Rivier College CS575: Advanced LANs ATM LAN Emulation

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1ATM LAN EmulationCS575

Rivier College

CS575: Advanced LANs

ATM LAN Emulation

ATM Network LAN

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Overview

0 Why Do We Need ATM LAN Emulation?0 What is ATM LAN Emulation?0 Layered Protocol Architecture of Emulated LAN0 Basic LAN Emulation Principles0 LAN Emulation Components0 LANE Conceptual Configuration0 Emulated LAN Connections0 LAN Emulation Operation0 LAN Emulation Operation Examples

Jain

CS575 ATM LAN Emulation 3

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Why Do We Need ATM LAN Emulation?

0 Permit coexistence and interoperability between ATM and legacy LANs

0 Emulate connectionless nature of shared-media legacy LANs0 Support multicast/broadcast services over ATM network similar

to multicast/broadcast services over a shared-media LAN 0 Use an ATM network as a scaleable, high capacity, high speed, low

latency backbone network for legacy LANs 0 Enable existing end systems on shared-media LANs such as

Ethernet to interoperate across an ATM network0 Emulate services provided by existing LANs to run across an

ATM network0 Applications and higher layer protocols built on top of the

connectionless IEEE 802’s MAC layer and run on legacy LANs will run on connection-oriented ATM network

0 Provide a migration path towards ATM-based LANs


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What is Emulated LAN?

0 An emulated LAN comprises a group of ATM-attached end systems

0 This group of end systems would be analogous to a group of LAN stations attached to an Ethernet/IEEE 802.3 or Token Ring/IEEE 802.5 LAN segment

0 Each end system on an emulated LAN must have a unique MAC address

0 Data interchange between end systems on the same emulated LAN involves the use of the MAC protocol and is transparent to the upper layers

0 An end system on a legacy LAN may exchange data with an end system attached directly to an ATM network

0 The ATM end systems must include a LAN emulation layer that emulates the MAC layer

0 A bridge is required to connect legacy LAN to ATM network


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What is Emulated LAN (concluded)

0 The bridge logic must be augmented by the capability of converting MAC frames to and from ATM cells

0 Several emulated LANs (ELANs) could be configured within an ATM network

0 Membership in an emulated LAN is independent of where an end station is physically connected

0 An end system could belong to multiple emulated LANs

0 A broadcast frame originating from a member of a particular emulated LAN is distributed only to the members of that emulated LAN

0 Communication between end systems on different emulated LANs is possible only through a router

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Layered Protocol Architecture

Physical

MAC

Physical

MAC

NDIS/ODI DriverInterface

Legacy LANApplications

Legacy LAN End System

ATM

AAL5

LANEmulati

on

Bridging

ATM-LAN Bridge

ATM End System

Physical

ATM

AAL5

LAN Emulation

NDIS/ODI DriverInterface

Legacy LANApplications

Physical

ATM

Physical

ATM Switch

Physical

ATM Network LAN


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Basic LAN Emulation Principles

0 The basic operation of LANE is to set up a point-to-point ATM connection between two ELAN end systems for data transmission

0 Before an ATM connection can be established, it is necessary to resolve destination MAC address to destination ATM address

0 A LAN emulation layer implemented in the ATM end system emulates the MAC layer of the legacy LAN

0 It communicates with application software through existing MAC drivers such as NDIS or ODI in such a way as if the applications were communicating with legacy LAN’s MAC layer

0 The LAN emulation layer hides the lower layer ATM and its complexity of setting up connections from higher layer applications

0 It makes the point-to-point ATM connections look and behave like a shared-media LAN to higher layer protocols such as IP, IPX, or AppleTalk


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LAN Emulation Components

0 LAN emulation operates in a client-server mode0 An emulated LAN consists of multiple LAN Emulation Clients (e.g.,

ATM workstations and ATM bridges) and one LAN Emulation Service

0 The LAN Emulation Service includes a LAN Emulation Configuration Server (LECS), a LAN Emulation Server (LES), and a Broadcast and Unknown Server (BUS)

0 The servers may reside in the same physical system or in separate physical systems

0 The clients interact with the LAN emulation service across an interface, referred to as LAN Emulation UNI (LUNI)

0 LUNI makes the clients unaware of any changes to the emulated LAN implementation

0 LAN Emulation Client (LEC)- An end system (host, bridge, or router) on an emulated LAN


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LAN Emulation Components (continued)

