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

Information identifiers: Statistically unique pair 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

Forwarding ID (FID): sent by RVP to the publisher 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 RENE <Bob_SId, Bob_RId, metadata> RV Point Router AP1 AP2 <Bob_SId, Bob_RId> Alice

The PSI Architecture RENE RV Point Bob Fid (Bob, Alice@AP1) Router AP2

In PSI caches are just alternative publishers Transparent caching 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 RENE <Bob_SId, Bob_RId, metadata> RV Point Bob Router AP1 AP2 <Bob_SId, Bob_RId> Alice

Caching in PSI RENE RV Point Bob Fid (Bob, Router) Router AP1 AP2 Fid (Router, Alice@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 <Bob_SId, Bob_RId, metadata> RV Point RENE Bob <Bob_SId, Bob_RId> <Bob_SId, Bob_RId, metadata> Router Smart Cache AP2 <Bob_SId, Bob_RId> AP1 Alice

Mobility in PSI: Reactive RV Point Bob Fid (Bob, SC) RENE Router Smart Cache AP2 Fid (SC, Alice@AP1) 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 <Bob_SId, Bob_RId, metadata> RV Point RENE Bob <Bob_SId, Bob_RId> <Bob_SId, Bob_RId, metadata> Router AP1 AP2 <Bob_SId, Bob_RId> Alice

Mobility in PSI: Proactive RV Point RENE Bob Fid (Bob, Router) Router Fid (Router,AP1) AP1 AP2 Alice

Mobility in PSI: Proactive RV Point RENE Bob Fid (Bob, Router) Router Fid (Router,AP1|AP2) AP1 AP2 Alice

Mobility in PSI: Proactive RV Point RENE Bob Router Alice’s new position Alice’s previous position

Mobility in PSI: Proactive How to select the candidate neighbors? Each neighbor incurs some caching costs Candidate brokers k m l i Current broker 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 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 Delivery cost Caching cost

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