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HOME REVIEWS CONTACT ABOUT March 14,
2009
Network Interface Cards (NIC)
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A NIC
(network interface card) is designed to communicate over a computer
network. It allows users to connect to
each other either by using cables or wirelessly if the NIC is a wireless NIC
(WiFi/WNIC). Every entity on a network,
a PC, printer, router, etc., that needs to communicate with other devices must
have a NIC if it is to communicate over the network. On older computers, the NIC is probably an
expansion card, usually PCI or PCI express.
High performance cards can cost less that $30. NIC functionality is now often integrated
into the motherboard chipset or implemented with a dedicated Ethernet chip on
the motherboard.
A
similar situation is true for laptop computers.
At one time, a PCMCIA network card would be used in a laptop computer
for the NIC just as the PCI card was used in desktop computer, but now, NIC
functionality is often integrated with the motherboard.
Ethernet
is the dominant standard for cable connections for wired computer networks. An
Ethernet connector looks similar to a telephone connector, only larger. This connector is called
"RJ45". Ethernet cables are
either a shielded or unshielded cable of four twisted pairs of 24 AWG
connectors, specified at 100 ohm impedance.
Maximum cable length for CATX cables is 100 meters.
Early
versions of Ethernet cables were CAT3 or CAT4 (CAT being short for
category). These versions were not long
lived. CAT5 and CAT5e are currently the
most commonly used cables (bandwidth of 100 MHz, 100 Mbps), with CAT6
(bandwidth of 250 MHz, 1 Gbps) available and the configuration of the
near-future. A CAT7 cable (bandwidth of
600 MHz) specification is in development, and should be available in a few
years.
Each
Ethernet NIC has a unique serial number called a "media access code"
(MAC address) that is used to identify the NIC and associated computer on the
network. No two NIC will have the same
address, because the NIC manufacturers must purchase blocks of addresses from
the
NIC
cards are capable of different speeds.
Speeds of up to one gigabit per second (Gbps) are now available. Two NIC
can communicate if they differ in speed ratings, but they will communicate at
the rate of the slower NIC.
On a
very simple network, NIC can be used to link personal computers (PC). If the computers are connected directly to
one another, the network is a "peer-to-peer" (P2P, also called an
"ad hoc") network. If
computers are connected directly to one another, a "cross-over"
Ethernet cable is needed (also called a "Null-Modem cable"). This cable is not
"straight-through" like standard Ethernet, but crosses the send and
receive connectors, so that send line from computer A connects to the receive
line of computer B.
For
networks of a few computers, a "hub" can be used, with all of the
computers connected to the hub. Any
message sent from any PC will be seen by all of the computers, but only the
computer with the correct MAC address will receive the message. P2P networks are useful for many purposes. File
and printer sharing are the most common applications.
Networks
with more than four active computers at a time will benefit from using a
“network switch” instead of a hub. A
network switch will direct the message to the appropriate destination, instead
of each message packet being broadcast across the network. Computer A can send a message to computer B,
while simultaneously, computer C sends a message to computer D. This increases the efficiency of the
network. This is a simple form of a
server network. An example of a
client-server design is a computer server where the clients initiate a download
or upload of files and the server reacts.
The server would also often be responsible for interacting with printers
and other servers on other networks, including satellite networks (SATCOM) or
the Internet.
"Latency"
is the delay caused by a network to communicate data. Latency causes not only slow service, but can
result in data loss as well. Latency is usually tested by sending a message
packet that is immediately returned to the sending computer. The round-trip time is defined as the
latency.
Networking
performance can be optimized for either latency or throughput. Networks can use
a technique known as "interrupt moderation" to increase throughput
and lower CPU utilization by queuing message packets and issuing fewer
interrupts to the CPU. A network optimized this way would favor large
transfers, reducing transfer overhead.
CPU and network throughput benefit, but network latency would increase. The alternative is to fragment each message
and pipeline the fragments through the network.
Multiple paths from source to destination can allow overlapping. Latency can also be addressed with techniques
such as prefetching (anticipating the need for data
requests) and/or using multiple execution threads (multithreading).
There
are two indicator LEDs on a typical NIC.
A single lit green LED indicates the computer is connected to the
network. This is called the "link" light. The second LED is amber in color. A flashing amber LED indicates message packet
collisions are occurring. Occasional
collisions are normal on a busy network, but a frequently lit amber LED is an
indication of problems. A quickly
flashing link LED (green) is a network activity indicator, meaning that
communication is occurring. If the green
link light is off, and the amber LED is blinking, then the NIC is in
"power save" mode.
A
wireless network interface controller (WNIC) is a NIC for connecting to a
wireless network (WiFi). The standard
for WiFi is IEEE 802.11. A WNIC uses an
antenna to communicate with an Rf signal, most often
at 2.4 GHz. Wireless connectivity
development in recent years has closely paralleled wired connectivity. Like its wired cousin, a wireless card was once
integrated with a PCI or PCMCIA add-on card.
Now, integrated WNIC's are becoming common, especially for laptop
computers.
Brian Bradshaw is an InfoComm Certified Technical Specialist (CTS), Microsoft Certified Technology Specialist (MCTS), and CompTIA A+ Computer Technologist. Areas of expertise include Video, HDTV, Audio, Computation, SATCOM Systems, and Communications.
Website: http://bradshaw-vacuum-technology.com/
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