1. Quality-aware Middleware
Marten van Sinderen
University of Twente
IPA Spring Days on Middleware
Kapellerput, Heeze, April 3-5, 2002
4 April 2002
IPA Middleware 2002

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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

16. 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

17. 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

18. 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