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Multi-Service Networks

– ATM –ATM Asynchronous Transfer Mode

www.comnets.uni-bremen.de ATM - 8 - 1

Multi-Service Network RequirementsMulti Service Network Requirements

One integrated network for all services: One integrated network for all services Integrated Services Digital Network (B-ISDN)• VoiceVoice• Data (e.g., file transfer, access to remote

databases, Internet access), )• Video conferencing• Remote monitoring and controlRemote monitoring and control• Access to remote picture sources for medical,

commercial or industrial design purposesg p p


Service Bit-Rate Burstiness

Data transmission( ti i t d)

1.5 ... 130 Mbit / s 1

Service Bit Rate Burstiness

(connection-oriented)Data transmission (connectionless) 1.5 ... 130 Mbit / s 1-50

Document transfer / retrieval 1 5 45 Mbit / s 1 20Document transfer / retrieval 1.5 ... 45 Mbit / s 1-20

Videoconference / video-telephony 1.5 ... 130 Mbit / s 1-5

Broadband video retrieval 1 5 130 Mbit / s 1 20Broadband video retrieval 1.5 ... 130 Mbit / s 1-20

TV distribution 30 ... 130 Mbit / s 1

HDTV distribution 130 Mbit / s 1HDTV distribution 130 Mbit / s 1


ATM Standardization• ITU-T since 1984• ATM Forum since 1991• ATM Forum since 1991

– Group of manufacturers and network operators, ...

– Industry standardsy– Product specification of compatible ATM

products and fast market introduction products and fast market introduction • Specifications ITU-T and ATM Forum

V i il f id i l– Very similar, often identical– Not always compatible


Multiplexing Gainp g

max. capacity

time


time

PCM• Pulse Code Modulation


Transfer Modesf

Channel Switching (STM - Synchronous Transfer Mode)Constant bit-rate connection, end-to-end, capacity is wasted

F F F

125 μs 125 μs 125 μs

, , p y

F F F

Packet Switching (PTM - Packet Transfer Mode)

125 125 125

g ( )Packets of variable length variable bit-rate, allows better utilization of capacity compared to STM

F F F

125 μs 125 μs 125 μs

Cell Switching (ATM – Asynchronous Transfer Mode)Packet switching with extremely small data packets (cells) of fixed length


Packet switching with extremely small data packets (cells) of fixed length

ATM Cell Structure

Cell header Information field5 byte 48 byte

• Cell length?

• Proposal USA: 64 + 548 + 5

• Proposal Europe: 32 + 4


BIT BIT

GFC VPIVPI VCI

12

VPI VPIVPI VCI

12

8 7 6 5 4 3 2 1 8 7 6 5 4 3 2 1

VCIVCI PT CLP

HEC

345

VCIVCI PT CLP

HEC

345CT

ET

CTET

HEC

Cell Payload

56.

HEC

Cell Payload

56.

OC OC

y(48 octets) ..

53

y(48 octets) ..

53

a) ATM Cell at UNIGFC General Flow ControlVCI Virtual Channel Identifier

b) ATM Cell at NNIVPI Virtual Path IdentifierPT Payload TypeVCI Virtual Channel Identifier

CLP Cell Loss PriorityUNI User Network Interface

PT Payload TypeHEC Header Error CheckNNI Network Node Interface

VPI VCI ? What is the advantage ?


VPI, VCI ? What is the advantage ?

VIRTUAL CIRCUIT and VIRTUAL PATH


Management Plane

Control Plane User Plane

Higher Layers Higher Layersg y g y

ATM Adaptation Layer

Pl M tATM Layer

Plane ManagementLayer ManagementPhysical Layer


High Layer Functions Higher LayersAAL - ATM adaptation layer

Convergence Sublayer CSAAL

Segmentation and Reassembly SAR

ATM- Asynchronous Transfer Mode

CS - convergence sublayer

HEC - header error control

LM L t

Generic flow controlCell header generation/extractionC ll VPI/VCI t l ti

ATM

LM - Layer management

PH - Physical layer

PM - Physical medium

SAR Segmentation and reassembly

LM

Cell VPI/VCI translationCell multiplex and demultiplexCell rate decoupling

SAR - Segmentation and reassembly

TC - Transmission convergence

VCI - Virtual channel identifier

VPI - Virtual path identifierHEC sequence generation/verificationCell delineationTransmission frame adaptation

