Univ. of TehranIntroduction to Computer Network1 An Introduction Computer Networks An Introduction to Computer Networks University of Tehran Dept. of EE and Computer Engineering By: Dr. Nasser Yazdani Lecture 14: Quality of Service

Univ. of TehranIntroduction to Computer Network2 Outline Realtime Applications Integrated Services Differentiated Services

Univ. of TehranIntroduction to Computer Network3 Realtime Applications Require “deliver on time” assurances must come from inside the network Example application (audio) sample voice once every 125us each sample has a playback time packets experience variable delay in network add constant factor to playback time: playback point Microphone Speaker Sampler, A D converter Buffer, D A

Univ. of TehranIntroduction to Computer Network4 Playback Buffer Sequence number Packet generation Network delay Buffer Playback Time Packet arrival Real-Time Audio  rate one per 125 micro-sec Limit on delay, at most 300 ms.

Univ. of TehranIntroduction to Computer Network5 Distribution of Delays Packets (%) 90%97%98%99% Delay (milliseconds) Blue is the delay distribution Others are cumulative percentages Variability of delay is consistent for almost all paths

Univ. of TehranIntroduction to Computer Network6 Taxonomy Applications Real time Tolerant AdaptiveNonadaptive Delay- adaptive Rate- adaptive Intolerant Rate-adaptiveDelay adaptive Interactive bulk Asynchronous Elastic Tolerant: Audio Intolerant: a robot control. Adaptive: can adjust playback time

Univ. of TehranIntroduction to Computer Network7 Approaches to QoS Fine –grained- Provide QoS to individual flows. Integrated service or RSVP and usually ATM Coarse-grained- For aggregated traffics. Differentiated Services.

Univ. of TehranIntroduction to Computer Network8 Integrated Services (RSVP) Produced by IETF around Service Classes Guaranteed, never arrive late. For tolerant, adaptive applications. controlled-load, not heavily loaded (i.e vat) Mechanisms signaling protocol, flowspec, resource reservation. admission control policing packet scheduling

Univ. of TehranIntroduction to Computer Network9 Flowspec Rspec: describes service requested from network controlled-load: none guaranteed: delay target Tspec: describes flow’s traffic characteristics average bandwidth + burstiness: token bucket filter token rate r bucket depth B must have a token to send a byte must have n tokens to send n bytes start with no tokens accumulate tokens at rate of r per second can accumulate no more than B tokens

Univ. of TehranIntroduction to Computer Network10 Per-Router Mechanisms Admission Control decide if a new flow can be supported answer depends on service class and policy not the same as policing Packet Processing classification: associate each packet with the appropriate reservation scheduling: manage queues so each packet receives the requested service

Univ. of TehranIntroduction to Computer Network11 Reservation Protocol Called signaling in ATM Proposed Internet standard: RSVP Consistent with robustness of today’s connectionless model Uses soft state (refresh periodically) Designed to support multicast Receiver-oriented Two messages: PATH and RESV Source transmits PATH messages every 30 seconds Destination responds with RESV message Merge requirements in case of multicast Can specify number of speakers

Univ. of TehranIntroduction to Computer Network12 RSVP Example R R R R R Sender 2 PATH PA RESV (merged) RESV Receiver B Receiver A Sender 1

Univ. of TehranIntroduction to Computer Network13 RSVP versus ATM (Q.2931) RSVP receiver generates reservation soft state (refresh/timeout) separate from route establishment QoS can change dynamically receiver heterogeneity ATM sender generates connection request hard state (explicit delete) concurrent with route establishment QoS is static for life of connection uniform QoS to all receivers

Univ. of TehranIntroduction to Computer Network14 Differentiated Services Problem with IntServ: scalability Idea: support two classes of packets premium best-effort Can be done by a bit. Who set the bit? What the router does with this bit? Per-hop behavior, means not end-to-end. Use TOS field in IP packet, DiffServ code points (DSCP) EF class: Expedite Forwarding, with min delay.

Univ. of TehranIntroduction to Computer Network15 Differentiated Services Guarantee Delay: Max entry to router Strict priority Assured Forwarding RED with In and Out P(drop) 1.0 MaxP Min in Max in Max out Min out AvgLen Mechanisms packets: ‘in’ and ‘out’ bit edge routers: tag packets core routers: RIO (RED with In and Out)