atm theory (anritsu)

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ATMATMTechnology IntroductionTechnology Introduction


ATMATM

Welcome to the world of ATM. Stands for Asynchronous Transfer Mode Derivative of Packet Switching. It is a Cell based switching fabric to carry all forms of traffic

(Telecom, Datacom & Videocom). ATM has been accepted as a Worldwide standard for

communications. All major carriers will be providing this service


Current InvestmentCurrent Investment vsvs New TechnologyNew Technology

The investment into existing technology and equipment runs into billions of dollars. The first challenge for ATM is to support the way the business is being done today (Circuits, LAN interconnections, WAN packet services. )


This means more complex networksThis means more complex networks

LAN

TCP / IP

Frame Relay

ATM Cell (AAL5)

SONET / SDH

WDM

Each protocol has its own network layer, operates independently and manages its own data flow.


Where are we headed? Where are we headed?

Welcome to theCity of ATM

Population 100+ vendors

Please stay in your assigned virtual channel


ATM StandardsATM Standards

Number Title I.113 Vocabulary for B-ISDN I.121 Broadband Aspects of ISDN I.150 B-ISDN ATM Functional Characteristics I.211 B-ISDN General Service Aspects I.311 B-ISDN General Network Aspects I.321 B-ISDN Protocol Reference Model and its Applications I.327 B-ISDN Functional Architecture I.350 QoS and NP in Digital Network I.356 B-ISDN ATM Layer Cell Transfer Performance I.361 B-ISDN ATM Layer Specifications I.362 B-ISDN ATM Adaptation Layer (AAL) Functional Description


ATM Standards ATM Standards -- ContinuedContinuedNumber Title I.363 B-ISDN ATM Adaptation Layer (AAL) Specifications I.364 B-ISDN Connectionless Data Service Support I.365.1 Frame Relaying Bearer Service Spec Convergence Sublayer I.371 B-ISDN Traffic Control and Congestion Control I413 B-ISDN User Network Interface (UNI) I432 B-ISDN UNI - Physical Layer Specifications I.555 Frame Relay Bearer Service Interworking I580 B-ISDN and 64kb/s ISDN Internetworking Arrangements I.610 B-ISDN OAM Principles and Functions G.804 ATM Cell Mapping into PDH


AsynchronousAsynchronous vsvs SynchronousSynchronous Asynchronous

No Clock is associated either in or part of the transmitted data bits. Each character is identified by a start and stop bits. For example RS232, X.21

Synchrnous A clocking signal is used to transmit bits at a regular rate. Both TX and RX should be able to drive/recover the clock within certain frequency

tolerance.

Sync SOM Control User Data CRC EOM

End of MessageStart of Message


ATM Cell Structure (Definition)ATM Cell Structure (Definition)After several debates and negotiations, the international community of Telecom, Datacom and Videocom agreed on an ATM cell of 53 bytes(B) in June 1989 at the ITU. The cell has 5 bytes of Header and 48 bytes of payload.

Header5 Bytes

Payload48Bytes

Order of Transmission (MSB first)

53 Byte ATM Cell

Header contains the information to allow cell to be forwarded to its destination.


ATM NetworkService Provider A

UNIUNI vsvs NNINNI

ATM NetworkService Provider B

NNI (B-ICI : B-ISDN Inter-Carrier Interface)

UNI

UNI

UNI : User to Network Interface (Can be Private or Public)NNI : Network to Network Interface

NNI

NNI


ATM Cell Structure (UNI / NNI)ATM Cell Structure (UNI / NNI)

GFC4b

VPI8b

VCI16b

PT3b

CLP1b

HEC8b Payload ( 48 Bytes)

GFC: General Flow Control - Allows multiplexers to control the rate of ATM terminalVPI: Virtual Path Identifier - Destination Address (Max 28=256 Virtual Paths)VCI: Virtual Channel Identifier - Destination Address (Max 216=65536 Virtual Channels)PT: Payload Type - Indicates if the cell contains User Data, Signaling

or Maintenance Information.CLP: Cell Loss Priority - Used during congestion interval to determine which cell

to discard.HEC: Header Error Check - Detects and corrects errors in the cell header.

UNI (User Network Interface) format

VPI12b

VCI16b

PT3b

CLP1b


NNI (Network Network Interface) format


ATM ATM -- VPI / VCI + InteroperabilityVPI / VCI + Interoperability

VPI (Virtual Path Identifier )Destination Address (Max 28=256 Virtual Paths)

VCI: Virtual Channel IdentifierDestination Address (Max 216=65536 Virtual Channels)

The fact is an ATM switch vendor may not use the maximum bits for VPI and VCI for a given ATM application. This leads to interoperability problems where one

device might ignore certain bits of VPI & VCI.

