Whether a service provider is offering a service like IP Centrex or simply transporting voice over IP traffic, access loops remain a significant potential bottleneck. However, some recent work by the MPLS and Frame Relay Alliance may help provide good quality of service over this least-reliable and least-controlled portion of the network.Those of you who also read Network World\u2019s WAN Newsletter heard a couple of weeks ago about the development of the Multi-protocol Label Switching (MPLS) User-to-Network Interface (UNI). (If you missed it, we have the links below.)The MPLS-UNI is quite significant because all the traffic management tools that until now have been available only in the core network now have the possibility of spanning the network end-to-end. This is of great importance - as the likelihood of having queue problems is greater in the access link, where there\u2019s simply less bandwidth available in most cases.At this point, the MPLS-UNI is only defined for PVC-type capabilities, where the service provider would set up a MPLS Label Switched Path (LSP), and the customer premise equipment would respond. For maximum effectiveness for VoIP, though, the LSPs need to be defined on the fly with requests coming from the IP PBX to set up SVC-type capabilities. This capability is on the way.According to Victoria Fineberg, who authored the paper \u201cQoS Support in MPLS Networks\u201d for the MPLS and Frame Relay Alliance, an MPLS SVC UNI (how\u2019s that for alphabet soup?) Implementation Agreement is under development, and this will provide the capability for end-user devices to request an LSP with specific QoS parameters.Will VoIP over MPLS be a major factor in networking in the coming years? There are no guarantees. Most significantly, customer premise equipment providers must offer devices with MPLS SVC UNI capabilities, and the service providers must offer the accompanying service. But we think the concept has tremendous potential.