asynchronous transfer mode - wpirek/grad_nets/spring2006/atm06.pdf · atm conceptual model four...

ATM

Asynchronous Transfer Mode

Computer Networks: ATM 1

Issues Driving LAN Changes• Traffic Integration

– Voice, video and data traffic– Multimedia became the ‘buzz word’

• One-way batch Web traffic• Two-way batch voice messages• One-way interactive Mbone broadcasts• Two-way interactive video conferencing

• Quality of Service guarantees (e.g. limited jitter, non-blocking streams)

• LAN Interoperability• Mobile and Wireless nodes



Stallings “High-Speed Networks”

AATMTM AAdaptationdaptation LLayersayersVoice

AALA/Dcellss1 , s2 …

Digital voice samples

Video


A/D … Compression AALcells

compressed frames

picture frames

cellsAALData

Bursty variable-length packets

Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies Figure 9.3

AAsynchronous synchronous TTransfer ransfer MModeode (ATM)(ATM)

MUX

Wasted bandwidth

TDM

4 3 2 1 4 3 2 1 4 3 2 1

Voice

Data packets

Images

`ATM4 3 1 3 2 2 1



ATM• ATM standard (defined by CCITT) is widely

accepted by common carriers as mode of operation for communication – particularly BISDN.

• ATM is a form of cell switching using small fixed-sized packets. [ to facilitate hardware switches]

Basic ATM Cell Format

48 Bytes5 Bytes

Header Payload



ATM Conceptual ModelFour Assumptions

1. ATM network will be organized as a hierarchy.User’s equipment connects to networks via a UNI (User-

Network Interface).Connections between provided networks are made through

NNI (Network-Network Interface).

2. ATM will be connection-oriented.A connection (an ATM channel) must be established before any cells are sent. [The connection setup phase is called signaling.]



X

X

X

X

X

X

X

X

X

Private UNI

Public UNI

NNI

Private NNI

Private ATM network

Public UNI

B-ICI

Public UNIPublic ATM network A

Public ATM network B

Figure 9.5Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies

ATM Connections

• two levels of ATM connections:virtual path connectionsvirtual channel connections

• indicated by two fields in the cell header:virtual path identifier VPIvirtual channel identifier VCI


ATM Virtual Connections

Physical Link

Virtual Paths

Virtual Channels



ATM Conceptual ModelAssumptions (cont.)

3. Vast majority of ATM networks will run on optical fiber networks with extremely low error rates.

4. ATM must supports low cost attachments• This decision lead to a significant decision – to

prohibit cell reordering in ATM networks.ATM switch design is more difficult.


GFC HEC (CRC-8)

4 16 3 18

VPI VCI CLPType Payload

384 (48 bytes)8

Figure 3.16 ATM Cell Format at the UNI


P&D slide

UNI Cell Format

GFC (4 bits) VPI (4 bits)

VPI (4 bits) VCI (4 bits)

VCI (8 bits)

VCI (4 bits) PT (3 bits) CLP (1 bit)

HEC (8 bits)

ATM cell header

Payload (48 bytes)



ATM Cell Switching

2

3

N

1Switch

N

1…

5

6

video 25

video

voice

data

32

32 61

2532

3261

7567

3967

N1

32

video 75

voice 67

data 39

video 67

…

…



c ATMSw1

ATMSw4

ATMSw2

ATMSw3

ATMDCC

ab

de

VP3 VP5

VP2

VP1

a

bc

deSw = switch

Digital Cross ConnectOnly switches virtual paths



ATM Protocol Architecture• ATM Adaptation Layer (AAL) – the protocol

for packaging data into cells is collectively referred to as AAL.

• Must efficiently package higher level data such as voice samples, video frames and datagram packets into a series of cells.

Design Issue: How many adaptation layers should there be?


Management plane

Physical layer

ATM layer

ATM adaptation layer

Higher layers Higher layers

Plane managem

entControl plane User plane Layer m

anagement



AAL

ATM

User information

User information

AAL

ATM

PHYPHY

ATM

PHY

ATM

PHY

…

End system End systemNetwork



Original ATM Architecture

• CCITT envisioned four classes of applications (A-D) requiring four distinct adaptation layers (1-4) which would be optimized for an application class:

A. Constant bit-rate applications CBRB. Variable bit-rate applications VBRC. Connection-oriented data applicationsD. Connectionless data application


ATM ArchitectureAn AAL is further divided into:

Convergence Sublayer (CS)manages the flow of data to and from SAR sublayer.


Segmentation and Reassembly Sublayer (SAR)breaks data into cells at the sender and reassembles

cells into larger data units at the receiver.

■ ■ ■ ■ ■ ■

AAL

ATM

AAL

ATM

Figure 3.17 Segmentation and Reassembly in ATM


P&D slide

Transmission convergence

sublayer

Physical medium dependent sublayer

Physical medium

ATM layer

Physical layer





• The AAL interface was initially defined as classes A-Dwith SAP (service access points) for AAL1-4.

