Part 1 of this series discussed the first component
of the OSI Physical Link Layer - cabling. Part 2 discussed the
physical layer electronics - hub's. The next physical layer component
is the "host" device connection point, or Network Interface
Cards (NICs). Occasionally, the terms LAN Adapter Card and network
adapter card have been used, but the preferred term is NIC.
In order to connect a device to the network, a network
interface must be installed in that device. For the most part,
we call any device that has a direct network connection a "host".
The use of host in this particular sense does not refer to the
mainframe or minicomputers, which have been traditionally called
Today, we have many different types of hosts: PCs,
Macintosh's, UNIX systems, notebook computers, minicomputers,
mainframes, printers, communications systems, routers, etc. All
of these devices, no matter their function or physical design,
will have a NIC installed in order to be connected to the network.
The I/O connector of the host that the NIC plugs
into can be one of many different types of buses. Some examples
of bus types are: ISA, EISA, MCA, PCI, PC Card, and proprietary.
In addition, the different bus types also have different I/O data
paths, or how many bits the bus moves at a time. Traditionally,
the ISA bus is an 8 or 16 bit bus, the EISA is a 32 bit bus, MCA
is a 16 or 32 bit bus, and PCI is a 32 bit bus.
In the realm of Ethernet NICs, there are many different
options to choose from today. In addition to connector styles
you may need to support on a network, there is also the speed
issue to deal with. Is the network running 10Mb/s, 100Mb/s or
even soon 1000Mb/s. Also, what about the upgrade path. A lot of
networks today run at 10Mb/s, but the cost of a 10/100 NIC is
usually only a little bit more than buying a 10Mb/s or 100Mb/s
only NIC. Given that, it is best to go ahead and install 10/100
NICs today, in order to facilitate either an upgrade or the potential
of swapping hosts around for servicing/redeployment. Since Ethernet
has been around for longer than forever (in networking time anyway),
there are three different connector/cable types to be supported.
The original AUI or DB15 connector for Thicknet cable, the BNC
coax connector for Thinnet and the RJ45 supporting UTP/STP modern
day cable plants. To further complicate the product offerings,
many NICs come with one specific connector (of any of the three
types), two connectors (usually the AUI and one other) or a combo
card of all three connectors. Certainly an Ethernet NIC that is
a dual speed 10/100 and combo connectors can support virtually
any network and any cable plant. However, the more options the
NIC has to offer, the higher the price.
Token Ring NICs have similar issues to deal with
like Ethernet. There are two speeds of Token Rings, 4Mb/s and
16Mb/s. Although the original Token Ring NICs were 4Mb/s only,
the current day Token Ring NICs are usually dual 4/16. Likewise,
there has also been multiple connector types. The early day Token
Ring cables terminated at the NIC via a DB9 connector. However
with the Cat5 structured cable systems of the 90's, the vendors
have been putting RJ45 connectors on most Token Ring NICs, even
some come with both connector styles.
Each NIC has a unique hardware level address, called
the MAC address. This address is "burned-in" by the
vendor, and usually cannot be changed. The MAC address is a 12
digit, hexadecimal number. The address is divided into two components,
the prefix (first 6 digits) and suffix. The prefix number is assigned
by the IEEE. Every NIC manufacturer applies to the IEEE to get
a NIC prefix address. Once obtained, during the NIC manufacturing
process the vendor takes their specific prefix and adds a suffix
- sequentially. This allows for all NICs to have an individual
12 digit address. If a vendor runs out of suffix addresses, they
apply for a new prefix and keep on going. If two or more NICs
on the same network had the same MAC address, you can imagine
the problems. Data would leave one NIC bound for a specific other
NIC, and maybe not ever get there. It would be like your whole
neighborhood having the same address and no names. You'd never
get the correct mail being sent to you.
Installing NICs can be an easy task or very troublesome.
Depending on the host platform type, bus type, operating system
and network drivers required, you can spend as little as 15 minutes
and up to many hours making NICs communicate on a network. Some
points to ease the pain: buy only name brand NICs (no "clones"),
verify the parameters of the host before buying NICs - are they
all compatible with each other, once you find a NIC that works
in your environment - stay with that brand, and be prepared during
the first installation - have all drivers required, documentation
and technical support numbers handy.
Just like every other component in a network, the
NIC is a very integral part. I have seen more networks with intermittent
problems when they had lessor quality NICs, trying to save a few
dollars, than if they had installed brand name products. When
NICs go bad, and they sometimes do, they can cause all kinds of
problems. Many problems are hard to troubleshoot, as they manifest
in ways that wouldn't normally point in that direction. Although
there are many diagnostic products available to assist, it always
helps when troubleshooting to have accurate documentation of the
network and the host types, NIC types, and driver software configurations
available. Often, the root problem with a NIC is a simple software
driver configuration error.
EISA Extended Industry Standard Architecture
ISA Industry Standard Architecture bus (sometimes referred to as the AT bus)
Mb/s Mega bits per second
MCA Micro Channel Architecture
NIC Network Interface Card
PC Card formerly the PCMCIA bus for notebook computers
PCI Peripheral Component Interconnect
In the next article I'll discuss topologies.
Copyright © 1997 Jeffrey L. Carrell. All Rights Reserved.
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