MPLS … or multiprotocol label switching … seems to be the buzzword for connecting enterprise data networks these days. But MPLS is really nothing new. Actually, it has been around for a while. Perhaps now it is only gaining more popularity and therefore notable public notoriety and acceptance. With good reason too. MPLS offers many advantages over traditional T1 point-to-point WAN architectures.
But … to decide if MPLS is really a good fit for your network requirements … there are a few things you need to understand first.
There is no “MPLS Service”. Much of what you get will depend on how the service provider designed and built its core network. Note that many operators do not own the entire network, but will assemble a service from other operators’ networks or interconnect with other operators to expand their reach.
MPLS in cellular mode was mentioned – basically this is ATM that has been retrofitted with MPLS. Be careful with this for VoIP applications because it can use bandwidth very inefficiently.
MPLS can support QoS, but many services are not designed with this, or only with very basic prioritization. Also, services are very often structured to reduce potential complexity and ensure that the network can cope. Note that a typical MPLS router can only carry a percentage of “high priority, real-time” traffic. If everyone sends all their data with high priority, the benefit is lost and the network may be affected. QoS is typically provided as a small number of Classes of Service, typically 3 or 4.
The biggest bottleneck in any service of this type is normally the tail circuit of each of its facilities. If you go from a T1 mesh to an MPLS service, you will probably find that some sites need more bandwidth than others. Tracking this bandwidth requirements is usually your problem, although the service you provide can provide some reporting tools to help you with this. You would avoid service providers that cannot offer this as it will be very difficult for you to manage your bandwidths.
If you consider multiple classes of service, managing these queue circuits becomes more complex, as you not only have to calculate how much bandwidth is required for each queue circuit, but how much should be reserved for each class of service.
In terms of resilience, within the core of service providers, the service is typically very resistant to failure. However, when failures occur, very often (depending on how the service is designed), the rerouting can take a second or two. During this reconvergence of the network, you will lose packets. Depending on the protocol your traffic uses, this can be unimportant or devastating. For example, some VPN and VoIP services don’t survive as well.
Resilience is not typically delivered automatically to the end to the customer. Typically, you will have a tail circuit and a router at each site. If it fails (or if the service provider’s PE router has problems), you will totally lose service from the site.
If this is a problem, you should be aware of dual connections. There are several ways to do this and different service providers will offer different options. Make sure to involve your network engineer as the devil is in the details here, and some options that seem to provide a fantastic level of resistance may not be as good as they sound, depending on how your internal network is configured.
And of course the key to all of this is SLAs – what do they offer? What if they break them? How do they inform you?
Generally speaking, MPLS services are a great way to run a multi-site data network, including VoIP services. I have seen many operators and their clients do this successfully over the years.
Strictly speaking, MPLS does not provide QoS. Quality of service is done by prioritizing traffic, and most IP routers, even those on the Internet backbone, can. The difference is whether they are configured to do this or not. In an MPLS network, MPLS is provided by standard features of the router. MPLS (specifically Traffic Engineering) technology gives the operator better control over how this traffic is prioritized and routed (and restored in the event of a network failure). All it does is give them the confidence to support SLAs.
As I mentioned, “QoS” is provided as a set of “classes of service”. Usually these are things like “real time,” “high priority,” and “everything else.” Assigning the actual traffic to these classes can be done in a number of ways, but this is largely up to you to control. For example, you could easily put web browsing traffic in “real time”, although that would normally be silly.
I would suggest that the case for MPLS in terms of performance, cost and continuity versus “traditional” or “legacy” data networks is now quite strong, ie MPLS provides significant advantages in all 3 areas.
Key considerations when migrating include vendor selection, means of access (for example, using Ethernet instead of SDH / SONET), the decision to purchase a managed or unmanaged service (often called just cables), and the ability to providers to assign your CoS / QoS to the applications you need to support. This is especially important if you are running proprietary applications.
There is also a growing trend to use WAN optimization / application management solutions, either as a value-added service from the vendor or alternative integrator, or indeed in-house. This is important for voice or applications like CITRIX.
MPLS providers also now offer a full suite of value-added services, such as integrated Internet, network-based managed firewalls, and remote user support. If these are important to you, make sure providers demonstrate how this is done.
When selecting your provider, make sure they have good geographic coverage in your areas and expertise within your market segment. I always recommend requesting up to 3 references. Similarly, I think it is wise to understand how important you as a customer will be to the supplier. It’s all very well to use the market leader (say according to Gartner) … but you will often get better service from a vendor who values and really wants your business.
Need help designing the right MPLS configuration for your network? There are tons of resources … free and paid … listed and discussed on Broadband Nation.
