Given today's economic contraints (actual or perceived) .... and the hypothetical situation that "you" are looking for a bandwidth solution for the backbone of your network infrastructure for a multi-site business .... what would you gravitate toward and why? (e.g. T1 based ... such as MPLS, DS3/OC3/Sonet based, Ethernet based, other).
In reality there is no universal answer for this.
I'd recommend a three step process:
1) Determine your bandwidth and performance needs.
2) Get quotes for various services, from various vendors that meet your needs.
3) Pick the lowest cost solution that comes from a vendor you trust.
In my opinion MPLS always makes the most sense (when available), because it's very cost effective and redundant (new or replacement). However, like anything else, it depends on the scenario. We have many different deployments of MPLS, DS3, T1's, OC3's, and in some cases E1's (outside of North America). However, no matter which pipe works for your particular deplyment, any sort of shared resource/cost model will always be more economical.
The answer is not quite that straightforward. The answer would depend on the size of the company, the number of offices, their geographic locations, the amount of bandwidth needed between offices, and the number of dollars they want to commit to the project.
If they are in a large metro area metropolitan ethernet may well be the cheapest form of connectivity. It's very easy to attach to the LAN at each location and as a Layer 2 transport supports any and all Layer 3 and higher protocols. It would also allow you to prioritize traffic and make priority changes as you desire. As implemented by most carriers, metropolitan ethernet is "layer 1 agnostic", meaning it doesn't care if it's running over a DS1, DS3, OC3, OC12, etc.
If they are spread across a wider geographic area MPLS would most likely be your best option. But it will require additional expertise at the router level and additional dollars to spend for routers and IOS software that support MPLS traffic. But again as a Layer 2 transport it supports almost any and all Layer 3 and higher protocols. And depending on the carrier selected, it too should allow you to prioritize traffic and make changes as you desire. As implemented by most carriers, MPLS (like metropolitan ethernet) is also "layer 1 agnostic".
If they are a small, financially conservative company with a dozen offices spread across a state or region a high quality site-to-site VPN may be the best option. It's very low cost, easy to set up and maintain and very well understood technology.
No matter which of these 3 you pick, they all have the potential for built-in redundancy which allows for traffic re-route around a cut line or other network failure. If you were going with a large deployment of MPLS (say national or international coverage) I would suggest implementing MPLS on 2 different carriers to protect you against carrier outages as well.
If you're looking at MPLS nationally, AT&T and Global Crossing are probably your best choices. They both understand MPLS very well, and both have it deployed in their own backbone networks (and have for 7+ years).
A key question to ask is whether or not the site equipment is being upgraded (i.e. Legacy PBX to VOIP-PBX) as well or just the backbone.
There exists the following possible scenarios:
1) If you are upgrading Legacy PBX's to IP-PBX's, then the infrastructure is simply an ethernet backbone for both voice and data.
2) If you are keeping the Legacy PBX's in place, you need an infrastructure that supports both T1 (or E1) for legacy voice and ethernet for data services.
a) Simplest way is to implement separate links for T1 (for the Legacy PBX's) and ethernet link for data services.
b) You could implement an all T1 solution for both legacy voice and data services. You would need an additional piece of equipment that maps Ethernet onto T1 (or E1) via EoPDH protocol.
c) You could implement an all ethernet solution for both legacy voice and data services. You would need an additional piece of equipment that maps T1 (or E1) from the Legacy PBX onto ethernet via the SAToP or CESoP protocols.
Of the above proposals, #1 and #2C are the preferred options.
For multiple sites, MPLS is a very good approach for VPNs. You can also use single VLANs (802.1q) or stacked VLANs (802.1ad) based equipment for creating VPNs.
Ultimately .... the answer would depend on the size of the business and the typical office set for the multi-location scenario to determine the most economically viable solution.
For a large Enterprise account or even an SMB the convergence of voice and data networks is the key in my opinion. Get more out of your wireline for less. The solution could be a hosted VoIP solution using a network based carrier that can overlay MPLS for data application sharing with a hosted VoIP product that offers QoS on the voice side. For a larger account where hosted may not work it could be IP enabled PBX at an HQ with all voice traffic funneling through there to remote offices using IP sets.
In either a hosted or premise based PBX scenario you can reduce costs by reducing copper lines as well as per minute usage charges by implementing the VoIP model. If it is a premise based solution the MPLS with QoS for voice for IP calling between locations is the critical piece.
Some carriers offer a high bandwidth solution at a low cost using EFM (Ethernet over First Mile) that can povide you with the same capabilities of a T1/DS3 from a network (or WAN) infrastructure standpoint in terms of high speeds, and overlay with MPLS, VPN, etc, while still being able to honor CoS requirements and provide QoS for voice calling to give you a converged solution.
Dynamic bandwidth (single or bonded IP backbone delivery broken up for voice and data) can be used in a converged solution in a bunch of different scenarios. But in today's world, as much if not more business is being done via the internet than over the phone. Therefore, maximizing the companies utilizations in the right way is the best way to determine what solution is best for them. Be it a network upgrade or new network construction/design, getting "the most for less" is critical with today's economic constraints.
To me the answers are always dependent on the true business requirements AND the flexibility and scalability your business plans call for.
For a new network ..... I would think you would especially gravitate to what you perceived to be the most scalable, both upwards and downwards. However, you also have to make a decision on the network availability your business requires. Do you require 99.999% availability? If so, then what providers have demonstrated this level of availability and what contractual remedies do they provide? Obviously, these are just a couple of examples that makes the selection process extremely dependent on your business requirements.
For upgrading or replacing your network ..... you have the "benefit" of having a very real track record of your business history and therefore your network infrastructure performance and dependencies in my specific environment.
However, the evaluation/decision criteria is the same.
In both scenarios, by now, you have a fairly good idea (based on your product and services) the impact the economy is having and will have on your customers .... and therefore you have scenarios based on "what if". This dictates and drives your decision process on how you can have a dynamic network infrastructure to serve your current needs .... and a network provider that has contractual conditions you are comfortable with in meeting your needs for "dialing up" and "dialing down" those needs.
Keep in mind that to find the best solution you'll need to determine your detailed set of requirements --
What is your application? Voice & Data? Just Voice? Just data? And by data, is your requirement for internet connectivity alone or inter-site data transmission? What are your bandwidth requirements? How concerned with quality are you? Do you need specific SLAs? Do you have mission critical data? Do you need redundancy? If so, at what layer? Where are your locations? (urban, suburban, rural, very rural, international?) Are the sites relatively close together? What are your latency and jitter requirements? Do you have specific security requirements? Lastly - what's available?
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As a Telecommunications Consultant, my job is to figure out what makes the most sense for each company on an individual basis. It's not a one size fits all world.
As a Telecommunications Consultant, I ask the necessary questions about business processes to determine what the bandwidth requirements are.
There are numerous scenarios from security, regulations, network usage, type of usage (video, VOIP, VPN), etc. that will define a solution for each client. It is rarely the same in all instances.
It also depends on Location. Ethernet is not available everywhere. Not every location has more than two choices. (It's called a Duopoly for a reason).
As a Telecommunications Consultant, the client is looking to me to ask the appropriate questions and design a solution for their specific needs.
That's what I do.