10. Mai 20061INF-3190: Multimedia Protocols Quality-of-Service Foreleser: Carsten Griwodz

10. Mai INF-3190: Multimedia Protocols Quality–of–Service (QoS) 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” Quality of Service Characterizes the well defined, controllable behavior of a system with regard to quantitatively measurable parameters

10. Mai INF-3190: Multimedia Protocols Quality–of–Service (QoS) 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” Quality of Service Characterizes the well defined, controllable behavior of a system with regard to quantitatively measurable parameters Indirect definition of QoS QoS requirements QoS parameter QoS specification QoS mapping QoS negotiation QoS contract QoS guarantee

10. Mai INF-3190: Multimedia Protocols QoS Requirements Different applications have different requirements concerning Bandwidth Delay Jitter (delay variation) Reliability (packet loss and bit error rate) … Examples File transfer (ftp, , web): high reliability Speech: bandwidth, low delay, synchronity Video: bandwidth

10. Mai INF-3190: Multimedia Protocols QoS Requirements of Continuous Media Applications Acceptable delay Seconds in asynchronous on-demand applications Milliseconds in synchronous interpersonal communication Acceptable jitter Milliseconds at the application level Tolerable buffer size for jitter compensation Delay and jitter include retransmission, error-correction,... Acceptable (lack of) continuity 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

10. Mai INF-3190: Multimedia Protocols Techniques to Fulfill Requirements Delay and jitter Reservation (sender, receiver, network) Buffering (receiver) Scaling (sender) Continuity 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)

10. Mai INF-3190: Multimedia Protocols QoS Requirements: Service Classification service elastic inelastic interactive asynchronous rate adaptive non- adaptive loss in- tolerant loss tolerant interaktive bulk rate adaptive delay adaptive non- adaptive ftp, web ssh, telnet IP tele- phony video- on- demand video confe- rencing original telephony, hard real-time v.c. with scalable video

10. Mai 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 Error probability at data transfer Duration of time to disconnect i.e. at disconnect phase Failure probability of disconnect Security With regard to “listening in” Priority Resilience Ability to work in spite of errors Against errors within the transport layer itself

10. Mai INF-3190: Multimedia Protocols QoS Mapping Application transport service access point Application QoS requirement: 25 video frames/sec, no loss network service access point QoS requirement: 225 kbyte/sec, lossless QoS requirement: 150 packets/sec, lossless

10. Mai INF-3190: Multimedia Protocols QoS Mapping Not only one possible mapping  QoS negotation  Service user and service provider negotiate a 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

10. Mai 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

10. Mai INF-3190: Multimedia Protocols QoS Negotiation Negotiation procedure How to set up QoS Peer-to-peer case – all components or resources must agree Different types Triangular all components (service user and service provider) allowed to change QoS Bilateral both service users allowed to change QoS Unilateral “take it or leave it” from initiating service user

10. Mai INF-3190: Multimedia Protocols QoS Classes Different semantics or classes of QoS: determines reliability of offered service utilization of resources max reserved A reserved B time resources unused available resources reserved C

10. Mai 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  QoS may be violated  unreliable service Deterministic guaranteed QoS hard bounds QoS calculation based on upper bounds (worst case) QoS is satisfied even in the worst case  high reliability  over-reservation of resources  poor utilization and unnecessary service rejects  QoS values may be less than calculated hard upper bound

10. Mai 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) resource capabilities can be statistically multiplexed  more granted requests  QoS may be temporarily violated  service not always 100 % reliable Predictive QoS 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

10. Mai INF-3190: Multimedia Protocols Resource Reservation Reservations is fundamental for reliable enforcement of QoS guarantees Per-resource data structure (information about all usage) QoS calculations and resource scheduling may be done based on the resource usage pattern Reservation protocols 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 calculate necessary amount of resources based on the QoS specifications reserve resources according to the calculation (or reject request) Resource scheduling Enforce resource usage with respect to resource administration decisions

10. Mai INF-3190: Multimedia Protocols Resource Management Phases user’s QoS requirements time Phase 1: Phase 2: Phase 3: admission test and calculation of QoS guarantees rejection or renegotiation resource reservationQoS guarantees to user negotiation data transmission QoS enforcement by proper scheduling monitoring and adaptation “notification” renegotiation reflection specification confirmation renegotiation stream terminationresource deallocation termination