Many carriers are replacing their aging ATM WAN services with Multi-protocol Label Switching services. Carriers and equipment manufacturers virtually have stopped enhancing their ATM networks and equipment. Fortune 500 companies are considering incorporating MPLS services into their WANs.

Nevertheless, potential users have many questions about MPLS - questions that carriers should address explicitly and directly.

ATM was priced according to precise parameters such as port speed, sustainable cell rate and service type. How do carriers plan to charge for MPLS service? Based on maximum access/port speed only? Based on some kind of class of service (CoS) or differentiated service? Based on distance? Based on number or type of label-switched paths?

How does one compare the cost of an ATM service with the cost of an MPLS service? When is one more cost-effective than the other? How does one compute total cost of ownership on an intranet using MPLS vs. ATM? How does a company financially justify migrating from one technology to the other? Carriers need to help users make the business case.

Carriers also should keep in mind that user companies want to lower their IT and telecom costs over time. Macro-level connectivity costs have been decreasing across the board at a rate of 10 percent to 20 percent per year for the past 10 to 15 years.

An organization that has used an ATM network for five years or more might expect substantial cost advantages if and when it moves to MPLS. When carriers launched frame relay services in the early 1990s, they priced the services to be competitive with the cost of private lines, which is what made frame relay so successful throughout the 1990s.

Some IP purists prefer IP to MPLS. Can carriers shed some light on why MPLS might be preferable for heavy-duty core WAN applications over simple IP?

How does an MPLS network handle different classes of applications? What mechanisms are available to manage different CoSs, prioritization and QoS? ATM provided a number of service types with different service levels. What do carriers offer in this arena for MPLS?

How does the carrier handle oversubscription, "burstiness," traffic management, traffic shaping and overall end-to-end service metrics? Clearly ATM had a lot to offer here. What comparable mechanisms are available in carrier MPLS services?

Security is a major user concern, and encryption often is a must-have. How are security and encryption supported in MPLS? Will the provider equipment handle encryption directly - and if so, how will key distribution work? Or will the task be relegated to the customer equipment?

These are just some of the most fundamental questions users eager to road test MPLS should ask. After the carriers give clear, direct, straightforward answers to these questions, perhaps a dozen more queries will be posed and answered ... and then we'll be ready to deploy MPLS in the enterprise.

Minoli is an adjunct professor in the Stevens Institute of Technology's graduate school and author of several books about enterprise networking. He can be reached at [email protected]