  NI, SCA, SCS, PEDRIVER, Cluster Port Drivers? 
 The Question is:
 
Hi - The device pea0: on an alpha 2100 cluster had a problem according to
 diagnose, causing the system to crash. What function does this device perform?
 It's also known as NI-SCA port.
 
   thanks,
 
 
 The Answer is :
 
  The Compaq Systems Communications Architecture (SCA) provides a
  framework for communication among the nodes of an OpenVMS Cluster.
 
  SCA includes the definition of the services for exchanging
  information across the interconnects available within a cluster.
  In particular, SCA specifies the System Communications Services
  (SCS) for datagrams, messages, and block transfers.
 
  SCS message traffic occurs among applications known as System
  Applications, or SYSAPs.
 
  SCS defines the connection between the host SYSAP and the physical
  interconnect medium as the Port.
 
  PEDRIVER is the OpenVMS device driver that permits SCS to communicate
  with other cluster members using an Ethernet network interconnection.
  PEDRIVER is the Port Emulator (PE) device.
 
  Other SCS port drivers include PUDRIVER (the UQ (UDA50-compatible disk
  controller interface), PADRIVER (CI-compatible interface) and PIDRIVER
  (DSSI-compatible interface).
 
  PEDRIVER itself communicates with the lower-level OpenVMS network device
  drivers via an internal and undocumented device driver interface known
  as the VAXcluster Communications Interface (VCI).  VCI is a kernel-mode
  interface that is used by kernel-mode code such as device drivers to
  communicate with arbitrary network device drivers.
 
  Within an OpenVMS Cluster, higher-level device drivers -- such as the
  generic MSCP disk device driver DUDRIVER -- are layered onto a port
  driver.  (MSCP is the Mass Storage Control Protocol, the cluster protocol
  used to communicate with served disk devices.  MSCP operates over SCS.)
 
  Without specific details of the bugcheck problem that was observed, no
  (more) specific answer is feasible beyond a request for the application
  of the available mandatory ECO kits for the OpenVMS version in use, and
  (if the problem persists) direct contact with the Compaq Customer Support
  Center.
 
 Answer written or last revised on  14-AUG-2001 
