Local Area Network Technology: Part 3 - Network Interface Cards (NICs)

by Jeffrey L. Carrell
Issue v1n3 - July 1997

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 host computers.

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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