Subscriber Mobility in Pub/Sub Systems: Pro-Active vs. Reactive Handoffs
| Thomas Kunz | |
| Systems and Computer Engineering | |
| Carleton University |
Publish/Subscribe Systems: Background
| The pub/sub service is a logically centralized service | ||
| intermediates the communication between publishers and subscribers in a distributed setting. | ||
| Basic primitives: sub, unsub, pub | ||
| Various routing topologies and semantics | ||
| The pub/sub communication paradigm provides: | ||
| space, flow, and timing decoupling between producers and consumers of information | ||
| content-based filtering and communication | ||
| Multi-way delivery | ||
| A frequently used communication paradigm | ||
| Proposed for mobile computing | ||
Pub/Sub System on Top of Wireless Network
Pub/Sub & Mobility: Problem Definition
| How to cope with mobile subscribers? | |||
| Disconnected operations: | |||
| Buffering & queue management | |||
| Handover protocol | |||
| relocating subscriptions and updating the topology | |||
| How to balance subscriber’s load in the event-service? | |||
| Load balancing strategy | |||
| Few studies focused on extending pub/sub | |||
| Goals of research | |||
| Develop a mobility support service for pub/sub systems | |||
| Validate its performance in a testbed | |||
Java Message Service (JMS): Overview
| API specification to implement MOM services | ||
| Two communication modes specified: | ||
| Point-to-point (one-to-one) | ||
| Publish/subscribe (event-based service) | ||
| Two subscription schemes adapted: | ||
| Durable scheme | ||
| Non-durable scheme | ||
| Two consumption modes supported: | ||
| Asynchronous mode | ||
| Synchronous mode | ||
| Other features | ||
Characterization of JMS Primitives
| Wired/wireless networks | ||
| JMS primitives | ||
| Compare primitives with high & low reliability | ||
| Detailed results appears in “Performance of Pub/Sub Systems in Wired/Wireless Networks”, in Proceedings of 64th IEEE VTC, September 2006 | ||
| Key observations | ||
| Non-durable subscriptions outperform durable ones | ||
| Durable subscriptions show comparable throughput results to non-durable ones in wireless domain | ||
| Reliability cost of durable subscriptions is relatively low in wireless environment | ||
| Reactive approach: state-transfer occurs only after the mobile subscribers reconnect to the new broker | ||
| Commonly used: JEDI, REBECA, SIENA, CEA, .. | ||
| Durable subscription-based approach: every broker buffers all the published messages irrespective of its current active subscriptions | ||
| Recently used: JMS implementations (OpenJMS, FiornaMQ, JBossMQ, JavaSMQ), Ivana et al., .. | ||
| Pro-active Approach: context transfer/caching occurs prior to the actual movement of the mobile subscriber (our proposal) | ||
| Passive subscriptions are propagated to neighbors of current broker | ||
| Subscriptions get activated once subscriber disconnects, start buffering messages | ||
| Once subscriber reconnects to a broker, will with high probability find active subscriptions and locally buffered messages, subscriptions in old and new neighborhood get updated accordingly | ||
| Is an undirected graph with a number of edges that represent the mobility paths between the vertices | |
| Provides the abstractions to identify the candidate subset of next potential brokers | |
| Forms the basis for pre-loading the subscriber context one hop ahead of its current broker | |
| Automatically generated and adaptively changes according to the mobility graph | |
| A timestamp based LRU method can be used to ensure the freshness of NG and remove the outlier edges | |
| Is stored in a distributed manner |
Implementing Pro-active Approach
Experimental Setup & Mobility State Diagram
Performance Results and Comparison I
| Mobility extension overhead | ||
| In terms of message processing time and message throughput | ||
Performance Results and Comparisons II
| Cumulative Distribution of Handoff Time |
Performance Results and Comparisons III
| Message Loss, Duplication, Throughput | ||
| As a function of the publication rate | ||
| Proactive approach to support mobile subscribers | |||
| Evaluated through small testbed | |||
| Superior performance to reactive approach: | |||
| Higher throughput | |||
| Lower message latency | |||
| Lower handoff latency | |||
| No message duplication | |||
| Low message loss rate | |||
| Future Work: | |||
| Larger testbed (some initial results) | |||
| Impact of mobility patterns/neighborhood graph approximation | |||
| Compare to durable approach (some initial results) | |||
| Analytical performance bounds/prediction models | |||