of service, which means you can set up a guaranteed rate of delivery for realtime voice and video, and ATM is the only technology that is designed for both LANs and WANs. What's more, ATM is scalable from 25, 45, 100, 155, 622 Mbps and on into the stratosphere. What could be more ideal?

ATM has gained momentum as a way to provide a flexible, scalable LAN backbone that will boost the current infrastructure as well as support future needs. Almost every government agency and private corporation has planned for ATM or is at least thinking about it. But, it hasn't taken off as had been predicted. Integrating ATM into legacy LANs is not trivial. There's a difference in basic architecture between connection-oriented switches and connectionless LANs, which require some fancy footwork to blend together.

The ATM Forum has developed and is continuing to develop ways to do this, but the approaches are foreign to network managers accustomed to Ethernet and Token Ring, so many are playing a wait-and-see game. ATM sales in 1995 were 2.5 percent of all networking products, which seems small compared to the attention ATM has garnered in the industry. Pundits are already predicting the demise of ATM (a sure sign to buy more stock in ATM companies), while others feel ATM's glory days are still coming.

As you wade into the wild world of ATM, here are some of the technologies you will need to investigate.


LAN Emulation, or LANE, is an ATM Forum standard that supports legacy LAN packets within an ATM environment. A LANE driver runs in hardware called an edge device (also edge path adapter, network access device and LAN access device). The driver encapsulates Ethernet and Token Ring packets into LANE packets and then converts them into ATM cells. Nothing has to be done to the Ethernet and Token Ring stations, but native ATM clients also need the driver if they are to communicate with these legacy LANs.



MPOA is an upcoming standard from the ATM Forum that supports routing of legacy protocols (IPX, IP, etc.) over ATM. MPOA works at layer 3, whereas LANE works at level 2. MPOA separates the route calculations from the actual forwarding. When an edge device does not know how to forward a packet, it queries a centralized route server, which returns the destination address so that a switched virtual circuit (SVC) can be set up in the ATM switch. MPOA maintains the quality of service lacking in LAN Emulation and provides a virtual routing capability when fully implemented. Newbridge Networks is already shipping a preliminary version of MPOA, even though the standard isn't expected to be finalized until later this year.



I-PNNI is an ATM Forum standard that is fully supported by Bay Networks with Cisco also getting in on the act. I-PNNI is an extension of the PNNI (Private Network to Network) protocol, which ATM switches use to inform each other of the network topology so they can make appropriate forwarding decisions. With I-PNNI, a separate route server is not used, rather I-PNNI is implemented in edge devices and legacy routers, which can share information with the ATM switches. With I-PNNI, all devices have full knowledge of the network topology. Like MPOA, I-PNNI supports ATM's quality of service.


Ipsilon Network's IP switch is very controversial, because it offers exceptional performance, but is proprietary. The IP switch means exactly that: "switching IP." If you have a mixed shop, you will have to tunnel your other protocols within IP or change to IP to take advantage of it. A Pentium-based IP switch controller sits next to the ATM switch and routes short-duration traffic (address resolutions, SNMP, etc.) through the controller. Ipsilon claims an average of more than a million packets per second,