© Dr. Z. Sun

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ATM and B-ISDN

Dr. Zhili SUNUniversity of Surrey

GuildfordSurrey

GU2 7XHTel: 01483 68 9493Fax: 01483 68 6011

Email: Z.Sun@eim.surrey.ac.uk

Components of DATA and INTERNET NETWORKING MSc MODULE

(EEM.din, Linked EE4.din)

ATM and B-ISDN

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ATM and B-ISDN

Table of Contents

1. ATM technology2. Quality of Service (QoS) 3. Traffic Control and Management4. Traffic Policing and Shaping Algorithms5. Recommended Texts

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ATM and B-ISDN

Aims

This lecture component is developed as part of the course moduleto provide you with information on advanced topics in ATM and Broadband Communications Networks and Technology.

This component covers a range of topics that provides you with acomprehensive view of Asynchronous Transfer Mode (ATM) and Broadband Integrated Service Digital Networks (B-ISDN) technology. The topics include review of ATM, ATM Standard, ATM switches, Traffic control, ATM networks, and Broadband services and applications.

If you have any comment or suggestion on this component, you are welcome to send it to me.

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ATM and B-ISDN

1. ATM Technology

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ATM and B-ISDN

ATM and B-ISDN

■ ITU-T definition of Broadband: • A service or system requiring transmission channels capable

of supporting rates greater than the primary rate.

■ Relationship Between ATM and B-ISDN• ATM evolved from the standardization efforts for B-ISDN. • ATM is the technology upon which B-ISDN is based.

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ATM and B-ISDN

ATM Technology

■ Cell Switching • 53 bytes cells• 48 payload and 5 byte header

■ Negotiated Service Contract• Connection Oriented • end-to-end Quality of Services.

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ATM and B-ISDN

Principle of ATM

■ cell-based transfer mode • this means that information from the source is transferred as

fixed-length cells

Head

5 Octets

Payload

48 Octets

Why 53 bytes?

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ATM and B-ISDN

Why fixed size 53 bytes?

■ Switching efficiency■ Transmission Efficiency = Linfo/(Linfo + Loverhead)■ Process Delay Factor = Dinfo/(Doverhead + Dinfo)

■ Europe (32) and US (64) due to echo cancellors

Payload

Overhead%

9.43%

48 bytes0

Delay ms

4

64 bytesPayload0

8

32

@64kbit/s

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ATM and B-ISDN

ATM cell stream

No blank space between cells

ATM cell

ATM cell-stream

unassigned cell

source 1

source 2

source 3

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ATM and B-ISDN

Head Structure at UNI and NNI Interfaces

GFC

CLPPTVCI

VCI

VPI

VPI VCI

HEC

1 2 3 4 5 6 7 8

1

2

3

4

5

at the UNI

CLPPTVCI

VCI

VPI

VPI VCI

HEC

1 2 3 4 5 6 7 8

at the NNI

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ATM and B-ISDN

VPs and VCs

Physical LayerVirtual Path (VP)

Virtual Channel (VC)

Each VP within the Physical Layer has itsown distinct VPI; each VC within a VP has itsown distinct VCI

■ VCs and VPs are an important property of ATM

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ATM and B-ISDN

Hierarchy of the ATM transport Network

Transmission Path Level

Digital Section Level

Regenerator Section Level

Physical Layer

ATM Layer

Virtual Path Level

Virtual Channel

Higher Layer (AAL)

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ATM and B-ISDN

VC & VP Switching

VC switch

Endpointof VPC

VP switch

VC and VP switching VP switching

VP switch

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ATM and B-ISDN

ATM Routeing and Header Translation

14

22

32

43

in out

76

54

66

87

a

b

c

d

w

x

y

z

Switchingfabric

port in Headera 1a 4b 2c 3c 2d 4d 3

port out Headerx 5w 6y 6z 8x 4w 7z 7

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ATM and B-ISDN

B-ISDN ATM Adaptation Layer (AAL) Service Classification(362)

Timing relationBitrate

Connectionmode

Class A Class B Class C Class D

required not required

constant variable

connection-oriented connection-less

Examples: A - Circuit emulation, CBR VideoB - VBR video and audioC - CO data transferD - CL data transfer

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ATM and B-ISDN

B-ISDN ATM Adaptation Layer (AAL) Types (363)

■ AAL 1 for Class A■ AAL 2 for Class B■ AAL 3/4 for Class C & D■ AAL 5 for Class C & D

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ATM and B-ISDN

AAL1 for Class A

Header functions include:

• SN - Sequence Number (Lost cell detect: used by Adaptive Clock Method), CSI - Convergence sublayer indication (0=no pointer, 1=pointer), SNP - Sequence Number Protection by CRC

• Byte alignment: allows channelise circuit emulation, e.g.,channelised DS 1

• Time stamp: used for end-to-end clock synchronisation, e.g., Synchronous Residual Time Stamp method

