Test-Um NT750 - Manual (Page 20)

LanScaper
TM
NIC
Polarity
Straight-Through Cable
Switch
T568A/B
UPLINK
= Network Interface Card - Typically an option card plugged into a PC card slot that provides
an Ethernet interface for that PC. LanScaper™ uses the term NIC to define the connector pin out
that allows for direct connection to a HUB device using a straight-through cable.
- Ethernet transmit and receive driver chips use differential voltages to improve noise
immunity. Thus each direction of transmission uses a pair of wires, one for the positive (+) side
and the other for the negative (-) side. Early Ethernet interface chips were not designed to
recognize and compensate for reversed cable pairs, so a crossed (+) and (-) pair could cause
problems. Modern Ethernet chips can compensate, so the wiring is not critical, but the
LanScaper™ can determine the difference, and will report it. In the Jack ID mode the polarity is
reported as NRM or REV.
- An Ethernet (CAT 5) cable which connects all 4 pairs in the cable
straight through to the corresponding pairs in the far end connector. This allows a NIC device to
connect directly to a HUB device.
- Similar to a HUB, a switch is a multiple port Ethernet connection device that allows for
multiple Ethernet devices to communicate between each other. Unlike a HUB, a switch has internal
logic that determines which port a specific MAC address is found on, and once it has determined
that, it only forwards traffic destined for that address to that port. This allows for fewer collisions
on the LAN by not re-transmitting every packet on every port. Multiple simultaneous point-point
communications can pass through a switch at the same time, as long as each end point is on a
different port on the switch.
Like a HUB, a switch (in its primary mode) has no IP or MAC address of it's own. Also like a
HUB, a switch uses HUB pin out on its connectors to allow direct connections to NIC interfaces.
Switches are more modern devices than HUBS and are usually capable of 100 Mbit/sec (100 Base-
Tx) operation.
As a result of the requirement of IEEE Ethernet specs requiring downward compatibility, all 100
Mbit interfaces must also support legacy 10 Mbit communications. This results in a requiring a
switch to have memory to store packets received at 100 Mbits for retransmission at 10 Mbits (Store
and Forward).
- The EIA/TIA structured wiring standards for telecommunications wiring. A and B
versions are electrically identical and can not be distinguished with a wiring test. The color codes
and pair numbering is different, however, and care must be taken to use one version within a
network. A cable wired to A on one end and B on the other results in a cross-over cable.
- A special connector, or a mechanical switch, that changes the pin out of one connector
on a HUB or switch to NIC pin out. This allows a straight-through cable to be used to connect one
HUB (or switch) to another while building a LAN.