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Labeled transport MPLS

Learn how labeled transport allows ISPs to expand coverage to diverse geographic locations.

In the last article I discussed Inter-AS/Interprovider MPLS VPN solutions that allowed multiple service providers to provide services to a single VPN customer. The providers exchange VPN-IPv4 routes via each provider's Autonomous System Border Routers (ASBRs). The ASBRs act as gateways of last resort for traffic between the provider clouds to the end customers who have sites on both backbones. The labeled transport solution focuses on providing backbone services for other carriers and Internet service providers (ISPs).

Labeled transport or carrier-of-carrier's MPLS solutions allow one provider to utilize another provider's backbone for transport only. Carriers have been selling transport to other ISPs and carriers for years so this is not a new concept. However, the difference is that the labeled transport service allows one carrier to transport another carrier's private IP traffic via MPLS labels. This allows for the extension of MPLS layer 3 VPNs across geographically diverse locations without the purchase of expensive long haul transport. In the old days, if a carrier wanted to expand its geographic presence, they would have to purchase backbone transport from other carriers or build out the infrastructure themselves. In addition, availability requirements created the need for diversity and redundancy. This can be very costly. For instance, if you wanted to expand geographically to Europe or South America from the United States and do so with diverse links, the costs would be very high to lease or build out the infrastructure required to interconnect the IP PoPs in each area.

With the advancements of MPLS technology in the form of label transport, carriers can sell IP transport via MPLS label exchange. The service is essentially an extended label switched path across a carrier's backbone that transparently delivers IP traffic from other carriers. The benefit of this service is that one carrier can purchase backbone transport across another provider's backbone that already has the redundancy and resiliency built in at the transport and IP layer. This can be significant in terms of expanding geographically to areas outside of the current provider's footprint.

The labeled transport services are targeted at Internet service providers and MPLS VPN service providers. These services provide two distinct features (Internet access and VPN connectivity), but in each case transport services are required. More and more ISPs are taking advantage of this service due to the fact that Internet service is best effort and the ISP does not have to rely on QoS guarantees and SLAs for real time or mission critical across the third party provider backbone. I have previously discussed the difficulties of providing QoS between providers in the tip entitled Interconnecting MPLS Clouds.

So let's go back to the example that I mentioned earlier about expanding geographic presence into Europe and South America. With the advent of labeled transport a carrier can build out IP PoPs in each of these countries and interconnect them over another carrier's backbone via labeled transport services. The carrier can dual home the PoPs to the third party carrier and rely on the third party carrier's resiliency and redundancy on the backhaul back to the United States. The carrier can then offer Internet services and potentially Layer 3 VPN services. The carrier does not have to manage or maintain the backbone interconnecting the PoPs as that is maintained by the third party carrier. This is a cost effective way to expand geographically for both Internet and Layer 3 VPN services.

This technology is available today, although it is not being utilized as much as it would seem. Most carriers have built out their backbones for Internet connectivity, but there is substantial room for growth in the Layer 3 VPN space. This service will become more and more attractive as organizations with International presence come to the carriers requesting MPLS Layer 3 VPNs. In the next article I will dive into the technical aspects of how this technology works. How do the MPLS routers build this virtual backbone between carriers?

Robbie Harrell (CCIE#3873) is the National Practice Lead for Advanced Infrastructure Solutions for SBC Communications. He has over 10 years of experience providing strategic, business, and technical consulting services to clients. Robbie resides 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.

This was last published in March 2005

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