ATM networks - univ-pau.frcpham.perso.univ-pau.fr/.../04-ATM-networks.pdf · C. Pham, University of...

ATM networksATM networks

C. PhamUniversité de Pau et des Pays de l’AdourLIUPPA Laboratoryhttp://www.univ-pau.fr/[email protected]

C. Pham, University of Pau, France

Issues Driving LAN ChangesIssues Driving LAN Changes

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

Quality of Service guarantees not possible with theIP/Ethernet model (e.g. limited jitter, non-blockingstreams)

LAN Interoperability Mobile and Wireless nodes


High-speed interconnectionHigh-speed interconnection

Interconnection of distant LANs must be flexible toprovide « bandwidth on demand »

Frame Relay was a first step to remove networkoverheads and put most of the processing into end-hosts

SMDS & DQDB was 2 technologies that offer aflexible multi-service interconnection infrastructure

SONET/SDH not flexible enough ATM is the continuation of these work

– Multi-service/multimedia network: voice, video, data– Hundred’s of Mbits/s rate– Quality of Service adapted to end applications– ATM standard (defined by CCITT) is widely accepted by

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


AsynchronousAsynchronous Transfer Transfer ModeMode

ATM (Asynchronous Transfer Mode)– Simplicity and performance of circuit switching– Flexibility of packet switching

Telco operator technology

MUX

`

Wasted bandwidth

ATM

TDM

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

4 3 1 3 2 2 1

Voice

Datapackets

Images


Limitation of Limitation of datagram packet switchingdatagram packet switching

R3

A

B

C

R1

R2

R4 D

E

FR5

R5F

R3E

R3D

Next HopDestination

DD

With IP datagram mode, difficult to provide qualityof service (no sequence, no ressourceprovisioning)

D

D


PABX

SW

SW

SW

SW

SW

PABX

SW

SW

Trunklines

Reliability of circuit switchingReliability of circuit switching


Traditional circuit in telephonyTraditional circuit in telephony

…

123

N

MUX…

123

N

De-MUX1 2 3 … N

1 sample every 125us gives a 64Kbits/s channel

Fixed bandwitdh

Simple, efficient, but lowflexibility and wastes

resources

ATM: take advantages of both worlds

Packet-switching with virtual circuit!


Virtual CircuitVirtual Circuit

R3

A

B

C

R1

R2

R4D

E

R5

Virtual Circuit:X.25 & FrameRelay.

ATM: sameprinciple butmuch smallerpacket size

478245

334123

LinkOUT

LabelOUT

LinkIN

LabelIN

R3

Link 1

Link

2

Link 3

Link 4

45

23

34

78

Connections &Virtual circuits table

label


ATM Conceptual Model, 4 assumptionsATM Conceptual Model, 4 assumptions

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).

ATM will be connection-oriented.– A connection (an ATM channel) must be established before any

cells are sent.

Vast majority of ATM networks will run on opticalfiber networks with extremely low error rates.

ATM must supports low cost attachments– This decision lead to a significant decision – to prohibit cell

reordering in ATM networks.


ATM, ATM, reference reference modelmodel

Plane managem

ent

Management plane

Control plane User plane

Physical layer

ATM layer

ATM adaptation layer

Higher layers Higher layers

Layer managem

ent


A/D

Voice

s1 , s2 …

Digital voice samples

A/D

Video

… Compression

compressedframes

picture frames

DataBursty variable-length

packets

cells

cells

cells

AAL

AAL

AAL

AdaptationAdaptation in in end-hostend-host


OSI vs ATMOSI vs ATM


An ATM network An ATM network with hierarchywith hierarchy

Admission controlTraffic control


Hop-by-hop cell forwardingHop-by-hop cell forwarding

Use labels to forward cells

Label in

Label out

Output port


Which Which size for a size for a cellcell??

European et japanese telcos– 32 bytes makes a packetization delay of 4ms avoiding echo

cancellation devices

Computer scientists– 64 bytes to reduce the header overhead– US telcos had no problems with 64 bytes because of an already

large deployed infrastructure of echo cancellation devices.

The trade-off…– 53 bytes! (DQDB packet was also 53 bytes)– 90.57% of efficiency at the maximum with 5 bytes for header


The The ATM ATM cell cell : 53 bytes: 53 bytes

– GFC: Generic Flow Control (UNI),– VPI & VCI: Virtual Path Identifier, Virtual Channel Identifier– PTI: Payload Type Identifier– CLP: Cell Loss Priority– HEC: Header Error Checksum

label


Pros & Cons of Pros & Cons of small small size size cellscells

Pros– Better management of buffers in ATM switches,– Make easier the building of large parallel switches,– Smaller switching delays.

