Asynchronous Transfer Mode

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ATM
Asynchronous Transfer Mode
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Definition
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Definition

• A new Technology
• Fixed size packets called CELLS
• Streamlined minimal error and flow control
• Small cells compared to other technologies
• High speed multimedia networking carry traffic
  at a speed up to 622Mbps
• ATM Standards are done Primarily by the ATM
  Forum Cisco systems, NET/ADAPTIVE, Northern
  Telecom, and Sprint in 1991.

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End of Module
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ATM Architecture WAN LAN
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Common LAN/WAN Architecture allowing ATM to be
used consistently from one desktop to another.
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WAN
DS-3 ATM PROBE and OC-3 ATM PROBE have a job of a
router
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ATM Architecture
Multiple switches and interfaces connecting ATM
devices
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ATM Architecture

• Two Types of Interfaces that interconnect ATM
  devices
  
  over point to point
  links
• User-Network Interface (UNI)
• Network-Network Interface (NNI)
• Third Type of Interface connect two public
  switches from different public networks
• Broadband Inter-Carrier Interface (BICI)

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ATM Architecture

• User-Network Interface

• UNI link connects an ATM end-system (client side)
  with an ATM switch (network site).
• ATM UNI standards specify how a user connects to
  the ATM network to access these services.

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ATM Architecture

• Network-Network Interface

• Also called Network Node interface (NNI).
• NNI link connect two ATM switches in this case
  both sides are network.
• NNI supports class of service-sensitive routing
  and bandwidth reservation.
• Parameters used as part of the path computation
  process include the destination ATM address,
  traffic class, traffic contract, QoS requirements
  and link constraints.
• (quality of service will be discussed later)

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ATM Architecture

• UNI and NNI are further subdivided into public
  and private UNIs and NNIs depending
  on the location and ownership of the ATM switch.

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ATM Architecture

• A private UNI connects an ATM endpoint and
  private ATM switch.
• A private NNI connects two ATM switches within
  the same private network.

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ATM Architecture
ATM Architecture
A router with an ATM interface processor (AIP)
can be connected directly to the ATM switch,
while the router without the ATM interface must
connect to an ATM data service unit (ADSU) and
from there to the ATM switch.
With AIP
Without AIP
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ATM Architecture

• A public NNI connects two ATM switches within the
  same public network.
• a public UNI connects an ATM endpoint or private
  switch to a public switch.
• A third type of interface, the Broadband
  Inter-Carrier Interface (BICI) connects two
  public switches from different public networks.

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End of Module
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ATM Fixed Length Cells
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ATM Cell

• Fixed Size
• 5 bytes header
• 48 bytes information field
• small cells reduce delay for high priority cells,
  and transfer video and audio faster
• fixed size facilitates switching in hardware
  carries payload-type information, virtual-circuit
  identifiers, and header error check.

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ATM Cell
Name of Part Length Description
Flow Control 4 bits Information Related to Flow Control
VPI 8 bits Whole connection is identified by VPI
VCI 16 bits When ATM creates physical connection, connection is identified by VCI.
Payload Type 3 3 bits Data Type Video, Sound
HEC/CRC 8 bits Error Control when needed
Priority 1 bit Priority of that cell
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ATM Cell
The ATM Cell includes 5 Bytes Header the header
can be in either UNI or NNI format depending on
the Interface.
ATM Cell HeaderUNI Format
ATM Cell HeaderNNI Format
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ATM Cell

• General Flaw Control Provides local functions,
  such as flow control from end point equipment to
  the ATM switch.
• Payload Type Indicates in the first cell whether
  the cell contains user data or control data.
• If the cell contains user data, the second bit
  indicates whether congestion is experienced or
  not, and the third bit indicates whether the cell
  is the last in a series of cells that represent a
  single AAL5 (ATM adoption layer 5) frame.
• If the cell contains control data, the second
  and third bits indicates maintenance or
  management flow information.

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ATM Cell

• Cell Loss Priority Indicates whether the cell
  should be removed if it encounters errors as it
  moves through the network.
• Header Error Control Contains Cyclic Redundancy
  Check (CRC) on the cell header.
• Virtual Path Identifier (VPI) Identifies
  semi-permanent connections between ATM end
  points.
• Virtual Channel Identifier (VCI) Have only local
  significance on the link between ATM nodes.

