The Mobile Environment u Environment –something which exists in a space, a concept defined with respect to the kind of system in focus (boundary). u Two (2) types of mobile environments defined by periods of interaction: –Changing location but long periods of interaction. E.g. Office  Train  Home etc. –Immediate changes due to volatility of instabilities of mobile communications (physics). u The mobile environment is characterized by change, the only thing that is constant is change.

Sources of Variability u Heterogeneous networks –variable link capacities (64kb/s Mbits/s and more) for ISDN, LANs, ATM –variable processing speeds of nodes –variable protocols (TCP/IP, ATM) stacks –congestion u Mobile networks –physics gives variable performance (turbulent environment, bandwidth, delay, jitter) u Clients –differ in CPU power, display resolution, memory e.t.c

Why traditional approaches fail to deal with Mobile Environments u Concentrates on functional decomposition –the environment is treated as a secondary issue. u A certain environment is assumed –specialization and generalization u Designs follow the “all or nothing law” u They tend to ignore variability in the supply and demand of resources –In reality, an application support environment is not static, hence some applications die in the face of variablility u Recognition of variability has resulted in: –robust systems, reconfigurable systems, evolving systems, adhoc adaptive systems

What is an adaptive System ? u From nature: u In a changing, unpredictable and more or less threatening environment, the behaviour of an animal is adaptive as long as the behaviour allows the animal to survive. u Under the same conditions, the behaviour of the application is considered to be adaptive as long as it continues to provide service for which it was developed. u Adaptation is the tuning of an application’s functionality to its environment and vice-versa –Co-specification and co-determination

u In order to adapt to a changing situation, a system must: –evaluate its presents situation »To determine if it leads to any danger in the not so far future –Try to change the situation to another less likely to lead to destruction »Normally impossible to find situation that never leads to destruction What is an adaptive System ?

Control under an Observer u Let O be the set of all possible output values and I be the set of possible input values: u O = { o 1, o 2, o 3, ….. } and u I = { i 1, i 2, i 3, ….. } u A system can be perfectly controllable if there is a mapping f from I onto O: f : I  O : i  f(i) = o

Adaptation and the Environment u Adaptation is about changing structure and functionality as the environment changes. u The concept of distinctions and the observer highlights the importance of observing the state of a system in order to adapt to changes. u Knowledge about the environment is central to adaptation (viewed as markers to an adaptation landscape) u Ability to elicit, analyse and infer new knowledge u Adaptation involves selection structures in order to control a system to a more secure state (under disturbances)

Some Guiding Laws and Principles u The law of requisite variety –Control can only be obtained if the variety of the controller is at least as great as the situation to be controlled. u The variety-adaptability principle –Systemic variety enhances stability by increasing adaptability u The over-specialization principle –Too much of a good thing may render systems unstable in the face of environmental change u Darkness principle –No system can be completely known

u The environment modification principle –To survive, systems have to choose to 2 main strategies. One is to adapt to the environment, the other is to change it. u The maximum power principle –Those systems that survive in competition between alternative choices are those that develop more power inflow and use it to meet the needs of survival. u The feedback principle –The result of behavior is always scanned and its success or failure modifies future behaviour (learning from experience) Some Guiding Laws and Principles

Mechanisms of Adaptivity u Defining two spaces: the performance space, P, and resource space, R. u P is dimensioned along user oriented QoS parameters (e.g play-out quality, response time, etc. ) u The acceptance region, AR, of P is defined as the region in which the application is considered to be working properly. u R is dimensioned by resource characteristics in the operational environment (CPU power, memory, bandwidth, jitter, loss rates, etc.) u Formally: “for a given application class without adaptation there exist a mapping M: P  R that maps AR onto region B in R. Introducing adaptation changes M so that AR now maps onto a larger region A where A normally includes B. “

Example of adaptation Space

Adaptation Space – Multimedia data

Designing Adaptive Systems u The design has to scale up, e.g from bits/sec to Gigabits/sec u The goal is to keep environmental changes in sync with application semantics u Application semantics should be co-defined with the environmental u Device capabilities have to be factored in u Task specs could be declared

Experience so far u Multimedia application –Audio conferencing u Adaptation space along –Audio quantisations –Speech to text –Vocabulary size u Static media –XML style sheets for device encoding

Research Issues u designing adaptive is adhoc –formalizing the process –proving the stability of the system (feedback loops) u using predictive schemes –enhances current approaches that only react when changes have occurred –can use established methods in AI, heuristics u measuring the performance of adaptive schemes –currently agility is defined along the lines of transient behaviour in control systems u development of primitives to support adaptability – Odyssey and MOST approaches

Conclusions u Adaptivity means : –a tool to maintain acceptable performance –deals with unpredictable and uncontrollable variations of mobile environments –requirement for primitives to support adaptability »including ability for applications to trade resources –raises the issue of what skills are involved, programming or engineering u Defining an adaptive framework is a challenge