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Sec.0a--Intro to pervasive computing 8.ppt
- 1. 1
© 2007 by Leszek T. Lilien
Based on: M. Satyanarayanan, “Pervasive Computing: Vision and Challenges,” IEEE Personal Communications, 2001
Pervasive Computing vs. Distributed Systems & Mobile Computing (50)
Drilling Down - The Difficult Problems (27)
4.7) [LTL:] Proactivity and Its Transparency [Paper: Balancing Proactivity and Transparency] – cont.2
[LTL:] Hypothesis: Talking about “balancing proactivity and
transparency” (see the paper) seems author’s mistake
Balancing of X an Y is needed only when:
More X can be obtained by reducing Y AND More Y can be obtained
by reducing X
Here can have 100% proactivity with either 0% or 100%
transparency
[LTL:] Finding (“balancing”) proper level of transparency for
proactivity
If too little or too much of proactivity transparency annoys a user
=> The goal of proactivity transparency is defeated
Need careful PERV design
Finding the proper transparency level by:
System’s self-tuning
A mobile user’s need & tolerance for proactivity (UNTP) are likely
to be closely related to his level of expertise on a task & his
familiarity with his environment
A system that can infer UNTP by observing user behavior &
context is better positioned to find the proper balance
- 2. 2
© 2007 by Leszek T. Lilien
Based on: M. Satyanarayanan, “Pervasive Computing: Vision and Challenges,” IEEE Personal Communications, 2001
Pervasive Computing vs. Distributed Systems & Mobile Computing (51)
Drilling Down - The Difficult Problems (28)
4.7) [LTL:] Proactivity and Its Transparency [Paper: Balancing Proactivity and Transparency] – cont3
Historically, transparency (not just for proactivity) was the ideal
in system design
E.g., caching is attractive in distributed file systems because it is
completely transparent
Ironically, sometimes users are hurt/annoyed by complete
transparency
E.g., servicing a cache miss on a large file over a low-bandwidth
wireless network — so slow that most users would rather be
asked first by the system if they really need the file
However, too many questions from file system can annoy the user
That is, again annoyed by too low level of transparency
A solution to this dilemma (suggested by Coda File System [21])
On a cache miss, Coda consults an internally-maintained user
patience model to predict whether the user will not be
annoyed by a transparent fetch request
If so, the fetch is handled transparently (user interaction is
suppressed)
Many subtle problems arise in designing a system that walks
the fine line between annoying visibility & inscrutable (hard to
understand) transparency
- 3. 3
© 2007 by Leszek T. Lilien
Based on: M. Satyanarayanan, “Pervasive Computing: Vision and Challenges,” IEEE Personal Communications, 2001
Pervasive Computing vs. Distributed Systems & Mobile Computing (52)
Drilling Down - The Difficult Problems (29)
4.7. Balancing Transparency in Proactivity – some research
problems:
How are individual user preferences and tolerances specified and
taken into account?
Are these static or do they change dynamically?
What cues can such a system use to determine if [LTL:] transparency
level is too low/high?
Is explicit interaction with the user to obtain this information acceptable?
Or, would such explicit interaction to obtain be an annoyance too?
Can one provide systematic design guidelines to application designers
to help in this task?
Can one retrofit [transparency] balancing mechanisms into existing
applications?
- 4. 4
© 2007 by Leszek T. Lilien
Based on: M. Satyanarayanan, “Pervasive Computing: Vision and Challenges,” IEEE Personal Communications, 2001
Pervasive Computing vs. Distributed Systems & Mobile Computing (53)
Drilling Down - The Difficult Problems (30)
4.8) Privacy and Trust
Privacy is greatly complicated by PERV
Was already a thorny problem in DISTR and MOBI
Some PERV mechanisms “spy” on user actions on an
almost continuous basis
E.g., location tracking, smart spaces, use of surrogates
As a user becomes more dependent on PERV =>
PERV obtains more information about the user
I.e., about user’s movements, behavior patterns, habit, …
Exploiting this information is critical to successful
proactivity & self-tuning
Unless use of information is strictly controlled, it can hurt the user
Illegitimate uses ranging from targeted spam to blackmail.
Potential for serious loss of privacy may deter knowledgeable
users from using a PERV system
- 5. 5
© 2007 by Leszek T. Lilien
Based on: M. Satyanarayanan, “Pervasive Computing: Vision and Challenges,” IEEE Personal Communications, 2001
Pervasive Computing vs. Distributed Systems & Mobile Computing (54)
Drilling Down - The Difficult Problems (31)
4.8) Privacy and Trust - cont.
Mutual trust between infrastructure & users in PERV
Greater reliance on infrastructure => users must trust
infrastructure to a considerable extent
Conversely, the infrastructure needs to be confident of
the users’ identity and authorization levels before
responding to their requests
It is a difficult challenge to establish this mutual trust with
minimal intrusiveness (= mimnimal visibility & thus maximum
transparency)
System identifies/authorizes users in intrusive (visible)
way
- 6. 6
© 2007 by Leszek T. Lilien
Based on: M. Satyanarayanan, “Pervasive Computing: Vision and Challenges,” IEEE Personal Communications, 2001
Pervasive Computing vs. Distributed Systems & Mobile Computing (55)
Drilling Down - The Difficult Problems (32)
4.8. Privacy and Trust - cont
Privacy and trust are likely to be enduring problems in
pervasive computing
Privacy and trust – some research questions:
How does one strike the right balance between seamless system
behavior and the need to alert users to potential loss of privacy?
What are the mechanisms, techniques and design principles relevant
to this problem? How often should the system remind a user that his
actions are being recorded? When and how can a user turn off
monitoring in a smart space?
What are the authentication techniques best suited to PERV?
Are password-based challenge-response protocols such as Kerberos
[36] adequate or are more exotic techniques such as biometric
authentication [15] necessary?
What role, if any, can smart cards [14] play?
How does one express generic identities in access control?
E.g., how does one express security constraints such as ‘‘Only the
person currently using the projector in this room can set its lighting
level?’’ Or: ‘‘Only employees of our partner companies can negotiate
QoS properties in this smart space?’’
- 7. 7
© 2007 by Leszek T. Lilien
Based on: M. Satyanarayanan, “Pervasive Computing: Vision and Challenges,” IEEE Personal Communications, 2001
Pervasive Computing vs. Distributed Systems & Mobile Computing (56)
Drilling Down - The Difficult Problems (33)
4.9) Impact on Layering [of the System]
A recurring theme in this paper: the merging of
information from diverse layers of a PERV system to
produce an effective response
E.g., Scenario 1 shows the value of combining low-level resource
information (network bandwidth) with high-level context
information (airport gate information)
Proactivity and adaptation based on corrective actions =>
exposure of much more information across layers
Much more than is typical in systems today
We want layering – it has benefits
Cleanly separates abstraction from implementation
Thus consistent with sound software engineering
Conducive to standardization
Encourages the creation of modular software components
- 8. 8
© 2007 by Leszek T. Lilien
Based on: M. Satyanarayanan, “Pervasive Computing: Vision and Challenges,” IEEE Personal Communications, 2001
Pervasive Computing vs. Distributed Systems & Mobile Computing (57)
Drilling Down - The Difficult Problems (34)
4.9) Impact on Layering [of the System] – cont.
Deciding how to decompose a complex system into layers
or modules is nontrivial
Remains very much an art rather than a science
The two most widely-used guidelines for layering
Parnas’ principle of information hiding [26]
Saltzer et al.’s end-to-end principle[28]
Both developed long before pervasive computing was
conceived
Parnas’ - early 1970’s
Saltzer et al.’s - early 1980’s