atmaal.ppt

8/13/2019 atmaal.ppt

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1ATM -

Asynchronous Transfer Mode

(ATM)



2ATM -

An Overview of ATM

A technology for multiplexing fixed-lengthcells from a variety of sources to a variety ofremote locations.

Capable of moving data at a wide range ofspeeds, but aimed at very high speed 100-1000 Mb/s).

Capable of handling data from a variety ofmedia e.g. voice, video, and data) using asingle interface.

ATM is a connection-oriented protocol.

Connections can be switched or permanent.

Signalling procedures are used to set upswitched calls.

Certain quality of service QoS) is guaranteedfor each connection . QoS parameters mayinclude as cell loss rate, max./avg. cell delay,



3ATM -

ATM operates on a best effort basis; cells witherrors, or that encounter congestion, aresilently dropped.

Two types of connections: point-to-point andmultipoint.

Service Carried in Fixed Length Cells 53octets).

5 Octets Header

48 Octets Payload

An Overview of ATM



4ATM -

ATM Networking

UNI: User-Network Interface

NNI: Network-Network

ES

IS IS

ES

IS



5ATM -

ATM

Cell

Format

酬載

48 Octets GFC VPI VCI PTI CLP HEC

4 8 16 3 1 8

酬載

48 Octets VPI VCI PTI CLP HEC

12 16 3 1 8

(a) UNI Cell format

(b) NNI Cell format

GFC: Generic Flow Control 4 bits). Used by the flow

control mechanism at the UNI.

VPI: Virtual Path Identifier 8 bits). Used for directing

cells within the ATM network.

VCI: Virtual Channel Identifier 16 bits).

PTI: Payload Type Identifier 3 bits). Identifies the type

of data being carried by the cell.

CLP: Cell Loss Priority 1 bit). 1 = low priority.

HEC: Header Error Correction 8 bits). Generated and

inserted by the physical layer. For first 4 octets.

Correct single-bit errors and detect some

multiple-bit errors.

bit 1: AAL indication

bit 2: EFCI upstreamcongestion)

bit 3: data or OAM cells



6ATM -

Pre-assigned VPI/VCI Values

Unassigned Cell Indication VPI = 0, VCI = 0)

Meta signalling VCI=1)

Meta signalling is the bootstrap procedure used to

establish and release a signalling VC. Not used forPVC setup.

General broadcasting signalling VCI=2)

OAM F4 flow indication -- segment and end-to-end VCI=3 and VCI=4)

F4: VP level OAM

F5: VC level OAM, segment or end-to-end PT=100 or101)

Point-to-Point Signalling VCI=5)

Carriage of Interim Local ManagementInterface ILMI) messages VPI=0, VCI=16)


http://slidepdf.com/reader/full/atmaalppt 7/397ATM -

Preassigned, Reserved

VPI/VCI Values

Usa e VPI VCI PT CLP

Unassi ned Cell

Idle Cell

Reserved for Ph sical la er

Meta si nallin

General broadcast si nallin

Point-to- oint si nallin

Se ment OAM F4 Flow Cell

End-to-end OAM F4 Flow

Cell

Se ment OAM F5 Flow Cell

End-to-end OAM F5 FlowCell

Resource Mana ement Cell

00000000

00000000

00000000

xxxxxxxx

xxxxxxxx

xxxxxxxx

0000000 0000000

0000000 0000000

0000000 0000000

0000000 0000001

0000000 0000010

0000000 0000101

0000000 0000011

0000000 0000100

zzzzzzzz zzzzzzzz

zzzzzzzz zzzzzzzz

zzzzzzzz zzzzzzzz

xxx

000

0A0

0AA

0AA

0A0

0A0

100

101

110

0

1

1

C

C

C

A

A

A

A

A

x: Don’t care y: Any value z: Any non-zero value C: Orignator set CLP

A: Used b a ro riate function : Reserved for Ph sical la er



Cell Multiplexing and Cell

Switching Examples

100 200 100 100200

150 150 150 100100

200 200 400 200400

300 300 300

100 100

VPI/VCI OP New VPI/VCI

100 0 100

150 2 200

0

1

2

3

0

1

2

3

VPI/VCI OP New VPI/VCI

100 1 300200 2 400

ATM Switch

100

100

200200

200

300

300 300

400

400

UTP

UTP

SMF

MMF

UTP

UTP

SMF

MMF



ATM Protocol Stack

Physical Layer PMD)

ATM Layer

ATM Adaptation Layer

Higher Layers Higher Layers

Control plane User plane

Management plane

Layer management

Plane managementirtual Channel Functions

Virtual Path Functions



ATM Layer Service

Transparent transfer of 48-octet data unit

Deliver data in sequence on a connection

Two levels of multiplexing VC, VP)

Three types of connections

Point-to-point

Point-to-Multipoint

Multipoint-to-Multipoint ??)