TC

VPI Virtual path identifier

Transmission frame generation/recovery

PH

Bit timing

Physical mediumPM


ATM Reference ModelATM-Reference Model

End unit End unitTransmissions

End-unit End-unit

AAL AALAAL

ATM

AAL

ATM

PHY PHY

UNI UNIATM Network

• PHY = Physical LayerUNI U N k I f• UNI = User Network Interface

• AAL = ATM Adaptation Layer• Different AAL-Protocols for different traffic types ( d t s h id )


(e.g. data, speech, video)

ATM VisionThe Ultimate Integrated Services Network

Speech

SpeechData

Speech

Speech

SpeechData VideoATM

NetworkData

Datap

Data

VideoVideo

VideoData

ATM network moves cells (fixed length packets with low delay

VideoVideo

variation...)


Physical Layere.g. SDH: Synchronous Digital Hierarchyg y g y

F F

125 μsSTM-1 frame

F F

. . .

s

Administration-information

1 frame(incl. 1 column administration information)9

lines

9 byte270 byte

9 x 270 x 8 / 125 μs = 155.52 Mbit/s total capacity

9 260 8 / 125 149 76 Mbi / i


9 x 260 x 8 / 125 μs = 149.76 Mbit/s user capacity

Cell Cells follow seamless (without flags)

A LA A L B C

Header Information fieldHeader Information field

Pulse frame (125μs)

Pulse frame (125μs)

SYNC A B B L CSYNC C SYNC LE

Asynchronous time-multiplex SYNC Synchronization Cella) ATM without pulse-frame L Vacant Cellb) ATM structured by pulse-frame A-E Data Cells

ATM Cell head:VPI virtual path identifierVCI virtual channel identifier

Routing label, fixed virtual connections


VCI virtual channel identifier

ITU-T Service Classification and AAL Types

Class A Class B Class C Class D

Timing Relation between source and destination

Required Not required

and destination

Bit-rate Constant Variable

Connection Connection-oriented Connectionlessmode

L L 1 L 2 L 3/4 L 3/4AAL types AAL type 1 AAL type 2 AAL type 3/4AAL type 5

AAL type 3/4AAL type 5


AAL 3/4: ATM adaptation layer

4 4 7 Bytes

Bytes

Data0-65535

ErrorControl

4ErrorControl

4-7 Bytes

442 2

User Data LISNCell

User Data LICRC

SNMID

llder

AAL 3/4 :• 44 byte user data per cell

User Data LICRC

SNMID

CellHeader

User Data CRCMIDHeader

44 byte user data per cell• CRC checking per cell• LI Length ID • MID (Message Identifier)

PAD LICRC

SNMID

CellHeader

• MID (Message Identifier)allows packets of different connectionsvia one virtual connectionSN S n N mb


• SN Sequence Number

AAL2• AAL2 is defined in the ITU-T Recommendation

I.363.2• AAL 2 provides for the bandwidth-efficient

transmission of low-rate, short, and variable k ts i d l s siti li ti spackets in delay sensitive applications.

• Main Advantages:AAL2 n bl s supp rt f r b th V ri bl Bit R t (VBR) – AAL2 enables support for both Variable-Bit-Rate (VBR) and Constant-Bit-Rate (CBR) applications within an ATM network.

– AAL 2 enables multiple user channels on a single ATM virtual circuit and varying traffic conditions for each individual user, or channel.individual user, or channel.

– AAL2 offers a variable payload within cells and across cells. This functionality provides a dramatic improvement in bandwidth efficiencyin bandwidth efficiency.

AAL2AAL2 i di id d i t t b l • AAL2 is divided into two sub-layers:

– Common Part Sub-layer (CPS)• identifying the users of the AALy g• assembling/disassembling variable payload associated with each

individual user • The multiplexing function in the CPS merges several streams of CPS

packets onto a single ATM connection• Provides error correction• relationship with the SSCS

– Service Specific Convergence Sub-layer Service Specific Convergence Sub layer (SSCS)

• SSCS is defined as the link between the AAL2 CPS and the higher layer applications of the individual AAL2 users

