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.
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. Now that we're evaluating the physical topology, let's look closely at the speeds of the backbone links.