History of Tag Switching to MPLS

Reference:- MPLS Fundamentals
http://www.ciscopress.com/bookstore/product.asp?isbn=1587051974

Cisco Systems started off with putting labels on top of IP packets in what was then called tag switching. The first implementation was released in Cisco IOS 11.1(17)CT in 1998. A tag was the name for what is now known as a label. This implementation could assign tags to networks from the routing table and put those tags on top of the packet that was destined for that network. Tag switching built a Tag Forwarding Information Base (TFIB), which is, in essence, a table that stores input-to-output label mappings. Each tag-switching router had to match the tag on the incoming packet, swap it with the outgoing tag, and forward the packet.

Later on, the IETF standardized tag switching into MPLS. The IETF released the first RFC on MPLS—RFC 2547, “BGP/MPLS VPNs”—in 1999. The result of this was that much of the terminology changed. Below table shows an overview of the old and new terminology.



Old Terminology --- New Terminology
Tag switching --- MPLS
Tag --- Label
TDP (Tag Distribution Protocol) --- LDP (Label Distribution Protocol)
TFIB (tag forwarding information base) --- LFIB (label forwarding information base)
TSR (tag switching router) --- LSR (label switching router)
TSC (tag switch controller) --- LSC (label switch controller)
TSP (tag switched path) --- LSP (label switched path)