Tuesday, December 30, 2008

Network Adapter Cards

Network Adapter Cards

The role of the network Adapter cards it to:
· Prepare data from the computer for the network cable
· Send the data to another computer
· Control the flow of data between the computer and the cabling system

NIC's contain hardware and firmware (software routines in ROM) programming that implements the
· Logical Link Control and
· Media Access Control
Functions of the Data Link layer of the OSI

Preparing Data
· Data moves along paths in the computer called a BUS - can be 8, 16, 32 bits wide.

· On network cable, data must travel in a single bit stream in what's called a serial transmission (b/c on bit follows the next).

· The transceiver is the component responsible for translating parallel (8, 16, 32-bit wide) into a 1 bit wide serial path.

· A unique network address or MAC address is coded into chips in the card

· card uses DMA (Direct Memory Access) where the computer assigns memory space to the NIC
if the card can't move data fast enough, the card's buffer RAM holds it temporarily during transmission or reception of data

Sending and Controlling Data
The NICs of the two computers exchanging data agree on the following:
1. Maximum size of the groups of data being sent
2. The amount of data to be sent before confirmation
3. The time intervals between send data chunks
4. The amount of time to wait before confirmation is sent
5. How much data each card can hold before it overflows
6. The speed of the data transmission

Network Card Configuration
· IRQ: a unique setting that requests service from the processor.

IRQ #---- Common Use---- I/O Address
IRQ 1 - Keyboard
IRQ 2(9)- Video Card
IRQ 3 - Com2, Com4 2F0 to 2FF
IRQ 4 - Com1, Com3 3F0 to 3FF
IRQ 5 - Available (Normally LPT2 or sound card )
IRQ 6 - Floppy Disk Controller
IRQ 7 - Parallel Port (LPT1)
IRQ 8 - Real-time clock
IRQ 9 - Redirected IRQ2 370 - 37F
IRQ 10 - Available (maybe primary SCSI controller)
IRQ 11 - Available (maybe secondary SCSI controller)
IRQ 12 - PS/2 Mouse
IRQ 13 - Math Coprocessor
IRQ 14 -Primary Hard Disk Controller
IRQ 15 - Available (maybe secondary hard disk controller)

Base I/O port: Channel between CPU and hardware
Specifies a channel through which information flows between the computer's adapter card and the CPU. Ex. 300 to 30F.

Each hardware device must have a different base I/O port

Base Memory address: Memory in RAM used for buffer area
Identifies a location in the computer's RAM to act as a buffer area to store incoming and outgoing data frames. Ex. D8000 is the base memory address for the NIC.

Each device needs its own unique address.

some cards allow you to specify the size of the buffer ( 16 or 32 k, for example)

Sometimes selected as on-board or external. External usually will use the AUI/DIX connector: Thicknet, for example

Use jumpers on the card to select which to use

Data Bus Architecture
The NIC must

· match the computer's internal bus architecture and

· have the right cable connector for the cable being used
· ISA (Industry Standard Architecture): original 8-bit and later 16-bit bus of the IBM-PC.
· EISA (Extended Industry Standard Architecture): Introduced by consortium of manufacturers and offers a 32-bit data path.
· Micro-Channel Architecture (MCA): Introduced by IBM in its PS/2 line. Functions as either 16 or 32 bit.
· PCI (Peripheral Component Interconnect): 32-bit bus used by Pentium and Apple Power-PC's. Employs plug and play.

Improving Network Card Performance
Direct Memory Access (DMA):
Data is moved directly from the network adapter card's buffer to computer memory.

Shared Adapter Memory:
Network adapter card contains memory which is shared with the computer.
The computer identifies RAM on the card as if it were actually installed on the computer

Shared System Memory:
The network adapter selects a portion of the computer's memory for its use.
MOST common

Bus Mastering:
The adapter card takes temporary control of the computer's bus, freeing the CPU for other tasks.
moves data directly to the computer's system memory
Available on EISA and MCA
can improve network performance by 20% to 70%

RAM buffering:
Ram on the adapter card acts as a buffer that holds data until the CPU can process it.
this keeps the card from being a bottleneck

·On-board microprocessor:
enables the adapter card to process its own data without the need of the CPU

Wireless Adapter Cards
· Used to create an all-wireless LAN
· Add wireless stations to a cabled LAN
· uses a wireless concentrator, which acts as a transceiver to send and receive signals

Remote-Boot PROMS (Programmable Read Only Memory)
· Enables diskless workstations to boot and connect to a network.
· Used where security is important.

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