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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



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)



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



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



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.



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



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



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





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.



TRAFFIC MANAGEMENT FUNCTIONS

• Connection Admission Control (CAC)• Usage Parameter Control (UPC)

• Traffic Shaping

• Network Resource Management• Selective Cell Discard

• Frame Discard

• Feedback Control



CONNECTION ADMISSION CONTROL (CAC)Can requested bandwidth and quality of service be supported?





USAGE PARAMETER CONTROL (UPC)Monitor and control traffic at the network entrance.





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





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)





TRAFFIC MANAGEMENT FUNCTIONS

, Connection Admission Control

, Usage Parameter Control

• Traffic Shaping

• Network Resource Management

• Selective Cell Discard

• Frame Discard



CONGESTION MANAGEMENT TECHNIQUES

• First in First Out (FIFO) Queue• Priority Queuing

• Fair Queuing

• Weighted Fair Queuing

• Custom Queuing



CONGESTION AVOIDANCE MECHANISM

• Tail drop

• DEC bit

• Random Early Dropping• Weighted Early Dropping



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.



ABR TRAFFIC MANAGEMENT MODEL

Taken From Prof.Jain's site.



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



RM CELL FORMAT

Taken from Prof. Jain’s site



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.



FEEDBACK CONTROL TECHNIQUES

• Binary Mode ABR

• Explicit Rate (ER) ABR

• Virtual Source/Virtual Destination (VS/VD) ABR



ABR FEEDBACK CONTROL TECHNIQUES

( Cont .)

Binary Mode ABR

ATM Theory and Application

by David E. McDysan and Darren L. Spohn

Pub. McGraww-Hill, 1999.




( Cont .)

Explicit Rate (ER) ABR







( Cont .)

Virtual Source / Virtual Destination (VS/VD) ABR






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.



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.




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.




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.



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.



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.

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