Atm công nghệ chuyển mạch

7/28/2019 Atm cng ngh chuyn mch

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ATM

Loan Pham


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Fast Relay Networks

Relaying traffic as quickly as possibleFast Relay

Frame Relay

(Variable sizePDUs frames)

Cell Relay

(Fixed sizePDUs cells)

PVC

(LAPD)

SVC

(Q.931)

ATM based

(For B-ISDN)

802.6 based

(For SMDS)

PVC SVC(Q.2931)


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Transfer Mode

Transfer mode Specific way of transmitting and switching through the network

Synchronous Mode

Synchronous systems negotiate the connection at the data-linklevel before communication begins. Basic synchronous systems will

synchronize two clocks before transmission. Asynchronous mode

Asynchronous systems do not send separate information to indicatethe encoding or clocking information. The receiver must decide theclocking of the signal on it's own. This means that the receivermust decide where to look in the signal stream to find ones andzeroes, and decide for itself where each individual bit stops andstarts.


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Switching technologies

Circuit Switching circuit is established for the complete duration

based on TDM (Time Division Multiplexing)

also referred to as STM (Synchronous Transfer Mode)

very inflexible, since once the duration of time slot is determined, the relative

bit rate is fixed

Packet Switching user information is encapsulated in packets

packets contain additional information used inside the network for routing,

error correction, flow control, etc

packets have variable length and hence require complex buffer management

inside of the network Frame relaying

eliminates as much as possible of the overhead of packet switched networks

no hop-by-hop flow control and error control

can be viewed as streamlined version of X.25


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Switching technologies (cont.)

Circuit

switching

Message

switching

Packet

switching

Frame Relay

(switching)

Cell Relay

(switching)

Directconnection

Store &forward

Hold &forward

Hold &forward

Hold &forward

Copper,wireless

Copper,wireless

Copper,wireless,optical



No suchthing

Variable,large tosmall



Fixed, verysmall

Very fast Slow Fast Faster Very fast


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ATM

ATM Introduction What is an ATM (Asynchronous Transfer Mode)?

ATM Overview

ATM Topology

Standard

Basic principle ATM Network Interfaces

ATM Cells

ATM virtual connections

ATM Reference Model Physical Layer

ATM Layer

ATM Adapted Layer

ATM Services


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ATM


ATM Overview

ATM Topology

Standard


ATM Cells



ATM Layer

ATM Adapted Layer

ATM Services


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ATM Introduction

ATM (Asynchronous Transfer Mode) is is anInternational Telecommunication Union-Telecommunication Standardization Sector (ITU-T)

standard for cell relay wherein information for multipleservice types, such as voice, video, or data, isconveyed in small, fixed-size cells

ATM is a cell-based, connection-oriented, switchingand multiplexing technology designed to be a fast,general purpose transfer mode for multiple services.


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ATM Overview

Proposed telecommunication standard for Broadband ISDN Circuit-switched, connection-oriented networking technology

Provides dedicated, high-speed connections to a virtually unlimitednumber of users

Dedicated media connections running in parallel allow ATM to support

simultaneously multiple transmissions Adding more users does not necessarily decrease the average

bandwidth available to connections on the network

Integrates voice, video, and data

Uses short, fixed length packets called cells

Best effort delivery system

Bandwidth on demand

Potential to remove performance bottlenecks in todays LANs and WANs


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ATM Advantages and Disadvantages

Advantages of ATM Flexible bandwidth allocation

Simple routing due to connection-oriented technology

High bandwidth utilization due to statistical multiplexing

Potential QoS guarantees Disadvantages of ATM

Overhead of cell header (5 bytes per cell)

Complex mechanisms for achieving QoS

Congestion may cause cell losses


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ATM Network Topology

Physically, an ATM network is composed of acollection or a mesh of ATM switches and stationswhich are interconnected via ATM media.

ATM switches are simply devices which participate in

the creation and in the tear-down of ATM virtualcircuits, and route ATM cells according to theappropriate virtual circuit.

