ISPs and service providers have deployed various forms of network intermediaries with accelerating frequency. The result of these deployments is an Internet composed of discrete subnetworks, attached at a relatively small number of choke points, lacking universal addressability, and including stateful in-network intermediaries as vital components. This work develops a novel technical mechanism---a new definition of the ``session layer''---as a way to manage the new complexity, retrieve some of the lost benefits of the original homogeneous model, and open a variety of new possibilities.
A session layer protocol allows endpoints to become aware of and manage intermediate services. Each endpoint of an application can specify which intermediate services it desires, permits, or prohibits to exist along the path between it and the other application endpoint. The session layer runs over a sequence of transport connections. Each intermediary is explicitly addressed, allowing it to be located anywhere in the Internet. The session layer verifies end-to-end delivery, offering a variety of semantics. A session can survive a change to the underlying transport parameters, including change of an endpoint's IP address.
Broader Impact: The extra layer of indirection provided by the session layer promises many benefits. Among them are a cleaner programming model for both applications and intermediate services; easier deployment of intermediate services; simplified physical network design; improved performance of an individual session; reduced congestion and greater bandwidth utilization for the Internet as a whole; better fault tolerance and manageability; and the enabling of important new services.
