One reason why IPv6 has slow adoption is that the seven layer model has created a “waist” where change is possible in some layers but impossible in others. As the diagram below suggests, change in applications and protocols (Layer 5/6/7) is possible while Layer 1/2 has slower change but it does happen. The one thing that cannot change is IPv4.
I’m onboard with this.
The Internet protocol stack has a layered architecture that resem- bles an hourglass. The lower and higher layers tend to see frequent innovations, while the protocols at the waist of the hourglass appear to be “ossified”. We propose EvoArch, an abstract model for study- ing protocol stacks and their evolution. EvoArch is based on a few principles about layered network architectures and their evolution in a competitive environment where protocols acquire value based on their higher layer applications and compete with other protocols at the same layer. EvoArch produces an hourglass structure that is similar to the Internet architecture from general initial conditions and in a robust manner. It also suggests a plausible explanation why some protocols, such as TCP or IP, managed to survive much longer than most other protocols at the same layers. Furthermore, it suggests ways to design more competitive new protocols and more evolvable future Internet architectures.