| MPLS... or Multi-Protocol Label Switching.... seems to be | | | | the devil is in the detail here, and some options which |
| the buzzword for connecting company data networks | | | | sound like they provide a fantastic level of resilience |
| these days. But MPLS is really nothing new. It's been | | | | may not be as good as they sound, depending on how |
| around awhile actually. Maybe now it's just gaining | | | | your internal network is configured. |
| more popularity and thus noticeable public acceptance | | | | And, of course, the key to all of this is SLAs: what do |
| and notoriety. Rightfully so too. MPLS offers lots of | | | | they offer? What happens if they break them? How |
| advantages over traditional T1 point-to-point WAN | | | | do they report them to you? |
| architectures. | | | | Generally speaking, MPLS services are a great way |
| But..... to decide if MPLS is really a good fit for your | | | | to run a multi-site data network including VoIP services. |
| network requirements..... there's some things you need | | | | I have seen many carriers and their customers doing |
| to understand first. | | | | this successfully for years. |
| There's no one "MPLS Service". A lot of what you get | | | | Strictly speaking MPLS does not provide QoS. QoS is |
| will depend how the service provider has Engineered | | | | done by prioritizing traffic, and most IP routers, even |
| and built their core network. Bear in mind that many | | | | those on the backbone of the Internet, can do this. The |
| carriers don't own the whole network, but will piece | | | | difference is whether they are configured to do this or |
| together a service from other carriers networks, or will | | | | not. In an MPLS network MPLS is provided by |
| interconnect with other carriers to extend their reach. | | | | standard router features. MPLS technology (specifically |
| Cell-mode MPLS was mentioned: basically this is ATM | | | | Traffic Engineering) gives the carrier better control |
| which has been retro-fitted with MPLS. Be careful with | | | | over how this traffic is prioritized and routed (and |
| this for VoIP applications because it can use bandwidth | | | | restored in case of network fault). All this does is give |
| very inefficiently. | | | | them the confidence to support SLAs. |
| MPLS can support QoS, but many services aren't | | | | As I mentioned, "QoS" is provided as a set of "service |
| engineered with this, or only with very basic | | | | classes". Typically these are things like "real-time", |
| prioritization. Also the services are very often | | | | "high-priority" and "everything else". Mapping actual |
| structured to reduce the potential complexity and to | | | | traffic into these classes can be done in a few |
| ensure the network can cope. Bear in mind a typical | | | | different ways, but this is largely up to you to control. |
| MPLS router can only carry a percentage of | | | | For instance, you could quite easily put web-browsing |
| "high-priority, real time" traffic. If everyone sends all their | | | | traffic into "real time" although this would normally be a |
| data as high priority then the benefit is lost, and the | | | | dumb thing to do. |
| network may suffer. Usually QoS is provided as a | | | | I would suggest the case for MPLS in terms of |
| small number of service classes, typically 3 or 4. | | | | performance, cost and continuity against 'traditional' or |
| The biggest bottleneck in any such service is normally | | | | 'legacy' data networks is now pretty robust, i.e. MPLS |
| the tail circuit to each of your premises. If you move | | | | provides significant advantages in all 3 areas. |
| from a T1 mesh to a MPLS service then you will likely | | | | The key considerations when migrating include |
| find that some sites need more bandwidth than others. | | | | provider selection, access media (e.g. using Ethernet |
| Tracking the requirement for this bandwidth is usually | | | | rather than SDH/SONET), the decision on procuring a |
| your problem, although the service provides may give | | | | managed or unmanaged service (often called |
| you some reporting tools to assist with this. I would | | | | wires-only) and the providers ability to map their CoS |
| avoid service providers who cannot offer this as it will | | | | QoS to the applications you need to support. This is |
| make it very difficult for you to manage your | | | | especially important if you are operating any |
| bandwidths. | | | | proprietary applications. |
| If you factor in multiple service classes then your | | | | There is also an increasing trend to use WAN |
| management of these tail circuits gets more complex | | | | Optimization/application management solutions either |
| as you no only have to work out how much | | | | as a value added service from the provider or from |
| bandwidth is required for each tail circuit, but how much | | | | an alternative integrator or indeed doing it in house. This |
| of it should be reserved for each service class. | | | | is important say for voice or applications such as |
| Regarding resilience, within the service providers core, | | | | CITRIX. |
| the service is normally highly resilient to failures. | | | | MPLS providers also now offer a whole suite of value |
| However, when failures do occur, very often | | | | added services such as integrated internet, managed |
| (depending on how the service is engineered) the | | | | network based firewalls and remote user support. If |
| rerouting can take a second or two. During this | | | | these are important to you make sure the providers |
| network re-convergence you will lose packets. | | | | demonstrate how this is achieved. |
| Depending on the protocol your traffic uses this can | | | | In selecting your provider ensure they have good |
| be unimportant or devastating. For instance, some | | | | geographic coverage in your areas and experience |
| VPN and VoIP services don't survive this well. | | | | within your market segment. I always recommend |
| Normally resilience is not automatically provided all the | | | | requesting up to 3 references. Equally I think it is wise |
| way to the customer. Typically you will have one tail | | | | to understand how important a client you will be to the |
| circuit and one router at each site. If either fails (or if | | | | provider. It's all well and good using the market leader |
| the Service provider's PE router has problems) you will | | | | (say according to Gartner)..... but you'll often get a |
| lose service to the site, totally. | | | | better service from a provider who values and really |
| If this is an issue, you need to factor in dual | | | | wants your business. |
| connections. There's multiple ways of doing this, and | | | | Need help designing the right MPLS configuration for |
| different service providers will offer different options. | | | | your network? There's a ton of resources..... free and |
| Make sure you get your Network Engineer involved as | | | | fee..... listed and discussed at Broadband Nation. |