Transport is best-effort

Network QoS negotiation

Traffic control and congestion control



ATM Layer Functions

Cell multiplexing and switching

Cell rate decoupling

Cell discrimination based on pre-defined

VPI/VCI

Quality of Service QoS)

Payload type characterization

Generic flow control

Loss priority indication and Selective celldiscarding

Traffic shaping



Cell Rate Decoupling and Cell

Discrimination

Cell Rate Decoupling

ATM sending entity adds unassigned cells to theassigned cell stream in order to adjust to the cell rateacquired by the payload capacity of the physical layer

R). The receiving ATM entity shall extract and discard the

unassigned and invalid cells from the flow of cellscoming from the physical layer R).

Cell Discrimination

Meta signalling

General broadcast signalling

Point-ot-point Signalling

Segment OAM F4 flow cell

End-to-end OAM F4 flow cell

ILMI message

User data



Virtual Channels, Virtual

Paths, and the Physical

Channel

虛擬路徑虛擬通道體線路

100 100

200 200

300 300

100

200

100200300

10203040

連線 VPI/VCI) =

100,100), 100,200), 200,100),

200,200), 200,300), 300,10),

300,20), 300,30), 300,40)

100/100200/300300/10300/40

100

200

100200300

10203040

虛擬路徑虛擬通道

細胞



Physical Link, Virtual Path,

and Virtual Channel

ATM

Layer

Phy.

Layer

virtual channel connection

virtual channel linkC link

virtual path connection

VP link VP link

transmission path

Digital Section

Regenerator SectionCrossing point

Endpoint



Virtual Channels

The virtual Channel VC) is the fundamental unit oftransport in a B-ISDN. Each ATM cell contains anexplicit label in its header to identify the virtualchannel.

a Virtual Channel Identifier VCI)

a Virtual Path Identifier VPI)

A virtual channel VC) is a communication channelthat provides for the transport of ATM cells betweentwo or more endpoints for the purpose of user-user,user-network, network-network information transfer.The points at which the ATM cell information payloadis passed to a higher layer signify the endpoints of aVC.

A Virtual Channel Identifier VCI) identifiers aparticular VC within a particular VP over a UNI or NNI.



Virtual Paths

A Virtual Path VP) is a group of Virtual Channelsthat are carried on the same physical facility andat a given reference point in the VP share the sameVirtual Path Identifier VPI) value.

The VP boundaries are delimited by Virtual PathTerminators VPT).

AT VPTs, both VPI and VCI are processed.

Between VPTs associated with the same VP, onlythe VPI values are processed and translated) atATM network elements.

The VCI values are processed only at VPTs, and arenot translated at intermediate ATM networkelements.



Why Virtual Paths and Virtual

Channel ?

A B

(1)

VCI OP

(1) 2 (2)

NewVCI

(127) 2 (35)

0 1

255

0 1

255

(2)

(3)

(127)(35)

(255)

(208)

(254)

(38)

(208) 2 (254)

01

255

VCI OP

(2) 1 (3)

NewVCI

(35) 1 (255)

(254) 1 (38)

01

255

Assume the identification field contains 8 bits. All used

as VCI. Then the size of the mapping table is 256.



18ATM -

Why Virtual Paths and Virtual

Channels ?

0

1

7

0

1

7

0

1

7

(0/1)

(7/1)

(1/1)

(1/31)

(0/31)

(0/31)

(7/25)

(1/25)

(7/25)

0 1

31

0 1

31

0 1

31

7

VPI OP

(0) 2 (7)

NewVPI

(1) 2 (0)

0

1

(7) 2 (1)

VPI OP

(7) 1 (1)

NewVPI

(0) 1 (0)

0

1

(1) 1 (7)

7

Assume the identification field contains 8 bits. VPI takes 3 bits

and VCI takes 5 bits. Then the size of the mapping table is 8.



