Fundamentals of Networking

Chapter 5

Network Adapter Cards

A Network Interface Card (NIC), also known, as the network adapter card is the most common device used to attach a PC to the network.

Defining the Workings of a Network Card – The NIC fits into one of the many expansion slots in a PC and the main functions of a NIC is to prepare and send data. Data inside a computer travels parallel (8, 16 or 32 bits at a time), and the NIC translates the data from parallel to serial form. At the receiving end, the data has to be translated from serial back to parallel form. A data bus is the pathway inside the computer that carries data between the hardware components. Bus architectures:

Bus Type	Bit size
Industry Standard Architecture (ISA)	8 Bit
Extended Industry Standard (EISA)	16 Bit
Micro Channel Architecture (MCA)	32 Bit
Peripheral Component Interconnect (PCI)	32 Bit

Today, PCI and EISA are the most common, since ISA is limited. IBM developed MCA for the PS/2 series that never caught on because it had to be licensed from IBM by other equipment manufacturers. The network interface (NDIS for MS and ODI for Novel operating systems) interacts with the network operating system. A NIC functions according to the signals and clocking.

Two types of signaling – 1.) Analog, and 2.) Digital

Analog is either defined as:

Frequency – rate at which the waveform changes

Amplitude – measures the strength of the waveform.

Digital signals have two discrete states, "on" or "off."

Clocking – the mechanism that counts and paces the number of signals being sent and received. Clocking synchronized the continuous flow of data.

Measurement of the Signal – the NIC has to read the signal, and the signals are grouped in two ways: 1.) Digital and 2.) Analog.

Digital – the manufacturer builds into the card two measurement mechanisms: 1.) Current State, and 2.) State Transition.

Current State – changes in the voltages designate "on" or "off." Common digital schemes for current state are known as Polar, Unipolar, and Biphase.

State Transition – is the change of the state of a network signal to represent a new transmission of data. Common state transitions measurement standards are Manchester, Differenital, and Biphase Space.

Measurement of Analog Signals – Analog signals do not have a discrete "on" and "off" like digital signals. Instead, analog signals can change frequencies.

Current State – Two mechanisms using current state measurement technologies are FSK (Frequency Shift Keying) and ASK (Amplitude Shift Keying). FSK uses a change in frequency to indicate a change in data where ASK uses a change in amplitude to indicate a change in data.

State Transition - measurement of a frequency phase during a clock count. A phase is a difference in transition of a frequency. The transition of a frequency is the change between two frequencies.

Steps in installing a NIC – Make sure NIC is compatible with NOS and determine the correct data bus architecture (ISA, EISA, Micro Channel, or PCI). Make sure the adapter card is configured for the correct cable connection (twisted pair, coax, etc.).

1. Physically plug NIC into expansion slot of PC.
2. Install NIC driver
3. Configure NOS to NIC
4. Select protocols to be used
5. Physically attach NIC to network cable

Some of these steps may be automatic if the NIC is "plug and play."

Configuring the NIC - Three ways to configure the NIC 1.) Jumpers, 2.) Dip Switches, or 3.) Plug and play. To communicate, the NIC and the NOS must agree on certain parameters and/or settings. Some of the common settings are:

• IRQ (Interrupt Request Line) - Part of the system hardware that receives interrupts when the NIC is contacting the CPU. Each device has to perform an interrupt on a different line. The IRQ settings (such as IRQ3, IRQ5 IRQ15) define which request line each device will use. When installing a NIC, make sure the IRQ for the card is unique and not already assigned to another device.
• Base I/O Port Addresses – Defines the memory address that data flows to and from the adapter, which defines a channel between the adapter and the processor.
• Base Memory Address – Marks the beginning of a buffer area reserved for the NIC. Not all NICs use RAM, so all NICs do not require base memory.
• DMA Channel (Directory Access Memory) – Used for quicker access to the CPU by the adapter card (usually channels 1 through 7). Not all NICs have the ability to set DMA channels.
• Boot PROM (Programmable Read Only Memory) - Used by diskless workstations to allow the NIC to boot up and connect to the network.
• MAC (Media Access Control) Address – The MAC (Hexadecimal and unique for each card) address is burnt into the NIC by the manufacturer and is a way to establish an address for each node on the network. The IEEE is responsible for assigning these addresses to the NIC manufacturers.
• Ring Speed – Used in Token Ring networks to set the ring speed (4Mbps, or 16Mbps). If the ring speed is not set correctly, the computer will not be able to connect to the network and could cause the entire network to fail.
• Connector Type – Connector on the NIC (BNC connector or RJ-45)

