Within today's WANs, IP is transported using both IP over ATM and PoS technologies. PoS is primarily used for the aggregation of backbone router traffic to extend the capacity of the original routers that supplied the backbone for Internet connectivity. Some of the largest IP providers use ATM for the same purpose—backbone transport of IP traffic. In addition, IP over ATM is used in the WAN to provide efficient aggregation of IP traffic toward the backbone and to provide transparent LAN services that interconnect remote sites over an ATM infrastructure. The next step is to adapt one or both of these infrastructures to respond to end-user demands for extended IP–based WAN services.

IP over ATM is uniquely suited to providing differentiated IP–VPN services to end-user business customers. The fundamental technology differentiator that makes this possible is the VCs that allow a service provider to provision, manage, monitor, and bill for an end-to-end connection that has a specific CoS for a specific customer. In addition, the built-in traffic-management and QoS parameters allow the adoption of IP SLAs for the first time. Combining IP with other ATM services also provides significant advantages in terms of mixing many different types of transport services (frame relay, cell relay, circuit emulation, voice services, SMDS) and different media (data, voice, video) and managing them as part of the same infrastructure.

PoS is a good solution for efficiently transporting bulk, undifferentiated IP–only traffic from point to point. It is not, however, suitable for providing end-to-end IP–based services such as VPNs. Future standards such as MPLS and new protocols such as RSVP and L2TP may allow service providers to offer VPNs with guaranteed service levels, but it is unclear when or if they will be able to work together, or if these networks will be manageable when they grow to accommodate hundreds of thousands of VPNs. In addition, networks of such complexity are not likely to be adapted to anything other than IP–based traffic. If and when all IP networks become a reality, and if the emerging standards are ratified to provide ATM–like traffic-and-network-management features, PoS may become a viable solution for providing true differentiated IP–based services.