Network Communication

Each VXI and VME crate contains a cpu (MVME 147) having an ethernet interface which is a node on the local area network and which also acts as a gateway for other CPU cards in the same crate. The use of UNIX and VxWorks enables common network software to be used in all components of the system

• Internet networking (IP)

• UDP/IP (User Datagram Protocol/Internet Protocol)

• RPC (Remote Procedure Calls)

• XDR (eXternal Data Representation)

• NFS (Network File System).

All communications between applications specific to the Data Acquisition System are based on the Client/Server model using Remote Procedure Calls. Using the network software RPC requests can be made between clients and servers across the ethernet, between VME cpus within a crate across the VME backplane, and within a single CPU or workstation.

This allows the software components to communication in a way which is independant of their location.

Fixed UDP/IP ports are used by the servers in order to avoid the delays which the use of dynamic ports and the Portmapper would involve.