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Transcript of Atm Presentation Workshop
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San Diego State University
Department of Mathematical and Computer Sciences
ATM TRAFFIC MANAGEMENT
By
P. Menon and S. Yaramada
Workshop
ATM Networking
San Diego, April 6-7, 2000
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ATM SERVICE CATEGORIES
• Constant Bit Rate (CBR)
• Variable Bit Rate (VBR)
• VBR Real Time• VBR Non Real Time
• Available Bit Rate (ABR)
• Unspecified Bit Rate (UBR)
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ATM SERVICE CATEGORIES ( Cont. )
ATM
Node
ATM
NodeComputer
Mac II
Television
Laptop computer
Fax Telephone
Television
Telephone
UBR or ABR
VBR
CBR
Constant Bit Rate ( CBR ) : Assured Steady supply of bandwidth,
defined by PCR value.Variable Bit Rate (VBR) : Assured supply of bandwith with :
rt:real-time and nrt-non-real-time
Available Bit Rate (ABR) : Bandwidth to keep application runningUnspecified Bit Rate (UBR) : Bandwidth as available with no assurance
ATM Foundation of Broadband Networks (Volume I)
by Uyless Black, Pub. Prentice Hall, 1999
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TRAFFIC PARAMETERS
• Peak Cell Rate (PCR)
• The maximum instantaneous rate at which the user will
transmit. It is the inverse of the minimum inter cell
interval.• Sustainable Cell Rate (SCR)
• Average rate that the user can send cells to the network
i.e., an average throughput.
• Maximum Burst Size (MBS)
• The maximum back-to-back cells that can be sent at thepeak cell rate without violating the sustained cell rate.
• Burst Tolerance ( BT )
• The maximum burst size that can be sent at the peak rate.
• Minimum Cell Rate (MCR)
• The is the minimum rate desired by the user.
• QoS Parameters
• Negotiable QoS
• Non-Negotiable QoS
Time
B
i t r a t e
Time
Time
Time
PCR
PCR
MCR
PCR
SCR
PCR
MBS
CBR
VBR
ABR
UBR
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NEGOTIABLE QoS PARAMETERS
• Cell Transfer Delay ( CTD )
• The delay experienced by a cell between the first bit of the cell that
is transmitted by the source and the last bit of the cell that is
received by the destination.
• Cell Delay Variation ( CDV )
• The difference of the maximum and minimum CTD experienced
during the connection. Peak-to-peak CDV and Instantaneous CDV
are used.
• Cell Loss Ratio ( CLR )
• The percentage of cells that are lost in the network due to error or
congestion and are not received by the destination.
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NON-NEGOTIABLE QoS PARAMETERS
• Cell Error Ratio ( CER )
This parameter measures the fraction of cells received with errors
at the destination.
CER = Errored Cells
Successfully Transferred Cells + Errored Cells
• Severely Errored Cell Block Ratio ( SECBR )
SECBR =Severely Errored Cell Blocks
Total Transmitted Cell Blocks
• Cell Misinsertion Rate( CMR )CMR =
Misinserted Cells
Time Interval
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RELEVANCE OF TRAFFIC PARAMETERS TO
SERVICE CATEGORIES
A T M Layer Service Categories
A ttributes C B R rt-V B R nrt-V B R U B R A B R
T raffic Param etersPC R , C D V T specified
SCR, M BS,C D V T
n/a specified n/a
M C R n/a specified
Q oS Parameters
Peak-to-peak C D V
specified unspecified
m ax C D V specified unspecified
C LR specified unspecified see note 1
O ther A ttributes
Feedback unspecified specified
note1 : CLR is low for sources that adjust cell flow in response to con trol inform ation.
W hether a quan titative value for CLR is specified is network spec ific. ATM Foundation of Broadband Networks (Volume I)by Uyless Black, Pub. Prentice Hall, 1999
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ATM FORUM SERVICE CATEGORIES
Service BandwidthGuarantee
DelayvariationGuarantee
ThroughputGuarantee
CongestionFeedback
CBR Yes Yes Yes No
Rt -VBR Yes Yes Yes No
Nrt-VBR Yes No No No
ABR Yes No Somewhat Yes
UBR No No No No
ATM Foundation of Broadband Networks (Volume I)
by Uyless Black, Pub. Prentice Hall, 1999
8/8/2019 Atm Presentation Workshop
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TRAFFIC CONTRACT
• Traffic Parameters• Describes an inherent characteristics of a traffic source
• Source Traffic Descriptors• Set of traffic parameters of the ATM source.