ATM forum has defined Interim Local Management Interface (ILMI)where a an ATM device can query the other device about the number of bits that system will support.


ATM ATM -- Physical, VP and VC RelationPhysical, VP and VC Relation

In ATM a physical line (e.g. fiber) can consist of up to 256 (28)Virtual Paths (VP) and each virtual path can consist of up to 65536 (216 ) Virtual Channels.

Physical

VP1 VC1VCn

VPm VC1VCn


ATM Cell SwitchingATM Cell Switching

Switching can occur based on VPI or VPI/VCI fields of each cell.

Switching based on the VPI field only forms a Virtual Path Connection (VPC).

Switching based on both VPI/VCI fields forms a Virtual Channel Connection (VCC).

VPC or VCC can be provisioned as PVC (Permanent Virtual Circuits) or by signaling protocols as SVC (Switched Virtual Circuits).


ATM Cell Structure (Payload)ATM Cell Structure (Payload)GFC4b

VPI8b

VCI16b

PT3b

CLP1b


Service OHby AAL

User, Signaling or Maintenance Data


ATM Cell TypesATM Cell Types

IdleCells

UnassignedCells

TrafficCells

VP OAMCells

UserData

MetaSignaling

Signaling VC OAMCells

ILMI


An ATM Workstation (VC and VP An ATM Workstation (VC and VP Concept)Concept)

AudioVideo

Virtual Channel(VC)1 VC2

Data

VC3

Virtual Path (VP) =1over a given Transmission Path

TextABC

Camera Microphone

ATM NICATM

Switch

Speaker

E3 PLCP

Priority Traffic Cells Mb/s1 Video 7 242 Audio 1 43 Data 1 3

Total 9 31 = E3 PLCP Payload


Virtual Channel Connection (VCC)Virtual Channel Connection (VCC)

Users request VCC

VPI=22VCI=89

VPI=12VCI=18 VPI=15

VCI=28

VPI=32VCI=48

VPI=62VCI=58

ATMswitch

Network switchesassign VCI and VPIfrom node to node


ATM Switches ATM Switches -- Different shapes and Different shapes and sizes.sizes.

Work Group ATM Switch Backbone ATM Switch Enterprise ATM Switch Edge ATM Switch Core ATM Switch


ATM Switches ATM Switches -- Work GroupWork Group

Work GroupSwitches

WorkStation

Datacom today with Voice & Video in future

SERVERETHERNET

TOKEN RING

HOSTRouter


ATM Switches ATM Switches -- BackboneBackbone

Work GroupSwitch

Work GroupSwitch

Work GroupSwitch

Backbone Switch


ATM Switches ATM Switches -- EnterpriseEnterprise

Work GroupSwitch

Work GroupSwitch

Work GroupSwitch

Backbone Switch

Work GroupSwitch

Work GroupSwitch

Work GroupSwitch

Backbone Switch

Enterprise Switches1.2Gb/s+


ATM Switches ATM Switches -- Edge & CoreEdge & CoreEnterprise Switches

1.2Gb/s+

Edge Switch2 to 10Gb/s




SDHTransport

Core100Gb/s

Core100Gb/s

Core100Gb/s

Core100Gb/s


Traffic PrioritizationBufferingCongestion ControlSignalingUsage StatisticsUser Parameter Control

Provide Bandwidth CapacityMinimize Cell Delay


Switching Fabric Switching Fabric -- BusBus BackplaneBackplane

Shared Bus: Bus Master& Arbitrator

1 2 n


ATM StackATM Stack

Application Layer

Network Layer

Data Link Layer

Service Layer

ATM Adaptation Layer

ATM Layer

Physical Layer

Higher Layers


ATM Stack ATM Stack -- Layer FunctionsLayer Functions

Higher Layer (Performs Higher Layer Functions)

AAL Convergence Sublayer

Common Part (CP) Service Specific (SS)

Segmentation And Reassembly (SAR) Layer ATM

General Flow Control, Header Generation/Extraction, VPI/VCI Translation, Cell Multiplex/Demultiplex

Physical Transmission Convergence Sublayer

Cell Rate Decoupling, Delineation, Frame Adaptation/Generation/Recovery Physical Medium- Bit Timing etc.


ATM Adaptation Layer (AAL)ATM Adaptation Layer (AAL) This is the process by which existing services or traffic

(Circuits, LANs, WANs) having fixed or variable frames sizes are grouped or cut and fitted into a 48 Byte payload of an ATM cell.


The 6The 6 AALsAALs

A A L F u n c t io n

0 C e ll R e la y S e rv ic e (R a w C e lls )1 C irc u it E m u la t io n / V id e o

2 V id e o

3 C o m b in e d w ith A A L 4

4 A A L 3 /4 fo r S M D S

5 F R , V ir tu a l L A N s , R o u tin g , S ig n a ll in g & M a n a g e m e n t


What is Circuit Emulation (What is Circuit Emulation (CECE)?)? Circuit Emulation (CE) is the ability to transport TDM based

circuits (PDH) over cell switching technology like ATM.