19ATM -

Virtual Channels Examples

1A D

1

C B

(300,10)

(100,20)(300,20)

(100,10)

(300,10)

(200,20) (200,10)

(100,10)

(100,20)

23

1 2

2

4

2

VPI/VCI OP

(100,10) 2 (200,10)

NewVPI/VCI

(100,20) 2 (200,20)

VPI/VCI OP

(200,10) 3 (300,20)

NewVPI/VCI

(200,20) 2 (300,10)

VPI/VCI OP

(300,20) 2 (100,20)

NewVPI/VCI

VPI/VCI OP

(200,10) 4 (300,10)

NewVPI/VCI

a

b

c

d

Port a,1)

Port c,2)

Port d,1)

Port b,1)

VPI/VCI OP

(100,10) 4 (200,10)

NewVPI/VCI

Port b,2)

4

1 (100,20)

VPI/VCI

1 (300,10)

VPI/VCI

1 (300,10)

VPI/VCI

1 (100,10)

VPI/VCI

連線

1 (100,10)

VPI/VCI

輸連線

2 (100,20)

(200,10)

輸出連線

輸連線

輸入連線

輸入連線連線

連線

連線

連線



20ATM -

Virtual Path/Virtual Channel

VP/VC) Switches

A

D

C

B

VP 1

VP 2

VP 3

VP 4

VC 1

VC 2

VC 3

VP Switch

VP/VC Switch

VP Terminator, VPT)

SW1

SW2

SW3

SW4

SW5

VC 4



21ATM -

ATM Adaptation Layers AAL)

AAL Reference Structure

AAL Type 1

AAL Type 2

AAL Type 3/4

AAL Type 5

SAAL

Physical Layer PMD)

ATM Layer

ATM Adaptation Layer

Higher Layers Higher Layers

Control plane User plane

Management plane

Layer management

Plane management

Virtual Channel Functions

Virtual Path Functions



22ATM -

AAL Reference Structure

Service Specific CS SCCS)

may be Null)

Common Part CS CPCS)

SAR Common)

AAL

Convergence

Sublayer CS)

SAR

SAP

SAP

Primitives

Primitives



23ATM -

AAL

AAL

Service Specific Layers

ATM

Transmission

Convergence Sublayer

PMD

L

ayer

MGMT

...

...

48 byte payloads

add 5 byte header

message



24ATM -

AAL Functions

Functions Parameters

Error Detection CRC, length, correlation tags

Framing of user data units Payload type/segment typeCell sequence indication Cell sequence count field

Multiplexing Message ID MID)

Error Correction FEC, retransmission

Flow Control Credit window

Timing Recovery Time stamp



25ATM -

ATM Adaptation Layers AAL)

In order to carry data units longer than 48octets in ATM cells, an adaptation layer isneeded.

The ATM adaptation layer AAL) provides for

segmentation and reassembly of higher-layerdata units and for detection of errors intransmission.

Since the ATM layer simply carries cellswithout concern for their contents, a numberof different AALs can be used across a single

ATM interface.

The AAL maps the user, control, ormanagement protocol data units into theinformation field of the ATM cell and viceversa.

To reflect the spectrum of applications, fourservice classes have been defined b CCITT.



26ATM -

CCITT Services Classifications

Timing between

source and

destination

Class A Class B Class C Class D

Required Not required

Bit Rate Constant Variable

Connection

modeConnection oriented Connectionless

CircuitEmulation

Packetized

voice/video

ConnectionOriented

DataDatagram

Attribute

Examples:

Class A CBR): 64kbps digital voice

Class B rt-VBR, nrt-VBR): Variable bit rate encoded video

Class C UBR,ABR): Frame Relay over ATM, File Transfer Telnet, FTP, TCP),...

Class D ABR): SMDS over ATM, IP over ATM,...

Class X: Raw Cell Service e.g., proprietary AAL)



27ATM -

AAL Service Classification

Timing between

source and

destination

Class A Class B Class C Class D

Required Not required

Bit Rate Constant Variable

Connection

ModeConnection oriented Connectionless

CircuitEmulation

Packetized

voice/video

ConnectionOriented

DataDatagram

Attribute

AAL1 AAL2 SAALAAL 5

AAL 4AL 3

Signalling

Q.93B)





29ATM -

AAL 1 Constant Bit Rate -

CBR) Functions

Emulation of DS1 and DS3 Circuits

Distribution with forward error correction

Handle cell delay for constant bit rate

Transfer timing information between source anddestination

Transfer structure information structure pointer)