• Used during connection establishment.
• Connection Traffic Descriptor• Specifies the traffic characteristics of the ATM connections.
• Cell Conformance and Connection
Compliance• Conformance applies cells as they pass the UNI.
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TRAFFIC MANAGEMENT FUNCTIONS
• Connection Admission Control (CAC)• Usage Parameter Control (UPC)
• Traffic Shaping
• Network Resource Management• Selective Cell Discard
• Frame Discard
• Feedback Control
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CONNECTION ADMISSION CONTROL (CAC)Can requested bandwidth and quality of service be supported?
ATM Foundation of Broadband Networks (Volume I)
by Uyless Black, Pub. Prentice Hall, 1999
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USAGE PARAMETER CONTROL (UPC)Monitor and control traffic at the network entrance.
ATM Foundation of Broadband Networks (Volume I)
by Uyless Black, Pub. Prentice Hall, 1999
8/8/2019 Atm Presentation Workshop
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USAGE PARAMETER CONTROL (Cont. )
Arrival of a cell at time ta(k)
TAT < ta(k) ?
TAT > ta(k) + L
?
TAT = ta(k)
TAT = TAT +1Conforming cell
Nonconformingcell
No
Yes
Yes
No
VirtualSchedulingAlgorithm
Virtual Scheduling Algorithm
TAT Theoretical arrival timeta(k) Time arrival of a cellI IncrementL Limit
ATM Foundation of Broadband Networks (Volume I)
by Uyless Black, Pub. Prentice Hall, 1999
8/8/2019 Atm Presentation Workshop
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USAGE PARAMETER CONTROL (Cont.)Leaky Bucket Algorithm
ta(k) Time arrival of a cellX Value of leaky bucket counterX1 Auxiliary variableLCT Last compliance timeI IncrementL Limit
X1 > L ?
X1 < 0 ?
X1 = X - ( ta(k) - LCT )
Nonconformingcell
No
X = X + 1LCT = ta(k)
Conforming Cell
X1 = 0
No
Yes
Yes
Continuous-State leaky
bucketalgorithm
Arrival of a cell at time ta(k)
ATM Foundation of Broadband Networks (Volume I)
by Uyless Black, Pub. Prentice Hall, 1999
8/8/2019 Atm Presentation Workshop
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TRAFFIC MANAGEMENT FUNCTIONS
, Connection Admission Control
, Usage Parameter Control
• Traffic Shaping
• Network Resource Management
• Selective Cell Discard
• Frame Discard
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CONGESTION MANAGEMENT TECHNIQUES
• First in First Out (FIFO) Queue• Priority Queuing
• Fair Queuing
• Weighted Fair Queuing
• Custom Queuing
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CONGESTION AVOIDANCE MECHANISM
• Tail drop
• DEC bit
• Random Early Dropping• Weighted Early Dropping
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ABR FLOW CONTROL
• Features• Goal is to make unused bandwidth available to
cooperating end-users in a fair, timely manner.
• Source has the ability to increase or decrease its
flow.
• Minimum cell rate is guaranteed by the network
with minimum cell loss.
• Rate based end-to-end closed loop model.
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ABR TRAFFIC MANAGEMENT MODEL
Taken From Prof.Jain's site.
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ABR PARAMETERS
Label Expansion Default Value
PCR Peak Cell Rate -
MCR Minimum Cell Rate 0
ACR Allowed Cell Rate -
ICR Initial Cell Rate PCR
TCR Tagged Cell Rate 10 cells/s
Nrm Number of cells between FRM cells 32
Mrm Controls bandwidth allocationbetween FRM, BRM and data cells
2
Trm Upper Bound on Inter-FRM Time 100 ms
RIF Rate Increase Factor 1/16
RDF Rate Decrease Factor 1/16
ADTF ACR Decrease Time Factor 0.5 ms
TBE Transient Buffer Exposure 16,777,215
CRM Missing RM-cell Count $\lceil$ TBE/Nrm $\rceil$
CDF Cutoff Decrease Factor 1/16
FRTT Fixed Round-Trip Time -
ATM Forum – Traffic Management Specification Version 4.0
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RM CELL FORMAT
Taken from Prof. Jain’s site
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IN-RATE AND OUT-OF-RATE RM CELLS
• In-Rate Cell Type
RM cells with CLP = 0
RM cells + data cells < ACR
• Out-Of-Rate Cell Type
RM cells with CLP = 1
Generated by switches ,destinations ,sources under exceptionalcircumstances.