- Represents one or more end users, identified by their MAC addresses

- The LAN emulation software (LAN emulation layer) provides a MAC level emulated 802.3 or 802.5 interface to higher level protocols, such as IP, or IPX

- Performs address translation (between MAC addresses and ATM addresses), address resolution, data forwarding, and other control functions

0 LAN Emulation Configuration Server (LECS)

- A component of the LANE service, responsible for initial configuration of LECs

- Provides configuration information to LECs prior to joining the emulated LAN

- Responsible for the assignment of individual LECs to different ELANs based on administrative policies


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LAN Emulation Components (Continued)

- Provides the LES’s ATM address to LEC

- One LECS serves one network that consists of many ELANs

0 LAN Emulation Server (LES)

- A component of the LANE service, implements control and coordination functions for the ELAN

- Controls the joining of LECs to its ELAN

- Provides registration service to LECs

- An LEC registers its MAC and ATM addresses with the LES

- Responsible for address resolution from MAC address to ATM address

- Has unidirectional point-to-point VCs for ARP data coming from LECs and unidirectional point-to-multipoint VCs for ARP data going to LECs

- Each ELAN has one LES


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LAN Emulation Components (continued)

0 Broadcast and Unknown Server (BUS) - A component of the LANE service, used by an LEC to forward

frames to broadcast/multicast addresses- Also used by an LEC to send unicast frames to all clients before

the destination is known - All broadcast, multicast, and unknown traffic to and from an

LEC passes through this single entity- The multicast server function provided in the BUS is required

as part of LANE to provide the connectionless data delivery characteristics of a shared-media network to LECs

- Has unidirectional point-to-point VCs for data coming from LECs

- Has unidirectional point-to-multipoint VCs for data going to LECs

- Each ELAN has one BUS


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LAN Emulation Components (concluded)

- Must always exist in the ELAN- All LECs must join its distribution group

0 Bridge- To connect legacy LANs (802.3 and 802.5) to the emulated LAN- To implement features required in the LUNI interface to

support both transparent and source routing bridging

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LAN Emulation Conceptual Configuration

LUNILUNI

ATMSwitch

LECS

(Ethernet)

LECs

ELAN 1

LES/BUS

(Ethernet)ELAN 2

LECs

LES/BUS

(Token Ring)

LECs

ELAN 3

LES/BUS

Token Ring

Bridge(LEC)

Ethernet

Bridge(LEC)


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Emulated LAN Connections

Workstation

LAN Emulation

Client (LEC)

Bridge

LAN Emulation

Client (LEC)

LegacyLAN

LAN EmulationConfiguration Server (LECS)

LAN Emulation Server(LES)

Broadcast and Unknown Server

(BUS)

LUNI Interface

LAN Emulation Services

Control Connection

Data Connection


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LAN Emulation Operation

0 The following are the functions of LANE operation

- Initialization

- Joining and Registration

- Address Resolution

- Data Transfer

0 Initialization

- The main goal of the initialization procedure is to reduce the required manual configuration of LEC when it first joins an ELAN

- Ideally, all configuration and initialization is done automatically without human interaction (plug-and-play)

- This is achieved by using LECS

- The LECS contains all the information required by an LEC such as


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LAN Emulation Operation (continued)

=The ATM address of its LES

=LAN type (Ethernet or Token Ring) to be emulated

=Maximum data frame size (1516, 4544, 9234, or 18190)

=Name of the emulated LAN (Engineering/Marketing)

- Prior to joining the emulated LAN, an LEC (after power-up) uses the following order to locate the LECS

=Get the LECS address via ATM Forum defined Interim Local Management Interface (ILMI) procedure which takes place between the LEC and the ILMI software in the switch

=If the ILMI procedure fails, use the well known LECS address defined by the ATM Forum’s LANE standards

=If the well known address fails, use the ATM Forum defined LECS PVC (VPI = 0, VCI = 17)

- LECS connection


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=Once the location of LECS is known, the LEC establishes a configuration Direct VCC to the LECS

- Configuration

=Once a connection is established between the LEC and the LECS, the LEC is configured automatically with the information provided by the LECS

0 Joining and registration

- To join an ELAN, LEC establishes a bi-directional point-to-point Control Direct VCC to its LES

- Transmits join request with ATM address, MAC address, proxy indication (workstation or bridge) to LES

- If the LEC is a proxy for a number of end systems on a legacy LAN (a bridge), it sends a list of all MAC addresses on the legacy LAN


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- This information will be used by the LES to perform address resolution functions.