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ATM Cell

• ATM is essentially a packet switched network with
  packets called cells.
• ATM Cells are switched, based on a Virtual Path
  Identifier (VPI), and Virtual Channel Identifier
  (VCI).
• A connection in an ATM network is achieved by
  tying together a series of VPIs/VCIs at multiple
  Interfaces.

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End of Module
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ATM Protocol Architecture
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ATM Protocol Model
ATM Protocol Model has 3 planes

1. User
2. Control
3. Management

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ATM Protocol Model
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ATM Services
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ATM Services

• There are three general ATM services
• Permanent Virtual Connection (PVC)
• Leased Line
• Switched Virtual Connection (SVC)
• Telephone call
• Connectionless Service

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ATM Services
Type of Service Advantages Disadvantages
PVC The guaranteed availability of connection Static connectivity and that they require manual administration to set up
SVC Connection flexibility Extra time and overhead required to set up the connection
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QoS Quality of Service
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ATM QoS

• Short for Quality of Service
• A networking term that specifies a guaranteed
  throughput level
• One of the biggest advantages of ATM over
  competing technologies such as frame relay and
  fast Ethernet
• It allows ATM providers to guarantee to their
  customers that end-to-end latency will not exceed
  a specified level

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ATM QoS

• ATM Provides the following QoS
• Constant Bit Rate (CBR)
• Variable Bit Rate (VBR)
• Unspecified Bit Rate (UBR)
• Available Bit Rate (ABR)

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ATM QoS
Constant Bit Rate (CBR)

• A quality service
• unchanged amount of bandwidth to the virtual
  channel
• specially suitable for voice-over-IP (Transfer
  fixed rate uncompressed video), and other traffic
  that requires steady, guaranteed throughput

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ATM QoS
Variable Bit Rate (VBR)

• B quality service
• Provides bandwidth only as needed up to a
  specified maximum rate
• specially suitable for LANs and bursty data
  traffic such as transmitting compressed video or
  audio to the end user

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ATM QoS
Available Bit Rate (ABR)

• C quality service
• Adjust the amount of bandwidth based on the
  amount of traffic in the network
• Aimed at data traffic such as file transfer and
  Email

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ATM QoS
Unspecified Bit Rate (UBR)

• D quality service
• Does not have any traffic parameters does not
  specify the bandwidth for the PVC
• When enable PVC for UBR, the PVC uses the cell
  left over CBR or VBR
• The only limit to UBR is the total bandwidth of
  the port

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End of Module
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Summary

• ATM is a new WAN and internet backbone
  technology.
• ATM high performance due to, small fixed cells,
  Packet switched, multiple QoS
• Small cells reduce delay for high priority cells,
  and transfer video and audio faster at a speed up
  to 622 Mbps
• ATM cell is 53 bytes, 48 bytes information field
  and 5 bytes header
• ATM Protocol Model has 3 planes User, control,
  and management
• ATM has multiple QoS CBR, VBR, ABR, UBR

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Thank you
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Sources
Online Education Internationa Engineering
Consortium. April 20,2003. www.iec.org/online/tuto
rials/atm_fund/index.html Trinity University.
April 20, 2003. www.trinity.edu/rjersen/245
glosf.html www.webopedia.com Searchable
glossary dictionary Glossarist. April
25,2003,www.glossarist.com/gsearch.asp A
Configurable Visualization and Simulation Tool
for ATM Switches VISTA, April 25,2003.
ltvip.cs.utsa.edu/systems/pubs/nrtthesis.htmlgt A
TM Technology Fundamentals CISCO Sys Inc. Jan
22,2003, April 29,2003 ltwww.cisco.com/univercd/c
c/td/doc/product/atm/c8540/12-0/13- 19/atg/basics.
htm1020131gt George C. Sackett,
Christopher Metz, "ATM and Multiprotocol
Networking," McGraw- Hill,
January 1997 pages 10-15 David E.
McDysan, Darren L. Spohn, "ATM Theory and
Applications," McGraw-Hill,
September 1998 Pp23