International Symposium on Distributed Objects and Applications (DOA 2002) MetaSockets MetaSockets Run-Time Support for Adaptive Communication Services S. M. Sadjadi, P. K. McKinley, E. P. Kasten Software Engineering and Networking Systems Laboratory Department of Computer Science and Engineering Michigan State University

Motivations  Mobile computing applications must adapt to the dynamic situations related to several cross-cutting concerns including: –Quality of Service –Security –Energy Consumption –Fault Tolerance  Solution? –Adaptive Middleware.

Our Approach  RAPIDware Project: –Addresses the design of adaptive software.  Adaptive Java (AJ): –An extension to Java that provides language constructs and compiler support for developing adaptive software (previously done).  MetaSockets: –An adaptable communication component developed in AJ as the heart of our Adaptive Middleware.

Adaptive Java Background  Adaptable Component Model: –Component: the basic building block that can be equated to adaptable classes (composed of invocations). –Meta-Object Protocol: a set of meta-level primitives (refractions and transmutations).

Adaptive Java Background (cont.)  Three-Dimensional Interfaces: –Invocations: normal component imperative operations. –Refractions: operations for inspecting components. –Transmutations: operations for modifying components.  Component Absorption and Metafication: send() close() joinGroup() send() close() insertFilter() removeFilter() getStatus() receive() base-level invocation send() close() transmutation refraction leaveGroup() base-level method replaced invocation Java MulticastSocket AJ SendMSocket Base-Component AJ MetaMulticastSocket Meta-Compnent

MetaSocket Internal Architecture get() put() send() close() Filter Pipeline put() get() receive() joinGroup() close() Filter Pipeline send() close() receive() joinGroup() leaveGroup() close() getStatus() insertFilter() removeFilter() insertFilter() removeFilter() FP LP Fltr MT SS LP FP Fltr MT RS invocation refraction transmutation FP : firstPacketBuffer SS : SendMSocket dependency packet flow direction RS : RecvMSocket LP : lastPacketBuffer Fltr : Filter MT : MetaSocketThread thread MetaSendMSocket Internal Architecture: MetaRecvMSocket Internal Architecture:

MetaSocket Absorption Code public component SendMSocket absorbs java.net.MulticastSocket { /* constructor */ public SendMSocket(...) { setBase(new java.net.MulticastSocket(...)); } /* invocations */ public invocation void send(...) { base.send(...); } public invocation void close() { base.close(); } }

MetaSocket Metafication Code public component MetaSendMSocket metafy SendMSocket { /* constructor */ public MetaSendMSocket(SendMSocket sendMSocket) { setBase(sendMSocket); } /* invocation that "replaces" the send() invocation in SendMSocket */ public invocation void send(...) {... firstPacketBuffer.put(packet);... } /* refractions */ public refraction byte[] getStatus() { return filterPipeline.getStatus(); } /* transmutations */ public transmutation void insertFilter(int position, Filter filter) {... filterPipeline.add(position, filter);... } public transmutation Filter removeFilter(int position) {... return filterPipeline.remove(position); } /* private fields */ private java.util.Vector filterPipeline = new java.util.Vector(); PacketBuffer firstPacketBuffer = new PacketBuffer(); }

MetaSocket Evaluation  Audio Streaming Application (ASA) –MetaSocket is used instead of MulticastSocket –Live audio stream from a desktop to multiple iPAQs –Physical experiment configuration: Access Point Wireless Receivers Audio Stream Wired Sender...

ASA Components Interaction Wired Network Wireless Network Trader Filter Pipeline Component Loader Decision Maker (DM) Player Event Mediator LP FP MT RS PB AL NL FD Dependency Reflection Event propagation invocation refraction and transmutation thread AL : RecvAppLossDetector FD : FECDecoder NL : RecvNetLossDetector

ASA Components  Decision Maker: a optional component that controls all the non-functional behavior of the subcomponents in its container component, according to its rule-base.  Component Loader: a unique component in an address space that loads components from a trader, according to a set of policies.  Trader: a server that works as yellow pages and replies to component requests.  Event Mediator: Supports asynchronous interaction among decoupled components using a publisher- subscriber pattern.  Player: plays the incoming audio stream.

 Wireless networks produce dynamic and location dependent packet loss because of signal strength, interference, antenna alignment.  b MAC layer does not provide link-level acknowledgement for multicast frames.  FEC can be used to improving reliability by introducing redundancy into the data channel. Block Erasure Code Operation

 MetaFECEncoder: a component in AJ that absorbs a FECEncoder class.  MetaFECDEcoder: a component in AJ that absorbs a FECDecoder class. Forward Error Correction Filters invocationrefraction transmutation FE : FECEncoder dependency event propagation path thread (a) MetaFECEncoder start() stop() setSrcPacketBuffer() setDstPacketBuffer() setNK() FE getSrcPacketBuffer() getDstPacketBuffer() getNK() start() stop() setSrcPacketBuffer() setDstPacketBuffer() setNK() FD` getSrcPacketBuffer() getDstPacketBuffer() getNK() FilterMismatchEvent FECMismatchNKEvent FD : FECDecoder (b) MetaFECDecoder

MetaSocket Performance Evaluation  FEC Filters inserted automatically at time 8, when loss rate exceeds 30%.  FEC Filters removed automatically at time 45, when loss rate drops below 10%.  Inserted again at time 60.  Removed again at time 80.

Conclusions and Future Directions  Conclusions: –Adaptive Java provides language support for run-time adaptation. –Experiments show that MetaSockets are an effective means to QoS- oriented adaptation.  Future Directions: –A MetaSocket is only one type of adaptable components. Any AJ component can be metafied and adapted at run time. –Other cross-cutting concerns (security, power consumption, and fault-tolerance) can be addressed with AJ components.  Acknowledgements: –This work was supported in part by the U.S. Office of Naval Research under Grant No. N , and in part by National Science Foundation grants CDA , NCR , CCR , EIA , and EIA –Special thanks to Dr. Kurt Stirewalt for his contribution to this work.