• AAL3 and AAL4 were so similar that they were merged into AAL3/4.

• The data communications community concluded that AAL3/4 was not suitable for data communications applications. They pushed for standardization of AAL5 (also referred to as SEALSEAL – the SSimple and EEfficient AAdaptation LLayer).

• AAL2 was not initially deployed.


Revised ATM Architecture

Revised ATM Service Categories


Class Description Example

CBR Constant Bit Rate T1 circuit

RT-VBR Real Time Variable Bit Rate

Real-time videoconferencing

NRT-VBR Non-real-time Variable Bit Rate

Multimedia email

ABR Available Bit Rate Browsing the Web

UBR Unspecified Bit Rate Background file transfer

QoS, PVC, and SVC


• Quality of Service (QoS) requirements are handled at connection time and viewed as part of signaling.

• ATM provides permanent virtual connections and switched virtual connections.– Permanent Virtual Connections (PVC)

permanent connections set up manually by network manager.

– Switched Virtual Connections (SVC)set up and released on demand by the end user via signaling procedures.

AAL 1 Payload

(b) CS PDU with pointer in structured data transfer

AAL 1 Pointer

1 Byte 46 Bytes

47 Bytes

optional

(a) SAR PDU header

CSI SNPSeq. Count

1 bit 3 bits 4 bits



AAL 1

User data streamHigher layer…b1 b2 b3

CS PDUsConvergence sublayer

474747


SAR sublayer

ATM layer

SAR PDUs

1 47 1 471 47

ATM Cells

H H H

5 48

H

5 48

H

5 48

H


Convergent SublayerPDUs

(a) CPCS-PDU format

CPI Btag BASize CPCS - PDU Payload

1 1 2 1 - 65,535 0-3 1 1 2 (bytes) (bytes) (bytes)

AL Etag LengthPad

Header Trailer

CPI Btag BASize Pad 0 Etag Len

8 16 0─24 8 8 16< 64 KB8

User data

Figure 3.18 AAL 3/4Computer Networks: ATM 31

P&D slide

Segmentation and AssemblyPDU

(b) SAR PDU formatTrailer (2 bytes)

Header (2 bytes)

ST SN MID SAR - PDU Payload

2 4 10 44 6 10 (bits) (bytes) (bits)

LI CRC

ATM header Length CRC-10

40 2 4

SEQ MIDType Payload

352 (44 bytes)10 6 10


Figure 3.19 AAL 3/4 P&D slide

CS-PDUheader

CS-PDUtrailerUser data

44 bytes 44 bytes 44 bytes ≤ 44 bytes

ATM headerAAL header

Cell payloadAAL trailer

Padding

Figure 3.20 Encapsulation and Segmentation for AAL3/4


P&D slide

AAL 3/4

Higher layerInformation User message

TPAD

Service specific convergence

sublayerAssume null

Common part convergence

sublayer

Pad message to multiple of 4 bytes. Add header and trailer.

H

44

2 44 2 2 44 2 2 44 2


SAR sublayer

ATM layer

Each SAR-PDU consists of 2-byte header, 2-byte trailer, and 44-byte payload.

…

Information

…Figure 9.15Copyright ©2000 The McGraw Hill Companies Leon-Garcia & Widjaja: Communication Networks

AAL 5 Convergent Sublayer Format

Information UU CPI Length CRCPad

0 - 65,535 0-47 1 1 2 4 (bytes) (bytes)

Figure 9.19Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies

CRC-32

< 64 KB 0─47 bytes 16 16

ReservedPad Len

32

Data

Figure 3.21 ATM Adaptation Layer 5


P&D slide


Higher layer

PTI = 0

Common part convergence

sublayer

SAR sublayer

ATM layer

Service specific convergence

sublayer Assume null

48 (1)

Information

TPAD

…

…

Information

48 (0)

48 (0)

AAL 5

Figure 9.18

Copyright ©2000 The McGraw Hill Companies

Leon-Garcia & Widjaja: Communication Networks

PTI = 0PTI = 1

User data

48 bytes 48 bytes 48 bytes

ATM header Cell payload

Padding

CS-PDUtrailer

Figure 3.22 Encapsulation and Segmentation for AAL5


P&D slide

Switchfabric

Controlprocessor

Outputport

Inputport

Figure 3.28 ATM Switch


P&D slide

Figure 3.30 4 x 4 Crossbar Switch


P&D slide


�Switchfabric

�Outputport

�Inputport

Original packetheader

�Switchfabric

�Outputport

�Inputport

�Self-routingheader

Sw it �chfabric

�Outputport

�Inputport

(a)

(b)

(c)

Figure 3.31

Self-RoutingHeaders

P&D slide

001

011

110

111

001

011

110

111

Figure 3.32 Banyan Switching


P&D slide

asynchronous transfer mode - wpirek/grad_nets/spring2006/atm06.pdf · atm conceptual model four...

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