Because ATM cells are uniform in structure, switching

of cells can be done very rapidly and with extremelylow latency. Cell switching is also accomplished inparallel over the various connections in a switch.


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ATM


ATM Overview

ATM Topology

Standard


ATM Cells



ATM Layer

ATM Adapted Layer

ATM Services


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Basic Principle of ATMs

Specific packet oriented transfer mode based on fixed cell length Each packet consist of an information field and a header (used to

determine the virtual channel and to perform appropriate routing)

Cell sequence integrity is preserved per virtual channel

Connection-oriented (header values are assigned to each section

of a connection for the complete duration of the connection)

Signalling and user information are carried on separate virtualchannels

Information field of ATM cells is carried transparently through thenetwork, no processing like error control is performed inside the

network

Connectionless services are provided by adaptation functions to fitinformation into ATM cells or to provide service specific functions


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Basic Principles of ATM (cont.)

Connection-oriented

connections are established for the duration of a call

Establishment includes

allocation of a Virtual Channel Identifier (VCI)

allocation of a Virtual Path Identifier (VPI)

allocation of the required recourses (usual in terms of throughput)

Establishment uses

negotiation between user and network, with respect to therecourses

separate signalling channel (for signalling messages) To establish and to release a signalling virtual channel a special

Metasignaling Channel is used (predefined VCI/VPI defined onUNI)


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ATM Network Interfaces

An ATM network consists of a set of ATM switchesinterconnected by point-to-point ATM linksor interfaces.

ATM switches support two types of interfaces: UNI (User to Network Interface): ATM endpoint-ATM switch

Public UNI, Private UNI

NNI (Network to Node Interface): ATM switch-ATM switch Private NNI (P-NNI)

Public NNI Inter-Switching System interface (ISSI)

The Broadband Interexchange Carrier Interconnect(B-

ICI) Connects two public switches from different service providers

Data Exchange Interface (DXI) Between packet routers and ATM Digital Service Units (DSU)


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ATM Network Interfaces (cont.)

Computer

Computer

Computer

PrivateSwitch

PrivateSwitch

Router

PublicSwitch

PublicSwitch

PublicSwitch

PublicSwitch

DigitalService

Unit (DSU)

Private

UNI

Private

UNI

DXI Private

UNI

Public

UNI

Public

NNI

Regional Carriers

B-ICI

B-ICI

Long Distance

Carrier

Private

NNI


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ATM Network Interfaces (cont.)


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ATM Virtual Connections

Virtual connection

Limited functionality in ATM headers source address, destination address, sequence number are not required

error control is only present if required by the service

no flow control mechanism

Remaining function is the identification of the virtual connection(performed by 2 sub-fields):

Virtual Channel Identifier (VCI)

Virtual Path Identifier (VPI)

Virtual channel Optical transmission links are capable of transporting hundreds of MBit/s

Virtual channels may fill only KBit/s

A large number of simultaneous channels have to be supported on an ATMtransmission link

VCI is assigned during call set-up

VCI is only significant on the link between ATM nodes

When the connection is released, the VCI values on the involved links willbe released and can be used by other connections

Enable multi-component services


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ATM Virtual Connections (cont.)

Virtual Path Enable semi-permanent

connections betweenendpoints

These connections have to

transport a large number ofsimultaneous connections

Concept is also known asvirtual network (resources ofthe network are semi-

permanently allocated) Allows efficient and simple

management

A VP is a bundle of VCs

VC1

VC2

VC3

VC1

VC2

VC3

VC1VC2

VC3


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VPI/VCI used in an ATM network

ATMNode 1

ATMNode 2

ATMNode 3

VPI = 7VCI = 1,2,3

VPI = 9VCI = 3,4

VPI = 7

VCI = 3,4

VPI = 5VCI = 1,2,3

VCI = 3,4VPI = 3


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VPI/VCI=0/0 used for Idle cells; 0/n used for Signalling Each cell contains a 24/28-bit connection identifier

