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Multi-Service Networks
– ATM –ATM Asynchronous Transfer Mode
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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
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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
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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
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Multiplexing Gainp g
max. capacity
time
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time
PCM• Pulse Code Modulation
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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
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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
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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 ?
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VPI, VCI ? What is the advantage ?
VIRTUAL CIRCUIT and VIRTUAL PATH
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Management Plane
Control Plane User Plane
Higher Layers Higher Layersg y g y
ATM Adaptation Layer
Pl M tATM Layer
Plane ManagementLayer ManagementPhysical Layer
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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
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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 )
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(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...)
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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
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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
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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
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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
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• 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
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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
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Format of the AAL2 CPS-PDU
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AAL2 Protocol
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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
HSDPA
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
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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
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Traffic Contract Negotiation• Traffic Contract: ATM UNI
– Traffic Parameters– Traffic Parameters– QoS Parameters– Conformance Definition
Generic Cell Rate Algorithm (GCRA)
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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)
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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
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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
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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.
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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
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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.
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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.
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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
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– 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)
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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
Constant Bit Rate traffic
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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.
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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
Variable Bit Rate traffic
Time
Constant Bit Rate traffic
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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
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– 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.
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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
Variable Bit Rate traffic
Time
Constant Bit Rate traffic
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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
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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)
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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)
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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
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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).
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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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