Figure 9-1 Basic LANE architecture.
Figure 9-2 LANE interconnectivity.
In its current form, LANE is designed to emulate Ethernet IEEE 802.3 and Token-Ring IEEE 802.5 LAN technologies. In addition, LANE only allows single media type emulation within an ELAN. In other words, it does
not allow mixing of end-stations running Ethernet and Token-ring emulation within an ELAN. However, it is possible to interconnect two such ELANs through an ATM router which belongs to both ELANs as shown in
Figure 9-3.
The network layer protocols like IP and IPX interface to the MAC Medium Access Control protocols of legacy LANs through well-defined interface procedures such as Open Data-Link Interface DDI, Network Driver
Interface Specification NDIS, and Data Link Provider Interface DLPI. These procedures define how to access a MAC driver via well-defined primitives and parameters. LANE provides in a sense the same type interfaces to
access the underlying ATM network. Hence, the main function of LANE is to provide the same type of interface look and feel of a legacy LAN to network protocols so that existing LAN applications can run over an ATM
network without knowing anything about the network. In other words, LANE hides the ATM network from the upper layers of protocol stack and provides the appearance of a MAC interface. The details of the operation of the
ATM network is taking care of by LANE as shown in Figure 9-4.
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by Abhijit S. Pandya; Ercan Sen CRC Press, CRC Press LLC
ISBN: 0849331390 Pub Date: 110198
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B. LANE Components
The LEC resides in the end-stations and provides the LUNI interface for the end-stations. The LUNI interface emulates MAC level services for Ethernet or Token-Ring to upper layers in the end-stations. Among the services provided include
address resolution, data forwarding and control functions.
The LES is responsible for the control coordination function within an ELAN. It performs a registration function and maintains a table of all registered active members of an ELAN. LECs register their MAC addresses they represent with the
LES. LES performs the address resolution function for LECs by maintaining a MAC andor route descriptor to the ATM address conversion table. The LES resolves an address resolution request either by itself if possible i.e., if the requested
address is registered with the LES or forwards the request to other clients through BUS so they may respond.
The BUS performs two major functions for ELAN: broadcastmulticast and address resolution for unknown clients, also known as the unknown server function. When a LEC wants to broadcast to all members of the ELAN using MAC address
“FFFFFFFFFFFF”, the broadcast task is performed by the BUS component. Similarly, the multicast is a derivative of the broadcast function in which case the broadcast is targeted to a specific set of members of the ELAN, i.e., to a multicast
group. The first unicast data exchange between two LECs has to be done through BUS if the destination LEC has not registered with the LES yet. The BUS server broadcasts the first message so that the unknown LEC will receive and
respond, thus providing its ATM address. Once the ATM address of this LEC is known, a direct VCC patch is established between the two LECs.
The BUS component of LANE is responsible for the administrative functions. It manages assignment of LECs to particular ELANs. An LEC can be a part of more than one ELAN. After validating an LEC request to join to a particular ELAN by
using policies and a configuration database, the BUS allows this LEC to become an active member of the ELAN by providing the ATM address of its LES server. This logical assignment capability allows independence from the physical
location. Hence, LECs from diverse locations can become a part of an ELAN. On the contrary, for the legacy LANs, the membership for the LAN is dictated by the physical location.
C. LAN Emulation User to Network Interface LUNI
The LUNI interface between the LE Clients and LE Service provides four basic functions for the operation of LAN Emulation. These four basic functions are summarized in Table 9-1.
Table 9-1LUNI interface functions.
Initialization • Obtaining the ATM addresses of LE Services
• Joining and leaving a particular ELAN • Declaring the need for Address Resolution
Address Resolution • Finding the ATM address of an LEC with particular MAC
address Data Transfer
• Encapsulation of LE-SDU in an AAL5 frame and sending by the LEC
• Forwarding the AAL5 frames by LE Service • Receiving and decapsulating the AAL5 frames by LEC
Figure 9-3 Interconnectivity between two ELANs emulating different LAN types Ethernet and Token-Ring.
Figure 9-4 LANE protocol interface.
D. LANE Connections
The LANE protocol uses a set of well-defined ATM connections among its components: LE Clients and LE Service element. These connections can be Switched Virtual Channel Connection SVCC, Permanent Virtual Circuit or a
combination of both. While the SVCC type requires ATM signaling function, i.e., call setup and call clear down procedures, the PVCC connection is handled by the layer management.
There are two types of VCC connections required for communication between LE Clients and LE Service components: control and data VCCs. The control VCC is used for carrying control traffic while the data VCC is used for transfer of
encapsulated EthernetToken-Ring frames. Each controldata VCC is dedicated for only one ELAN. The control VCCs between an LE Client and LE Service components LES and LECS are shown in Figure 9-5. The data VCC can be set up
between two LE Clients or between an LE Client and BUS as shown in Figure 9-6.
Figure 9-5 LANE control connections.
Figure 9-6 LANE data connections.
The control VCCs are established during the LEC initialization sequence strictly for the purpose of carrying LE_ARP traffic and control frames.
The Configuration Direct VCC is a bi-directional point-to-point control connection between LEC and LECS. It is established using B-LLI signaling during the LEC connect phase to obtain configuration information such as the address of
LES. The B-LLI signaling is used to indicate that the connection is carrying “LE Control” packet formats. Once the LEC
The Control Direct VCC is a bi-directional point-to-point control connection between LEC and LES. It is established during the LEC initialization phase. In contrast to the Configuration Direct VCC, the LEC and LES are required to preserve this
VCC connection throughout the participation of the LEC in the ELAN.
The Control Distribute VCC is a unidirectional point-to-point or point-to-multipoint control connection from LES to LEC s. This is an optional control connection which the LES may establish during the initialization of an LEC. Once it is
established, the LEC and LES are required to maintain this control connection throughout the participation of the LEC in the ELAN.
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