Asynchronous Transfer Mode Networks

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Asynchronous Transfer ModeNetworks

• Nirmala Shenoy
• Information Technology Department
• Rochester Institute of Technology

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Asynchronous Transfer Mode

• Scope
• Purpose
• Cells vs packets
• Topology
• Virtual connections
• VP and VPC switching
• ATM layers

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Asynchronous Transfer Mode

• Scope
• Delays in ATM networks
• Service QoS
• Traffic control
• UNI
• B-ICI
• Switch fabric
• ATM addressing

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Asynchronous Transfer Mode

• Purpose
• Cells over frames
• Optimal use of transmission and equipment
  technology
• Interface with various packet switching networks
• WAN connectivity

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Asynchronous Transfer Mode

• Purpose
• Easy and inexpensive implementation
• Support exiting telecommunication hierarchies
• Local loops, local providers, long distance
  carriers
• Connection oriented reliable and predictable
  delivery especially for real-time application
• protocol functions from sw to hw
• High-speed low delay packet switching for all
  types of traffic

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Asynchronous Transfer Mode

• Cell vs Frames
• Frames - Packets
• Current packet sizes- 200bytes to 64kbytes
• Elaborate software at intermediate nodes to
  accommodate variable size packets
• Variable header evaluations
• Packets to be checked for integrity
• Non-uniformity of service for different types of
  packet networks

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Asynchronous Transfer Mode

• Packets
• Consistent data rate delivery not possible
• In-time delivery for some packets
• Real-time packets may be smaller compared to data
  packets
• Cells
• Predictable processing
• Uniformity guaranteed

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Asynchronous Transfer Mode

• Cells
• Deterministic delays ncell transmission
• High speed small cell size continuous stream
  effect
• Cells handled as cells not as bit stream faster
• Fixed cells more hardware implementable

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Asynchronous Transfer Mode

• Asynchronous TDM

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Asynchronous Transfer Mode

• Topology

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Asynchronous Transfer Mode

• Topology
• Similar to ISDN has all reference points and
  functional groupings (b tag)
• Public and private UNI may use different
  different interfaces schemes
• ATM can be used as a LAN, WAN, hub
• interconnecting networks, backbone

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Asynchronous Transfer Mode

• Virtual connections
• Transmission Path
• Physical connection between two points
• Switches and end points or between switches
• Virtual Path
• Transmission path is divided into several virtual
  paths

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Asynchronous Transfer Mode

• Virtual connections
• The set of all virtual path transmission path
• Virtual circuit
• A single message flow circuit
• A number of virtual circuits make a virtual path

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Asynchronous Transfer Mode

• Virtual connections relationship

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Asynchronous Transfer Mode

• Virtual connections relationship

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Asynchronous Transfer Mode

• Virtual connections relationship
• VPI VCI

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Asynchronous Transfer Mode

• Virtual connections set-up
• PVC permanent virtual circuit
• Negotiated with the network on long term basis
• SVC switched virtual circuit
• On per call basis

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Asynchronous Transfer Mode

• Virtual connections set-up

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Asynchronous Transfer Mode

• VP switching

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Asynchronous Transfer Mode

• VPC switching VP VC switching

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Asynchronous Transfer Mode

• ATM layers
• ATM Adaptation Layer AAL
• Convergence Sub layer
• Segmentation and Reassembly sub layer
• ATM Layer
• Physical layer
• SONET/SDH

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Asynchronous Transfer Mode

• ATM layers the OSI layers
• ATM layer performs layers 2 3 functions of the
  OSI layers
• AAL combines, 2,4 and 5 of the OSI layers
• Not adhering to the OSI layers
• OSI layers getting obsolete?

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Asynchronous Transfer Mode

• ATM Planes
• SSCF service specific coordination function
• SSCOP service specific connection-oriented
  protcol

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Asynchronous Transfer Mode

• ATM Adaptation Layer at the end points
• ATM Physical layer through the network

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Asynchronous Transfer Mode

• ATM Adaptation Layer application specific
• Classification of traffic
• Class A constant bit rate
• Class B - variable bit rate, connection
  oriented, timing requirements
• Class C- Variable Bit Rate, connection oriented,
  timing not required
• Class D Variable Bit Rate, connectionless,
  timing not required

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Asynchronous Transfer Mode

• ATM Adaptation Layer
• AAL1 to support Class A
• AAL2 Class B later for voice
• AAL3/4 connection oriented data
  connectionless data, Class C D
• AAL5 signaling data
• Simple and most popular

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Asynchronous Transfer Mode

• ATM Adaptation Layer- AAL1
• Convergence Sub layer
• Segments PDU from upper layer to 47 byte segments
• Passes to SAR

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Asynchronous Transfer Mode

• ATM Adaptation Layer- AAL1
• Segmentation And Reassembly layer SAR
• adds a 1 byte header
• 1bit CSI convergence sublayer id
• 3 bits sequence count
• 3 bits CRC on the above
• 1 bit parity

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Asynchronous Transfer Mode

• Delays and real-time service support
• Transmission efficiency Li/(LiLo)
• Li information field length
• Lo length of control header
• Variable SDU Li can be large
• Processing delays at switch
• Fixed SDU predictable delays

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Asynchronous Transfer Mode

• Transmission delay
• To provide for time transparency
• Circuit emulation for some applications
• Responsibility of the AAL
• Buffering schemes
• Delay at sender end
• Convergence and reassembly C/S1
• At the receiver end C/S2
• Propagation Delay PD 4-5? sec per Km
  

