Transcript Mobility in a Publish Subscribe Internetwork George Xylomenos Mobile Multimedia Laboratory Dept. of Informatics Athens University of Economics and Business PURSUIT Summer School, August 31

Mobility in a Publish Subscribe Internetwork
George Xylomenos
Mobile Multimedia Laboratory
Dept. of Informatics
Athens University of Economics and Business
PURSUIT Summer School, August 31 2011
Outline
•
•
•
•
•
•
•
•
Introduction
Why PSI for mobility?
The PSI Architecture
Caching in PSI
Mobility in PSI: Reactive
Mobility in PSI: Proactive
Conclusion
Credits
Introduction
• End-to-end (E2E) Internet Architecture
– Endpoint centric, based on telephony
– Accused as the root of all evil (NAT, CDN, MIP)
• Publish/Subscribe (Pub/Sub) Internet Architecture
– Information Centric Networking (ICN)
– Information decoupled from location
• The PSI Architecture
– The Pub/Sub architecture of PSIRP/PURSUIT
– Supports multicast, anonymity and asynchrony
– Seamlessly supports mobile nodes (MNs)
What is the difference with mobile IP?
• Handover in mobile IP
– Data sent during disconnection are lost
– Mobile IP extensions reduce handover delay
• Micro mobility keeps handovers local
• Context transfer allows fast reconnections
• Handover in mobile PSI
– The built in PSI mechanisms simplify things
– Asynchrony: no need for rendezvous in time
• Data can be cached during disconnection
– Multicast: allows multicast assisted mobility
• Target multiple Access Points (APs)
– Anonymity: data can be provided by anyone
The PSI Architecture
• Three main entities
• Publisher: advertises availability of information items
– Issues publication messages
– Sends information items upon request
– Information items may have many publishers
• Subscriber: expresses interest on information items
– Issues subscription messages
– Receives information items from some publisher
• Event notification service
– Brings publishers and subscribers together
The PSI Architecture
• Information identifiers: Statistically unique pair
– Rendezvous ID (RID): application derived
– Scope ID (SID): access control and policies
• Example: Scope_A/ Scope_B/…/Scope_Z/RID
• Rendezvous Network (RENE)
– Provides the event notification service
– Consists of Rendezvous Nodes (RN)
– Each information item handled by an RN
• The Rendezvous Point (RVP) of the item
– RENE matches publishers and subscribers
• Instructs publishers to start forwarding data
The PSI Architecture
• Forwarding ID (FID): sent by RVP to the publisher
– Source routing path to subscribers (multicast)
• Each link has a statistically unique Link ID
– Within its AS or network area
• A path is encoded as a Bloom filter of Link IDs
• Each node tests its Link IDs against the FID
• Native multicast without extra cost
– Publishers do not know subscribers (anonymity)
• FIDs do not betray location
• FIDs can be frequently changed/invalidated
– Pub/Sub decoupled in time (asynchrony)
The PSI Architecture
RV Point
RENE
Bob
Router
AP1
AP2
Alice
The PSI Architecture
RV Point
RENE
Bob
Router
AP2
AP1
Alice
Caching in PSI
• Caching in PSI
– In PSI caches are just alternative publishers
• The RVP may point at cached data copies
– Transparent caching
• The cache stores in transit data
• The RVP is notified about the cached data
– Non-transparent caching
• The cache intercepts subscription requests
• Information explicitly delivered in two stages
– One FID from the publisher to the cache
– Another FID from the cache to the MN
Caching in PSI
RV Point
RENE
Bob
Router
AP1
AP2
Alice
Caching in PSI
RV Point
RENE
Bob
Router
AP2
AP1
Alice
Mobility in PSI
• What happens when the MN moves?
