Switched Fast Packet VPNs

During the middle and late 1990s, VPNs utilizing frame relay and/or ATM connections—what
have come to become known as fast packet connections, though ATM is not really packet
based—became popular, and they are still present in the marketplace today, particularly
deployments where frame relay traffic is encapsulated within an ATM overlay. Such VPNs are
also known as virtual private wire services (VPWSs) because the connections themselves are
treated as if they are hardwire circuit connections rather than virtual circuits—that is, fixed
allocations of bandwidth set up by the ATM and frame relay protocols. In terms of ensuring privacy
and high availability, there is nothing wrong with frame relay VPNs, but the speeds
supported by frame relay service providers have been unimpressive, and the efficiency and
robustness of frame relay networks are inferior to that of Multiprotocol Label Switching
(MPLS)–enabled IP networks that offer similar benefits. Frame relay, because of a relative
lack of redundancy and error correction mechanisms, is not well suited to the wireless realm
and has seldom been employed in wireless broadband networks. However, as indicated in
Chapter 1, the 802.16 standard does support ATM. In theory, an ATM-based VPN service offering
is perfectly possible within a broadband wireless network, but it squanders precious
bandwidth. Furthermore, in the case of remote locations outside of the wireless operator’s own
service area, it compels the operator to purchase expensive end-to-end ATM connections
through the backbone from long-distance service providers.