Tearing down the Protocol Wall with Software Defined Networking

The letter of the law of Software Defined Networking (SDN) is the OpenFlow specification, combined with appropriate controllers. The spirit of the law of SDN affords much more potential for innovation. We take the position that the future of communications is at stake unless the Protocol Wall is overcome. By "Protocol Wall" we mean the artificial barrier which, until recently, has been placed between the inflexible, protocol-bound communications space, and the application space in which far fewer constraints are placed on the programmer and in which far more innovative results can be achieved. Overcoming the Protocol Wall allows fully programmable, software-defined behaviour in both the data plane and the control plane, and opens the way for much-needed innovations in networking. In the stereotypical case, of which sockets are an example, the application functionality and the physical layer are separated between kernel and user respectively, with the kernel below the transport service layer, and the application above it. Archetypically, the router and host are separated between Internet Protocol (IP) and Transmission Control Protocol (TCP) respectively, where IP is responsible for hop-by-hop forwarding and TCP for end-to-end services. The Protocol Wall between application functionality and the physical layer constitutes a hegemony over innovation which is not being challenged sufficiently by current SDN approaches. We assert that the realisation of unconstrained Software Defined Networking is closer at hand than anyone has yet acknowledged, and that networking can be evolved more quickly if we are guided by the spirit of the law of SDN. User mode network software, running on today's commodity and specialised communications hardware, can safely support satisfactory performance, while opening up potential for the same very high rate of innovation in networking as has been seen in appliances - for example, in smart mobile devices - in recent years.