ATM LAN Emulation

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ATM LAN Emulation

• Ezra Miksic
• Will Plishker
• Steve Schneider

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Purpose of LANE

• An Emulated LAN is a LAN implemented with a
  service on a non-traditional network instead of
  the LANs traditional medium
• Many networks and applications are founded on the
  functionality provided by LAN (IEEE 802)
• LANE provides for a way in which ATM and LAN to
  work together
• Allows for greater efficiency and scalability due
  to the power of ATM
• IS and IT Professionals are not willing to scrap
  existing LANs

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History of LANE

• Brief overview of LAN
• Brief overview of ATM
• Beginnings of LANE

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Local Area Networks

• Grew to being a key business tool within the past
  15-20 years
• Links computers and other devices within a small
  geographic area quickly
• Can also be interconnected within campus of
  buildings to extend connectivity
• Popular because they permit the sharing of vital
  computing resources electronically

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Local Area Networks

• Most widely used LAN technology in use is
  Ethernet
• Defined in IEEE 802.3
• First experimental Ethernet system was developed
  in the early 1970s
• September 1980 - Version 1.0 of the first
  Ethernet specification released

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LANs ATMs

• Internetworking - three devices bridges,
  routers, and switches
• ATM grew from ISDN
• ATM LANs as the combination of these ideas
• Problems- interoperability of end systems.
  Solution LANE

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ATM LAN Emulation

• ATM Forum
• Jan 1995 - LAN Emulation over ATM 1.0, specifies
  the standards of LANE V1.0.
• Sept 1995 - LAN Emulation Client Management
  Specification
• Dec 1995 - LANE 1.0 Addendum
• Mar 1996 - LANE Servers Management Spec v1.0
• July 1997 - LANE V2.0

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Problems

• ATM Networks use ATM addresses while Stations
  only know MAC addresses
• ATM Networks are based on connection-oriented
  services, while LAN MAC protocols are based on
  connectionless service.
• Multicasting is a service easily accommodated by
  a shared medium, but not by an ATM network.

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Players

• LAN Emulation Client (LEC)
• Imbedded within network devices
• Handles data forwarding and address resolution
• Main function providing MAC connectionless
  service to higher layers
• LAN Emulation Server (LES)
• Handles address resolution and control
  information
• Registers and resolves MAC addresses to ATM
  addresses

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Players

• Broadcast and Unknown Server (BUS)
• Carries broadcast or multipoint data
• LAN Emulation Configuration Server (LECS)
• Dynamically assigns different LECs to different
  emulated LANs
• provides the clients with the address of the most
  appropriate LES
• maintains a database of the resultant
  associations

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Basic Network Setup
LES
Control direct VCC
Control direct VCC
Control distribute VCC
LEC
LEC
Data Direct VCC
Multicast forward VCC
Multicast send VCC
Multicast send VCC
BUS
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Providing for Connectionless Service

• Server-based Methods
• Connectionless servers are dedicated to the
  transmission of connectionless packets
• Short Addresses
• 2 byte header is added to each cell, while the
  normal ATM address is set to a value
  corresponding with connectionless
• Connection-based Methods
• A VCC is setup for every transmission

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Frame Formats

• Supports IEEE 802.3 (Ethernet) frames and IEEE
  802.5 (Token Ring)
• In both cases it appends a 2 byte header to the
  normal frame for the LEC ID and strips the Frame
  Check Sequence field (FCS)
• Only two are supported due to incompatible LANs
• Due to a compromise between supporting all MAC
  formats with only one

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Frame Format
Ethernet
Token Ring
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Unknown Frames

• Frames sent to the BUS when the ATM address has
  not yet been resolved
• Types of BUSes for handling Unknown Frames
• Broadcast BUS (B-BUS)
• Intelligent BUS (I-BUS)
• After a broadcast, LECs may filter out frames by
  examining the LEC ID which was appended to the
  frame.