Provide indication of unrecoverable lost or erroredinformation

Header SN SNP 47 Octets Payload

SAR PDU

CSISeq

CountEPRC

1 3 3 1



30ATM -

AAL1 Supports Circuit

Emulation

Synchronous Residual Time Stamp SRTS)

DS1, DS3

Require accurate frequency clock

4-bit Residual Time Stamp RTS) for clock aligning

RTS is generated once every 8 cell times, carried inCSI bit of odd cells

Structured Data Transfer SDT)

nxDS0 64kbps)

1-octect pointer carried in payload once every two

cells even cells) indicates the offset into the currentpayload of the first octect of an nxDS0 payload

The octect contains 1 reserved bit and 7-bit offsetfield which points to start of up to 93 octect structure47+46=93)



31ATM -

AAL 2 VBR) Protocol Data

Unit PDU)

Header SN IT 47 Octets Payload LI CRC

SAR PDU

ATM PDU

SN: Sequence number

IT: Information Type:BOM,COM,EOM,SSM

Length Indicator



32ATM -

AAL 3/4

The variable bit rate VBR) adaptation layer,defined in CCITT recommendation I.363, isdefined for services e.g. data) that requirebursty bandwidth.

Comprises two sublayers:

the convergence sublayer CS)

the segmentation and reassembly sublayer SAR)



33ATM -

AAL 3/4 CS and SAR PDU

Structures

CS-PDU

Header

4 Octets

CS-PDU User Information

<= 65,535 Octets

CS-PDU

Trailer

4 Octets

PAD

0-3

Octets

Common

Part

Indicator

BTag BASize Alignment CS User Infor. Length

ETag

1 1 2 1 1 2

CPI:00000000

Btag/Etag: Beginning/Ending Tag -- 256 increment counters

BAsize: receiving side maximum buffering requirement >= CPCS-PDU)

Pad: make CPCS-PDU on 32-bit boundary

AL Alignment): make trailer 32-bit aligned

Length: CPCS-PDU size



34ATM -

AAL 3/4 SAR Sublayer

SAR-PDU

Header

2 Octets

Segmentation Unit ,SAR-PDU Payload

44 Octets

SAR-PDU

Trailer

2 Octets

SAR

Type Length

SAR

SNMID SAR-PDU CRC

2 4 1 9 6 10

p

ST: COM 00),BOM 10),EOM 01),SSM 11)

SN: Modulo 16 sequence counter

P Priority): 1- Priority CS-PDU, 0- Normal CS-PDU

MID Multiplexing ID) -- Multiplexing multiple CPCS connections on a

single ATM connection

LI: Length <=44

CRC on Cell Header, SAR-PDU payload and LI



35ATM -

AAL 5 PDU Structure

The Simple and Efficient Adaptation LayerSEAL), attempts to reduce the complexity

and overhead of AAL 3/4.

It eliminates most of the protocol overhead of

AAL 3/4. AAL 5 comprises a convergence sublayer and

a SAR sublayer, although the SAR isessentially null.CS-PDU User Information

<= 65,535 Octets

CS-PDU

Trailer

8 Octets

PAD

0-47

Octets

Protocol

Control CRCLength

2 2 4



36ATM -

AAL 5 Segmentation and

Reassembly

CPCS-PDU Payload CPCS-SDU)

<= 65,535 Octets

CS-PDU

Trailer

8 Octets

PAD

0-47

Octets

Control CRC-32Length

2 2 4

User SDU

User Dataore

= TUser Data

ore

= TData T

ore

= F...

Control CPCS-UU -- CPCS User-to-User Indication

1 octet). Transparently transfer CPCS user

to user information

CPI -- Common Part Indicator 1 octet). Align

trailer to 64 bits. Possible identification of

layer management message.

48 octets 48 octets

ATM cell ATM cell ATM cell





38ATM -

SAAL Structure

Service Specific Coordination

Function SSCF)

Service Specific Connection Oriented

Peer-to-Peer Protocol SSCOP)

Common Part AAL Peer-to-Peer

Protocol CP-AAL)

Service

Specific

Convergence

Sublayer

Common Part

Peer-to-Peer

Message

Peer-to-Peer

Message

Primitives

Primitives



SAAL

Reside between Q.93B and ATM Layer.

SAAL is used to provide reliabletransport of Q.93B messages betweenpeer Q.93B entities.

SAAL CP-AAL uses AAL5 Common PartProtocol.

SSCOP can be used for any reliableservice.

SSCF maps primitives from MTP 3 tothe required SSCOP signals and viceversa, and

flow control

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