Where: TDM: Time Division Multiplexing PDH: Plesiochronous Digital Hierarchy


CE: AAL1 CE: AAL1 -- Synchronous Residual Time Synchronous Residual Time Stamp Stamp

RX

CLK

CPE

ATM

CLK

TX

CLK

CPE

ATM

CLK

Payload HATM Cell

ATM NetworkE1/E3

IF TX CLK > RX CLK : RX accumulates undelivered bits until storage overflowsIF TX CLK < RX CLK : Network is Bit Starved, forcing RX to send AIS cells. To avoid the data loss the clocks need to be maintained

such that( ATM CLK - En CLK ) < 8 clock cycles

These clock cycles can be represented by a 4 bit valuecalled SRTS.


CE: AAL1 CE: AAL1 -- Clock Recovery by SRTSClock Recovery by SRTSConvergenceSub-LayerIndicator (CSI)1b

SequenceCount(SC)3b

47B (SRTS Traffic) DS1/E1 or DS3/E3

Sequence Number (SN) Payload

CyclicRedundancy Check (CRC)3b

Parity

1b

Sequence No. Protection

1MSB

2 3 4LSB

4 bit SRTS Value transmittedin CSI bit over 8 cells

SC1357


AAL2 AAL2 -- Transporting Audio and VideoTransporting Audio and Video

AAL2 is in undefined state, but in the past it was defined for the following traffic:

This ATM Adaptation Layer will mainly be used to carry Full Motion Picture and its associated audio.

The standards are still being debated to accommodate Variable Bit Rate (VBR) traffic

The Motion Picture Expert Group (MPEG) defines the compression and frame differentiation standards (MPEG2)

AAL5 will now carry this traffic type.


AAL3AAL3

AAL3 was combined to form AAL3/4 To be discussed in future


AAL5 AAL5 -- SSCS & SSCOPSSCS & SSCOP Service Specific Convergence Sub-Layer (SSCS) Service Specific Connection-Oriented Protocol (SSCOP)


AAL5 AAL5 -- SSCSSSCS

SSCS ( Service Specific Convergence Sub-Layer) Today

Frame Relay - SSCS SMDS - SSCS

Future Video (Desktop and Entertainment quality) Multicast LAN and LAN Emulation


AAL5 AAL5 -- SSCOPSSCOP

SSCOP (Service Specific Connection Oriented Protocol) Protocol designed to support peer-to-peer communication Error detection, correction and retransmission. Sends Keep Alive message when no data transmission.


AAL5 AAL5 -- Loading User Data into PayloadLoading User Data into Payload138 Bytes of User Data

= 2 Block of 48Bytes and 42Bytesof Remainder

Trailer8B

PAD0B

User Data40B

Trailer8B

PAD38B

User Data2B

User Data96B

SAR PDU #1SAR PDU #4

48B Payload48B Payload48B Payload48B Payload

CPCS-PDU

Payload48B

Header5B

Payload48B

Header5B

Payload48B

Header5B

Payload48B

Header5B

ATM Cells


What are Legacy LANs?What are Legacy LANs?

With the introduction of ATM based networks the existing installed base networks are classified as Legacy LANs

SERVERETHERNET

TOKEN RING

HOST


Legacy LANs to ATM a Gradual MoveLegacy LANs to ATM a Gradual MoveNo customer is going to throw their existing investment ($$$) of its current LANs and make new investment in cell switching technology like ATM. The move to ATM will be gradual. Initially the network is going to be combination of both.

SERVERETHERNET SERVER

ETHERNET

ATM Switch

SERVER

E3 or STM-1 Link


Legacy LANs and ATMLegacy LANs and ATM

Transporting Legacy LANTraffic over ATM

L-UNIby

ATM Forum

RFC 1577by

IETF

L-UNI: LAN Emulation (LAN-E) User Network Interface

RFC 1577: Request for Comment (RFC)1577 was forwarded byInternet Engrg. Task Force (IETF). It supports classical IP over ATM switch.


Internet Protocol (IP) SuiteInternet Protocol (IP) Suite Funded by Defense Advanced Research Project Agency (DARPA) back

in 1973s to overcome the problem of communication between dissimilar computer systems like the IBM, DEC etc..

The Research was conducted by Stanford University and Bolt, Beranekand Newman (BBN) to create series of communication protocols.


