Transcript ATM LAN Emulation

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Rivier College
CS575: Advanced LANs
ATM LAN Emulation
ATM Network
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ATM LAN Emulation
LAN
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Overview
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Why Do We Need ATM LAN Emulation?
What is ATM LAN Emulation?
Layered Protocol Architecture of Emulated LAN
Basic LAN Emulation Principles
LAN Emulation Components
LANE Conceptual Configuration
Emulated LAN Connections
LAN Emulation Operation
LAN Emulation Operation Examples
Jain
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Why Do We Need ATM LAN Emulation?
0 Permit coexistence and interoperability between ATM and legacy
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LANs
Emulate connectionless nature of shared-media legacy LANs
Support multicast/broadcast services over ATM network similar to
multicast/broadcast services over a shared-media LAN
Use an ATM network as a scaleable, high capacity, high speed, low
latency backbone network for legacy LANs
Enable existing end systems on shared-media LANs such as
Ethernet to interoperate across an ATM network
Emulate services provided by existing LANs to run across an ATM
network
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
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
LAN
ATM Network
Legacy LAN End System
ATM End System
Legacy LAN
Applications
ATM-LAN Bridge
NDIS/ODI Driver
Interface
Bridging
ATM
Physical
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NDIS/ODI Driver
Interface
LAN
Emulatio
n
LAN Emulation
AAL5
Legacy LAN
Applications
ATM Switch
MAC
MAC
ATM
ATM
Physical
AAL5
Physical
Physical
ATM LAN Emulation
Physical
Physical
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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 mode
0 An emulated LAN consists of multiple LAN Emulation Clients (e.g.,
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ATM workstations and ATM bridges) and one LAN Emulation
Service
The LAN Emulation Service includes a LAN Emulation
Configuration Server (LECS), a LAN Emulation Server (LES), and
a Broadcast and Unknown Server (BUS)
The servers may reside in the same physical system or in separate
physical systems
The clients interact with the LAN emulation service across an
interface, referred to as LAN Emulation UNI (LUNI)
LUNI makes the clients unaware of any changes to the emulated
LAN implementation
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
LES/BUS
LUNI
LECs
LUNI
ELAN 1
ATM
Switch
(Ethernet)
Token Ring
Bridge
(LEC)
LES/BUS
LECs
ELAN 2
(Ethernet)
Ethernet
Bridge
(LEC)
LECs
ELAN 3
(Token Ring)
LECS
LES/BUS
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Emulated LAN Connections
LAN Emulation Services
LAN Emulation
Configuration Server
(LECS)
Bridge
Workstation
LAN Emulation Server
(LES)
LAN Emulation
Client (LEC)
LAN Emulation
Client (LEC)
Legacy
LAN
Broadcast and
Unknown Server (BUS)
LUNI Interface
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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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LAN Emulation Operation (continued)
= 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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LAN Emulation Operation (continued)
- 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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LAN Emulation Operation (continued)
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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LAN Emulation Operation (continued)
- 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 ELAN
0 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
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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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References
W. Stalling, Local and Metropolitan Area Networks, 6th edition,
Prentice Hall, 2000, Chapter 11
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.
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