First 8/12 bits: Virtual Path, Last 16 bits: Virtual Channel

The use of VPIs for static connections on the ATM

network Site-to-site connectivity

Between service provider and customer

VPIs have local significance

VCIs are for dynamic connections on ATM network They are for the actual connections between applications on

ATM network


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VP connections (VPCs) = Series of VP Links

VC connections (VCCs) = Series of VC Links to make an end-to-end link

Call = Multiple connections


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ATM connection types

Point-to point

For direct connectivity, using for connectionsbetween adjacent network nodes

Point-to-multipoint For multicast or broadcast-type services

Multipoint-to-multipoint

For conference arrangements, ATM network node

is responsible for sending out multiple copies of asingle cell received on a single in port


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ATM


ATM Overview

ATM Topology

Standard


ATM Cells



ATM Layer

ATM Adapted Layer

ATM Services


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ATM Reference Model


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ATM Reference Model (cont.) ATM reference model contains three Planes: User Plane, Control

Plane, and Management Plane as shown in Figure 1. User Plane we have already discussed extensively for data

transmission

Control Plane Performs Set-up of the connection (SVC, PVC),Manage the end-to-end connection, and release of the connection

Management plane deals with two items: Layer management which deals with managing the network resources

Plane management which deals with co-ordination of other planes.

AAL

ATM

PHY

AAL

ATM

PHY

ATM

PHY

ATM

PHY

End system End systemNetwork

User Information User InformationUser Plane


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ATM Reference Model (cont.)

Management Plane is divided into: Layer management andPlane management.

Layer management function is further split into Controlplane management and User plane management.

Layers in the control plane management are the functions neededto performs setting up the connection , monitoring anddisconnection. We have discussed this above.

The above functions are only needed in the switched virtualconnection and is not required in permanent virtual connection.

Layers in user plane comprise the functions required for thetransmission of user information.


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ATM Reference Model (cont.) Plane management functions supervise the operations of the whole network

and has no layered structure. This includes operation and maintenance (OAM) Performance monitoring

Long term system evaluation

Short term service quality control or preventive actions

Defect and failure detection Enables failure detection localization

System protection Failed entity will be excluded from operation

Minimizing the effect of the failure

Failure or performance information Informs other management entities (system protection)

Fault localization Internal or external test systems will localize the failed entity

Fault-management OAM cells have the leading 4 bits of the cell payload set to0001.

The function type (FT) field, indicate the type of function performed by the cell:alarm indication signal (AIS), signaled by FT = 0000; far end receive failure (FERF),signaled by FT = 0001; and loopback cell, signaled by FT = 1000.


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VPC: F4

VCC: F5

GFC VPI VCI PT CLP HECOAM

cell typeFT

Function-specific

field

CRC-10

Same as user,s cells

3: Segment

4: End-to-end

Same as user,s cells

100 = segment

101 = End-to-end

0001 = Fault management

Function type: 0000 = AIS

0001 = FERF

1000 = Loopback

Terminal

or router

Terminal

or router

Private

ATM

switch

Private

ATM

switch

Public

ATM switch

Public

ATM switch

End-to-end

Segment


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ATM Layered Model (cont.)

ATM Adaptation layer (AAL) How to break application messages to cells

ATM layer

Transmission/Switching/Reception

Congestion control/Buffer management

Cell header generation/ Remove at Destination/Source Reset the connection identifiers for the next hop

Cell address translation

Sequential delivery

Physical layer (PHY)

Transmission the information through physical media


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ATM and OSI Model


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ATM Physical Layer

ATM physical layer transmits the ATM cells as asequence of bits link by link through the ATM network

Two sub-layers

Physical Medium Sublayer

Responsible for the correct transmission and reception of bits on

the appropriate physical medium

Lowest level is media dependent (optical, electrical, ...)

Upper level guarantees a proper bit timing reconstruction at thereceiver

Transmitting peer entity inserts required bit timing information and

line coding


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ATM Physical Layer (cont.)

