1. SIENA: Wide-Area Event Notification Service
Antonio Carzaniga
David S. Rosenblum
Alexander L. Wolf

2. Event Services Are Not New!
Event models
simple (UNIX signals)
sophisticated (database triggers)
Event notification services
LAN message servers (e.g., SUN ToolTalk, DEC Fuse, HP SoftBench)
USENET News (NNTP)
Basic communication infrastructure
point-to-point (TCP/IP, RPC, CORBA, RMI)
multicast (MBONE)

3. Challenges Scalability Expressiveness
many-to-many communications
large number of objects and events
decentralized control
heterogeneous platforms and protocols
Expressiveness
rich event notification model
expressive subscription language (an IP multicast address just doesn’t cut it)
Tradeoffs between scalability and expressiveness

4. SIENA Event Service Event Service NASDAQ financial institution
object of interest
interested party
advertisement
subscription
NEW
subject = stock
name = *
price = *
subject = stock
name = MSFT
advertise
subscribe
unadvertise
unsubscribe
notification
Subject = stock
name = MSFT
price = 123
diff = -1.0%
publish
notify

5. Filters and Patterns Filter Pattern X: price < $5 XY*Z time X Y Z
publish
publish
publish
publish
publish
publish
publish
publish
publish
price=$2
stock=MSFT
date=
curr=Lira
qty=4321
curr=Lira
qty=4321
diff=10%
price=$3
stock=DEC
price=$12
stock=DEC
price=$1
price=$10
price=$2
price=$7 X Y Z X:
price < $5
XY*Z y x y x z z x
notify
notify
notify
price=$1
price=$2
price=$2
stock=MSFT
date=
curr=Lira
qty=4321
curr=Lira
qty=4321
diff=10%
price=$3
stock=DEC

7. Event Service Topologies
peer-to-peer
acyclic
graph
centralized
servers
clients
hierarchical
peer-to-peer
generic
graph

8. Subscription Forwarding
subscriptions are forwarded to every server
notifications follow (backwards) the paths set up by subscriptions
publish
subscribe
notify

9. Advertisement Forwarding
advertisements are forwarded to every server
subscriptions follow (backwards) and “activate” the paths set up by advertisements
notifications follow the paths “activated” by subscriptions
publish
advertise
subscribe
notify

10. Optimization
Multicasting is done downstream (closer to interested parties)
Filters and patterns evaluated upstream (closer to objects of interest)
pattern
assembly
A+B=AB X
multicast of
notification A
advertisement X
subscription
advertisements A X AB B B
subscriptions AB AB X A A AB

12. Design Validation
Problem: validation of server topologies and routing strategies with respect to
network traffic
memory usage
CPU usage
SIENA approach: simulation

13. Parameters for Simulations
Network:
topology, latency, bandwidth, cost function
Servers:
location, topology, routing strategy
Objects of interest and interested parties
number, location, primary server, behavior

15. Prototype C++/Java servers C++/Java client interface
XML data representation
Several communication protocols
SMTP ( ), HTTP, plain TCP/IP

16. Conclusions
SIENA is an architecture that implements a scalable and flexible event service
event service interface
notification model
service topologies
notification dispatching strategies
validation through simulation
prototype