Lecture 23 24 25 26

Lecture 23 24 25 26 - EE 555 Spring 2009 Broadband Network...

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EE 555 Spring 2009 Broadband Network Architectures Traffic Management Prof. John Silvester Traffic Management Techniques Congestion/Flow Control – to adjust the rate at which traffic enters the network to reduce congestion. e.g. TCP window mechanism, explicit rate control Shaping – mechanism to change the smoothness of the traffic flow. Used to reduce or manage burstiness e g Leaky Bucke reduce or manage burstiness. e.g. Leaky Bucket Policing – mechanism to enforce a policy – typically related to a maximum rate or amount of burstyness that a connection may send to a network or connection e.g. Token Bucket and Leaky Bucket Scheduling – queuing disciplines to give priority to some traffic over other traffic or to allocate fractions of the channel among different classes of traffic. e.g. FIFO, Priority Queueing, Round Robin (RR), Weighted Fair Queueing (WFQ) Buffer management – how to share the buffer space; also deciding which packets to drop when congestion occurs. e.g. sharing policies, RED usc-den-ee555-spr2009: 5. Traffic Management 2
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Congestion/Flow Control To adjust the rate at which traffic enters the network to reduce congestion. (e.g. TCP window mechanism, explicit rate control) How to share a channel among competing flows? – Channel of capacity C K flows at rates ( f 1 , f 2 , … f K ) where Could assign each flow an equal share C / K Max-Min fair. Assume rates are ordered (smallest to largest) i f C > ; for 1 to cCkK iK cc = Example: C=24 flow 2 7 12 16 if then else ;1 ii i i i fr f r kk rkk < ←← ←− rate 2 7 7.5 7.5 usc-den-ee555-spr2009: 5. Traffic Management 3 Shaping Shaping – mechanism to change the smoothness of the traffic flow. Used to reduce or manage burstiness. (e.g. Leaky Bucket) source traffic minimum smoothed traffic τ minimum inter-packet gap usc-den-ee555-spr2009: 5. Traffic Management 4
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Leaky Bucke Leaky Bucket packets “Pure” leaky bucket with infinite depth – does smoothing only “bucket” (buffer) drain rate 1 does smoothing only. Used in ATM with fixed size packets. r=1/ τ Can be generalized to variable length packets. Can model the bucket operation like a queue with deterministic service rate. 1 (1 )m a x { ( )1 , 0 } t bt a + += − + usc-den-ee555-spr2009: 5. Traffic Management 5 Leaky Bucket of size K packets “bucket” (buffer) drain rate 1 Leaky bucket with finite depth – does smoothing and burst size (or delay) constraint. Overflowing packets are typically dropped. K r=1/ τ 1 i n { m a x { ( , 0 } ,} t a K + usc-den-ee555-spr2009: 5. Traffic Management 6
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Token Bucke Token Bucket rate • Token bucket – burst control. Largest burst is of size K tokens “bucket” r=1/ τ is of size K. • Packet needs a token to be accepted. • Otherwise dropped or tagged (marked). • Marked packets are given lower priority K packets inside network.
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This note was uploaded on 12/22/2010 for the course EE 555 taught by Professor Silvester during the Fall '08 term at USC.

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Lecture 23 24 25 26 - EE 555 Spring 2009 Broadband Network...

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