The ATM LAN emulation specification defines how an ATM network can emulate a sufficient set of the medium access control (MAC) services of existing LAN technologies such as Ethernet and Token Ring, so that higher layer protocols can be used without modification. An emulated LAN (ELAN), which provides the appearance of either an Ethernet or Token-Ring LAN segment over a switched ATM network, is composed of a collection of LE Clients and a set of co-operating service entities: LAN Emulation Configuration Servers (LECSs), LAN Emulation Servers (LESs), Broadcast and Unknown Servers (BUSs), and Selective Multicast Servers (SMSs).
The LAN Emulation LUNI defines the protocols and interactions between LAN Emulation Clients (LE Clients) and the LAN Emulation Service, including initialization, registration, address resolution, and data transfer procedures. Each LE Client connects across the LUNI to a single LES and BUS, may connect to a single LECS, and may have connections to multiple SMSs.
Communication among LE Clients and between LE Clients and the LE Service is performed over ATM virtual channel connections (VCCs). Each LE Client must communicate with the LE Service over control and data VCCs. LANE assumes the availability of point-to-point and point-to-multipoint Switched Virtual Circuits (SVCs). Multicast Forward and Control Distribute flows are carried on point-to-multipoint VCCs. Data Direct, Control Direct, Configure Direct, Default Multicast Send and Selective Multicast Send flows are carried on point-to-point VCCs. Only Data Direct flows may be LLC-multiplexed. All other flows are non-multiplexed.
LAN Emulation encompasses both Ethernet and Token Ring emulation. In Ethernet emulation, a LAN Emulation component need examine only a data frame's destination MAC address in order to direct the frame towards its ultimate destinations. In Token Ring emulation, however, a LAN emulation component may have to use a Route Descriptor extracted from the data frame's Routing Information Field (RIF) in order to properly direct the frame over the Emulated LAN.
Most LAN emulation service would be implemented as device drivers below the network layer in ATM-to-legacy LAN bridges and ATM end systems. In LANE, the bandwidth management capability is currently supported by the "available bit rate" (ABR) service.
Protocol Structure
LE Data Frames:
1) for 802.3 (Ethernet) Frame C Non-multiplexed data frame:
| 0 | LE Header | Destination Address |
| 4 | Destination Address | |
| 8 | Source Address | |
| 12 | Source Address | Type / Length |
| 16 and on | user info | |
2) for 802.5 (Token Ring) FrameC Non-multiplexed data frame:
| 0 | LE Header | AC PAD | FC | |
| 4 | Destination Address | |||
| 8 | Destination Address | Source Address | ||
| 12 | Source Address | Type / Length | ||
| 16-46 | Routing Information Field | |||
| User Info | ||||
- LE Header- LAN Emulation header which contains either the LAN Emulation client identifier value, the sending client, or X"0000".
LE Control Frame:
All LAN Emulation control frames, except for LLC-multiplexed Data with Direct VCCs, such as LE_FLUSH_REQUESTs, READY_IND and READY_QUERY, use the format described below:
| 0 | MARKER = X"FF00" | PROTOCOL = X"01" | VERSION = X"01" | |
| 4 | OP-CODE | STATUS | ||
| 8 | TRANSACTION-ID | |||
| 12 | REQUESTER-LECID | FLAGS | ||
| 16 | SOURCE-LAN-DESTINATION | |||
| 24 | TARGET-LAN-DESTINATION | |||
| 32 | SOURCE-ATM-ADDRESS | |||
| 52 | LAN-Type | MAX-Frame-Size | Number-TLVS | ELAN-Name-Size |
| 56 | TARGET-ATM-ADDRESS | |||
| 76 | ELAN-NAME | |||
| 108 | TLVs BEGIN | |||
OP-CODE - (2 Bytes) Control frame Operation type. Some defined OP-Code are:
| OP-CODE Value | OP-CODE Function |
| X"0001" & "X0101" | LE_CONFIGURE_REQUEST & LE_CONFIGURE_RESPONSE |
| X"0002"& X"0102" | LE_JOIN_REQUEST & LE_JOIN_RESPONSE |
| X"0003"& X"0103" | READY_QUERY & READY_IND |
| X"0004"& X"0104" | LE_REGISTER_REQUEST & LE_REGISTER_RESPONSE |
| X"0005"& X"0105" | LE_UNREGISTER_REQUEST & LE_UNREGISTER_RESPONSE |
| X"0006"& X"0106" | LE_ARP_REQUEST & LE_ARP_RESPONSE |
| X"0007" & X"0107" | LE_FLUSH_REQUEST LE_FLUSH_RESPONSE |
| X"0008"& X"0108" | LE_NARP_REQUEST & Undefined |
| X"0009"& X"0109" | LE_TOPOLOGY_REQUEST & Undefined |
| X"000A"& X"010A" | LE_VERIFY_REQUEST & LE_VERIFY_RESPONSE |
Status - (2 Bytes) Control frame Operation status. Some defined Status codes are:
| Code (dec) | Name | Code (dec) | Name |
| 0 | Success | 1 | Version Not Supported |
| 2 | Invalid request parameters | 4 | Duplicate LAN Destination registration |
| 5 | Duplicate ATM address | 6 | Insufficient resources to grant request |
| 7 | Access denied | 8 | Invalid REQUESTOR-ID |
| 9 | Invalid LAN Destination | 10 | Invalid ATM Address |
| 20 | No Configuration | 21 | LE_CONFIGURE Error |
| 22 | Insufficient Information | 24 | TLV Not Found |
TLV - Type / Length / Value Encoded Parameter.
LANE LLC-multiplexed Frame - it has a 12-octet LLC multiplexing header:
| 0 | LLC- X"AA" | LLC-X"AA" | LLC X"03" | OUI-X"00" | ||
| 4 | OUI-X"A0" | OUI-X"3E" | Frame-Type | |||
| 8 | ELAN-ID | |||||
| 12-28/58 | LANE Data Frame Header (802.3 or 802.5) | |||||
| User Info | ||||||
LLC field is three octets, containing the constant value XAAAA03, indicating that an OUI follows.
OUI field is three octets, containing the constant value X00A03E, indicating ATM Forum.
The next two octets are a FRAME-TYPE field containing the value X000C for IEEE 802.3 data frame, X000D for IEEE 802.5 data frame, X000E for for LANE LLC-multiplexed READY_IND and READY_QUERY control frames.
The ELAN-ID field identifies the emulated LAN for this data frame.
Related protocols: DS1/E1, DS3/E3, AAL0-AAL5, CES, PNNI and MPOA, Q.2931
Sponsor Source:
The ATM protocols are based on standards developed by the ITU.
ftp://ftp.atmforum.com/pub/approved-specs/af-lane-0084.000.pdf: LAN Emulation Over ATM LUNI Specification Version 2 (AF-LANE-0084.000), July 1997
Reference:
ftp://ftp.atmforum.com/pub/approved-specs/af-lane-0112.000.pdf: LAN Emulation Over ATM LNNI Specification Version 2.0 (AF-LANE-0112.000), February 1999
The ATM Forum, UNI Signalling Version 4.0 Specification, af-sig-0061.000, 1996
ITU-T Recommendation I.363, B-ISDN ATM Adaptation Layer (AAL) Specification
http://www.atmforum.com/standards/approved.html#uni ATM User-Network Interface Specification
http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/atm.htm: ATM Overview