AAL2 Structure


Format of the AAL2 CPS Packet

• CID- Channel IDentification• LI- Length Indicator: the length of the packet payload associated

i h h i di id l l i l h h k l d with each individual user, value is one less than the packet payload and has a default value of 45 bytes (may be set to 64 bytes)

• UUI- User-to-User Indication, provides a link between the CPS and i t SSCS th t ti fi th hi h l li tian appropriate SSCS that satisfies the higher layer application

• HEC- Header Error Control • Information payload - Contains the CPS/SSCS PDU


Format of the AAL2 CPS-PDU


AAL2 Protocol


UMTS R l 99UMTS Release 99

FP

AAL2

PDCP*

RLC

MAC

FP

AAL2AAL2

ATM

PHY

AAL2

ATM

PHY

NodeB RNCLaptop

Laptop

PDA

Iub LinkCell phoneCell phone

Reference• ITU-T Recommendation I.363.2: B-

ISDN ATM Adaptation Layer Type 2 ISDN ATM Adaptation Layer Type 2 Specification

Example Capacity Assignment f ATM Transfer Services

max. capacity

UBRUBR

ABR

CBR

VBR

time


ATM-Transfer ServicesITU-T I.371ATM Transfer Capability

ATM Forum TM 4,0ATM Service Category

Typical Use

DBR CBR l iDBRDeterministic Bit Rate

CBRConstant Bit Rate

real-timeservice guarantees

SBR nrt-VBRNon real time

statistical multiplexingStatistical Bit Rate Non-real-time

Variable Bit Rate* rt-VBR

real-timeV i bl Bit R t

statistical multiplexingreal-timeVariable Bit Rate real-time

ABT - DT/ITATM Block TransferDelayed / Immediate T i i

*stream controly

TransmissionABRAvailable Bit Rate

ABRAvailable Bit Rate

utilization of sourcesstream control

* UBRUnspecified Bit Rate

best effortno guarantee of service quality


Traffic Contract Negotiation• Traffic Contract: ATM UNI

– Traffic Parameters– Traffic Parameters– QoS Parameters– Conformance Definition

Generic Cell Rate Algorithm (GCRA)


Traffic Descriptors• PCR: Peak Cell Rate• SCR: Sustainable/Sustained Cell RateSCR: Sustainable/Sustained Cell Rate• MBS: Maximum Burst Size

MCR Mi i C ll R• MCR: Minimum Cell Rate• CDVT(PCR): ( )

Cell Delay Variation Tolerance (Peak Cell Rate)( a at )

• CDVT(SCR): Cell Delay Variation Tolerance Cell Delay Variation Tolerance (Sustainable Cell Rate)


Required Traffic Descriptors by Service Category

CBR rt-VBR nrt-VBR ABR UBR

PCR Yes Yes Yes Yes YesSCR N/A Yes Yes N/A N/AMBS N/A Yes Yes N/A N/AMCR No No No Yes NoCDVT(PCR) Yes Yes Yes Yes YesCDVT(PCR) Yes Yes Yes Yes YesCDVT(SCR) N/A Yes Yes N/A N/A


Application Requirements

Bandwidth• Peak Cell Rate (PCR)• Sustained Cell Rate (SCR)• Minimum Cell Rate (MCR)

Delay

( )

• Cell Transfer Delay (CTD)• Cell Delay Variation (CDV)

Reliability

Cell Delay Variation (CDV)

• Cell Loss Ratio (CLR)Reliability • Cell Loss Ratio (CLR)

Cost ($ or Admin) • Link Weighting


CBRCBR• CBR service offers a constant bit rate in connection

oriented circuits that also require some level of reliability q yand error detection. Therefore, there is a sequence number associated with each cell like the one found in TCP/IP.

• These sequence numbers allow for easy error detection of lost cells, hence giving the receiver the possibility to detect the problem and ask for retransmission, if detect the problem and ask for retransmission, if necessary.

• As part of the constant bit rate requirement, there is also a need for timing synchronization between the also a need for timing synchronization between the transmitting and receiving station.

• The AAL format to handle this service is also called the AAL type 1. It uses 1 byte of the 48 user bytes for the sequence number, thus leaving 47 bytes to the user.


