08 - Chapter 8 Network Traffic Control and Quality of...

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Chapter 8 Network Traffic Control and Quality of Service Support
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Two Fundamental Goals of Network Resource Allocation To satisfy QoS requirement of end users To maximize network usage
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Controls at Different Time Scales Connection Setup: VC setup (seconds to hours) VP setup (hours to days) routing; forwarding table setup; bandwidth allocation; decision on whether QoS can be satisfied Cell level control Traffic shaping at the source Policing between source and entrance of network Cell scheduling at multiplexers/switches Feedforward (open-loop) versus feedback (closed-loop) for ABR services.
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Fig. 8.1. (a) On-off cell traffic source; (b) Approximate on-off cell traffic with fluid-flow traffics T T T On time Off time (a) T T T On time Off time (b) peak Fluid flow on time Modeling On-off Cell Traffic with Fluid One cell every T seconds during on time
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Modeling on-off Cell Traffic with Fluid 53 8 bits/s 0 bits/s 1 bits/s 1 1 1 1 where average on time; average off time on time peak off time on time ave r r T r r r μ λ μ μ λ - - - × = = = = + = =
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Fig. 8.2. An analogy between a transmission buffer of output rate C and a leaky bucket Source 1 Source 2 Source N C bits/s Leaky Bucket Source 1 Source 2 Source N C bits/s Buffer Size = B bits (Statistical Multiplexing)
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Fig. 8.3. A leaky bucket with a single source (a) Cumulative traffic-versus-time arrival and departure curves b 1 b 2 t t 1 t 2 slope = c departure bit i slope = r peak Arrival t 1 - t 2 = delay of bit i Time(sec) Cumulative Traffic (bits) b2 - b1 = buffer occupancy at time t Single Source C r peak >C Arrival curve Departure curve
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Fig. 8.3. (b) Traffic rate-versus-time arrival and departure curves Arrival curve Departure curve Time(sec) Traffic Rate (bits/sec) C r peak
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Fig. 8.4. The arrival and departure curves of a fluid-flow multiplexer Arrival curve Departure curve Time Arrival Traffic Rate 1 2 3 Two sources on Three sources on Source 1 Source 2 Source N 1 < C < 2 r peak =1 Time Cumulative Traffic slope = 1 2 1 2 1 3 slope = c c (Slope = n r peak if m sources have arrivals)
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Figures in previous slides give a “global view”. QoS (performance) of individual sessions not reflected. For performance of individual sessions, a service discipline must be specified FIFO Round-robin; approximated by equal-service discipline (or fair queueing) in fluid flow model.
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Fig. 8.5. A multiplexer with two sources: the cumulative arrival and departure curves for the total traffic and the traffic of stream 1 Arrival Traffic Rate (Source 1) 1 Time t 0 t 2 Arrival Traffic Rate (Source 2) 1 Time t 1 t 4 Arrival Traffic Rate (Source 1 and 2) 1 Time t 0 t 4 2 t 1 t 2 Source 1 Source 2 1 < C < 2 r peak =1 Equal-service discipline
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Fig. 8.5. A multiplexer with two sources: the cumulative arrival and departure curves for the total traffic and the traffic of stream 1 Cumulative Traffic (Sources 1 and 2) Cumulative Traffic (Source 1) Time Time slope = 1 2 1 1 2 1 < C < 2 1 1 C/2 slope = 1 t 0 t 4 t 1 t 2 t 3 When both sources busy, divide capacity evenly Arrival curve Departure curve
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