Migrating from T1 to fiber WAN

Migrating from multisite MPLS to 100Mbps Ethernet can save you a bundle; here's how

Back in the old days, the only realistic way to connect multiple remote sites was by T1 or T3 delivered either point-to-point or via Frame Relay. These were either slow and expensive or fast and unbelievably expensive. Then came MPLS, which dispensed with the need for point-to-point circuits from site to site, but was still bound by high expense. You got what you paid for. These circuits were not only reliable, but if a T1 or T3 circuit dropped, you could generally count on the carrier to jump on the problem quickly and resolve it with some expediency.

As cable and DSL networks began expanding, the ISPs introduced the concept of a business-class circuit. With significantly higher bandwidth than a T1 for far less money, these circuits are quite attractive -- but susceptible to the vagaries of their physical plant, which is to say that they're not as reliable as the T1s and T3s of old. In many cases, that trade-off is acceptable since the cost savings can be measured in the tens of thousands of dollars per year.

However, alternative ways to connect remote sites may enter the picture depending on their physical locations. The ideal solution is to be fortunate enough to find that all of your sites are served by a single fiber carrier, such as Optimum Lightpath. In other cases, you may find that your last-mile carrier (such as Verizon) has fiber to your locations, and a carrier such as Cogent can tie up all those ends into a connection served by a single end-to-end network. This way, you get bidirectional speeds up to 1Gbps between sites served by the same carrier, all for a lower monthly cost than a few 1.5Mbps T1s. If possible, this offers the ability to treat remote sites as local, enabling all kinds of replication and application delivery options that simply aren't available with lower-bandwidth circuits.

The new WAN: Weighing the options

For this case study (see "How to slash your WAN costs" for the background), we're detailing a migration from an MPLS network fed with multiple bundled T1 circuits at each site to 100Mbps fiber circuits installed at two sites with a common carrier and a business-class cable circuit feeding a smaller office. These sites are spread across three states, hundreds of miles apart. The previous design was simple: four T1 circuits at HQ, three at the large remote site, and a single T1 at the small office. Each location was linked to a single MPLS provider to handle internal routing.

The design and build were relatively simple, and the network functioned well, with an average latency of around 30ms between sites. However, with all Internet traffic flowing across the MPLS network for egress through an Internet circuit at HQ, the 4.5Mbps and 1.5Mbps pipes to the remote offices were suffering. Adding more T1s or a fractional T3 to the mix was a possible solution -- but a very expensive option for a minimal increase in bandwidth.

After some research, it became clear that a single fiber carrier could serve all three offices, and plans were hatched to deliver 100Mbps service to the large sites and 10Mbps service to the small office. Each circuit would be configured as an Internet circuit and assigned public IP subnets. The first two parts of the build were delayed significantly by Verizon, the last-mile provider, but were eventually built and tested. The small site proved to be the biggest problem.

Due to lack of planning and poor design stewardship by the building owner, only a single conduit fed from the fiber interconnect at the street to the large office building housing the small site. Although four conduits were specified in the building plans, only a single conduit could be found in the basement wiring room; the others may or may not have been present on the other side of the concrete foundation. Naturally, the existing conduit was full, with no more room to pull the fiber through.

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