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Stacks of LANE Components
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Exchanging User Data

• Primitives for Higher Layer to communicate with
  the LEC
• LE_UNITDATA.request (destination_address,
  source_address, routing_information if
  applicable, frame type if applicable, data,
  priority if applicable)
• LE_UNITDATA.indication (destination_address,
  source_address, routing_information if
  applicable, frame type if applicable data,
  priority if applicable, service class if
  applicable)

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Logical LANs vs Physical LANs

• The same ATM network can be used to support
  multiple emulated LANs
• There must be a LES/BUS pair for each Logical LAN
• Bridges can provide ATM connections for a legacy
  LAN by mapping all of the MAC addresses behind it

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LAN Emulation In Action

• An example to better understand LANE
• Initialization Finding the LECS
• Configuration
• Joining an Emulated LAN
• Registration and BUS initialization
• Managing ATM Broadcasts

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Finding the LECS

• Client needs ATM address of LES
• Four options for locating the LECS
• Use a "well-known address," conceptually an
  address like 1-800-FIND-LECS.
• Send Interim Local Management Interface (ILMI)
  messages to its ATM switch.
• Use a predefined VCC.
• LECS can be bypassed completely by configuring
  the ATM address of a LES in the LEC.

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Configuration

• LEC sets up a connection and forwards its
  information
• ATM address, MAC address, LAN type, maximum frame
  size
• LECS responds with
• Actual LAN type, Actual maximum frame size, ATM
  address of a LES

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Configuration
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Joining an Emulated LAN

• LEC sets up control connection to LES
• LEC issues JOIN REQUEST to LES
• LES sends back JOIN RESPONSE indicating
  acceptance or rejection

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Registration and BUS initialization

• LEC registers its MAC address and associated ATM
  address with the LES
• LES assigns the client an LEC ID
• LEC now can resolve MAC addresses to ATM
  addresses
• LEC needs BUS ATM address.
• LEC sends message to the LES requesting the ATM
  address associated with the broadcast address
• LES responds with ATM address of the BUS
• LEC sets data connection to the BUS

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Data Transfer

• LEC sets up a VCC to the BUS
• BUS in turn observes the ATM address of the
  client
• BUS participates in forwarding of unicast and
  broadcast/multicast messages
• A LEC can use BUS connection to broadcast unicast
  frames to all stations on emulated LAN
• LES locates unknown ATM address of intended
  receiver and performs the necessary handshaking
  operations to establish the data-direct
  connection

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Managing ATM Broadcasts

• When LEC receives MAC data frame leading bit of
  the destination MAC address indicates whether
  packet unicast or broadcast/multicast
• Leading 1 indicates broadcast/multicast message
• Zero indicates a unicast message
• LEC immediately passes broadcast/multicast frames
  to BUS via VCC established initially (1)
• BUS forwards message to all LECs on the emulated
  LAN (2)
• If BUS receives two broadcast or multicast frames
  simultaneously, it buffers one briefly and sends
  other out
• AAL5 allows LEC to reassemble one data frame at a
  time on single VCC

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Managing ATM Broadcasts
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Data-Direct VCCs and Unicast Frames

• When LEC receives unicast data frame for
  transmission LEC checks its local tables to
  identify ATM address associated with MAC address
• If ATM address is unknown LEC cannot immediately
  set up a data-direct connection to target
• LEC has three options
• Throw the frame away but start resolution of MAC
  address to ATM address
• Hold onto frame until it learns the ATM address
  of the target and set up VCC
• Forward frame to BUS

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Alternatives and Improvements

• Multiprotocol over ATM (MPOA)
• Virtual Local Area Networks
• LANE 2.0

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Multi Protocol Over ATM

• LANE inter-subnet traffic needs to go through
  routers
• MPOA essentially allows direct communication
  without requiring routers
• Goal - efficiently transfer inter-subnet unicast
  data in a LANE environment
• MPOA also can locate the optimal exit from the
  ATM cloud
• MPOA also ensures interoperability with the
  existing infrastructure of routers

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Virtual LAN

• Are a logical segmentation within a device
• Can create workgroups based on function
• VLANs give the added benefit of security
• Are easily modified
• However, current implementation is
  non-standardized

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LANE 2.0

• Supersedes LANE 1.0
• Provides enhanced capabilities like LLC
  Multiplexing for VCC sharing
• LANE Network-Network Interface (LNNI)

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Questions and Answers