ATMAsyncronous Transfer Mode

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ATM(Asyncronous Transfer Mode)

• Erdem Üçüncü
• Önder Atli
• Salahattin Sami Güzel

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What is ATM?

• Cell relay which is regarded one of the
  packet-switching technology is used by ATM for
  high-speed transfer of voice, video and data
  through public and private networks.
• ATM uses 53 bytes.(48b for payload, 5b for
  header)
• It is connection oriented

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The advantages of ATM

• Small Packets
• Flexible and suitable for both transmission and
  switching
• ATM provides low latency and very high quality of
  service for audio and video streams
• Dynamic bandwith

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The advantages of ATM(cont.)

• ATM supports common LAN/WAN architecture
• Opportunities for simplification via switched VC
  architecture in billing, traffic management,
  security and configuration management.

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The disadvantages of ATM

• Management and troubleshooting tools are young
• Protocols are very complex and still in
  development
• Developing ATM equipment and applications is slow
  and expensive

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ATM Devices and the Network Environment

• Using asynchronous technology makes ATM more
  efficient than synchronous technologies
• ATM Cell Basic Format
• Fixed-size cell which consists of 53
• The first 5 bytes contain header information
• The rest, 48 bytes contain the data

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ATM Devices and the Network Environment(Cont.)

• The size of a unit of data is not needed to be
  detected
• The delays could be eradicated using small packets

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ATM Device Types

• One or more ATM switches and endpoints are used
• ATM network interface adapter is included in ATM
  endpoint such as LAN switches

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ATM Network Interface Types

• Two network interface types which are UNI and NNI
• The UNI connects ATM end systems (such as hosts
  and routers) to an ATM switch
• NNI connects two ATM switches
• Public and private NNIs and UNIs
• Depends on the ownership and location of an ATM
  switch

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Public and Private NNI and UNI
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ATM Cell Header Formats

• Consist of 5-byte header
• It can be either UNI or NNI format
• UNI has six fields which are GFC, VPI, VCI,
  Payload Type, Cell Lost Priority and Header Error
  Control

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ATM Services

• Two types of ATM services which are permanent
  virtual circuits (PVC), switched virtual circuits
  (SVC).
• In PVC (permanent virtual circuit), virtual
  circuit is established during configuration
  process. It is not cancelled
• In SVC the virtual circuits are established
  before the communication and virtual circuits are
  cancelled after the communication

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ATM Virtual Connections

• Prior to data transfer, virtual channel must be
  established
• Virtual path identifiers (VP) and virtual channel
  identifier (VC)
• VC is identified by VCI included in ATM cell
  header
• VP is identified by VPI included in the ATM cell
  header

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Switching Operations

• An ATM switch has a straightforward job
• checks the incoming cell
• perform a replication step for point-to-multipoint
  connections
• number of modifications is made to the
  cell(VPI/VCI translation, setting the Early
  Forward Congestion Indicator (EFCI) bit, setting
  the CLP bit)

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The ATM Referance Model
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The ATM Referance Model (Cont.)

• Physical layer The ATM physical layer manages
  the medium-dependent transmission.
• ATM The ATM layer is responsible for cell
  multiplexing and passing cells through the ATM
  network (cell relay).
• ATM adaptation layer (AAL) The AAL is
  responsible for isolating higher-layer protocols
  from the details of the ATM processes.

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The ATM Referance Model (Cont.)
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ATM Addressing

• subnetwork or overlay model of addressing The
  ATM layer is responsible for mapping network
  layer addresses to ATM addresses.
• network service access point (NSAP) addresses
  address format based on the structure of the OSI
  

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Point-to-Point and Point-to-Multipoint
Connections

• Point-to-point connects two ATM end systems and
  can be one-way communication or two-way
  communication.
• Point-to-multipoint connects a single-source end
  system (known as the root node) to multiple
  destination end systems (known as leaves).

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ATM and Multicasting

• AAL layer does not support multicast
• To realize multicasting there are 3 solutions
• VP multicasting
• multicast server
• overlaid point-to-multipoint connection

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ATM Signaling and Connection Establishment

• The ATM Connection-Establishment Process
• the source end system sends a connection-signaling
  request
• the connection request is propagated through the
  network
• connections are set up through the network
• connection request reaches the final destination

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ATM Signaling and Connection Establishment(Cont.)

• Connection-Request Routing and Negotiation
• Governed by ATM routing protocol (Private
  Network-Network Interface PNNI)
• Negotiating a connection request that is rejected
  by the destination is limited

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ATM Signaling and Connection Establishment(Cont.)
ATM Devices Establish Connections through the
One-Pass Method
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ATM Connection-Management Messages

• Manages ATM networks
• A number of connection-management message types
• including setup, call proceeding, connect, and
  release, are used to establish and tear down an
  ATM connection
• The source end system sends a setup message

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Connection-management messages (cont.)

• Source end system sends a setup message, which is
  forwarded to the first ATM switch (ingress
  switch) in the network
• The signaling request is propagated across the
  network

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Connection-management messages (cont.)

• The exit switch (called the egress switch)
  receives the message
• The egress switch (exit switch) forwards the
  message to the end system
• ATM end system sends a connect message if the
  connection is accepted

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Connection-management messages (cont.)

• The connect message traverses back through the
  network along the same path to the source end
  system
• Data transfer can then begin

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PNNI (private network to network interface)

• PNNI is the ATM routing protocol that enables
  switches to automatically discover the
• topology
• characteristics of the links interconnecting the
  switches

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PNNI (private network to network interface)

• PNNI provides two significant services
• ATM topology discovery
• call establishment
• For switches to build connections between end
  points, the switch must know the ATM network
  topology

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PNNI (private network to network interface)

• When a significant event occurs, PNNI announces
  the change to the other switches
• When a station sends a call setup request to its
  local switch, the ingress switch references the
  PNNI routing table to determine a path

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Designated Transit List

• The switch attached to the source then builds a
  list defining each switch hop to support the
  circuit to the destination
• DTI is a list of nodes that completely specify a
  path across a single PNNI peer group.

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Integrated Local Management Interface

• Local Management Interface (LMI) is a signaling
  standard used between routers and frame relay
  switches
• ILMI enables devices to determine status of
  components at the other end of a physical link

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LAN Emulation

• LAN Emulation (LANE) is a standard that gives to
  stations attached via ATM the same capabilities
  that they normally obtain from legacy LANs, such
  as Ethernet and Token Ring.

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Multiprotocol over ATM

• Multiprotocol over ATM (MPOA) provides a method
  of transmitting data between ELANs without
  needing to continuously pass through a router

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Multiprotocol over ATM

• Normally, data passes through at least one router
  to get from one ELAN to another
• MPOA, however, enables devices in different ELANs
  to communicate without needing to travel hop by
  hop

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Questions

• What is the primary difference between the UNI
  and NNI? What is the difference between their
  header?
• Describe the difference between PVC (Permanent
  Virtual Connection) and SVC (Switched Virtual
  Connection)?
• What is the purpose of the adaptation layer? Give
  two examples of AAL layers.
• What is the difference between ATM and other
  technologies that uses packet switching such as
  IP and Ethernet?

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References

• http//www.iec.org/online/tutorials/atm_fund/index
  .html
• http//en.wikipedia.org/wiki/Asynchronous_Transfer
  _Mode
• http//www.cisco.com/univercd/cc/td/doc/cisintwk/i
  to_doc/atm.htm
• http//www.cisco.com/univercd/cc/td/doc/product/at
  m/c8540/12_1/pereg_1/atm_tech/index.htm