Transport Convergence (TC)

Cell rate decoupling Insertion and extraction of idle cells.

Header error control (HEC) generation and verification HEC is generated on the ATM cell header fields by the sender andverified by the receiver. That is, the HEC is generated andcompared with the received value. If the cell header errors can be

corrected and the cell processed. If not, the entire cell is discarded Cell delineation In the receiver, detection of cell boundaries

Transmission frame adaptation Adapts cell flow according tothe payload of the Physical level frame being used, e.g. for SDH

Transmission frame generation and recovery Transmission

frame usage will involve more than just packing ATM cells bit by bitinto a transmission frame and sending it out.


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ATM Layer

This layer is independent of the physical medium over whichtransmission is to take place.

ATM layer consists of a stream of cells (OAM cells, data cells,signaling cells) Generic flow control (GFC) function. This can be used to

alleviate short term overload conditions above the ATM layer, as it isaccessible by the user.

Cell header generation and extraction. At the transmitter, addsheader information to a cell, and at the receiver removes it.

Cell multiplex and demultiplex. At the transmitter, multiplex cellsinto one continuous stream, and at the header demultiplex the cellsaccording to VPI and VCI values.

Switching. Eventually a translation at ATM switches andcrossconnects is required (performed on the VCI and VPI separatelyor on both simultaneously)


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ATM Cells

Cells used by the ATM Layer are called ATM cells Contain 53 byte (5 byte header, 48 byte payload)

Information field of an ATM cell carries ATM userdata normal user data

Signalling data

Metasignaling data

Management data related to the ATM Layer

ATM Cell Header Bits

Priorities are provided via a Cell Loss Priority (CLP) bit in theheader

Payload Type (PT) field, Idle Cells, Unassigned Cells,Physical Layer, OAM Cells, Signalling Cells


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ATM cells (cont.)

ATM transfers information in fixed-size units calledcells. Each cell consists of 53 octets, or bytes

GFC


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ATM Cell-Header Fields

General Flow Control (GFC):Slow down senders in heavily used portions of thenetwork

Used in UNI, not in NNI

Virtual Path Identifier (VPI):conjunction with the VCI, identifies the nextdestination of a cell

Virtual Channel Identifier (VCI):conjunction with the VPI, identifies the nextdestination of a cell


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ATM Cell-Header Fields (Cont.)

Payload Type (PT)Indicates whether the cell contains user data or control data

user data

signalling data

VP-OAM data (Virtual Path - Operation and Maintenance) VC-OAM data (Virtual Cannel - Operation and Maintenance)

Congestion Loss Priority (CLP)

Indicates whether the cell should be discarded if it encountersextreme congestion

Header Error Control (HEC)

Calculates checksum only on the header itself.


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QoS

Process of determining and delivering the required QoS parameters

for each connection on an ATM network is referred as the trafficcontract specification

Traffic contract: constrain data bursts, limit peak data rate, cell-loss rate

Traffic shaping: forcing your traffic to conform to a certain specified behavior(adhering to the

contract) allocate resources inside the network such that guarantees about availability

of bandwidth and maximum delays can be given

Traffic policing: estimates the the parameters of the incoming traffic and takes some action if

they measure traffic exceeding agreed parameters

QoS parameters CBR (Constant Bit Rate)

VBR-NRT (Variable bit rate non-real time)

VBR-RT (Variable bit rate real time)

ABR (Available bit rate)

UBR (Unspecified bit rate)


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Traffic management

The process of controlling traffic on a UNI in an ATM network ATM traffic management are to deliver quality-of-service (QoS)

guarantees and provide overall optimization of network resources The various functions of ATM traffic management can be

categorized into three distinct elements

Nodal-level controls implemented in hardware and include queues

supporting different loss and delay priorities, fairly weighted queue-servicing algorithms, and rate controls that provide policing and trafficshaping.

Network-level controls the heart of any traffic-managementsystem, it is implemented in software including connection admissioncontrol (CAC) for new connections, network routing and reroutingsystems, and flow-control-rate adaptation schemes.

