Is MPLS access via DSL or Cable Modem for you?

All decisions about a wide area network must consider the cost versus the benefit.  Depending on the benefit that a high performance WAN will provide your company, you may or may not be able to cost justify the investment.

Most MPLS networks are provisioned with T1, E1 or DS3 loops, which offer symetric upload and download bandwidth and optimal circuit stability and service level agreements.  Fiber is increasingly used for local loops, depending on your locations. In some cases, the cost of the local loop could make the pricing prohibitive.  In these circumstances, provisioning portions of your network with DSL or cable modem access may be the perfect option.

There are two approaches to DSL access for MPLS networks: Routed Encapsulation and Bridged Encapsulation.

With Routed Encapsulation, the DSL modem with integrated router encapsulates your circuit that is then routed to the DSLAM (DSL Aggregation Access Multiplexer) and statically mapped to VRFs (Virtual Routing & Forwarding).  From this point, the MPLS carrier takes your circuit onto their pure MPLS network, with DSL simply providing the local loop.  In lay terms:  your MPLS circuit is delivered via DSL using an encapsulated tunnel or VPN which is transparent to the customer.

Bridged Encapsulation works in a similar fashion to Routed Encapsulation, but all devices sitting behind the customer DSL modem are assigned addresses by the provider and authenticated by the provider, typically with PPP over Ethernet.  This is of greater benefit to the provider, who can then charge by the number of devices attached to the DSL modem.

Cable access is another option for MPLS access.  Again, a VPN is used to encapulate data at the Virtual Home Gateway for the local access.

Naturally, the use of DSL or cable for access will also hinge on your upload and download bandwidth requirements.  If each site needs primarily robust download bandwidth and can live with lower upload bandwidth, this could be a perfect solution.  Also be aware that SLAs for DSL and Cable are not as stringent as for T1s.  As a practical matter, service is usually fine, but it you absolutely cannot live without your network at a location for an entire day, then you should go with T1/E1 access if you can afford it.  Additionally, cellular 4G and LTE offer affordable access in areas where local loops are prohibitively expensive. It all comes down to cost versus benefit, doesn’t it?

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