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tag switching

A layer 3 switching technology from Cisco that is used in large enterprise networks (WANs). It uses tags (labels) containing forwarding information. Tag switching uses routers (Tag Edge Routers) that sit on the periphery of the network and make forwarding decisions for all the routers in the backbone. They append this information to each packet in fixed positions in the header that can be quickly examined by interior backbone routers (Tag Edge Switches), saving the time involved in decoding the packet and its associated table lookups. See MPLS.



MPLS

(1) (MultiProtocol Lambda Switching) An earlier name for generalized multiprotocol label switching (see GMPLS).

(2) (MultiProtocol Label Switching) A standard from the IETF for directing packets in a wide area IP network. Operating below the IP layer and above the optical layer, MPLS is used to ensure that packets take the same route. It is deployed by telcos and ISPs to support service level agreements (SLAs) that guarantee bandwidth. Large enterprises may also use MPLS in national private networks.

Label Edge Routers and Label Switching Routers
Similar to Cisco's tag switching, an MPLS router attaches labels (tags) containing forwarding information to outgoing IP packets. These "label edge routers" (LERs) sit at the edge of the network and perform the complex packet analysis and classification before the packet enters the core of the network. The routers within the core, known as "label switching routers" (LSRs), quickly examine the label and forward the packet per its directions without having to look up data in tables and compute the forwarding path each time. The edge routers at the receiving end remove the labels. See VPLS, GMPLS and Diffserv.




An MPLS Core
Using IP and MPLS in the core, a service provider can offer its customers a virtual private VPN service for IP traffic with guaranteed bandwidth.






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