Flow control involves adjusting the cell rate of the source inresponse to congestion conditions and requires the implementation ofclosed loop congestion mechanisms.


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Traffic management

Parameters

Cell loss ratio (CLR)

Cell misinsertion ratio (CMR)

Severely errored cell block ratio

Mean cell transfer delay (MCTD)

Cell delay variation (CDV)


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ATM Switching

ATM switching principle The cell is received across a link on a known VCI or VPI value

The switch looks up the connection value in a localtranslation table to determine the outgoing port (or ports) ofthe connection and the new VPI/VCI value of the connectionon that link.

The switch then retransmits the cell on that outgoing linkwith the appropriate connection identifiers.


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ATM Switching (cont.)

Switch

23

Video

56

Data

37

Data

34

Voice2

1

3

4

5

6

23

56

65

76

In Out

Port VPI/VCI Port VPI/VCI

1 0/37 3 1/23

1 0/34 4 0/56

2 0/23 5 0/65

2 0/56 6 4/76


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ATM Switching (cont.)


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ATM Adaptation Layer

An applications data needing to be sent across an ATMnetwork typically will have to be adapted to the ATMnetwork

This layer is responsible for mapping the service offeredby ATM to the service expected by the higher layers

Segmentation and reassembly (SAR) SAR is responsible for presenting the ATM service to the higher

layers

SAR makes cells of higher-layer data units and remakes the dataunits at the destination

Convergence services (CS) CS makes sure that the cell stream set up and sent is capable of

providing the needed service to the application

CS is responsible for, at the transmitter, splitting the higher levelPDU into 48 octet chunks, and at the receiving side, to reassemblethe 48 octet chunks back into the original PDU.


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ATM Adaptation Layer (cont.)

The AAL may enhance the service provided by theATM Layer to the requirements of a specific service(user, control, management). Acts on ATM Layer data streams (mapping for the next

higher layer)

Different requirements of the protocols on top of the AAL

several AAL protocols are required

AAL protocols are characterized by a common set offunctions required by several protocols to be run over an ATM network

specific adaptation requirements of protocols (originally

designed for other network types) Provides several Layer Services with different layers in OSI-

RM

User data and Signalling data typically require adaptation bythese Services


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Up to now, 4 (basic) AAL protocol stacks (AAL types) are defined

AAL1, AAL2, AAL3/4, AAL5

AAL Types support different user data stream requirements

AAL functions contain SARfunctions and some CS functions

CS of these stacks has been further sub-structured:

Upper Service Specific CS (SSCS) Lower Common Part of the CS (CPCS)


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AAL1- supports connection-orientedservices that requireconstant bit ratesand have specific timing and delayrequirements

AAL2- supports connection-orientedservices that do notrequire constant bit rates(in other words, variable bit rateapplications like some video schemes)

AAL3/4- this AAL is intended for both connectionless andconnection oriented variable bit rateservices (originally twodistinct adaptation layers)

AAL3 and 4 have been merged into a single AAL which is namedAAL3/4 for historical reasons

AAL5 - supports connection-less variable bit ratedata services

Provides a smaller bandwidth overhead (then AAL3/4), simplerprocessing requirements, and reduced implementation complexity

AAL5 has been proposed for use with both connection-oriented andconnectionless services


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AAL1

The layer services provided by AAL type 1 to the AALuser are:

Transfer of Service Data Units (SDU) with a constant source bit

rate and the delivery of them with the same bit rate

Blocking / deblocking

Transfer of timing information between source and destination

Transfer of structured information between source and

destination

Indication of lost or defective information which is not recovered

by AAL type 1 if needed

Typical Application: constant bit rate audio (e.g. ISDN-

Telephony)


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AAL1 - SAR/CS-PDU format

SN: Sequence Number (4 bits)

SNP: Sequence Number Protection (4 bits)

CRC: Cyclic Redundancy Check (3 bit)

