routing under user-signaling control based on both the VCI and VPI fields. With the ascent of IP networks in the 1990s, several solutions were proposed to transport IP over ATM. Unfortunately, this resulted in solutions that were complex, difficult to manage, and in some scenarios resulted in excessive computational complexity (Davie & Rekhter, 2001). Many of the lessons learned from this resulted in the creation of Multiprotocol Label Switching (MPLS) (Rosen, Viswanathan, & Callon, 2001) in the late 1990s, which also employs the "label-swapping" scheme, originally implemented in ATM. Commercial ATM/Frame Relay Services Example Initially, services such as ATM and Frame Relay were made up of dedicated WAN switches. The original expectation was that ATM switches would eventually dominate data. network- ing architectures, and many customers decided to install ATM-compatible interfaces to their corporate networks to prepare for such a trend. In terms of ATM adoption, providers limited themselves to overlay networks. Furthermore, toward the end of the 1990s vendors started to offer multiple services on a single-chassis platform. Alcatel and Cisco Systems were two vendors leading the way in converging features on a single platform. Alcatel's 7670 RSP and MSP (www.alcatel.com) were designed specifi- cally to be a single chassis capable of carrying ATM, X.25, Frame Relay, SMDS, and circuit emulation services. Cisco Systems offered the Strata COM BPX and MGX ATM carrier plat- forms (www.cisco.com). Service providers in the late 1990s started to converge their disparate networks onto similar unified platforms. In the United Kingdom, British Telecom (BT) rolled out a multiple- node Multi-Service Intranet Platform (MSIP) (see Figure 12.10). This state-of-the-art WAN service incorporated BT's commercial corporate data offerings of Framestream, Cellstream, and MegaStream Ethernet onto a single network and greatly improved service delivery time and failure response. The network was implemented as a three-tier system and incorpo