– Two generic approaches: reactive and proactive
– Assume that each MN is served by a broker
• Reactive approach
– On disconnection the old broker starts caching data
– On reconnection data are available from there
• Proactive approach
– Old broker selects candidate neighbor brokers
– On disconnection candidates cache data for the MN
– On reconnection the new broker already has the data
Mobility in PSI: Reactive
• PSI Reactive approach
– A Smart Cache (SC) is selected for the MN
– The SC caches data non-transparently
• It explicitly mediates on behalf of the MN
• The RENE is aware of the SC
– MN disconnection: the SC starts caching data
• Data sent during disconnection are not lost
– MN reconnection: the SC makes data available
• The RENE uses the SC as the source of cached data
• No data loss and quick recovery
– The FID to the SC does not change
• Rerouting is a local procedure
Mobility in PSI: Reactive
RV Point
RENE
Bob
Router
Smart
Cache
AP2
AP1
Alice
Mobility in PSI: Reactive
RV Point
RENE
Bob
Router
Smart
Cache
AP2
AP1
Alice
Mobility in PSI: Reactive
RV Point
RENE
Bob
Router
Smart
Cache
Fid (SC, Alice@AP2)
Alice’s new
position
Alice’s previous
position
Mobility in PSI: Reactive
• Smart Caches are not an extension to PSI
– SCs are simply alternative publishers
– MNs benefit by a built-in feature of PSI
• How to select a good SC?
– Ideally it should serve the MN for many handovers
• SC selection makes the scheme proactive/reactive
• RVP forecasting (RVPf)
– RVP is aware of topology around the MN
– The RVP forecasts future MN positions
– SCs are designated in advance by the RVP
Mobility in PSI: Reactive
• AP based (APb)
– APs forecast handovers via signal strength
• Works only for wireless networks
• Mobility is not limited to wireless!
– The AP notifies the RVP before the handover
• The AP sends information about nearby APs
– The RVP selects the SC dynamically
• No need to know the topology in advance
• Also supports dynamic (ad-hoc) topologies
– Extra control messaging compared to RVPf
• May delay handovers
Mobility in PSI: Proactive
• PSI Proactive approach
– A broker serves each MN
• Could be the AP or a nearby cache
– The broker selects candidate neighbor brokers
• Need an algorithm to select the best candidates
– MN disconnection
• The old broker notifies the selected neighbors
• The selected neighbor brokers start caching data
– MN reconnection
• The new broker becomes known on reconnection
• Data are already available at the new broker
Mobility in PSI: Proactive
RV Point
RENE
Bob
Router
AP1
AP2
Alice
Mobility in PSI: Proactive
RV Point
RENE
Bob
Router
AP2
AP1
Alice
Mobility in PSI: Proactive
RV Point
RENE
Bob
Router
Fid (Router,AP1|AP2)
AP2
AP1
Alice
Mobility in PSI: Proactive
RV Point
RENE
Bob
Router
Alice’s previous
position
Alice’s new
position
Mobility in PSI: Proactive
• How to select the candidate neighbors?
– Each neighbor incurs some caching costs
Candidate
brokers
k
m
l
Current
broker
i
j
MN
Mobility in PSI: Proactive
• Conventions
– S: the set of neighboring brokers
– S*: the set of selected candidate brokers
– Phit: probability that the MN will handover in S*
– Chit: cost to serve the MN from a broker in S*
– Cmiss: cost to serve the MN from the publisher
– Ccache: cost to cache data during MN disconnection
– |S*|: number of selected candidate brokers
• Input: handover probabilities
• Output: the optimal set S*
Mobility in PSI: Proactive
•
Select subset S* to minimize cost
Phit*Chit+(1-Phit)*Cmiss + |S*|*Ccache
Delivery cost
Caching cost
• Evaluation procedure
– Assume pik is the probability to handover to k
•
•
•
•
Order the neighbors k in descending pik order
Add the next k to S*
Add pik to Phit and increment |S*|
Evaluate the cost function
– Select the S* that minimizes the cost function
Mobility in PSI: Proactive
• How to evaluate the pik values?
• Past handover behavior
– The broker tracks actual handovers
– Probabilities take into account actual handovers
• MN mobility context
– Each MN has a mobility context
– The context can be used to predict direction
• Signal strength measurements
– The MN sends to the broker its measurements
– The broker predicts the most likely new brokers
Conclusion
• Mobility handling in PSI
– Based on multicast, anonymity, asynchrony
– Exploits embedded support for caching
– Does not require any new mechanisms
– Specifically based on information centrism
• Open issues
– How to evaluate mobility solutions for PSI?
– Traffic models for pub/sub?
– Mobility patterns for pub/sub?
– Evaluation metrics for pub/sub?
Credits
• Authors of papers used for this presentation
– Paris Flegkas
– Nikos Fotiou
– Varvara Giannaki
– Konstantinos Katsaros
– George Parisis
– George C. Polyzos
– Mikko Sarela
– Vasilios A. Siris
– Vasilis Sourlas
– Charilaos Stais
– Dirk Trossen
– Xenofon Vasilakos