P: Pointer

(8 bits)

CSI:

CS Indication

(1 bit)

Parity (1 bit)

Offset (7 bit) sequence count (3 bit)

SAR-PDU payload = SAR SDU(47 octets)

SNPSNCell header

CSISequence

countCRC parity

Non-P formatCSI = 0

P format

CSI = 1AAL user data (47 octets)

P AAL user data (46 octets)

parity offset


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AAL 2

The layer services provided by AAL type 2 to the AALuser may include:

Transfer of service data units with a variable source bit rate

Transfer of timing information between source and

destination

Indication of lost or defective information which is not

recovered by AAL type 2, if needed

AAL2 CPS fits the problem of low bit rates

Transmission of only partially filled cells is necessary

It avoids partially filled cells by multiplexing several datastreams into the same cell

Typical application: variable bit rate high quality audio

and video


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AAL 2 - SAR-PDU format

IT (Information Type) indicates beginning of message,

continuation of message, or end of message and also acomponent of the video or audio signal

SN (Sequence Number)

LI (Length Indication) (6 bit) Indicates the number of octets of

the CS (Convergence Sublayer) PDU (Protocol Data Unit) that is

included in the SAR (Segmentation and Reassembly) payload CRC (Cyclic Redundancy Check) (10 bits) Used to detect errors

up to two correlated bit errors in the SAR PDU

SAR-PDU payload(44 octets)

ITSNCell

headerCRCLI

SAR-PDU header SAR-PDU trailer

SAR-PDU (48 octets)


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AAL 3/4

Supports the non-assured transfer of user dataframes

An internal multiplexing function allows the

establishment of several concurrent AAL type 3/4

user connections on one ATM connection On each of such connections, the integrity of the data

sequence is maintained and transmission errors are

detected

Two new appendices describe the multiplexing AALtype 3/4 connections on an ATM connection using

the Multiplexing Identification (MID) field and one

procedure for dynamic MID allocation


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AAL3/4 - SAR-PDU format

ST: Segment Type (2bits)

ST coding interpretation: 0 0 COM: Continuation of Message

0 1 EOM: End of Message

1 0 BOM: Begin of Message

1 1 SSM: Single Segment Message

MID: Multiplexing Identifier (10 bits)

SN: Sequence Number LI Length Indication (6 bit)

CRC: Cyclic Redundancy Check (10 bits)


STCell

headerCRCLI

SAR-PDU header SAR-PDU trailer

SAR-PDU (48 octets)

SN MID


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AAL3/4 - CPCS-PDU format

CPI: Common Part Indicator (1 octet) Btag: Beginning Tag (1 octet)

BA Size: Buffer Allocation Size (2 octets)

PAD: PADding (0 to 3 octets)

AL: Alignment (1 octet) Etag: End Tag (1 octet)

Length: length of CPCS-PDU payload (2 octets)


CPI ALPAD

CPCS-PDU header CPCS-PDU trailer

CPCS-PDU (up to 65544 octets)

Blag BA Size Elag Length


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AAL 3/4 - Services

Message Mode service CPCS-SDU is passed across the CPCS interface in one CPCS-IDU

provides the transport of a single CPCS-SDU in one CPCS-PDU.

Streaming Mode service

CPCS-SDU passes in one or more CPCS-IDUs across the CPCS

interface transfer across the CPCS interface may occur separated in time

provides the transport of all the CPCS-IDUs belonging to a single

CPCS-SDU in one CPCS-PDU

internal pipelining function in the CPCS may be applied which

provides the means by which the sending CPCS-entity initiates thetransfer to the receiving CPCS-entity before the complete

CPCSSDU is available

includes an abort service by which the discarding of a CPCS-SDU

partially transferred across the interface can be requested


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AAL5

Designed to support packet_oriented AAL user data transferwith minimum transmission overhead but with nevertheless

`machine_friendly' PDU formats.

