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Traffic Shaping in ATM Networks

Traffic Shaping in ATM Networks. Raj Jain Professor of Computer and Information Sciences The Ohio State University Columbus, OH 43210 http://www.cse.ohio-state.edu/~jain/. Overview. Leaky bucket Generic Cell Rate Algorithm GCRA Implementations: Virtual Scheduling Algorithm

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Traffic Shaping in ATM Networks

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  1. Traffic Shaping in ATM Networks Raj Jain Professor of Computer and Information SciencesThe Ohio State UniversityColumbus, OH 43210http://www.cse.ohio-state.edu/~jain/

  2. Overview • Leaky bucket • Generic Cell Rate Algorithm • GCRA Implementations: • Virtual Scheduling Algorithm • Leaky bucket algorithm • Examples

  3. Leaky Bucket • Provides traffic shaping:Input bursty. Output rate controlled. • Provides traffic policing: Ensure that users are sending traffic within specified limitsExcess traffic discarded or admitted with CLP = 1 Overflow Non-Conforming Conforming

  4. Theoretical Arrival Time Last Cell Time No OK Yes I-L L Time I I L Generic Cell Rate Algorithm: GCRA(I, L) • I = Increment = Inter-cell Time = Cell size/PCR • L = Limit  Leaky bucket of size I + L and rate 1

  5. GCRA: Virtual Scheduling Algorithm Cell Arrival at t Yes (late) TAT<t? Late? No (early) Non Conforming Cell TAT = t TAT > t + L? Too early? Yes No TAT =Theoretical Arrival Time TAT = TAT + IConforming Cell

  6. GCRA: Leaky Bucket Algorithm F = X-(t-LCT) Yes F < 0? No F = 0 Non-Conforming Cell Yes F > L? No LCT = Last Compliance TimeX = Bucket contents at LCTF = Bucket contents now X = F + I; LCT = tConforming Cell

  7. GCRA Examples •  = cell time = 2.73 s at 155 Mbps • GCRA(4.5 , 0.5 ): Arrivals TAT Time 0 4 8 12 16 • GCRA(4.5 , 7 ): Arrivals TAT Time 0 4 8 12 16

  8. Maximum Burst Size  = cell time at PCR, I = cell time at SCR, L=Limit N = Maximum burst size GCRA(I , L ): 0  (N-1) Arrivals 0 I (N-1) I TAT Time 0 4 8 12 16 (N-1) I - (N-1) < L MBS= N= Int[1+ L/(I-)] L = (MBS-1)(I-)

  9. Summary • Leaky bucket is used to smooth bursty arrivals • GCRA requires increment (inter-cell arrival time) and limit (on earlyness) • Two implementations: Virtual scheduling and leaky bucket

  10. Homework • Read pages 505-513 of Stallings’ ISDN and Broadband ISDN with Frame Relay and ATM • Conduct Lab exercise 1

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