- If accepted, LES responds with a join response indicating acceptance=Then a Control Distribute point-to-multipoint VCC is established

from LES to LEC used for address resolution functions=LES provides LEC with the ATM address of the BUS=LEC creates a bidirectional multicast send VCC to BUS =LEC accepts a unidirectional multicast forward VCC from BUS =At this point, the LEC is registered and ready to transfer data


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0 Data Transfer

- Once a client is registered, it is able to send and receive MAC frames

- There are three cases to consider:

=Unicast MAC frame, ATM address known

=Unicast MAC frame, ATM address unknown

=Multicast or broadcast MAC frame

- If the client knows the ATM address of the unicast frame (in its internal cache), it checks whether it has a virtual data connection already established to the destination client

- If so, it sends the frame over that connection (as a series of ATM cells)

- Otherwise, it uses the ATM signaling to set up a connection and then sends the frame


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- If the destination ATM address is unknown, the LEC asks LES for address resolution

- While waiting, the LEC transmits frame(s) via BUS- When an LES response is received, the LEC establishes a direct

connection with the destination - Connections are timed out on inactivity - If the MAC frame is a multicast or broadcast frame, the LEC

sends the frame to the BUS - The BUS replicates that frame and sends it over the virtual data

connections to all clients on the ELAN0 Address Resolution

- In ELAN, the destination stations are usually known by their MAC addresses

- Only ATM addresses can be used for connection set up in the ATM network


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LAN Emulation Operation (concluded)

- LES allows LECs to request the resolution of a target MAC address into ATM address to to be used to establish a direct VCC to the target end system

- For MAC group address, a single ATM address is returned as the root of a point-to-multipoint VCC for the support of multicast service


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LAN Emulation Operation Examples

0 Example 1:

- LEC A wants to send a unicast message to LEC B- If LEC B’s ATM address is not in LEC A’s cache, LEC A issues

an LE_ARP to LES requesting an ATM address corresponding to LEC B’s MAC address

- If the LES finds LEC B’s ATM address in its table, it is returned to LEC A; otherwise, LES broadcasts a message to all LECs on the network to find LEC B’s ATM address

- LEC A enters LEC B’s ATM address in its address table and establishes a VCC to LEC B

- Message is sent to LEC B via that VCC- The VCC is also stored in the table and used for future

communications with LEC B


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LAN Emulation Operation Examples (continued)

0 Example 2- LEC A wants to send a unicast message to LEC B- There is no direct VCC between LEC A and LEC B- LEC A sends unknown frame to BUS- BUS has a point-to-multipoint SVC to all members of the ELAN- BUS retransmits frame on point-to-multipoint SVC- ATM infrastructure replicates cell stream at branching points- Once LEC A knows LEC B’s ATM address (may be via address

resolution), LEC A establishes a direct SVC to LEC B- LEC A then sends a “Flush” frame to BUS- Once flush is ACKed, BUS is no longer used


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LAN Emulation Operation Examples (concluded)

0 Example 3- LEC A wants to send a message to a client C attached to a

legacy LAN- Client C’s ATM address is not in the cache (it has no ATM

address)- LEC A issues an LE_ARP to LES requesting an ATM address

corresponding to Client C’s MAC address- Client C’s ATM address is not in LES’s address table (of course

not), LES forwards the LE ARP on Control Distribute VCC to all LECs, including all bridges

- The bridge that has client C’s MAC address in its address table will respond to the LE ARP with its own ATM address

- LEC A will establish a VCC with the bridge to carry all unicast traffic between them


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W. Stalling, Local and Metropolitan Area Networks, 6th edition, Prentice Hall, 2000, Chapter 11

References

W. Stalling, Data and Computer Communications, 6th edition, Prentice Hall, 2002, Chapters 11-12

A. Wu, Advanced Local Area Networks, Lectures & Slides, Rivier College, 2001.

Documents

Rivier College CS575: Advanced LANs ATM LAN Emulation