In a normally routed environment, frames pass from a source to a destination in a hop-by-hop basis. Transit routers evaluate each frame's Layer 3 header and perform a route table lookup to determine the next hop toward the destination. This tends to reduce throughput in a network because of the intensive CPU requirements to process each frame. Although some routers implement hardware and software switching techniques to accelerate the evaluation process by creating high-speed cache entries, these methods rely upon the Layer 3 routing protocol to determine the path to the destination.
Unfortunately, routing protocols have little, if any, visibility into the Layer 2 characteristics of the network, particularly in regard to quality of service (QoS) and loading. Rapid changes in the type (and quantity) of traffic handled by the Internet and the explosion in the number of Internet users is putting an unprecedented strain on the Internet's infrastructure. This pressure mandates new traffic-management solutions. MPLS and its predecessor, tag switching, are aimed at resolving many of the challenges facing an evolving Internet and high-speed data communications in general.
To meet these new demands, multiprotocol label switching (MPLS) changes the hop-by-hop paradigm by enabling devices to specify paths in the network based upon QoS and bandwidth needs of the applications. In other words, path selection can now take into account Layer 2 attributes. Before MPLS, vendors implemented proprietary methods for switching frames with values other than the Layer 3 header. (MPLS is described in more detail in a later section.)
Based upon Cisco's proprietary tag-switching protocol, the IETF is defining MPLS as a vendor-independent protocol. (At the time of this writing, the MPLS definitions were not quite complete.) Although the two protocols have much in common, differences between them prevent tag-switching devices from interacting directly with MPLS devices. MPLS will likely supercede tag switching. However, this chapter starts with a comparison of terms involved with tag switching and MPLS.
Download Links:
KnowledgeNet Implementing Cisco Mpls 2.0 Student Guide
Mpls Training Guide - Building Mpls Networks.chm
Cisco.Press.CCIP.MPLS.Implementing.Cisco.MPLS.v2.1.Vol.2.2004
CiscoPress Traffic Engineering with Mpls
IP Mpls Infrastructure Evolution
MPLS.Configuration.on.Cisco.IOS.Software
Fault-Tolerant IP and Mpls Networks.chm
Cisco Press - Mpls And Vpn Architectures
Building MPLS-Based Broadband Access VPNs
Cisco CCIP Mpls 642-611 V2.29 Pass4sure
Morgan.Kaufmann.MPLS.Next.Steps.Apr.2008.eBook-BBL
Mesh-Based Survivable Networks Options and Strategies for Optical Mpls SONET and ATM
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