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Asynchronous Transfer Mode

• Transmission delay
• Cell loss
• Loss of one cell 4-16 msec
• Switching Delay SD fixed 2-100 ?sec
• Delays to overcome jitter
• Queuing Delay traffic peaks

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Asynchronous Transfer Mode

• Transmission delay
• C/S 12000 ?sec (6000 ? sec at each end)
• PD 2000 ? sec
• SD 72 ? sec (24 ? sec for each switch 3)
• QD 225 ? sec (total for 3 switch)
• Predominant PD and C/S
• C/S can be higher if some other layers include
  more mapping convergence

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Asynchronous Transfer Mode

• ATM Adaptation Layer- AAL3/4
• Convergence sub layer

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Asynchronous Transfer Mode

• ATM Adaptation Layer- AAL3/4
• Convergence Sub layer bits
• T type
• BT Begin Tag
• BA Buffer Allocation
• PAD- padding to proper multiple size
• AL align trailer to 4 bytes
• ET End Tag
• L length of data unit

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Asynchronous Transfer Mode

• ATM Adaptation Layer- AAL3/4
• Segmentation and Reassembly sub layer

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Asynchronous Transfer Mode

• ATM Adaptation Layer- AAL3/4
• SAR sub layer bits
• ST segment type
• CSI convergence sublayer identifier
• SC - Sequence count
• MID Multiplexing identifier
• LI length indicator
• CRC -

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Asynchronous Transfer Mode

• ATM Adaptation Layer- AAL5
• SEAL Simple and Efficient Adaptation Layer
• Assumes most sequencing and error control if
  required are provided by end system ULP

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Asynchronous Transfer Mode

• ATM Adaptation Layer- AAL5
• UU user-to user id
• T type
• L- length
• CRC - checksum

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Asynchronous Transfer Mode

• ATM layer

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Asynchronous Transfer Mode

• ATM layer
• PT payload type (3 bits) 1st bit
• User Data 0
• Management data 1
• User data
• 2nd bit 0- no congestion, 1 congestion
• 3rd bit 0 no signaling, 1 signaling bit

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Asynchronous Transfer Mode

• ATM layer
• Management data 1st bit 1
• 00 link associated
• 01 end-to-end management
• 10 resource management
• 11 reserved
• CLP cell loss priority bit
• HEC- header error correction/detection

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Asynchronous Transfer Mode

• Services supported over ATM
• CBR
• VBR
• rt, nrt
• ABR
• UBR

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Asynchronous Transfer Mode

• Utilization of bandwidth by Services

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Asynchronous Transfer Mode

• Quality of Service QoS
• User oriented
• SCR Sustained Cell Rate
• PCR Peak Cell Rate
• MCR Minimum Cell Rate
• CVDT cell variation delay tolerance

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Asynchronous Transfer Mode

• Quality of Service QoS
• Network oriented
• CLR cell loss ratio
• CTD cell transfer delay
• CDV cell delay variation
• CER Cell Error Ratio
• Traffic Descriptors

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Asynchronous Transfer Mode

• Network parameters
• Error Free Cells arriving before a specified time
  T are successfully delivered cells
• Lost cells if it arrives after time T or
  discarded, header error
• Mis-inserted cells due to wrong header
• Severely damaged cells

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Asynchronous Transfer Mode

• Allocation of resources

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Asynchronous Transfer Mode

• Traffic control
• CBR Peak cell rate pcr
• VBR pcr, scr and maximum burst size
• Burst tolerance - BT
• BT (MBS 1)/(1/SCR 1/PCR)
• Generic cell rate algorithm
• Virtual scheduling
• Continuous leaky bucket

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Asynchronous Transfer Mode

• Virtual scheduling algorithm
• Theoretical Arrival Time TAT is the expected
  arrival time
• Cell arriving before TAT L is confirming
• Cell arrival time is ta, then TAT is set to ta if
  it was a confirming cell

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Asynchronous Transfer Mode

• ATM at the UNI
• Supports symmetric and asymmetric connections
• bandwidth allocation independent in the 2
  directions
• Negotiation of QoS

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Asynchronous Transfer Mode

• ATM at the UNI
• Identification of end-to-end capabilities
• Client registration
• Address, administrative information exchange
  across the UNI
• Facilitate network administrator
• A number of messages defined to facilitate the
  above

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Asynchronous Transfer Mode

• ATM B-ICI Inter carrier interface
• Internetworking specification
• ITU-T -gt NNI based on SDH
• ATM Forum B-ICI based on SONET , DS3
• To accommodate
• Frame Relay
• Cell relay service as ATM cells
• Circuit emulation service DS1, DS3
• SMDS

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Asynchronous Transfer Mode

• Switch fabric crossbar switch

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Asynchronous Transfer Mode

• Switch fabric Knockout switch

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Asynchronous Transfer Mode

• Switch fabric Knockout switch
• To avoid collisions at switch
• Two input cells to one output
• Uses distributors and queues
• n2 crossover points still required
• n number of inputs/outputs

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Asynchronous Transfer Mode

• Switch fabric Banyan switch

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Asynchronous Transfer Mode

• Switch fabric Batcher Banyan switch

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Asynchronous Transfer Mode

• ATM Addressing
• OSI model
• Initial Domain Part IDP
• Authority Format Identifier
• DCC ATM format
• ICD ATM format
• E.164 format

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Asynchronous Transfer Mode

• ATM Addressing
• Initial Domain Identifier
• Domain Specific Part
• DFI
• AA administrative authority
• RD routing domain id
• Area
• ESI end system id
• SEL ULP entities not used in ATM network