ATM

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Chapter 7
ATM
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Background

• Improvement in network media results in the
  need of new technology to provide
• higher throughput,
• higher bandwidth,
• better cost effectiveness,
• capability of using modern network technology
• e.g. fiber optic networks

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Design Goal

• To optimize the use of high data-rate
  transmission media, such as optical fiber.
• To interface with existing systems to provide
  wide area interconnectivity of the various packet
  networks.
• To have an inexpensive implementation so that
  cost is not a barrier to adoption.
• To work with the existing telecommunication
  hierarchies ( local loops, local providers, long
  distance carriers and so on ).
• To be connection oriented to ensure accurate and
  predictable delivery.
• To move as much functions to hardware as possible
  to achieve higher speed.

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ATM Characteristics

• Cell switching
• Fixed length cell (53 bytes 5 bytes overhead
  48 bytes of data)
• Statistical multiplexing
• No link-to-link flow control and error control
• Can provide guaranteed bandwidth for voice and
  video
• Can support different media
• Scalable speed (from 25 Mbps, 155 Mbps up to 622
  Mbps)

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ATM Basics

• Using Asynchronous TDM technology
• A cell switching network
• Used to support B-ISDN
• Started from WAN service providers as in B-ISDN
• Extended to include all LAN and networking vendors

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Multiplexing Using Different Packet Sizes
Multiplexing Using Cells
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ATM Multiplexing
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ATM Virtual Connection

• Transmission path (TP)
• the physical connection between an end point and
  a switch, or between two switches. A transmission
  path can be divided into several virtual paths.
• Virtual path (VP)
• provides a connection or a set of connections
  between two switches. It can be divided into a
  bundle of virtual circuits that have the same end
  points.
• Virtual circuit (VC)
• a logical connection in ATM, variable-rate, full
  duplex.

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TP, VPs, and VCs
Each cell contains a 24/28 bit connection
identifier First 8/12 bits Virtual path Last 16
bits Virtual circuit
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Connection Identifiers
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Example of VPs and VCs
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Architecture of an ATM Network
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Virtual Connection Identifiers in UNIs and NNIs
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An ATM Cell
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SVC Setup
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Routing with a VP Switch
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A Conceptual View of a VP Switch
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Routing with a VPC Switch
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A Conceptual View of a VPC Switch
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Virtual circuit connection(VCC)

• i) Circuit switching technique virtual path
  identifier (VPI)
• and virtua1 circuit identifier (VCI)
  switching
• ii) Logica1 connections in ATM
• iii) Associated with VPI and VCI , which can
  be changed
• or updated from switch to switch in the
  network
• iv) Data connection-VCC
• A connection with constant or variable rate, full
  duplex flow of fixed size cells (user
  communication data)
• v) Signaling connection
• Used in user-network exchange (control signaling)
  network-network exchange (network management and
  routing)
• vi)Normally used in private networks

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Virtual path connection(VPC)

• i) A path switching technique
• ii)A bundle of VCCs that have the same endpoints
• iii)Virtual path techniques provide benefit of
  cost control by grouping connections sharing
  common paths
• iv)VCI of a connection is not changed or updated
  from switch to switch in the network
• v) Commonly used in public networks

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VCC or VPC characteristics

• Each VCC or VPC connection is associated with
  traffic parameters or Quality of Services (QoS)
  parameters
• Bandwidth Cell Rates ( Class of Service,
  discuss later ).
• Delay Cell Transfer Delay (CTD) and Cell Delay
  Variation(CDV).
• Re1iability Cell Loss Ratio (CLR), of loss of
  cells.
• Guaranteed cell sequence integrity sequence
  of transmitted cells within VCC is preserved
  because they are connection-based.
• Traffic parameters can be negotiated between
  UNI AND NNI
• Once the connection is estab1ished, network
  will monitor usage for the connection in order to
  commit the QoS.

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ATM Layers
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ATM adaptation layer (AAL)

• Segmentation and re-assembly of upper layer
  protocol data unit (PDU) to and from 48 byte data
  payload of cell.
• Provides suitable functions for different classes
  of services (discuss later).

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ATM layer

• Cell switching
• Congestion control /buffer management
• Cell header generation / removal at source
  /destination
• Cell address translation
• Sequential delivery

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Physical layer

• Transmitting and receiving data
• Adds routing information
• Timing and synchronization

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ATM Layers in End-Point Devices and Switches
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AAL Types
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AAL1
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AAL2
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AAL3/4
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AAL5
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ATM Layer
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ATM Header
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ATM Header fields

• Virtual path identifier (VPI)
• A routing field for the network, 8 bits for UNI,
  12 bits FOR NNI.
• Virtual circuit identifier (VCI)
• Used for routing to and from the end user.
• VPI/VCI 0/5 is a defau1t signaling connection
  used to establish SVC between user-to-user.
• Payload type identifier (PTI)
• Identify the data cell or management cell

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ATM Header fields (cont)

• Cell loss priority (CLP)
• 0 relatively high priority
• 1 lower priority. It is discard eligible within
  the network under congestion
• Header Error Control (HEC)
• Error-protection function for single-bit header
  errors
• Protect header only
• Optional correction mode correct single bit
  errors
• Discard cells with bad HEC
• Recalculated at each hop

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PT Fields
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Classes of ATM traffic

• CBR Circuit emulation, voice and real
  time video, video conferencing
• VBR-RT Real time compressed voice or video
• VBR-NRT Bursty high priority data, Frame relay
  and
• ATM internetworking
• ABR Delay tolerant bursty data
• UBR Low priority bursty data, e-mail
• application and broadcast messages

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Service Classes
User can specify a class of service based on the
application need. An ATM connection can be set up
based on this request if the network have the
resources available. Class of Service (or QoS
parameters) can be specified by signaling for SVC
establishment or manually specified and created
by user for PVC establishment.
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Service Classes and Capacity of Network
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QoS
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ATM Applications

• WAN
• as a high-speed WAN service to provide support
  for multi-media transmission
• LAN
• LAN backbone
• Workgroup LAN switch
• Needs to use LAN emulation services for
• broadcast services
• learning new devices / services
• virtual LAN services

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ATM WAN
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Ethernet Switch and ATM Switch
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LANE Approach
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LEC, LES, and BUS