With the advent of connectionless web-based computing, I feel we have lost something by stubbing out the Session and Presentation layers of the OSI RM.

The Session Layer provides for continuity of service despite major disruptions in the service and even the peer device. This level of reliability is what is required if distributed computing, software as a service, cloud computing, etc. are ever to be successful for non-trivial applications.

The Presentation Layer is the OSI home for encryption. This would have provided much better security than the current practice of encrypting at a device level. With this in place, all data leaving an application would be encrypted to the appropriate level without regard to whether the target was the Internet, intranet, hard drive, thumb drive, or tape back up.

The OSI RM provided a strong architecture for reliable, secure communications and unfortunately we have taken too many "simplifying" steps and lost some improtant capabilities along the way.