Payload

4 bits 47 or 46 bytes

SNPCS

I

SN

1 3 bits

Pointer(optional)

8 bits

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ATM and B-ISDN

AAL2 for Class B

SN - Sequence Number, IT - Information Type

LI - Length Indicator, CRC - Cyclic Redundancy Check

PayloadIT

48 bytes

SN CRCLI

1 byte 2 bytes

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ATM and B-ISDN

AAL3/4 for Class C&D

44 bytes of data per cellST - Segment Type (COM,BOM,EOM,SSM)LI - Length Indicator

Cyclic Redundancy Check (CRC) per cellMessage Identifier (MID) allows muitipleinterleaved packets on a virtual connection

ErrorChecking

2 4 10bits 6 10 bits

4

44 bytes

Data

ErrorChecking

4 or 8 bytes

0 - 65535 bytes

CRCUser DataMIDSNST LI

CRCUser DataSNST MID LI

CRCUser Data PADSNST MID LI

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ATM and B-ISDN

AAL5 for Class C&D

48 bytes of data per cellUse PTI bit to indicate last cellOnly one packet at a time on a virtual connection

0 User Data

48

Data

0 - 65535 bytes

0 User Data

48

148

PAD

Last cell flag

0-47

0 LEN

CRC

2 2 4 bytes

Error Detection Fields

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ATM and B-ISDN

Mapping ATM into STM-1

270 bytes

11

2

3

4

5

6

7

8

9

Section overhead

AU ptr

Section overhead

9 10 270

9 bytes

125 microseconds

STM-1 Payload

J1

B3

C2

G1

F2

H4

Z3

Z4

Z5

VC-4

POH

...... ......

ATM Cells

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ATM and B-ISDN

Mapping ATM into Cell Based Transmission

......1 2 26 27 28

......1 2 26 27 28

29

OMA Cell

ATM layer: 149.760 Mbit/s

Physical Layer: 155.520 Mbit/s

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ATM and B-ISDN

ITU-T

■ ITU - International Telecommunication Union (Formally known as CCITT)• three main sectors: ITU-T, ITU-R and ITU-D• five classes of member: Administrative (PTT), Private operators (BT),

Regional telecom organisation (ETSI), Telecom vendors and scientific organisation, others

• Study group, work parties, expert teams, ad hoc groups,

■ ITU-T Responsible for Public ATM network Specifications

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The ATM Forum

■ International non-profit organization formed in 1991. With the objective of accelerating the use of ATM products and services through a rapid convergence of interoperability specifications.

■ Promotes industry cooperation and awareness.■ Consists of Technical Working Group, three

Marketing Working Groups for North America, Europe and Asia-Pacific as well as the Enterprise Network Roundtable, through which ATM end-users participate.

■ Responsible for Private ATM network Specifications

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ATM and B-ISDN

Summary of Physical Layer UNI Interface

(ATM Forum).(* Underdevelopment, SMF - Single Mode Fibre)

Frame Format Bit Rate (Mbit/s) Transmission MediaDS1 1.544 Twisted pairDS3 44.736 Coax pair

STS-3c, STM-1 155.520 SMFE1 2.048 Twisted pairE3 34.368 Coax pairJ2 6.312 Coax pair

N x T1 * N x 1.544 Twisted pairN x E1 * N x 2.048 Twisted pair

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ATM and B-ISDN

2. Quality of Service (QoS)

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ATM and B-ISDN

ATM Service Categories

■ CBR: Constant Bit Rate• Continuous flow of data with tight bounds on delay and delay

variation

■ rt-VBR: Real Time Variable Bit Rate• Variable bandwidth with tight bound on delay and delay variation

■ nrt-VBR: Non-Real Time Variable Bit Rate• Variable bandwidth with tight bound on cell loss

■ UBR: Unspecified Bit Rate• No guarantees (i.e., best effort delivery)

■ ABR: Available Bit rate• Flow control on source with tight bound on cell loss

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ATM and B-ISDN

Traffic parameters and descriptors

■ PCR: Peak cell rate is the maximum rate at which the send is planning to send.

■ SCR: Sustained cell rate is the expected or required cell rate averaged over a long time interval.

■ MCR: Minimum cell rate is the minimum number of cells/second that the customer considers as acceptable.

■ CDVT: Cell delay variation tolerance tells how much variation will be presented in cell transmission times.

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ATM and B-ISDN

Cell transfer performance and QoS parameters

■ CTD: It is the extra delay added to an ATM network at an ATM switch, in addition to the normal delay through network elementsand lines.

■ CDV: The 1-point CDV describes variability in the pattern of cell arrival events observed at a single boundary with reference to the negotiated 1/T. The 2-point CDV describes variability in the pattern of cell arrival events observed at an output of a connection with the reference to the pattern of the corresponding events observer at the input to the connection.

■ CLR: lost cells divided by the total transmitted cells.

■ CER: errored-cells / (successful-transferred-cells + errored-cells).

