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[[File:TCPIP-arch.png|thumb|350px|Figure 4. Functional layering of the TCP/IP architecture]]
The current architecture just provides two scopes: data link (scope of layers 1 and 2), and global (scope of layers 3 and 4). However, layer 4 is just implemented in the hosts, therefore the “network side” of the Internet ends at layer 3. This means that the current Internet is able to handle a network with heterogeneous physical links, but it is not designed to handle heterogeneous networks, although this is supposed to be its operation. To be able to do it, it would require an “Internetwork” scope, which is now missing.<ref name="lostlayer"/> As ironic as it may sound, the current Internet is not really an internetwork, but a concatenation of IP networks with an end-to-end transport layer on top of them. The consequences of this flaw are several: both inter-___domain and intra-___domain routing have to happen within the network layer, and its scope had to be artificially isolated through the introduction of the concept of [[Autonomous
With an internetwork layer none of this would be necessary: inter-___domain routing would happen at the internetwork layer, while intra-___domain routing within each network would occur at each respective network layer. NATs would not be required since each network could have its own internal address space; only the addresses in the internetwork layer would have to be common. Moreover, congestion could be confined to individual networks, instead of having to deal with it at a global scope as it is done today. The internetwork layer was there in previous internetwork architectures, for example, the INWG architecture depicted in Figure 3, which was designed in 1976. It was somehow lost when the [[Network Control Program]] was phased out ant the Internet officially started in 1983.
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