Network Topology
Network topology is one of the most important criteria to consider when choosing a provider. Looking at the network topology can help you understand how vulnerable the network is to outages, how much capacity is available when the network is loaded more heavily than usual and most importantly, how well the provider understands network engineering.

Any competent provider should be happy to show you their network topology. It's a good way for them to demonstrate how well they understand their business.

Look closely at what they show you. Some providers will give you a virtual backbone map. Virtual networks are meaningless. Your data does not travel on a virtual network -- it travels on a physical network. A virtual network map is merely a representation of all the theoretical paths that could be implemented by the supplier's virtual circuit switching equipment and is an attempt to side step the issue of physical capability. Your supplier needs to understand the physical network to understand what is important for serving their customers. If they tell you that the physical topology is unimportant, they either don't understand how to engineer a network or they are trying to disguise something. Remember, there is nothing inherently wrong with using frame relay, ATM , or other technologies that use virtual circuits as part of the backbone. However, your provider must understand the physical topology on top of which their virtual (logical) network is running.

Network Link Speeds
Now that we're evaluating the physical topology, let's look closely at the speeds of the backbone links. If they won't show you the speeds, then they're really hiding something. The first thing to understand is that your network connection can only be as fast as the slowest link in the path.

It doesn't matter if you are connected to a T-3 node if there is a 56 Kbps link between you and your destination. This is like hooking a half-inch garden hose to a fire hydrant. The limit is the garden hose, not how much water the hydrant can put out!

Next, ask if the topology you are being shown is operational now. Some providers like to show links that are not operational as part of their backbone infrastructure. Some even go as far as to label the planned links with solid lines and the operational links with dashed lines! You're in for a big surprise if you don't notice this switch! Similarly, don't confuse the press release about a new high speed network link with that link actually being operational.

External Network Links
Now look at the external links of your candidate's backbone. Do they have a single connection to the rest of the world, e.g.? This is a potential single point of failure. Look for multiple, direct connections to other network providers. The more of these connections the better. This shows that the provider is concerned about external connectivity and does not want to be dependent on some third party for interconnection. If they have a single connection to the outside world, ask them how often it fails and how long they usually are isolated. If they can't give you these statistics, are they managing their network well enough to manage yours?

Now ask yourself if you have enough confidence in their plan to risk your connectivity to the rest of the world.

High Speed Backbone
If they claim to have a high speed backbone, check to see if it is that speed now or if it is just "planned." Some providers claim to have a T-3 (45 Mbps) backbone, but if pushed, will admit that what they really mean is "T-3 capable." A 2400 bps dial-up modem is also T-3 capable because tomorrow it is capable of being replaced with T-3. If they are misleading you about something as fundamental as their network capacity, what else are they trying to sneak past you?

The next thing to ask yourself about high speed backbones is if you can actually connect to it for a reasonable cost. All service providers require you to buy the local loop segment from your facility to their closest Point Of (service) Presence or POP. You will have to buy this directly or indirectly from one of the telephone companies serving your local area. Some providers offer their service in such a way that the local loop cost is greater than their fee to provide you with the service in the first place. Think of the hose analogy again. If you're limited by the local loop speed because the price of a high speed loop is not cost effective, then how useful is a high speed backbone?

Many providers will claim some impressive number of POPs. Find out what constitutes a POP by their definition. Some providers claim a POP anywhere they deliver service. Find out if many of their "POPs" are single customers at the tail end of low speed lines or if those POPs house high end routers linked by physically redundant high speed connections. Network POPs should be designed to scale with additional customers who, themselves, have growing requirements.