There are several possible ways to adapt between the various different protocols, ranging from gateways that strip off the protocol specific parts of data packets (i.e. the headers) and ‘repacketize’ the information (i.e. the content/data) using different protocols, to adaptive and composable protocols, and, finally, to the use of customizable network nodes capable of interpreting the protocol information attached to a packet as it arrives. The complexity of networks and network interconnection, however, has led to the implementation of stratified protocol structures whereby different layers offer their particular services to the next higher layer. This ‘protocol stack’ model not only reduced the complexity of protocol implementations but it also introduced different levels of abstraction.The rationale to separate protocols into several distinct layers is based on a number of
principles:

• a layer should be introduced where an additional layer of abstraction is required;
• each layer within a protocol stack should perform a clearly defined function;
• functionality of layers should be defined as generally as possible (to enable open system development);
• layers should be defined to provide minimized interfaces to neighburing layers (i.e. encapsulation of complexity);
• the number of layers should reflect the number of identified protocol functions, but should not blur the clarity of the protocol stack architecture.

These principles are the basis of the open systems initiative(OSI) reference model for protocol stacks and have been applied for most of the commonly used protocol stacks (e.g. GSM). Open system protocols are rigidly defined and standardized, with the result that they lack any reconfigurability or capacity for adapting to changing communication requirements. More versatile protocol stack constructs are thus required to enable and simplify terminal reconfigurability and to meet the needs of integrated communication environments. Adaptable , composable and reconfigurble protocols are techniques that can provide such versatility.

"SYSTEM RECONFIGURABILITY"

"Terminal-Centric View of Software Reconfigurable System Architecture and Enabling Components, and Technologies"