webservice – Learning Web applications and network architecture. Newbie questions on how many tiers?

I’m in school right now and having a debate about web applications and flat networks. There is a debate ongoing right now in a class/group about a network diagram we are looking at. The network is flat with zero network segmentation and there are numerous web applications within the network. Everything is in that “network”, all servers/db. The web applications are each on their own server and there is one database within that network for all the data being stored. There is also all the user computers within that network. Clients can log into the web application and look at their information, so there is that aspect as well.

So we’re all having a debate about the exact architecture of the applications and I think we’re getting tripped up on how we interpret the wording.

One group is saying that the architecture is single tier for the applications because the network is flat and there is no true segmentation except for the various servers and the database.
One person is saying it’s two tier because it’s a flat network but there is the presentation layer outside of the network in the form of the clients (client) computers.

Other people saying it’s three tier architecture, just in a flat network with no segmentation.

My take is that it is three tier application architecture because the presentation layer is split out from the business logic on the web app and the database. Even though the user computers are inside the network, they’re still separate from the web application and the db. It’s just in a poorly segmented network.

I know this seems pretty simple, but there are a few people that are confused by this due to the lack of segmentation and what their understanding of what a tier is.

Any input is highly appreciated.

Thank you all.