Technical data

Connecting Instruments to LAN 5
Agilent Connectivity Guide 99
General Issues with LAN Configuration
Basic design considerations for a LAN-based test system include:
Dynamic nature of IP addresses If instruments are assigned IP
addresses by DHCP or AutoIP, the IP address will occasionally change.
With DHCP, this could happen when the DHCP lease expires (unlikely
since most configurations grant the same IP address) or when the
instrument is turned off and on (this is more likely). With AutoIP, it is
more likely that instruments will show up at different addresses.
Therefore, do not rely on dynamically assigned IP addresses as the
primary way to address an instrument controlled from your programs.
Using hostnames Accessing instruments via hostname requires that
the instrument’s hostname is registered with DNS. Most LAN
instruments provide a default hostname composed of the manufacturer,
instrument ID, and serial number. The instrument then requests that
hostname via DHCP when it requests an IP address. If DHCP supports
Dynamic DNS, then registers the hostname. After discovering an
instrument, Agilent Connection Expert does a reverse DNS lookup to
determine if the instrument has a hostname and it has been successfully
registered with DNS. The same reverse DNS lookup solution works if
the hostname and IP addresses are both statically assigned by IT.
Security Private networks generally involve direct connections
between the PC and the test instruments and may include switches or
routers. Access to the instruments is limited to users connected to the
private network as opposed to users on a site (corporate) network that
could locate and access the instruments from any location -- possibly
disrupting tests in progress. Code generation is often simplified as
protection against unauthorized users may not be required.
Performance Test systems where large amounts of data are
transferred usually have faster throughput on private networks. On a site
network, heavy and unpredictable LAN traffic affects each instrument
on the network. Test system repeatability is difficult to achieve as
latencies are difficult to account for.
Reliability Private networks are fundamentally more reliable than
site networks as they host fewer users and are less complex. Private
networks are isolated from conditions that might crash a site network.