Resolving Hardware Conflicts – A hardware conflict occurs when multiple devices compete for the same resources such as interrupt lines, base I/O port addresses, and memory base addresses. Other devices installed on a computer such as modems, sound cards, and scanners can also cause conflicts.

Common	Resource	Allocation	On a PC
Resources	IRQ	I/O Address	Memory	DMA
System Timer	0
Key Board	1	060-06F
VGA Display	2/9	3C0-3CF	A0000-AFFFF	0
COM2	3	2F8-2FF
COM1	4	3F8-3FF
LPT2	5	278-27F
Floppy Drive		3F0-3F7
Controller
LPT1	7	378-37F
Math Coprocessor	13	0F0-0F8
Primary hard drive controller	14	1F0-1F8
Secondary hard Drive Controller	15	170-177

LAN Adapter Cards or (NICS)

Purpose of the LAN Adapter Card - Listens to traffic going by the cable and gets messages for your workstation. When a workstation sends a message the card waits for a break in the cable traffic and puts the message on the cable. On the receiving end, it verifies that the message arrived intact, and resends if necessary.

Prices of cards- under $100 to $1000 per workstation more. Money - more speed. Speed is more important on larger networks.

Speed is measured in Mbps - (Megabits per second), 4Mbps to 16Mbps. Divide by 8 and multiply by 1000 to see how many Kilobytes per second.

Ex. 16Mbps / 8 = 2 * 1000 = 2000 K char. Per second.

4Mbps / 8 = .5 *1000 = 500 K char. Per second.

16,000,000 / 8 = 2,000,000 (2000K)

A LAN is slower than its rated speed.

16Mbps = 10Mbps

4Mbps = 2Mbps

****The LAN is no faster than its slowest component. The elapsed time of a transfer is the disk retrieval time, workstation processing time, and File Server hard drive and processing time. The slowest component is probably workstation hard drive. It governs the rate of the data transfer. Traffic (volume) on the network may also slow down the transfer.

Types of Adapters (NICs) -

1. LANtastic Adapters – made by Artisoft (LANtastic is also a Network Operating. System.) 2 MBPS (mega bits per sec.) (Faster now)
2. Arc Net- one of oldest types developed by Data Point Corp. Today there are many clones. Speed is 2.5Mbps. Easy to install, easy to diagnose errors. Operates like Token Ring.
3. Ethernet Adapters- allows connecting different types of equipment to Network. (Unix, Apple, IBM.)

Three Varieties

1. Thinnet – Greater distance (Can be bought from many different vendors.)
2. UTP - Twisted pair (10BASET)
3. Thicknet

Speed - 10Mbps. Fiber- (Fast Ethernet) 100Mbps

If a workstation requests information from a File server, and the File Server. is sending info to another workstation a collision will occur.

*Only 2 computers can communicate through the same cable at the same time. They both back off and try again. Ethernet network cards use CSMA/CD- Carrier Sense Multiple Access/Collision Detection to detect the collision, and they each back off for a random amount of time. Contention- shares the line (first come, first served). The more traffic, the more collisions making response time slower.

1. Token Ring- most expensive except for fiber optic. Token Ring- Shielded or Unshielded Twist Pair

Token Ring is used in very large networks especially if connected to mainframe or minicomputer.

Speed - 4MbpstTo 16Mbps.

100Mpbs and up - using fiber optic

A Token is passed from one workstation to another. Only when a workstation receives the token can the workstation send data. The actual "Token" is a (packet) short message that indicates the network is idle.

*Token passing seems slow, but it takes no time to circulate a LAN with 100 to 200 workstations.

*Priorities can also be given for more access time.

Handles high traffic better than Ethernet.

Which card do you choose for your network?

Depends on volume, P.C. hardware and budget, NICs, and Distance.