The application of AAL5 forsignalling message transport, for the

support of the DL_Core Service as used to implement e. g. the

Frame Relaying Bearer Service is currently standardised. It is also highly probable that AAL5 will be used to support at

least short term solutions for Video on Demand applications

based on quasi constant bit rate transmission of MPEG

Transport Streams.

The Message Mode service, Streaming Mode service, andassured and non-assured operations for AAL type 5 are

identical to those defined for AAL type 3/4


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AAL5 - Protocols

AAL5 SAR protocol

The AAL5 SAR protocol only provides for a simple CPCS_PDUdelineation mechanism using the AUU bit in the cell headerto differentiate between end and non_end CPCS_PDU

segments. AAL5 CPCS protocol

The AAL5 CPCS protocol maps CPCS_SDUs of variable sizeto/from the 48_octet ATM_SDUs, supports the transparenttransfer of an additional, separate octet of CPCS user data

and includes bit error and cell loss and misinsertiondetection capabilities.


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AAL5 - CPCS-PDU format

PAD: PADing (0 to 47 octets)

CPCS-UU: CPCS-to-CPCS User indication (1 octet)

CPI: Common Part Indicator (1 octet)

Length: Length of CPCS-PDU payload (2 octets)

CRC: Cyclic Redundancy Check (4 octets)


CRCLength

CPCS-PDU trailer

CPCS-PDU (n * 48 octets)

CPCS-UU

PAD CPI


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ATM Signaling and Addressing

ATM signaling is initiated by an ATM end-system thatdesires to set up a connection through an ATM network

Signaling packets are sent on a well known*5* virtualchannel, VPI=0, VCI=5.


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UNI Signaling

As shown below in the figure the signaling message istransferred across the UNI using the services of SAAL (Signaling

AAL layer) layer in the control plane.

UNI Signaling


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UNI Signaling (cont.)

Signaling procedures specify the sequence of messageexchanges to establish and release connections as shown in thebounce diagram below. Many error conditions are accountedwhich for simplicity has been removed here. An extreme simplecase is only considered.

Network

UNI UNI

Source DestinationSetup

Setup

Connect ack

Connect ack

ReleaseRelease

Signaling Example


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UNI Signaling (cont.)

Sequence of messages are1. Host A sends a SETUP message on VPI/VCI = 0/5 (Default value for AAL5)

identifying the destination (host B) and Other Parameters specifying details ofthe requested connection.

2. The first switch analyzes the contents of the SETUP message to see whether itcan handle the requested connection. If the switch can handle the request, thenetwork returns a CALL ROCEEDING message to the host containing theVPI/VCI (0/5)for the first link. It also forwards the SETUP message across thenetwork to the destination.

3. Upon arrival of the SETUP message, the destination sends a CALLPROCEEDING message.

4. If the destination accepts the call, it sends a CONNECT message that isforwarded across the network back to host A. The CONNECT messages triggerCONNECT ACKNOWLEDGE messages from the network and eventually from thesource.

5. The connection is now established, and the source and destination canexchange cells

6. Either party (caller or called) can subsequently initiate the termination of thecall by issuing a RELEASE message. This step will trigger RELEASE COMPLETEmessages from the network and from the other party.


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PNNI Signaling

PNNI uses source routing where the first switch selects the route to the

destination. Here, the source host requests a connection to host B by sendinga SETUP message, using UNI signaling. The first switch carries out theconnection admission control (CAC) function and returns a CALL PROCEEDINGmessage if it can handle the connection request. The first switch maintainsand uses a topology database to calculate a route to the destination that canmeet the requirements of the connection contract. The route consists of a

vector of switches that are to be traversed.

The SETUP message propagates across the network, using the source route.Each switch along the path performs CAC and forwards the SETUP messagealong the next hop if it can handle the connection request.

