5t4
Can publishnew events
Connect(movein)
Disconnect(moveout)
t2
moveout
Publisher
1 2
. . . . . .
movein
Publisher
Aug. 30, 2005 (MobiCom ’05) Mobile-ToPSS (University of Toronto) 17
Evaluation
Aug. 30, 2005 (MobiCom ’05) Mobile-ToPSS (University of Toronto) 18
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
Aug. 30, 2005 (MobiCom ’05) Mobile-ToPSS (University of Toronto) 19
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
Aug. 30, 2005 (MobiCom ’05) Mobile-ToPSS (University of Toronto) 20
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
Aug. 30, 2005 (MobiCom ’05) Mobile-ToPSS (University of Toronto) 21
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
Aug. 30, 2005 (MobiCom ’05) Mobile-ToPSS (University of Toronto) 22
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
Aug. 30, 2005 (MobiCom ’05) Mobile-ToPSS (University of Toronto) 23
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
Aug. 30, 2005 (MobiCom ’05) Mobile-ToPSS (University of Toronto) 24
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