ATM LAN Emulation A detailed look at LANE 1.0, including a general overview of LANE concepts, by Klessig. Klessig is vice chairman of the ATM Forum Technical Committee and a director for 3Com Corp.'s sys- tems marketing department in Santa Clara, Calif. He can be reached via the Internet at bob_klessig @3com.com.

By Bob Klessig
Network World, 6/2/97

The ATM Forum's LAN Emulation (LANE) standard for seamlessly integrating legacy LANs and ATM is used in an estimated 20,000 building or campus networks today. This type of deployment is expected to continue with the impending availability of an enhanced version.

LANE Version 2.0, which will be backward-compatible with its predecessor, will help preserve investments in ATM backbone and edge devices and bring higher levels of interoperability, scalability and quality of service (QoS) to enterprise ATM networks.

LANE 2.0 lowdown

LUNI 2.0, which looks similar to the current LANE (LUNI) specification in organization and content, is technically stable. It is undergoing final Letter Ballot in the ATM Forum and will probably be ratified by the end of this quarter.

As for LNNI 2.0, developers have resolved the major technical issues, so they now need to write the detailed specification. The ATM Forum likely will ratify LNNI 2.0 before year-end.

LNNI will define a method for deploying multiple LANE servers, even from disparate vendors, in different physical devices in a single emulated LAN. The goal is to support as many as 20 LANE servers and 2,000 LAN emulation clients per emulated LAN.

This goal represents a modest improvement in scalability over what is found typically in today's emulated LANs. It also means a robust emulated LAN in the sense that the failure of one LANE server will not knock out connectivity for all LAN emulation clients in the network.

Furthermore, the LNNI will support redundant LANE servers. These could be dedicated backup servers or distributed redundancy.

With distributed redundancy, the LAN emulation clients being served by a failed LANE server are automatically reassigned to the other active LANE servers until their primary server returns to service.

Then and now

Because LANE 2.0 will be fully backward-compatible with LANE 1.0, they will be able to mix LANE 2.0 servers and clients with 1.0 clients. Despite supporting different versions of the standard, the devices will be able to fully interconnect.

Furthermore, most of the LANE 2.0 benefits can be attained by upgrading 1.0 clients with software. Details will de-pend on the particular implementations, so check with your vendors.

LANE 2.0 also offers new broadcast/multicast capability and support for QoS.

The broadcast/multicast ca-pability in LANE 1.0 is intended primarily for broadcast discovery protocols such as IP Address Resolution Protocol.

LANE 2.0 will allow selective multicast for applications such as video newsfeeds. LAN emulation clients that want to receive the multicast will register with the server.

This will improve network efficiency compared to LANE 1.0 and allow larger emulated LANs.

One of the powerful concepts of LANE 1.0 is that it makes ATM look just like a LAN, allowing continued use of existing network protocols. However, this approach also hides some of the power of ATM, namely QoS.

For QoS, LANE 2.0 uses available bit rate (ABR) flow control. With ABR, nonreal-time traffic can use transient spare capacity in the ATM network.

This can greatly improve efficiency in the network and is an ideal way to send many types of data traffic.

In addition, enterprise managers will be able to specify ATM QoS on Data Direct virtual channel connections (VCC). QoS can be defined within ATM terminal devices as needed.

These features are an important step toward integrated services building and campus backbone ATM networks.

In certain LANE 1.0 configurations, an ATM terminal with several LAN emulation clients may need to support a large number of Data Direct VCCs.

For example, a one-armed route, which routes between two emulated LANs, could have a handful of connections to each of a large number of LAN edge devices.

LANE 2.0 can alleviate this burden by allowing multi- plexing of data traffic between two devices onto one virtual connection.

Lastly, it's worth noting that LANE 2.0 contains protocols used by Multi-protocol Over ATM (MPOA) clients and servers to find each other. MPOA will not replace LANE; the reality is that MPOA is built on LANE.