It also issues a CALL PROCEEDING message to the preceding switch along the

route. If the destination accepts the call, a connect message is returned across the

network to the source. Connection release proceeds in similar fashion asshown in Figure below


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ATM Addressing

These existing protocols all have their own addressing schemes and

associated routing protocols. One proposal was to also use thesesame addressing schemes within ATM networks

Hence ATM endpoints would be identified by existing network layeraddresses (such as IP addresses), and ATM signaling requests wouldcarry such addresses

Peer Model

Overlay Model

ATM


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ATM


ATM Overview

ATM Topology

Standard


ATM Cells


ATM Reference Model Physical Layer ATM Layer

ATM Adapted Layer

ATM Services


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ATM Services

Frame-relay bearer services

Connectionless services

LAN Emulation (LANE) services

ATM video and audio services Video over ATM

ATM circuit emulation services Voice over ATM(CES)


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Frame-relay bearer services

Connect frame-relay bearer service (FRBS) networksover the ATM network or even to establish connectionsthat interconnect frame-relay network and ATMnetworks.

To support FRBS, the ATM network must provide theinterworking function(IWF) at the AAL (AAL 5).

FR Router FR RouterFRnetwork

IWF IWFATM FRnetwor

k

ATM Interworking Function


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Connectionless services

LANs are connectionless networks, the network

linking them together should be connectionless also.These will use AAL-3/4 for transporting their trafficover an ATM network.

Uses VPI= 0, VCI = 15 as the default connection for

connectionless services over a UNI

IP Datagram

User B

User A

Workstation

ATM Switch

Router

Router

LAN A

LAN BCells

CLNS

To otherATMnodes

l i i ( )


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LAN Emulation Services (LES)

Where the ATM network may connect distant LANs totally transparently to users

and application and even connect separate private ATM networks over anintervening LAN

LES actually emulates a LAN itself, making the two separate LANs think they areactually all one big LAN, whether they are separated by two floors or 2000 kms.

ATM Switch ATM Switch

LES server

ATM client

Bridge

Non-ATM client

ATM client

1. Clients get

recipient'saddress fromLES and setupa VC.

3. Messages for

ATM clients aredelivered directly.

Broadcast/unknown server

2. Clientssendsmessages onVC.

4. Messages fornon-ATM clients

are forwarded

through a bridge

l i S i


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LAN Emulation Services (cont.)

LAN E l i S i


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LAN Emulation Services (cont.)

LANE components LAN Emulation Client (LEC):A LEC is the entity in an end system that

performs data forwarding, address resolution, and other control functions for asingle end-system within a single ELAN. A LEC also provides a standard LAN

service interface to any higher layer entity that interfaces to the LEC.

LAN Emulation Server (LES): The LES implements the control function for aparticular LAN. There is only one logical LES per LAN, and to belong to a particular

LAN means to have a control relationship with that LAN's particular LES. Each LESis identified by a unique ATM address. The operation of the LES is describedbelow.

Broadcast and Unknown Server (BUS): The BUS is a multicast server that isused to flood unknown destination address traffic and forward multicast andbroadcast traffic to clients within a particular LAN. Each LEC is associated with

only a single BUS per LAN, but there may be multiple BUSs within a particular LANthat communicate and coordinate in some vendor- specific manner; this action isoutside the scope of the Phase 1 LANE protocol. The BUS to which a LEC connectsis identified by a unique ATM address. In the LES, this is associated with thebroadcast MAC address ("all ones"), and this mapping is normally configured intothe LES.

ATM id d di i


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ATM video and audio services

Sending video and the accompanying audiosoundtrack on ATM networks is quickly becoming ascomplex an offering as data

All video used to be constant-bit-rate video, so AAL-1 was a

nice fit With a video compression, it is now just a lowdelay,

variable-bit-rate service (provided by AAL 2) is a good fit aswell.

ATM i it l ti i


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ATM circuit emulation services

Take existing leased private lines and run them over theATM network.

This is the easiest way to bring ATM services into an existing network

Use the ALL-1 interface (Constant bit rate)

IWF IWFATM

ATM Interworking Function

CBRchannels

CBRchannels

T-1 or E-1 links

PBX PBX

TelephoneTelephone

Q&A


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Q&A

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