At the lowest level in the architecture figure is a configurable network protocol layer that will allow COBS to customize its operation over several communication protocols, including a real-time protocol offering guarantees for quality of service, a zero copy ATM protocol offering very high performance communications across homogeneous machines, and a configurable communication protocol permitting the on-line reconfiguration and adaptation of selected protocol processing. Conventional protocols will be used as well.
In order to insulate the system from machine differences and provide for efficient heterogeneous operation, a portable binary I/O package (PBIO)[Eis94] is being used in several situations. PBIO is a self-describing data meta-format capable of representing structured information and transmitting it between machines in a reader-makes-right protocol. COBS uses PBIO above the network layer for the transmission information required for its operation. In the past year, PBIO has been extended to support non-connected network communication styles so that it can be used over UDP and similar network protocols.
Above PBIO, a library called DataExchange[ES96a] is used to manage multiple connections, provide server location functionality and to support dynamic connection of new clients.
The Georgia Tech Cthreads library is also used as part of the COBS infrastructure. This library provides user-level threads support on a variety of uniprocessors and shared memory multiprocessors. The instrumentation support in Cthreads allows system and application performance information to be extracted for on-line or post-mortem performance analysis or tuning. This data extraction is done with minimal system perturbation and should prove invaluable in tuning applications and experimenting with new system configurations and protocols.