Data Portability
Using Protocol Adapters

The output of an os_bstream is a stream of primitives sent to a specific device via an os_protocol and an os_adapter . Because many types of devices are supported, the reader of the data stream can be on another computer.

Use of sockets or sharing files between multiple computers are common cases where this occurs. To allow two different computer architectures, such as SPARC and Intel, to communicate in such situations, data portability must be assured.

With Streaming<ToolKit> you can use different data protocols by providing a flexible protocol mechanism. A protocol adapter is a data translation layer that translates between platform-specific primitive data types and portable data representations. The protocol interface is defined by the abstract base class os_protocol , which is designed to be easily extensible.

By default, the os_bstream class uses the Network Data Representation (NDR) protocol to binary encode primitives. For information on how to build and use alternative protocols, refer to the "Changing Protocols in the Universal Streaming Service" section of this chapter. NDR is an efficient protocol, because of the negotiation between the reader and the writer when the connection is initially established. During this initialization phase, information about each side's memory architecture, word size, and other values are exchanged in a predefined packet known as a format label.

The format label enables each side to determine which data conversions, if any, are necessary to communicate with the other party.

If both parties have the same format label, no conversions are necessary and communication can proceed at an uninhibited rate.
If the formats are different, only conversions that are necessary occur.

Compare this approach to other protocols that require both the reader and the writer to convert primitives to a common, "neutral" data format.

All NDR protocol-specific data translation is performed by the protocol adapter class os_ndr .

Data Portability Using Protocol Adapters

Data Portability
Using Protocol Adapters