Cons– Size of header is significant when compared to data,– segmentation & reassembly is costly,– At 622Mbits/s it’s a cell every 700ns!– ATM switch design is more difficult.


The physical The physical layerlayer

Cell rate adaptation, HEC generation and verification,


Supported throughputSupported throughput

Multimode Fiber: 100 Mbps using 4b/5b, 155 Mbps SONET STS-3c, 155 Mbps 8b/10b Single-mode Fiber: 155 Mbps STS-3c, 622 Mbps Plastic Optical Fiber: 155 Mbps Shielded Twisted Pair (STP): 155 Mbps 8b/10b Coax: 45 Mbps, DS3, 155 Mbps Unshielded Twisted Pair (UTP) UTP-3 (phone wire) at 25.6, 51.84, 155 Mbps UTP-5 (Data grade UTP) at 155 Mbps DS1, DS3, STS-3c, STM-1, E1, E3, J2, n × T1 …


ATM ATM over over SONET/SDHSONET/SDH


The The ATM layerATM layer

multiplexing & demultiplexing of cells, generation & extraction of headers, processing of

VPs & VCs, Generic flow control (GFC).

Virtual Circuit

Transmission PathVirtual Path


VP & VCVP & VC

A VPC = 1 VP or a concatenation of several VPs. A VCC = 1 VC or a concatenation of several VCs. A VP contains several VCs Avantages

– Simple connection setup for most used paths– Easy definition of Virtual Private Networks (VPN),– Simplier traffic management: traffics with different constraints

can be transported in different VPs for isolation.

Virtual Circuit

Transmission PathVirtual Path


Virtual PathVirtual Path

c ATMSw1

ATMSw4

ATMSw2

ATMSw3

ATMDCC

ab

de

VP3 VP5

VP2

VP1

a

bc

deSw = switch

Digital Cross ConnectOnly switches virtual paths


Virtual ChannelsVirtual Channels


Advantages Advantages of VP of VP and and VC VC hierarchyhierarchy

Re-routing a VP automatically re-routes all VCs ofthe VP


QoSQoS, PVC, and SVC, PVC, and SVC

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

ATM provides permanent virtual connections andswitched 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 signalingprocedures.


ATM ATM switches switches & interface& interface

Optical fiber for long-distance

Twisted copperpossible for smalldistance

High-speed connectionmatrix Fore ASX 200


ReviewReview: c: crossbarrossbar, , general general designdesign

Simplest possible space-division switch

Crosspoints can be turnedon or off, long enough totransfer a packet from aninput to an output

Expensive– need N2 crosspoints– time to set each crosspoint

grows quadraticallyconfiguration

Dat

a In

Data Out


Switch Fabrics: Buffered crossbarSwitch Fabrics: Buffered crossbar ( (packetspackets))

What happens ifpackets at two inputsboth want to go tosame output?

Can defer one at aninput buffer

Or, buffer cross-points:complex arbiter


Switch fabric elementSwitch fabric element

Goal: towards building “self-routing” fabrics Can build complicated fabrics from a simple

element

Routing rule: if 0, send packet to upper output, elseto lower output– If both packets to same output, buffer or drop

0

1

data 10

data 00


Banyan Banyan element element (1 possible configuration)(1 possible configuration)

110

001

ATM has boosted research on high-performance switches

0

1

data 10

data 00


Buffer Buffer managementmanagement

Input buffers

Output buffer


Knockout switchKnockout switch

Too costly!


Batcher-Banyan switchBatcher-Banyan switch

a same direction than arrow if a > b,a opposite direction if a is alone

5

7

5

7

101

111


ATM Protocol ArchitectureATM Protocol Architecture

ATM Adaptation Layer (AAL) – the protocol forpackaging data into cells is collectively referred to asAAL.

Must efficiently package higher level data such as voicesamples, video frames and datagram packets into aseries of cells.

Design Issue: How many adaptation layers should therebe?

CCITT envisioned four classes of applications (A-D)requiring four distinct adaptation layers (1-4) whichwould be optimized for an application class:– Constant bit-rate applications CBR– Variable bit-rate applications VBR– Connection-oriented data applications– Connectionless data application


AAL ArchitectureAAL ArchitectureFirst end-to-end layer in the ATM network modelAn AAL is further divided into:

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

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

cells into larger data units at the receiver.


OriginalOriginal ATM Architecture ATM Architecture

The AAL interface was initially defined as classesA-D with SAP (service access points) for AAL1-4.

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

The data communications community concludedthat AAL3/4 was not suitable for datacommunications applications. They pushed forstandardization of AAL5 (also referred to as SEAL –the Simple and Efficient Adaptation Layer).

AAL2 was not initially deployed.


