Given a scenario that you are developing the network architecture for a business (single or multi-site)....what would be the best application(s) where you would choose MPLS as the (or part of the) solution? This may not be as simple as it sounds.....thus the frustration faced by many responsible for a company network infrastructure solution.

First, I recommend reading "MPLS Enabled Applications: Emerging Developments and New Technologies". A simple Google search will find the best source to obtain a copy.

For additional resources check out one of these books:

MPLS and VPN Architectures, Volume I & Volume II
by Jim Guichard; Ivan Pepelnjak; Jeff Apcar

Definitive MPLS Network Designs
by Jim Guichard; Franois Le Faucheur; Jean-Philippe Vasseur

Traffic Engineering with MPLS
by Eric CCIE #4122 Osborne; Ajay CCIE #2970 Simha

Internet Routing Architectures, Second Edition
by Sam Halabi; Danny McPherson

Generally, MPLS is often thought of when considering replacing an existing frame relay network. MPLS is best at supporting the QoS needed for supporting integrated VoIP and data. Plus, MPLS is significantly easier for to engineer and roll out than say a new frame relay cloud.

A good scenario would be an enterprise WAN with multiple service delivery needs, teleconferencing, VoIP, video, and data. Each of these services has different data delivery requirements. VoD needs bandwidth but after the initial push it is not time sensitive, data is not in any reasonable sense time sensitive, VoIP and video conferencing are both extremely time sensitive applications.

In this situation MPLS is an excellent choice as transport. Not only is it fast, not requiring deep packet inspection beyond the ingress point to prioritize traffic, it also allows for multiple levels of service which puts you in a position to future proof your network to some extent.

MPLS is also refered to as tag switching. The way that it works is at the network ingress point each packet is 'tagged', or a header put on the packet, which gives it a network identifier and a service level if service levels have been implemented. When switching within the network each router needs only inspect the tag to prioritize and forward the packet.

In addition, network service providers are moving to MPLS because of its ease of implementation and the ability to transparently provision multiple customers on the same network, as opposed to frame relay which requires a separate network for each customer, and keep those customers perfectly digitally segregated. So, it's a case of faster, cheaper, better for the service provider.

QoS for VOIP and video is the big thing. MPLS gets used a fair bit for bandwith guarantees and limits for things like Disaster Recovery (DR). A good example is when a business has two offices in different geographical areas, and wants to use a data-syncing solution (SAN replication, for example) between them for disaster recovery. But they have limited bandwidth, and don't want the DR traffic to swamp the normal or VOIP traffic. Being able to label your traffic and set guarantees (for both minimum and maximum bandwidth) is pretty powerful. This also offers guarantees for in-order packet delivery (very important for VOIP/voice).

For a single-site business, I would probably not deploy MPLS unless there was a serious amount of bandwidth in use, or if the campus was significantly large enough to justify using label switching for speed / QoS considerations. Unfortunately, there's no easy answer for this scenario.

For a multi-site, geographically diverse business, I would strongly consider MPLS as part of the solution, particularly if I am using a service provider such as Sprint, Level 3, BT, or any others to provide the meat of the network. This arrangement allows me to leverage the availability, redundancy, and scalability of their network to take the shortest path between sites.

Most companies moving to MPLS were previously operating their private-line networks with either direct connections between offices, or utilizing frame-relay connections. A hub-and-spoke architecture is only efficient if all the data flows to/from the central location. However, most frame networks are meshed together, to facilitate office-to-office networking without overwhelming the hub site. It's very easy for a large number of sites to turn into complex and unwieldy collections of frame circuits and PVCs. If the company's IGP is not set up properly, traffic patterns can become stable at best, and down right chaotic at worst.

Using MPLS with a provider eliminates the need to worry about any of the meshing that would have been handled by multiple private lines or frame-relay networks. Usually, routing is exchanged with a provider via BGP, or in the case of smaller networks, statically routed.

An excellent application of MPLS seen in practice is that with a BGP-connected network, it is possible to set up a disaster recovery scenario at any other site connected to the network by a simple matter of moving the routing announcement for the primary location's IP block to the DR location. It's possible to do this on frame relay as well, but it can get complicated if the network is not configured properly.

For application-specific items, MPLS can handle any variety of traffic classifications, which make it an ideal candidate for multi-site voice traffic to go along with your data.

The downside of MPLS is that you're at the mercy of your provider if there's a configuration mistake or if their redundant network doesn't redirect around an outage properly. Additionally, routing can become complex if there is a private network on the back end connecting two or more sites that also share an MPLS connection.

As an overview of MPLS.......

The Pros:
* Site to Site Routing
* Enhanced Carrier Aware QoS
* Reduced Deployment Complexities
* Enhancing High Availability
* Quickened Disaster Recovery Readiness

The Cons:
* Initial Architectural Design Cycles
* Reduced Visibility of Transport Network
* Enhanced Security Concerns

In summary MPLS is really just one alternative for the WAN communication backbone. The advantages are clear over a Frame Relay network.....as are the pitfalls. Whether you choose MPLS as all or part of your network infrastructure solution must takes those into account.

Michael is the owner of FreedomFire Communications....including DS3-Bandwidth.com and Business-VoIP-Solution.com. Michael also authors Broadband Nation where you're always welcome to drop in and catch up on the latest BroadBand news, tips, insights, and ramblings for the masses.

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