PDF of this tutorialMPLS was designed out of the need to address new connection-oriented needs of the new Internet. It is adapting and evolving to new technologies just as the IP protocol itself has been evolving over the past 30 years. As with all new protocols, there is still a fair amount of work to be accomplished. The need to support traffic-engineered routes in the Internet has required new extensions to traditional IGP and EGP protocols such as OSPF and BGP. Advances in fiber optics are requiring more modifications to MPLS in the areas of routing as well as signaling.
Both CR–LDP and TE–RSVP provide very similar functionality for establishing traffic-engineered, labeled switched paths. Each has its strengths and weaknesses. While LDP is the younger of the two protocols, RSVP has been previously deployed and has operational experience. It is true that there have been extensive enhancements to RSVP in order to support the needs of MPLS. As both CR–LDP and TE–RSVP evolve they will offer more and more similar functionality.
Eventually, MPLS traffic engineering should evolve into a single entity that combines the best-of-breed attributes from both TE–RSVP and CR–LDP. In the meantime, any MPLS implementation by original equipment manufacturers (OEMs) developing LER or LSR platforms should consider supporting both TE–RSVP and CR–LDP to ensure interoperability.
It should be noted that the intrinsic value of having an entry point to providing policy-based management to the core is extremely compelling. The lure of MPLS and the benefits of IP circuit switching for latency-sensitive traffic is no longer a case of "the emperor’s new clothes."