Internet Protocol (IP) SuiteInternet Protocol (IP) Suite Transmission Control Protocol(TCP) and Internet Protocol(IP) are the two best

known protocols. Original Goal at the time of development (1973) was to support WAN traffic of

inherently unreliable networks. Hence features like checksum (bit error detection) and timer based packet lost

detection were built in the protocol. TCP/IP can be used to communicate across any set of interconnected networks

(LANs and WANs)


IPIP--Role of BBNRole of BBN

TCP was developed as connection oriented end_to_end protocol. IP was developed to route packets across different networks. IP is a strictly a datagram. Upon Congestion IP discards the

packets and lets TCP (running at the end system) detect loss of packet and initiate retransmission.


IPIP--Role of BBNRole of BBN

To exchange routing information between routers new protocols were developed IGP (Interior Gateway Protocol) EGP (Exterior Gateway Protocol)

Since then other routing protocols have emerged OSPF (Open Shortest Path First) IS-IS (Intermediate System - Intermediate System) IGRP(Interior Gateway Routing Protocol) RIP (Routing Internet Protocol)


ATM Layer ATM Layer -- FlowsFlows System Flow Level SDH F1 Regenerator Section SDH F2 Line Section SDH F3 Transmission PathATM has introduced 2 additional flows (OAM) ATM F4 Virtual Path Connection (VPC) ATM F5 Virtual Channel Connection (VCC)

GFC4b

VPI8b

VCI16b

PT3b

CLP1b

HEC8b

OAM 4b

Function 4b

Function Specific 45 B

Reserved6b

CRC-1010b

For F4 (VPC) VCI=3 (Segment) and VCI=4(End to End)

For F5 (VCC) PT=100Bin (Segment) and PT=101Bin (End to End)


ATM Layer ATM Layer -- OAM Cell FormatOAM Cell Format

GFC4b

VPI8b

VCI16b

PT3b

CLP1b

HEC8b

OAM 4b

Function 4b

Function Specific 45 B

Reserved6b

CRC-1010b

Failure Type1B

Failure Location 9 B

Unused (6A stuffed in all bytes)35 B

Note: b=bit and B=ByteFailure Type and Location TBD.


ATM Layer ATM Layer -- Performance MeasurementPerformance Measurement

The ability to perform the measurements without impacting the customer traffic is called In-service measurements detailed

This Performance (I.350) consists of two parts Network Performance (NP) Quality of Service (QoS)

QoS

End User

QoS

End User

Network


ATM Layer ATM Layer -- Cell Exit & Entry PointsCell Exit & Entry Points

Network

Payload H

UNIUNI

Payload H

CPE CPE

Cell Exit Cell Entry

A maximum expected time value is assigned between Cell Exit and Cell Entry and is called Tmax. The time it takes for a cell to travel between two end pointsis cell travel time such that Tcell travel = Tcell entry _ Tcell exit

Tcell travel could be less (good) or greater (bad) than Tmax


ATM Layer ATM Layer -- Cell Performance Cell Performance ParametersParameters

Cell Transfer TX RX Time Header PayloadCondition Cell Cell Travel ContentContentsa) Sucessful Yes Yes < Tmax Good Goodb) Error Yes Yes < Tmax Bad Goodc) Lost Yes No Tmax expired * *d) Misinserted No Yes * * *e) Severly Error Cells is condition when in a given block of N transmitted cells catagory

b) c) or d) were detected on a given connection.


ATM Layer ATM Layer -- Cell Performance RatiosCell Performance Ratios

Cell Error Ratio CERSeverly Errored Cell Block Ratio SECBRCell Loss Ratio CLRCell Transfer Delay CTDMean Cell Transfer Delay MCTDCell Delay Variation CDV


ATM Layer ATM Layer -- Cell Performance RatiosCell Performance Ratios Cell Error Ratio = Error Cells

Successful cells + Errored Cells

Severely Errored= Severly Errored Cell BlocksCell Block Ratio Total Transmitted Cell Blocks

Cell Loss Ratio = Lost CellsTotal Transmitted Cells

Cell Misinsertion Rate = Misinserted CellTime Interval


ATM Layer ATM Layer -- Cell Transfer Delay (Time Cell Transfer Delay (Time Stamp)Stamp)

ATMNetwork

Source Time Stamp (STS)

STS H

Destination Time Stamp (DTS)

STS H

Extract

Absolute Delay

Memory

Cell Delay (CD)= STS - DTS

Differential Delay


ATM Layer ATM Layer -- Cell Transfer Delay (1 Cell Transfer Delay (1 Point)Point)

ATMNetwork

T

Constant Bit Rate (CBR)source will transmit cellsevery T seconds

T

Cells Received havevariation in delay

Dispersion

Clumping

CDV= Interarrival time of RX cells - TCDV= + (Cell Clumping)CDV= - (Cell Dispersion)


ATM Layer ATM Layer -- Cell Delay VariationCell Delay Variation

Count

Time

Delay

Variation

atm theory (anritsu)

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