Multi Protocol Label Switching (MPLS) is a core networking technology that operates essentially in between Layers 2 and 3 of the OSI model; for this reason, MPLS has been referred to as operating at Layer 2.5. MPLS can overlay existing technologies such as ATM (Asynchronous Transfer Mode) or Frame Relay, or it can operate in an entirely IP native environment; this can allow users to take advantage of existing CPE (Customer Premises Equipment) while making a move towards converging all network traffic, such as data, video and voice, at a pace that users can accommodate and afford. MPLS provides its users a number of advantageous features such as traffic engineering, network convergence, failure protection, and the ability to guarantee Quality of Service (QoS) over IP. MPLS Vans take advantage of the inherent characteristics of MPLS to provide secure data networking, typically for business users, in conjunction with other VPN technologies to help increase scalability while keeping costs at a manageable level. This paper should help to provide a basic understanding of MPLS technology, its advantages and limitations, and its application as an IP VPN.
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