RevisedRevised ATM ATM Service Categories Service Categories

Background filetransfer

Unspecified Bit RateUBR

Browsing the WebAvailable Bit RateABR

Multimedia emailNon-real-time Variable Bit RateNRT-VBR

Real-timevideoconferencing

Real Time Variable Bit RateRT-VBR

T1 circuitConstant Bit RateCBR

ExampleDescriptionClass


Generic AALs Generic AALs Segmentation Segmentation and Reassemblyand Reassembly

Each AAL is divided in 2 parts: SAR (Segmentationand Reassembly) and CS (Convergence Sublayer).CS makes the specific adaptation required by end-user/application.


(b) CS PDU with pointer in structured data transfer

AAL 1Pointer

1 Byte 46 Bytes

47 Bytes

Figure 9.11

AAL 1 Payload

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

optional

(a) SAR PDU header

CSI SNPSeq. Count

1 bit 3 bits 4 bits


…Higher layer User data stream

Convergencesublayer

SAR sublayer

ATM layer

CS PDUs

SAR PDUs

ATM Cells

47 47 47

1 47 1 47 1 47

H H H

5 48

H

5 48

H

5 48

H

b1 b2 b3

Figure 9.10

AAL 1



(a) CPCS-PDU format

(b) SAR 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

ST SN MID SAR - PDU Payload

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

LI CRC

Header(2 bytes)

Trailer(2 bytes)

Figure 9.16

AAL 3/4CS and SAR PDUs



Higher layer

Common partconvergence

sublayer

SAR sublayer

ATM layer

Service specificconvergence

sublayer

Information

Assume null

TPAD

User message

Pad message to multipleof 4 bytes. Add headerand trailer.

Each SAR-PDU consistsof 2-byte header, 2-bytetrailer, and 44-bytepayload.

H

4 4

2 44 2 2 44 2 2 44 2

…

…

Information

Figure 9.15

AAL 3/4



Information

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

UU CPI Length CRCPad

Figure 9.19

AAL 5

Convergent Sublayer Format

SAR Format

48 bytes of DataATMHeader

1-bit end-of-datagram field (PTI)Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies


Higher layer

Common partconvergence

sublayer

SAR sublayer

ATM layer

PTI = 0

Service specificconvergence

sublayer Assume null

48(1)

Information

TPAD

…

…

Information

48(0)

48(0)

PTI = 0PTI = 1

Figure 9.18

AAL 5

Leon-Garcia & Widjaja: Communication Networks

Copyright ©2000 The McGraw Hill Companies


ExampleExample: AAL 1, : AAL 1, jitter jitter compensationcompensation

for audio restitution

Variable jitter not suitable for audio AAL1 Fixed-spacing foraudio restitution

buffering


ATM LAN (obsolete)ATM LAN (obsolete)

ATM switches as hub

Station ATM

Station ATM

Station ATM

Station ATM

Station ATM

bridge

Bridge

Ethernet

Ethernet

HUBSwitch ATM

source G. Beuchot


ATM in ATM in the backbonethe backbone

C

Layer 0Transport

Layer 2QoS

Layer 3Aggregation

WDMWDM FIBER

SONET/SDH

IP

ATMATM

FRFRVOICEVOICE

Leased LinesVPNVoice

Layer 1Restoration

ATMATM

IPIP

source alcatel


ATM ATM and and ADSLADSL

Upstream 128 ou 256 Kbps

Downstream 500 Kbps ou 1 Mbps

ATU-R

Splitter

CopperWire

Customer

D< 3,5 Kms

DSLAM(DSL AccessMultiplexer)

CAA

Central Office

BAS(Broadband

Access sever)

ATM Network

LocalLoop

POTS

PSTN

BROADBANDNETWORK

Source FT


ATM for ADSLATM for ADSL

ATM Network

splitter

splitter

ATU-R

LANNetissimo

1 VC ATM / CustomerNetissimo 1 (128 kbit/s, 500 kbit/sNetisimo 2 (256 kbit/s, 1000 kbit/s)

DSLAM - BAS

1 VP ATM

Turbo IP

1 VC ATM for flow 11 VC ATM for flow 2

BAS

DSLAM

DSLAM

IP Routeur for ISP

ATU-R

Source FT


ATM in ATM in the telcothe telco’’s s networknetwork

BASATM Switch

SDH/SONET

DSLAM

DSLAM

DSLAM

ADM

ADMADM

INTERNET

Source FT


SummarySummary: : ATMATM’’s s curriculumcurriculum

Reduce overhead in core networks, pushprocessing into end-host (Frame Relay philosophy)

Software components (AALs) adapt the networkservice for end applications

Several (and complex) quality of service Fixed and small size packet=cell, suitable for audio Connection-oriented at the network layer Packet switching philosophy with virtual circuits VP & VC hierarchy

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