token bucket leaky bucket
DESCRIPTION
Token Bucket Leaky Bucket. Leaky Bucket. (a) A leaky bucket with water. (b) a leaky bucket with packets. Token Bucket. We want to allow some burstiness . x(t) is the instantaneous sending rate, . Max bits b(u). Slope= average rate. Max burst rate. Interval size u. b(u)= r u +b. - PowerPoint PPT PresentationTRANSCRIPT
Token BucketLeaky Bucket
Leaky Bucket
(a) A leaky bucket with water. )b( a leaky bucket with packets.
Token Bucket
x(t) is the instantaneous sending rate ,
ut
t0t dt)t(xmaxub Max bits b(u)
Interval size u
Max burst
rate
Slope=average rate
b(u)=r u +b
We want to allow some burstiness.
Token Bucket Regulator (Shaper)
What is it good for?
• Traffic shaper– Shape the traffic to conform to contract
• Traffic policer– Drop packets that do not conform
• Traffic marker– Color packets by conformance to contract– Rate estimator
Remarks
• When tokens are not available– Store packet (shaper)– Discard packet (policer)
• The sum of two regulated flows (b1,r1)& (b2,r2) behave like a regulated flow (b1+b2,r1+r2)
• Cascading t.b. after a l.b. can shape the burst rate
Shaping Examples
(a) Input to a leaky bucket.
(b) Output from a leaky bucket.
Output from a token bucket with capacities of (c) 250 KB, (d) 500 KB, (e) 750 KB,
(f) Output from a 500KB token bucket feeding a 10-MB/sec leaky bucket.
Traffic Marker
Packet arrival
Enough tokens in
bucket?
Color greenColor red
Packet forwarding
IETF Packet Marking
• Two types of markers are available:– RFC 2697: A Single-Rate, Three-Color Marker
• Committed Information Rate (CIR), • Committed Burst Size (CBS), • Excess Burst Size (EBS)
– RFC 2698: A Dual-Rate, Three-Color Marker• Peak Information Rate (PIR) • Committed Information Rate (CIR), • Committed Burst Size (CBS), • Peak Burst Size (PBS)
• Suggested in the context of DiffServ
Heinanen and Guerin, 1999
Single-Rate Three-Color MarkerUsage:•Mark conforming traffic with a low drop precedence•Mark exceeding traffic with a high drop precedence•Drop violating traffic
Definitions:•CIR – Committed Information Rate•CBS – Committed Burst Size (max)•EBS – Excess Burst Size (max)•Tc – Current size of CBS bucket•Te – Current size of EBS bucket
Two-Rate Three-Color MarkerUsage:•Mark packets within CIR as conforming•Mark packets between CIR and PIR as exceeding •Drop packets above the PIR
Definitions:•CIR – Committed Rate•PIR – Peak rate•CBS – Committed burst size (max)•PBS – Peak burst size (max)•Tc – Current size of CBS bucket•Tp – Current size of PBS bucket
Marker Locations and Size
Frame Relay header
ATM Cell header
ISL or 802.1q/p header
Part of 20 bit MPLS label
Six most significant bits of TOS byte in IPv4 and IPv6 headers
Three most significant bits of TOS byte in IPv4 and IPv6 headers
Bits Location
1Frame Relay DE Bit
1ATM CLP Bit
3Ethernet CoS Bits
3MPLS Experimental )EXP( Bits
6Differentiated Services Code Point )DSCP(
3IP Precedence
#of BitsType of Marking
©Juha Heinanen13
RED with Multiple ThresholdsDiscard
Probability
AverageQueue Length0
1
“Red”Threshold
0 “Yellow”Threshold
“Green”Threshold
“Red”Packets
“Green”Packets
“Yellow”Packets
Full
©Juha Heinanen14
Metering, Marking and Policing
Host
EnterpriseNetwork
ISP
May police hostbehavior and
classify packets onbehalf of host
Polices aggregatebehavior and remarks
or drops excess
May meter aggregatebehavior, classify,
(re)mark, drop, andshape packets
May meter hostbehavior and
shape packets
R
R R
May classifypackets to
service classesMay select outgoing packets
and drop excess
Leaky Buckets in ATM
Chapter 13: ATM Traffic & Congestion Control16
ATM Traffic Parameters• Source Traffic Descriptor
– Peak Cell Rate (PCR)Peak Cell Rate (PCR): upper bound on traffic submitted by source (PCR = 1/T, where T = minimum cell spacing
– Sustainable Cell Rate (SCR)Sustainable Cell Rate (SCR): upper bound on average rate of traffic submitted by source (over a larger T)
– Maximum Burst Size (MBS)Maximum Burst Size (MBS): maximum number of cells sent continuously at PCR
– Minimum Cell Rate (MCR)Minimum Cell Rate (MCR): used with ABR and GFR… minimum cell rate requested, access to unused capacity up to PCR (elastic capacity = PCR-MCR?)
– Maximum Frame Size (MFS)Maximum Frame Size (MFS): maximum size of a frame in cells available for GFR service
17
Generic Cell Rate Algorithm (GCRA): Virtual Scheduling
GCRA (I, L):I = IncrementL = Limitta(k) = Time of arrival of a cellTAT = Theoretical arrival time
At time of arrival ta(1) of the first cell of connection, TAT = ta(1)
Algorithm takes two arguments, I and L
With PCR of R, I = T = 1/R CDVT limit, = L Then peak cell rate algorithm is
expressed as:GCRA(T, )
I.e., this cell arrived too late.
Late arrival OK
Reset TAT
Early arrival within limit OK
Early arrival beyond limit NOT OK
Early arrival TEST
• Virtual scheduling algorithm – Conforming cell
– Non-conforming cell
* At the time of arrival of the first cell of the connection, TAT = ta(k)
I
Time
ta(k)
TAT(k)
L
TAT(k)
TAT(k+1)TAT(k-1)
)a(
I
Time
ta(k)
TAT(k)
TAT(k+1)TAT(k-1)
)b(
L
I
Time
ta(k)
TAT(k-1)TAT(k)TAT(k-2)
Leaky Bucket
Multiple Leaky Buckets
Can we create traffic differentiation?
Scenario
At the Edges: Multiple Cascading Token Buckets (FRQ?)At Core router : Multi-GRED drop Model
RED differentiation
Simulation Set-Up
04/22/23 24
Definitions
• The committed rate of R: comm(A) = • The excess link rate of R ex(R) = bw(R) − comm(A).• CIR aggregation level: AGGCIR = comm(A)/bw(R) .• The EIR aggregation-level is the entire EIR allocated on a
bottleneck link divided by its excess rate, AGGEIR =
• The fair throughput of an aggregate i is composed of its CIRi and its fair share of the excess bandwidth
EIRaggi = (EIRi/AGGEIR).
Ai
iCIR
)(/ RexEIRAi
i
SLAa
Token Bucket Rate Assignment
Aggregate Traffic Mix
Three-Color Marking Goodput Per Aggregate )a(
0
300000
600000
900000
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
Tim e )10 seconds(
Goo
dPut
)Byt
es(
Six-Color Marking Goodput Per Aggregate )b(
0
300000
600000
900000
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
Tim e )10 seconds(
Goo
dPut
)Byt
es(
Betterdifferentiation
Effect of Packet Size
Things to Remember
• Increasing the number of colors indeed improving differentiation between the aggregates according to the committed and the excess rates.
• The token bucket coloring policies, which is widely used for this purpose, prefer short packets and mark them with a higher priority colors.
• The differentiation process is more difficult for the short TCP connections that remain in the slow start phase, than for the long connections that are usually in the congestion avoidance phase.