copper pair wiring, originally running to the SS7 digital exchange for POTS services, can be reused and provisioned as leased lines, DSL, Frame Relay tail circuits, and SO on. The SDH/SONET network allows circuits down to T1/E1 rates to be provisioned end-to-end across the cloud. Lower- bandwidth circuits are provisioned over SDH/SONET by means of a further set of multi- plexers and demultiplexers. Frame Relay Services Frame Relay is standardized in ITU-T Q.922 (ITU-T, 1992) and was originally conceived as part of the ISDN protocol standards (Figure 12.7). It uses the notion of a Data Link Connec- tion Identifier (DLCI) to identify the individual PVCs established manually across the cloud. The UNI is referred to as the Local Management Interface (LMI). This establishes a PVC to X.25 Services IP = 172.16.4.1/24 Local DLCI=30 Required Mappings or Inverse-ARP Frame Relay Q922 LMI Remote Layer 3 Local Layer 2 Frame 172.16.4.2/24 Relay Undefined IP = 172.16.4.2/24 Local DLCI 33 Required Mappings or Inverse-ARP Frame Frame Relay Q922 LMI Relay Remote Layer 3 Local Layer 2 172.16.4.1/24 ARP-Address Resolution Protocal Fig. 12.7 Basic IP-over-Frame Relay services. the CPE for limited signaling. LMI uses a well-known DLCI number depending on the LMI standard being used. There are three LMI standards: ANSI's T1.617 Annex D (American National Standards Institute, 1991), ITU-T's Q.933A (ITU-T, 2003), and the Cisco, DEC, Strata COM and Nortel (Gang of four) de facto standard. When this LMI DLCI is established, the switch informs the CPE of the DLCI numbers that the CPE is connected to. The CPE devices are defined as Frame Relay Access Devices (FRAD) and are commonly IP routers with Frame Relay functionality. Frame Relay defines a service in terms of an access datarate, a Committed Information Rate (CIR), and an Excess Information Rate (EIR). Frame Relay is an alternative to costly higher-rate leased-line connections. Frame Relay services are offered at a maximum port speed of DS-3 (45 Mbit/s), although much lower speeds, with