Transcript
Quality-of-Service Foreleser: Carsten Griwodz Email:
[email protected]
11. Mai 2005
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INF-3190: Multimedia Protocols
Quality–of–Service (QoS) !
Quality of Service !
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“QoS represents the set of those quantitative and qualitative characteristics of a distributed multimedia system that are necessary to achieve the required functionality of an application”
Quality of Service !
Characterizes the well defined, controllable behavior of a system with regard to quantitatively measurable parameters Delay
Throughput Loss
11. Mai 2005
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INF-3190: Multimedia Protocols
Quality–of–Service (QoS) !
Quality of Service !
!
Quality of Service !
!
“QoS represents the set of those quantitative and qualitative characteristics of a distributed multimedia system that are necessary to achieve the required functionality of an application”
Characterizes the well defined, controllable behavior of a system with regard to quantitatively measurable parameters
Indirect definition of QoS ! ! ! ! ! ! !
QoS QoS QoS QoS QoS QoS QoS
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requirements parameter specification mapping negotiation contract guarantee
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INF-3190: Multimedia Protocols
QoS Requirements !
Different applications have different requirements concerning ! ! ! ! !
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Bandwidth Delay Jitter (delay variation) Reliability (packet loss and bit error rate) …
Examples ! ! !
File transfer (ftp, email, web): high reliability Speech: bandwidth, low delay, synchronity Video: bandwidth
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INF-3190: Multimedia Protocols
QoS Requirements of Continuous Media Applications !
Acceptable delay ! !
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Acceptable jitter ! ! !
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Milliseconds at the application level Tolerable buffer size for jitter compensation Delay and jitter include retransmission, error-correction, ...
Acceptable (lack of) continuity ! !
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Seconds in asynchronous on-demand applications Milliseconds in synchronous interpersonal communication
Streams must be displayed in sequence Streams must be displayed at acceptable, consistent quality
Acceptable (lack of) synchronity ! !
Inter-media: different media played out at matching times Intra-media: time between successive packets must be conveyed to receiver
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INF-3190: Multimedia Protocols
Techniques to Fulfill Requirements !
Delay and jitter ! ! !
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Continuity ! ! ! ! !
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Reservation (sender, receiver, network) Buffering (receiver) Scaling (sender) Real-time packet re-ordering (receiver) Loss detection and compensation Retransmission Forward error correction Stream switching (encoding & server)
Synchronity ! ! ! ! !
Fate-sharing and route-sharing (networks with QoS-support) Time-stamped packets (encoding) Multiplexing (encoding, server, network) Buffering (client) Smoothing (server)
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INF-3190: Multimedia Protocols
QoS Requirements: Service Classification service elastic
inelastic loss tolerant nonadaptive
adaptive
delay adaptive
video conferencing
videoondemand
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loss intolerant rate adaptive
interactive
nonadaptive
v.c. with scalable video
interaktive bulk
ssh, telnet
rate adaptive
asynchronous
ftp, web
email
original telephony, hard real-time
IP telephony
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INF-3190: Multimedia Protocols
QoS Parameters ! !
Measurable value to express one or more requirements Examples ! ! ! !
Error probability at connection set-up phase Throughput Transfer delay Remaining error rate !
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Duration of time to disconnect !
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i.e. at disconnect phase
Failure probability of disconnect Security !
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Error probability at data transfer
With regard to “listening in”
Priority Resilience ! !
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Ability to work in spite of errors Against errors within the transport layer itself
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INF-3190: Multimedia Protocols
QoS Mapping QoS requirement: 25 video frames/sec, no loss Application transport service access point
network service access point
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Application QoS requirement: 225 kbyte/sec, lossless QoS requirement: 150 packets/sec, lossless
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INF-3190: Multimedia Protocols
QoS Mapping !
Not only one possible mapping 1 video frame/sec max delay 1 sec success prob.
8kbyte/sec max delay 1 sec no loss
8kbyte/sec max delay 0.33 sec 1 retransmission
8kbyte/sec max delay 0.2 sec 2 retransmissions
⇒ QoS negotation " Service user and service provider negotiate a mapping 11. Mai 2005
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INF-3190: Multimedia Protocols
QoS Negotiation and Guarantee !
QoS negotation " Service user and service provider negotiate a mapping " Service user states " QoS requirements
" Service provider proposes " QoS contract between " Application (on all hosts) " Network
" Contract may specify conditions " A price " A traffic specification
" Service user accepts contract " Service provider guarantees compliance " Service user guarantees compliance
" Service user has received a QoS Guarantee 11. Mai 2005
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INF-3190: Multimedia Protocols
QoS Negotiation !
Negotiation procedure ! !
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How to set up QoS Peer-to-peer case – all components or resources must agree Different types !
Triangular !
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Bilateral !
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both service users allowed to change QoS
Unilateral !
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all components (service user and service provider) allowed to change QoS
“take it or leave it” from initiating service user
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INF-3190: Multimedia Protocols
QoS Classes !
Different semantics or classes of QoS: !
max
resources
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determines reliability of offered service utilization of resources
reserved C
unused
reserved B
available resources reserved A time
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INF-3190: Multimedia Protocols
QoS Classes !
Best effort QoS !
system tries its best to give a good performance no QoS calculation (could be called no effort QoS)
☺
simple – do nothing
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QoS may be violated % unreliable service
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Deterministic guaranteed QoS !
hard bounds QoS calculation based on upper bounds (worst case)
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QoS is satisfied even in the worst case % high reliability
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$ $
over-reservation of resources % poor utilization and unnecessary service rejects QoS values may be less than calculated hard upper bound
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INF-3190: Multimedia Protocols
QoS Classes !
Statistical guaranteed QoS !
QoS values are statistical expressions (served with some probability) QoS calculation based on average (or some other statistic or stochastic value)
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resource capabilities can be statistically multiplexed % more granted requests
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QoS may be temporarily violated % service not always 100 % reliable
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Predictive QoS ! !
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$ $
weak bounds QoS calculation based previous behavior of imposed workload resource capabilities can be statistically multiplexed % more granted requests possibly more exact workload description (if past and actual behavior matches) QoS may be temporarily violated % service not 100 % reliable QoS values may be less than calculated hard upper bound
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INF-3190: Multimedia Protocols
Resource Reservation !
Reservations is fundamental for reliable enforcement of QoS guarantees ! !
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Per-resource data structure (information about all usage) QoS calculations and resource scheduling may be done based on the resource usage pattern Reservation protocols !
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Negotiate desired QoS by transferring information about resource requirements and resource usage between the end-systems and the intermediate systems participating in the data transfer Reservation operation ! !
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calculate necessary amount of resources based on the QoS specifications reserve resources according to the calculation (or reject request)
Resource scheduling !
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Enforce resource usage with respect to resource administration decisions
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INF-3190: Multimedia Protocols
time
Resource Management Phases Phase 1:
user’s QoS requirements
specification rejection or renegotiation
admission test and calculation of QoS guarantees
resource reservation
negotiation confirmation
QoS guarantees to user renegotiation
Phase 2:
data transmission
QoS enforcement by proper scheduling monitoring and adaptation “notification”
Phase 3: 11. Mai 2005
stream termination
resource deallocation 17
reflection renegotiation
termination INF-3190: Multimedia Protocols
