Transcript Classical IP over ATM

371-1-0291: An Introduction to
Computer Networks
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Handout #16: IP over ATM
Lect-12-1: IP over ATM
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Motivation for IP over ATM
By now ATM has a large installed base
 Although intended to be ubiquitous, the
ATM-only dream was not realized
 ATM co-exists with many legacy networks
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legacy networks: Ethernet, Token Ring etc.
IP remains a popular internetworking solution
 Therefore, we need to know how to run IP
over ATM networks

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IP over ATM Architectures
IP machines (desktop or router) connected
to ATM networks need mechanisms to run
connectionless IP over connection-oriented
ATM
 Two standard mechanisms
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LAN Emulation (ATM Forum Solution)
Classical IP over ATM (IETF, RFC2255)
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LANE : Motivations
Quick deployment of ATM
 Makes ATM look like either Ethernet or
Token Ring
 No changes required for existing network
software
 Existing network protocols and software,
e.g. IP, IPX, AppleTalk, running on Ethernet
will also run on ATM

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LANE Address Structure
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Each host connected to a LANE
network has three addresses
IP address : needed for
internetworking
MAC address: an Ethernet or
Token Ring address to emulate
an Ethernet or a Token Ring
ATM address : physical ATM
address to locate devices in
ATM network
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IP Address
Ethernet Address
ATM Address
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LAN Emulation (LANE)

Each host runs a LAN Emulation Client (LEC); it
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does the address resolution (MAC-ATM) for the host
sets up data connections to other hosts
sets up control connections to LANE servers
Each host communicates with 3 servers
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Broadcast and Unknown Server (BUS)
LAN Emulation Server (LES)
LAN Emulation Configuration Server (LECS)
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LANE Servers
LECS
LEC
LES
LEC
BUS
LEC
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LEC
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What LANE Servers Do
Server Functions
LECS
Provides LES's ATM address and the MAC type details to
the LEC
LES
Does MAC-ATM address resolution
BUS
When a host wants to broadcast a packet, it sends it to
BUS, the BUS then forwards it all the hosts connected to
the Emulated LAN (ELAN)
IP-MAC address resolution is done by ARP servers as
usual. On top of that, MAC-ATM resolution is needed.
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LANE Sequence of Events
(LECS) Initialization
Discover LECS’s ATM address and establish
communication with the LECS
Configuration
Based upon some policy, the LECS assigns the client to a
particular LES (gives the LES’s ATM address to client)
Registration with LES
The client joins the ELAN by registering its ATM and MAC
address with the LES
(BUS) Initialization
The client obtains the BUS’s ATM address from LES. This
address is used for broadcasting.
Data Transfer
The client now can send MAC frames. Address resolution
with LES may be necessary. ATM VC setup may be req’d.
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Interoperability
Legacy LAN and LANE
Ethernet LAN
ATM-LAN
Converter
ATM LANE
Physical Scenario
Extended Ethernet
Logical Scenario
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Classical IP over ATM (CLIP)
Motivation
LANE hides ATM technology and mimics
Ethernet
 Since LANE mimics Ethernet, it inherits
Ethernet’s undesirable features
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broadcast-like competition for resources
No ATM QoS available to network layer
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CLIP Basics
CLIP treats ATM as a new link layer network
technology
 Advantages : With CLIP, the host software is
aware of ATM and makes use of ATM QoS
 Disadvantages
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Ethernet-based software will not work
CLIP is IP-only solution, (does not cover IPX etc.)
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LANE vs CLIP
Existing IP
Existing IPX
Existing Netbeui
LANE
Supports all existing software
CLIP
New IP
Cannot support any existing software,
supports only new IP software
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CLIP Components
There is only one server, called ATM ARP
Server
 Instead of using broadcasting, the IP host
communicates with this server directly
whenever it needs to resolve IP-ATM
addresses

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Classical IP Over ATM
Connecting Hosts with ARP Server
Client
ATM ARP Server
ATM ARP
Request
Reply to ARP
Request
ATM Network
Client
Client
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CLIP Sequence of Events
Registration with ARP Server
When an IP host joins a LAN, it registers its ATM and IP
addresses with the ATM ARP server
Obtain ATM addr of dest
When an IP host wants to communicate with another, it
obtains the ATM address of the dest from ARP server if it
is not in the local cache
Data Transfer
Lect-12-1: IP over ATM
The client sets up an ATM VC (if such a VC is not there)
with the destination and sends ATM cells over the VC.
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