R&S NRP
Supplement
1144.1400.12-04- Supplement
3
E-1
Communication channels of a VXI11 connection
Channel
Meaning
Core
All client-server communication, excluding aborts and interrupts, is handled via this channel.
Abort
Since the commands in the core channel are serialized and therefore cannot be interrupted,
asynchronous abort commands must be transmitted via a separate, independent channel. This
channel serves no further purpose.
Interrupt
Service requests (SRQs) are reported to the network instrument client via this channel. As all links
share this channel, the client must subsequently determine which device triggered the SRQ by
polling the status bytes (device_readstb() function) of all connected devices.
Connection setup
A socket connection is set up for each channel. All commands via the core or abort channel contain an
ID that is used to assign the command to a link. The interrupt channel, which is also implemented using
sockets, is shared by all links. Commands transmitted via this channel do not contain a link ID. The
setup is handled by the network instrument client, which first requests the connections from the network
instrument server's portmapper service at port 111. The portmapper subsequently activates the channel
in the R&S NRP and tells the client at which ports channel services can be addressed. For this reason,
it is important that any firewalls or routers between the client and the R&S NRP enable free access from
the controller to the R&S NRP (core and abort channels) and vice versa (interrupt channel). As the
ports for the channels are dynamically assigned, reliable information regarding the port numbers used
cannot be provided.
Remote control via VXI11
The following possibilities are suggested for remote-controlling the R&S NRP via VXI11:
1. The simplest way to create remote-control programs is by using a VISA (virtual instruments
software architecture) implementation and creating the remote-control programs under Visual Basic
or C/C++. VISA implementations provide an application programming interface (API) that offers all
necessary functions. Knowledge about VXI11 is helpful but not required.
The VISA resource identifier used to identify a VXI11 device has the following format:
TCPIP::<IP address>::INSTR
The IP address is specified using the familiar dot notation (e.g. 89.10.65.59).
2. The "TCP/IP Instrument Protocol Specification VXI11" contains in annex C an RPCL description of
the protocol. The program
rpcgen
, which is contained in any ONC RPC distribution, is used to
generate stubs, which can be inserted into separate C programs, where the functions from the
following table can be called like ordinary library functions.
This procedure requires RPC programming skills.
