How The Internet Got Its Hourglass Shape

Researchers at Georgia Tech have come up with an hourglass model that consists of six protocol and application layers that originate from a single bubble - IPv4. The scientists understand this model called EvoArch as an evolutionary process that leads to conclusions why some protocols survive and others do not. These new understandings could be used in future developments to evolve the Internet and help develop new uses and better security, the researchers said.

"To avoid the ossification effects we experience today in the network and transport layers of the Internet, architects of the future Internet need to increase the number of protocols in these middle layers, rather than just push these one- or two-protocol layers to a higher level in the architecture," said Constantine Dovrolis, an associate professor in the School of Computer Science at the Georgia Institute of Technology.

According to the model, there is a "plausible explanation" for the Internet's hourglass shape: "At the top, protocols are so specialized and selective in what underlying building blocks they use that they rarely compete with each other. When there is very little competition, the probability of extinction for a protocol is close to zero," the researchers explained.

"In the top layers of the Internet, many new applications and application-specific protocols are created over time, but few things die, causing the top of the hourglass to get wider over time," said Dovrolis.

In the higher layers, a new protocol can compete and replace an incumbent only if they provide very similar services, according to the EvoArch model. An example would be HTTP that largely replaced FTP. At the bottom, protocols serve as "general building blocks and share many products in the layer above." However, no bottom layer protocol can dominate as they are "used in an abundant way", which protects them from being eliminated. The researchers mentioned Ethernet as an example.

The key conclusion of the model is that few powerful and old protocols will be in the in the middle layers that are referred to as "evolutionary kernels", which include the pillars of the Internet and ensure its stability - IPv4, TCP and UDP. While these elements are difficult to replace, there can be a replacement, according to the scientists. The EvoArch model suggests designing protocols "that are largely non-overlapping in terms of services and functionality so that they do not compete with each other." Once the overlapping factor reaches 70 percent of their functions, protocols begin competing with each other.

Quality of the protocol is not always a guarantee for its success: "It is not true that the best protocols always win the competition," noted Dovrolis. "Often, the kernels of the architecture are lower-quality protocols that were created early and with just the right set of connections."