CONSTANT BIT RATECONSTANT BIT RATE

F d b d d h • Fixed bandwidth transmission circuit• Intended for voice, uncompressed video, p

circuit emulation (T1, E1 etc.)• The amount of bandwidth can be described The amount of bandwidth can be described

by a single parameter (PCR - Peak Cell Rate)(PCR - Peak Cell Rate)

ndw

idth

Ba

Ti

Constant Bit Rate traffic


Time

CBR (Constant Bit Rate)Th CBR i l i i t d d f l ti • The CBR service class is intended for real-time applications.

• The consistent availability of a fixed quantity of The consistent availability of a fixed quantity of bandwidth is considered appropriate for CBR service. Cells which are delayed beyond the value specified by CTD (cell transfer delay) are assumed to be of CTD (cell transfer delay) are assumed to be of significantly less value to the application.

• For CBR, the following ATM attributes are specified: F , f g p f– PCR/CDVT (peak cell rate/cell delay variation tolerance) – Cell Loss Rate– CTD/CDV– CLR may be unspecified for CLP=1.


VBR• VBR service is designed to handle audio and

video. It does not require the constant bit rate f if h i i d i h f feature if the receiving device has a few hundred bytes of buffering.

d h l k h • It does, however, require clock synchronization like that of Class A. The AAL type 2 packet supports this service supports this service.

• The ITU added 3 bytes of overhead in each cell for lost packets scrambled data and even cell for lost packets, scrambled data and even variable-length data streams.

• A sequence number data length indicator and a • A sequence number, data length indicator and a 10 bit CRC. The 3 bytes of overhead left the user with only 45 out of the 48 data bytes.


y y

Real time VBR• Sources are expected to transmit at a rate

which varies with time. Equivalently the source b d ib d "b " C ll hi h can be described as "bursty". Cells which are

delayed beyond the value specified by CTD are assumed to be of significantly less value to the assumed to be of significantly less value to the application. Real-time VBR service may support statistical multiplexing of real-time sources, or p g ,may provide a consistently guaranteed QoS.

• For real time VBR, the following ATM , gattributes are specified: – PCR/CDVT – CLR – CTD/CDV

SCR d BT ( t i bl ll t d b t t l ) www.comnets.uni-bremen.de ATM - 8 - 40

– SCR and BT (sustainable cell rate and burst tolerance)

Non-real time VBR• The non-real time VBR service class is intended for non-

real time applications which have 'bursty' traffic characteristics and which can be characterized in terms characteristics and which can be characterized in terms of a GCRA (Generic Cell Rate Algorithm).

• For those cells which are transferred, it expects a bound pon the cell transfer delay. Non-real time VBR service supports statistical multiplexing of connections.

• For non real time VBR the following attributes are • For non-real time VBR, the following attributes are supported: – PCR/CDVT – CLR – CTD

SCR and BT (sustainable cell rate and burst tolerance) – SCR and BT (sustainable cell rate and burst tolerance)


VARIABLE BIT RATE• Intended for bursty traffic• Bursts must not exceed specified • Bursts must not exceed specified

maximum or durationdt

hBa

ndw

id

Variable Bit Rate traffic

Time



Time

UBR• VBR is not good at supporting a LAN data

connection, because the variation in bandwidth used is so great that we can never be sure of a used is so great that we can never be sure of a Maximum Burst Size. Luckily, LAN data will just take whatever bandwidth the other connections aren’t using.

• This kind of best-effort, open-ended contract is called an Unspecified Bit Rate (UBR) connection called an Unspecified Bit Rate (UBR) connection. If UBR connections become congested, then data just spends some time in a buffer. If the buffer j pgets too full, then the data is thrown away. In simple terms, UBR contracts were intended to offer just the kind of best-effort service that offer just the kind of best effort service that router networks provide.


UNSPECIFIED BIT RATE• Variable bandwidth

transmission circuit• Best effort –

open ended contractopen ended contract• No flow control or

feedbackUnspecified Bit Rate or Available Bit Rate Traffic feedback

ndw

idth

Ban


Time



UBR (Unspecified Bit Rate)• The UBR service class is intended for delay-tolerant or

non-real-time applications, i.e., those which do not require tightly constrained delay and delay variation such require tightly constrained delay and delay variation, such as traditional computer communications applications. Sources are expected to transmit non-continuous bursts of cells of cells.

• UBR service supports a high degree of statistical multiplexing among sources. m p g m g .

