Methods of ATM Internetworking What is LAN Emulation

Methods of ATM Internetworking

What is LAN Emulation? l Lan Emulation provides for: – – all existing LAN applications to run over ATM the use of ATM as a backbone to interconnect existing “legacy” LANs the interconnection of ATM-attached servers/workstations to each other and to those on “legacy” LANs multiple Emulated LANs which are logically separate, to use the same physical ATM network Ethernet Token Ring ATM Network Ethernet Token Ring

Physical and Emulated LANs

Scenario 1 l An ATM network interconnecting multiple Ethernet segments and ATM-attached end-systems – – – Ethernet to ATM to ATM Ethernet Bridge Ethernet ATM Network ATM-attached stations Bridge

Scenario 2 l An ATM network interconnecting multiple Token-Ring rings and ATM-attached end-systems – – – Token Ring to ATM to ATM Ring Bridge Ring ATM Network ATM-attached stations Bridge

LAN Emulation Protocol Stack ATM Host ATM Switch ATM-LAN Bridge LAN Host Existing Applications IP IP NDIS/ODI Driver I/f Bridging LAN Emulation MAC AAL 5 LAN Emulation AAL 5 ATM Physical Layer NDIS/ODI Driver I/f ATM Physical MAC Physical Layer

Emulated LAN Types l An Emulated LAN provides the functionality of a single LAN segment: – – l an Ethernet/802. 3 segment, or a Token-Ring/802. 5 ring An Emulated LAN does not emulate all the segment-specific details of the emulated type, e. g. : – – No collisions No tokens, no beacon frames

LANE Architecture LAN Emulation UNI LAN Emulation Service LAN Emulation Client: ATM Workstation LAN Emulation UNI Initialization Address Registration Address Resolution Data Forwarding Legacy LAN Emulation Client: ATM Bridge ATM workstation: One LANE Client for each emulated LAN

LE Service Components l LE Configuration Server – l LE Server – l Provides configuration information, address of LE Server Implements Address Registration/ Resolution functions Broadcast/Unknown Server – Performs all broadcasting and multicasting and unknown unicast distribution

LE Service Components

LANE Control Connections C C V t c re u g i nf o C e Dir LE Configuration Server Control Direct VCC LE Server LAN Emulation Client Control Distribute VCC Other LE Clients Broadcast/Unknown Server (BUS)

LANE Data Connections LE Configuration Server Multicast Send VCC LE Server Multicast Forward VCC LAN Emulation Client Data Direct VCCs Broadcast/Unknown Server (BUS) Other LE Clients

LUNI Protocol Overview l l l Initialization Configuration Joining Registration and BUS Initialization Data Movement

Initialization l l l Must determine the ATM address of the LECS Use SNMP ILMI to get address from a table in the switch and place call to that address Use well-known ATM address If that fails, use the VPI/VCI 0/17 PVC as the connection to the LECS If LECS is not available, try the LES

Configuration l LE Client provides the LECS with: – – – l ATM address MAC address LAN types and frame sizes requested LECS Returns: – – LES address LAN type and frame size to use

Joining l l Create Control Direct bi-directional VCC Transmit Join Request (ATM address, LAN info, proxy indication, optional MAC address) Possibly accept Control Distribute VCC before Join Response is received May time out or fail

Registration and BUS Initialization l l Register any MAC addresses Resolve 0 xffffff MAC address to get ATM address of BUS Create bi-directional Multicast Send VCC to BUS Accept bi-directional Multicast Forward VCC from BUS

Data Movement l l l When a data frame is available for transmission, check internal cache If unknown, ask the LES While waiting for response, may transmit frame(s) via BUS Establish direct connection when response is received Connections are timed out on inactivity

LAN Applications l The advantage of LAN Emulation is that – l The disadvantage of LAN Emulation is (also) that – l l the use of ATM is hidden from the applications All existing applications can use LAN-Emulation New applications, in order to use the power to ATM: – – l the use of ATM is hidden from the applications need to be cognizant of ATM, and thus need to use an ATM-aware API (e. g. , Classical IP) Both types of applications can co-exist, side by side

Interoperability l l l A logical “subnet” is either an Emulated LAN or an ATM-aware subnet Logical subnets are interconnected via routers The driver for the ATM-adapter card needs to support the relevant type of logical subnet. “ATM-aware” subnet Emulated LAN Router or ATM Server “ATM-aware” subnet Emulated LAN

LAN Emulation Version 2. 0 l LUNI 2. 0 – – – l Compatible with LUNI 1. 0 Optional to multiplex ELANs on same VCC Improved Qo. S support Additional support for Multicast Persistent Data Direct VCCs stay up across server failures LNNI 2. 0 – – Multivendor LE service component interoperability Up to 20 LES/BUS pairs; up to 2000 LE Clients Standardized server failover Selective Multicast Server to offload multicasts from BUS

Summary l l l All existing LAN applications can run on an Emulated LAN Emulation allows ATM to be used as a backbone to interconnect “legacy” LANs and ATM-attached hosts To exploit the power of ATM, new applications need to use ATM-specific API’s, rather than LAN-Emulation