- BECN from the switches.
- Source periodically sense the state of the network when ACR = 0
- Used by the destinations of VCs whose reverse direction ACR is
either zero or not sufficient to return all RM cells received in theforward direction.
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FEEDBACK CONTROL TECHNIQUES
• Binary Mode ABR
• Explicit Rate (ER) ABR
• Virtual Source/Virtual Destination (VS/VD) ABR
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ABR FEEDBACK CONTROL TECHNIQUES
( Cont .)
Binary Mode ABR
ATM Theory and Application
by David E. McDysan and Darren L. Spohn
Pub. McGraww-Hill, 1999.
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ABR FEEDBACK CONTROL TECHNIQUES
( Cont .)
Explicit Rate (ER) ABR
ATM Theory and Application
by David E. McDysan and Darren L. Spohn
Pub. McGraww-Hill, 1999.
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ABR FEEDBACK CONTROL TECHNIQUES
( Cont .)
Virtual Source / Virtual Destination (VS/VD) ABR
ATM Theory and Application
by David E. McDysan and Darren L. Spohn
Pub. McGraww-Hill, 1999.
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SOURCE BEHAVIOR
1. MCR < ACR < PCR
Source Rate < ACR
2. After successful connection setup, source shall set ACR < ICR. Firstin-rate cell should be forward RM cell.
3. The relative priority of data cells , FRM cells and BRM cells
( corresponding to the reverse flow ) is different at different
transmission opportunities.
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SOURCE BEHAVIOR ( Cont. )
4. Cells send with the above rules should have CLP = 0.
5. If a source does not transmit any RM cells for a time periodequal to its timeout interval ADTF( ACR Decrease time
factor ),and also if ACR >ICR ,then the ACR should bereduced to the ICR. ADTF can be negotiated with thenetwork during connection setup.
6. Before sending in an in- rate forward cell, and afterfollowing the rule #5, if CRM FRM cells have been sentand the source did not receive any BRM,,the source shouldsuspect network congestion and should reduce the ACR byat least ACR * CDF,unless the reduction would result invalue less than the MCR.
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SOURCE BEHAVIOR ( Cont. )
7. When sending an FRM , the sources should indicate their
current ACR in the CCR field of the RM cells.
8. This indicates how the network should react to network
feedback.The feedback consists of ER,CI, and the NI bits.
9. When a BRM cell is received and after the ACR is
adjusted according to the source behavior#8 ACR is set to
the most minimum of the ACR as computed in #8 and
the ER field.
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SOURCE BEHAVIOR ( Cont. )
10. Sources should initialize the various fields of the RM cell,while generating the FRM cells.
11. FRM cells may be send out-of-rate .The out-of-rate FRMcells shall not be sent at a rate greater than TCR.
12. The source shall reset the EFCI bit on every data cell itsends.
13. The source may implement a use-it –or-lose-it policy toreduce its ACR to a value which approximates the actual
cell rate transmission.
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DESTINATION BEHAVIOR
1. Destinations should monitor the EFCI bits on the incomingcells and store the value last seen on a data cell.
2. Destinations are required to turn around the forward RMcells with minimal modifications.The DIR bit shall be changedfrom forward to backward, BN shall be set to zero and theCCR, MCR, ER, CI, and the NI fields should not be changedin the RM cells except under certain conditions.
3. If a forward RM cell is received by the destination, whileanother turned around RM cell is scheduled for an in-ratetransmission.
• The contents of the old cell are overwritten by the contents of thenew cell.
• The old cell after being overwritten be sent out-of-rate;or it may bediscarded or remain scheduled for an in-rate transmission.
• It is required that the new cell be scheduled for an in-ratetransmission.
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RESEARCH
• Many new algorithms are being implemented to
improve the “Explicit Congestion Notification”.
• Analysis of QoS parameters over Multiprotocol
Label Switching using Traffic Engineering.
• Analyze the behavior of the service categories under
heavy traffic network using various techniques.