• UBR service includes no notion of a per-VC allocated bandwidth resource. Transport of cells in UBR service is

t il t d b h i ti t not necessarily guaranteed by mechanisms operating at the cell level. However, it is expected that resources will be provisioned for UBR service in such a way as to make it usable for some set of applications. For UBR, the following ATM attributes are specified: – PCR/CDVT


– PCR/CDVT

ABR• Available Bit Rate (ABR) contracts were developed

to add flow control techniques to UBR. Instead of just allowing congestion to happen ABR includes just allowing congestion to happen, ABR includes protocols that allow the backbone switches and the ATM end systems to notify each other about y ycongestion.

• Despite the addition of flow control protocols, ABR i ti ll till b t ff t t h i ABR is essentially still a best-effort technique, and is focused on supporting LAN data connections.conn ct ons.


AVAILABLE BIT RATE

• Variable bandwidth transmission circuittransm ss on c rcu t

• Best effort• End to End flow • End to End flow

control

wid

th

Unspecified Bit Rate or Available Bit Rate Traffic

Ban

dw


Time



ATM Delays• Connection set-up time depends on

the speed of the Network Call the speed of the Network Call Processor and the number of ATM switchesswitches

• Message Delays:g y– PD: Packetization Delay– TD: Transmission Delay– TD: Transmission Delay– QD: Queuing Delay

FD F d h D l– FD: Fixed Switching Delay– DD: Depacketization Delay


p y

ATM-Networks: Time DelaysyTransmission delay

(TD=TD1 + TD2 + TD3)

TM N k

TD1 TD2 TD3

ATM-Network

QD1+FD1 QD2+FD2

Q i d l (QD)Packetization De-PacketizationQueuing delay (QD)

+fixed switching delay (FD)

delay (PD)De acket zat on

delay (DD)


ATM Application Areas• ADSL (Asymmetric Digital Subscriber Line) :

– ATM Cells are transmitted over the ADSL line. – In the network switch (Vermittlungsstelle)

these cells are further transported in the ATM network of the ADSL provider network of the ADSL provider.

– User data is transported in ATM Cells. – This can be e g Ethernet packets PPP packets This can be, e.g., Ethernet packets, PPP packets

or IP packets. • Backbone Network for UMTS:ac on N twor for M S

UMTS UTRAN (UMTS Terrestrial Radio Access Network) connections between NodeB (base stations) and RNC (radio network control)


ATM Forum

... "First and foremost, ATM. For 20 years now, ATM has been the cornerstone of international standards that define multiservice co ne stone of inte national standa ds that define multise viceinfrastructure. It works for voice, it works for data - and both service providers and end users accept those truths. RBOCs love ATM, and the RBOC investment in broadband access modernization is the first fstep our industry will take out of its current doldrums. Do the numbers on ATM edge deployment, and you come up with a minimum of 100,000 ATM-based remote concentrators, 15,000 Central Office (CO) ATM switches, 6,000 tandem/regional network ATM switches, and 100 million ATM edge devices - all in the United States alone.

Okay, I know ATM isn't glamorous anymore, but in the early 1990s, the media and you - the reading public-loved it. Better learn to love it again. " ...g

Tom Nolle: August 2001


Regional Bell operating company (RBOC)is a term describing one of the U.S. regional telephone

companies (or their successors) that were created as a result of the breakup of American Telephone anda result of the breakup of American Telephone and Telegraph Company (AT&T, known also as the Bell System or "Ma Bell") by a U.S. Federal Court consent decree on December 31, 1983. The seven original regional Bell operating companies were Ameritech, Bell Atlantic BellSouth NYNEX Pacific BellBell Atlantic, BellSouth, NYNEX, Pacific Bell, Southwestern Bell, and US WEST. Each of these companies owned at least two Bell operating

i (B ll ti ) Th BOCcompanies (Bell operating company). The BOCs were given the right to provide local phone service while AT&T was allowed to retain its long-distance gservice. The RBOCs and their constituent BOCs are part of the class of local exchange carriers (LECs).


Selftest:

http://www.iec.org/online/tutorials/atm_fund/selftest.html

Oth it :Other sites:

http://www atmforum org/http://www.atmforum.org/

http://www.wikipedia.org/http //www.wikipedia.org/

http://www.iec.org/online/tutorials/atm_fund/topic03.html


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