Quality-aware Middleware Marten van Sinderen University of Twente sinderen@cs.utwente.nl IPA Spring Days on Middleware Kapellerput, Heeze, April 3-5, 2002 4 April 2002 IPA Middleware 2002

Quality-of-Service Service: observable behaviour of system functional: what non-functional: how well QoS: non-functional aspects of service {select, play, pause, stop} receive_frame send receive 4 April 2002 IPA Middleware 2002

QoS specification (1) QoS aspects represented by QoS parameters time related; integrity related different (sets of) parameters at different levels user level: more subjective; system level: objective More primitive service 4 April 2002 IPA Middleware 2002

QoS specification (2) Set of <parameter type, parameter value>, where parameter value can be upper bound, lower bound, range Throughput 1.8 Mbit/s Minimum Transfer delay 23 ms Maximum Packet loss 1% Maximum Delay variation +/-3 ms Maximum 4 April 2002 IPA Middleware 2002

QoS contract Agreement on QoS that will be provided by system to user(s) negotiation: matching (user) requirements with (system) capabilities selection of appropriate support in system ‘End-to-end’ QoS several subsystems may contribute to the same qoS parameter user is only interested in end-result 4 April 2002 IPA Middleware 2002

QoS mechanisms Internal system functions that focus on improving certain QoS parameters improving reliability (decrease loss) re-transmission forward error-correcting code improving response time caching load distribution replication 4 April 2002 IPA Middleware 2002

QoS management Establishing and maintaining QoS static: fixed or one-time selection of system support admission control QoS negotiation resource reservation dynamic: adapt system support when system conditions make this desirable monitoring adaptation re-negotiation policing 4 April 2002 IPA Middleware 2002

Current object middleware Ease process of creating complex distributed applications Mask out problems of heterogeneity and distribution provide unified programming model Examples: CORBA, Java RMI, DCOM/.NET 4 April 2002 IPA Middleware 2002

Object request broker (IIOP) Example: CORBA Static programming model only method invocations (operational interface) no access to lower level details (black box) Extensions: dynamic invocations portable interceptors Object request broker (IIOP) Server stub Client stub Server object Client object IDL spec of interface 4 April 2002 IPA Middleware 2002

Quality-awareness? limited set of features for the configuration and re-configuration of the platform often, these features are not available at run-time no or little support for multimedia (different interfaces) and mobility (changing conditions) Conclusion best-effort QoS and one-size-fits-all are not good enough specific or configurable solutions are needed 4 April 2002 IPA Middleware 2002

Research motivation AMIDST project Extend middleware platforms to support different QoS requirements and adapt to changes application environments resources Development of an architectural framework to guide our experiments Architectural framework should support operation and stream interactions 4 April 2002 IPA Middleware 2002

Middleware concepts Client and server interfaces specifications [considering operations…] Client and server interfaces specifications IDL specifications can be extended with QoS specifications (QML style) required QoS  client side offered QoS  server side QoS negotiation and explicit binding must be supported agreed QoS: QoS contract 4 April 2002 IPA Middleware 2002

Middleware concepts Example QoS-aware ORB Naming Client Context Object interface NamingContext { void bind(in Name n, in Object obj); void bind_context(in Name n, ...); Object resolve (in Name n); ... } agreed QoS Delay < 80 Rate < 7 required QoS Delay < 100 Rate > 5 offered QoS Delay > 60 Rate < 7 Naming Context Object Client Object binding request for binding QoS-aware ORB 4 April 2002 IPA Middleware 2002

QoS control architecture Assumption: a QoS-middleware has to monitor and maintain the agreed QoS Based on control systems: controlled system: ‘classical’ middleware (including resources) controller: QoS-middleware extension in terms of a ‘control loop’ (observations, calculation of differences and manipulations) General architecture for operations and streams, different control strategies, etc. 4 April 2002 IPA Middleware 2002

QoS control architecture Middleware platform Applications Computing and communication resources input output Interpreter measurements Sensor probes observation Controlling algorithm (Decider) Middleware control model Control strategy difference QoS meta model Comparator agreed QoS required QoS (client object) offered QoS (server object) middleware QoS QoS reference base instantiations of control action Translator Actuator Interpreter measurements QoS meta model difference Comparator agreed QoS required QoS (client object) offered QoS (server object) middleware QoS QoS reference base instantiations of Controlling algorithm (Decider) Middleware control model Control strategy probes control action Translator Actuator Sensor probes observation 4 April 2002 IPA Middleware 2002

Feasibility of the architecture Control architecture overhead should not jeopardise QoS  many QoS requirements are related to performance! Be careful about how often and how the control loop is ‘executed’  use idle periods and lower priority threads? Construct versions of the architecture with increasing complexity / capabilities Avoid oscillation (intrinsic to control systems)  Analytic models for prediction? Heuristics? 4 April 2002 IPA Middleware 2002

Current situation QoS-control architecture defines directions for the development of QoS support Construction of QoS support mechanisms is being done ‘bottom-up’ QoS negotiation mechanisms for operations and streams Manipulations of protocol characteristics (e.g., using DiffServ and RSVP) Software architecture for the complete QoS control architecture is being built 4 April 2002 IPA Middleware 2002

More details ... provided in the following presentations: Aart van Halteren: Meta-object and partial implementation of QoS control architecture Maarten Wegdam: QoS mechanisms - load distribution Marcel Harkema: Quantitative performance modelling - mathematical model to predict QoS 4 April 2002 IPA Middleware 2002