Oxygen 78-6896-01 Manuel D’Utilisation

Volt-ohm meters and digital multimeters measure parameters such as AC and DC voltage, current,
resistance, capacitance, and cable continuity. They check physical connectivity.

Using cable testers (scanners), you can also check physical connectivity. Cable testers are available for
foil twisted-pair (FTP), unshielded twisted-pair (UTP), 10BaseT, and coaxial and twinax cables.
A given cable tester can perform any of the following functions:

Test and report on cable conditions, including near-end crosstalk (NEXT), attenuation, and noise

Perform time domain reflectometer (TDR) functions, traffic monitoring, and wire map functions

Display media access control (MAC)-layer information about LAN traffic, provide statistics such
as network utilization and packet error rates, and perform limited protocol testing (for example,
TCP/IP tests such as ping)

Similar testing equipment is available for fiber-optic cable. Due to the relatively high cost of fiber cable
and its installation, test fiber-optic cable both before installation (on-the-reel testing) and after
installation. Continuity testing of the fiber requires either a visible light source or a reflectometer. Light
sources capable of providing light at the three predominant wavelengths, 850 nanometers (nm),
1300 nm, and 1550 nm, are used with power meters that can measure the same wavelengths and test
attenuation and return loss in the fiber.

TDRs quickly locate open circuits, short circuits, crimps, kinks, sharp bends, impedance mismatches,
and other defects in metallic cables.

A TDR reflects a signal off the end of the cable. Opens, shorts, and other problems reflect back the
signal at different amplitudes, depending on the problem. A TDR measures the time it takes for the
signal to reflect and calculates the distance to a fault in the cable. TDRs can also measure the length of
a cable, and some TDRs can calculate the rate of propagation based on a configured cable length.

Fiber-optic measurement is performed by an optical time domain reflectometer (OTDR). OTDRs can
accurately measure the length of the fiber, locate cable breaks, measure the fiber attenuation, and
measure splice or connector losses. An OTDR can take the signature of a particular installation, noting
attenuation and splice losses. This baseline measurement can then be compared with future signatures
when you suspect a problem in the system.

Network monitors continuously track packets crossing a network, providing an accurate picture of
network activity. Network monitors do not decode the contents of frames. They are useful for creating
a baseline of normal performance.

Monitors collect information such as packet sizes, the number of packets, error packets, overall usage
of a connection, the number of hosts and their MAC addresses, and details about communications
between hosts and other devices. This data can be used to create profiles of LAN traffic and assist in
locating traffic overloads, planning for network expansion, detecting intruders, and distributing traffic
more efficiently.