Multi-Protocol Label Switching (MPLS) transport is a funny thing -- what it means depends on who you are talking to at the time. If you are talking to an engineer who is responsible for designing and developing MPLS services for a carrier, he or she will more than likely discuss MPLS in terms of MPLS backbone transport.
MPLS backbone transport is analogous to both frame relay and ATM WAN circuits, in that MPLS, frame and ATM all use the concept of virtual circuits. Frame relay uses permanent virtual circuits (PVCs) between the WAN routers, ATM uses VPI/VCIs, and MPLS uses label-switched paths (LSPs).
There is a major difference, however. The LSPs on the MPLS backbone are built between the provider's routers (called PE or provider edge routers). With traditional ATM and frame WAN backbones, you had to build these PVCs between all of your WAN routers or use a hub-and-spoke topology to enable traffic flows from remote site to remote site. With MPLS transport as the WAN, a customer can connect one interface to the MPLS cloud and have access to all of the remote WAN routers over one single physical and logical interface. The concept of sub-interfaces that are found in most ATM and frame WAN architectures goes away.
So, understanding a little about how the carrier transport has changed, it only makes sense now to discuss how this affects the access (transport) links that connect to the MPLS backbone. The access circuit now becomes the transport between your sites and the carrier's MPLS router sitting on the MPLS backbone.
Interestingly enough, you can (in theory) connect your sites with multiple types for WAN access circuits because a router sits between the access circuits and the MPLS backbone. For example, let's say you have a three-site WAN where each site has a local circuit option to the MPLS clou
To continue reading for free, register below or login
To read more you must become a member of SearchNetworking.com
d. You could provision one circuit as ATM, another as frame relay and another as Ethernet, and each of the sites could talk to the others over the carrier's MPLS core using IP. Legacy WANs required like interfaces because the virtual circuits were built from customer router to customer router, not from customer router to provider router. You could do this, but it is not recommended. The point is that the transport options remain the same for legacy WAN and MPLS WANs, but one is carried over routers (MPLS) and the other over frame and ATM backbones.
Choosing your MPLS transport
Why is the choice of MPLS transport important? As mentioned above, you can use ATM, frame and Ethernet, as well as private line, Broadband DSL and others. The choice of one or the other depends on multiple factors, and an analysis is required to determine the best fit.
To summarize, MPLS transport provided by the carrier is transparent to you as a customer and allows you to pick multiple access methods into the MPLS cloud. The importance for you is therefore the local access transport between your sites and the MPLS nodes/PoPs on the carrier's backbone. Your choice of transport should consider the ability of the current environment to support the offered transports, the bandwidth available, and whether or not the carrier offers the transport option for each of the sites being upgraded.
About the author:
Robbie Harrell (CCIE#3873) is the National Practice Lead for Advanced Infrastructure Solutions for SBC Communications. He has more than 10 years of experience providing strategic, business and technical consulting services. Robbie lives in Atlanta and is a graduate of Clemson University. His background includes positions as a principal architect at International Network Services, Lucent, Frontway and Callisma.