■ SECBR: Total severely errored cell block / Total transmitted cell blocks.

■ CMR: misinserted cell / Time interval

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ATM and B-ISDN

3. Traffic Control and Management

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ATM and B-ISDN

Traffic Control and Resource Management (371)

■ Protect network, provide QOS & optimise resource usage■ Connection admission control■ Usage parameter control (Policing function)■ Network parameter control (Policing function)■ Priority control■ Congestion control■ Traffic Parameter: type, peak, mean burst, peak duration ■ QOS: delay, delay variation & loss

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ATM and B-ISDN

Traffic Management

■ Problem: provide Quality of Services (QoS)• How should ATM network resources be allocated to ensure

good performance including preventing congestion control, e.g., how many virtual channels should be assigned to a particular transmission link?

■ Solution: Traffic Management• Specify the traffic “contract” on each virtual channel/path• Route (including rejecting setup request) each virtual

channel/path along a path with adequate resources (Connection Admission Control - CAC)

• Mark (via cell loss priority bit) for loss all cells that violate the contract (traffic policing)

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ATM and B-ISDN

Traffic contract between customer and Network

■ The traffic to be offered (traffic parameters and descriptors)

■ The service agreed upon (QoS)■ The compliance requirements

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ATM and B-ISDN

Usage and Network Parameter Control

Network interface 1

0

NP0

P0 ?

P1 ?Output

NP1

+

A. No cell tagging.

Network interface 1

0

NP0

P0 ?

P1 ?Output

NP1

+

B. Cell tagging.

+

Tagging

P ? Control of parameter P

Cell discard

NP0: CLP=0 cell flowNP1: CLP=1 cell flow

Network Performance Objective:

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ATM and B-ISDN

4. Traffic Policing and Shaping Algorithms

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ATM and B-ISDN

Leaky Bucket

B u cke t S ize :L + I

1 to ken fo r e a ch

ce ll a rr iva l

1 to ke n le ak p e r

u n it o f tim e

A T MSw itch

A T M ce lls

T o ke nO ve rflo w

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ATM and B-ISDN

Leaky Bucket - Generic Cell Rate Algorithm (GCRA)

For a sequence of cell arrival time {ti} determine which cells conform to the traffic contract

Bucket Size: L+ I

1 token for each cell arrival

1 token leak per unit of time

A counter scheme based on two parameters denoted GCRA(I,L):

• I - Increment Parameter, affects cell rate

• L - Limit Parameter, affects cell burst

Leaky Bucket:

• Finite-capacity bucket

• Contents leak out 1 per unit time

• Contents are increased by 1 if L is not exceeded

A cell that would cause the bucket overflow in non-conforming

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ATM and B-ISDN

Generic Cell Rate Algorithm (GCRA)

Arrival of a cell at time ta(k)

X’ = X - (ta(k) - LCT)

NonconformingCell

X’ < 0?

X’ > L?

X = X + ILCT = ta(k)

Conforming Cell

Yes

X = 0

Yes

No

No

TAT < t a(k)?

TAT > t a(k) + L?

TAT = TAT + I

Conforming Cell

Yes

TAT = t a(k)

Yes

No

NoNonconforming

Cell

VirtualSchedulingAlgorithm

Continuous-stateLeaky BucketAlgorithm

TAT: Theoretical Arrival Timeta(k): Time arrival of a cellX: Value of leaky bucket counterX’: Auxiliary variableLCT: Last compliance time

I: IncrementL: Limit

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ATM and B-ISDN

Leaky Bucket - GCRA(1.5, 0.5)

Time

Cell Cell Cell CellNo cell

GCRA(1.5, 0.5)

1

2

t- t+

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ATM and B-ISDN

Leaky Bucket - GCRA(4.5, 7)

Time

Cell Cell CellNo cell

GCRA(4.5, 7)

5

10

No cell

1

2

3

4

0

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ATM and B-ISDN

Virtual Scheduling Algorithm

cell 1 cell 2

TimeI

L

cell 2cell 2 cell 2 cell 2

Nonconforming Conforming

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Maximum Burst Size

The maximum number of conforming cell back-to-back

N <= 1 + L/(T - d)Where T = 1/PCR, d is cell transmission time

units, and L is CDVT

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ATM and B-ISDN

Traffic shaping: token bucket

Traffic shaping is used to smooth out a traffic flow and reduce cell clumping

Server

Token generator

Arrivalcells Departing

cellsCapacity K

Capacity β

Rate α

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ATM and B-ISDN

Recommended Text Books

■ Tanenbaum A. Computer Networks - 3rd edition. Prentice Hall 1996, 0-133-499456. £27.95

■ Uyless BLACK, “ATM: Foundation for Broadband Networks”, Prentice Hall Series in Advanced Communication Technologies, ISBN: 0-13-297178-X , 1995.

■ L. G. Cuthbert, “ATM: Broadband Telecommunications Solution”, IEE Telecommunication Series No.29, ISBN: 0852968159, 1993.