Networks
and the Computer
Network Interface Card
Presented by:
Daniel D. Kochmanski
Michael A. DiVito
1
Advantages of Networks



Allow groups of users to exchange information
and share data.
Allow easy and efficient communication among
individuals, including e-mail.
Allow users to share peripherals such as printers,
scanners, fax machines, and other devices.
2
Local Area Networks (LANs) and Internetworks


A Local Area Network is also known as an
Intranet. It works within a limited geographical
area.
i.e. within one building or complex
Internetwork is a network 100 or more
computers at distances in excess of 1000 feet.
3
Wide Area Networks (WANs) and the Internet


Wide Area Network (WAN) – span distances
measured in miles.
i.e. two or more separate LANS linked together
Internet – global WAN internetwork; includes
millions of machines and users on the world wide
web connected via Network Interface Cards inside
each computer.
4
Network Interface Card (NIC)




Also known as a Network Adapter.
Integrated circuit board that plugs into the internal
circuitry of the computer.
Allows the members of a local-area network to
communicate with each other.
NIC is the physical interface from the computer or
peripheral to the medium.

The Medium may be physical cable, such as twisted
pair wiring, coaxial cable, fiber optic or even wireless.
5
Network Cards Convert Data from
Parallel to Serial, and vice versa


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
Most computers use parallel data lines internally
to send data between the CPU and the adapter
cards. This is called a Bus.
Most networking media transmit data in a single
line, called serial transmission.
The NIC translates parallel into serial for outgoing
messages and serial into parallel for incoming
messages.
Prior to the invention of NICs, data was sent via
serial ports on the computer.
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First Computer Networks used
Serial Communications Ports
 Serial Com ports use the RS232 standard
DB9 or DB25 type connector
+ / - 12volts
Serial means one bit at a time.
Uses
• Networking computers
• Modem
• Mouse & Printers, which are somewhat historical now
TX
RX
Grnd
RX
TX
Grnd
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Asynchronous Communications

Both ends agree to a protocol and a speed.
 i.e.


Protocol
1 start bit, 1 stop bit,
1 parity bit & 7 data bits.
Speed (baud) 300 - 115,200 bps
Sender transmits start bit and both transmitting
and receiving clocks start almost simultaneously.
Data is transmitted
 Each
clock is now working independently. The
block of data is short enough so that clocks do not
significantly drift out of sync.

Next block of data causes the clocks to be reset.
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Sending a character
1 0 0 0 0 0 1
Line
Idle
Line
Idle
Data Bits
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Receiving a character
Receiver’s clock
Clock
Start
Signal
Receiver reads voltage
at each agreed interval
Line
Idle
Line
Idle
Data Bits
10
Parallel Data Transmission
 Used on a Computer’s Bus where the adapter
card plugs in.
 i.e. ISA or PCI card bus slots
 Used for the parallel LPT port where the
printer or scanner plugs in. Parallel ports have:
 5Volt Logic.
 Transmission of 1 Byte at a time or 8 bits.
 Bi-directional capabilities.
Grnd
Grnd
D
A
T
A
Handshake
11
Understanding the Bus inside the Computer



Bus width refers to number of parallel lines, each
able to move one bit at a time.
Industry Standard Architecture (ISA) slots have an
8-bit or 16-bit bus.
Peripheral Component Interconnect (PCI) slots
have a 64 bit bus and are the most popular bus used
today.
12
The Network Interface Card’s Transceiver




NICs access the transceiver to transmit data onto
the cable.
Most NICs include the transceiver.
Some Ethernet NICs offer multiple interfaces as
you will soon see but most are designed for a
specific medium.
Newer NICs generally have only one type of
media connector.
13
Network Interface Card Data Packets


Packets are basic units of data for network
transmission and reception.
NICs create packages of data bits called packets,
then:


Transmit packets serially onto the network medium,
and
Act as a gatekeeper, allowing only inbound packets
intended for its computer via an electronic serial
number known as a MAC address.
14
The MAC Address

NICs have a unique identifier, called a
Media Access Control (MAC) address.
 It
is programmed into a ROM chip on the NIC.
 It’s a 48-bit number, written as six two-digit
hexadecimal numbers separated by colons.
 The first part identifies the manufacturer.
 The second part is unique to each NIC.
15
IP Address

Network Cards can have a second address called
an IP address.

IP Address is software configurable.
 IP currently uses 32 bits split into four sections
separated by dots.
 i.e. 165.255.110.133 – These are decimal values.
 Only used in certain network protocols such as TCP/IP.
16
Network Protocols

Network protocols are a common set of data
transmission rules that:




define how to interpret signals and identify individual
computers.
initiate and end networked communication,
manage information exchange across the network
medium.
Protocols include TCP/IP, NetBEUI, IPX/SPX,
and NWLink
17
OSI Reference Model Structure
For Networking

Breaks networked communications into
seven layers. Layers help clarify the process of
networking.
 Application
 Presentation
 Session
 Transport
 Network
 Data Link
 Physical
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19



Each layer of the OSI model communicates and
interacts with layers immediately above and
below it.
Each layer is responsible for the different aspects
of data exchange.
Each layer puts an electronic envelope around data
as it sends it down the layers or removes it
as it travels up the layers for delivery.
20
Data Flow

Data is broken into packets or PDUs as it moves down
the stack.


PDU stands for protocol data unit, packet data unit, or
payload data unit.
Packets are a self-contained data structure from one
layer to another.

At the sending end, each layer adds special formatting or
addressing to the packet.
 At the receiving end, each layer reads the packet and strips
off information added by the corresponding layer at the
sending end.
21
Packet Structure

Each packet contains:





Address of the target machine
Address of the source machine
Encapsulated Data
Error Checking Data
The receiving machine checks all the packets. It
accepts those with it’s address, then replies with
an acknowledgement.
22
Network Interface Card Data Encapsulation
Source Serial # (48), Destination Serial # (48) and Protocol type
Source IP (32), Destination IP(32)
Offset in the byte stream, Acknowledgement,
port number, connection number
HELLO THERE
Ethernet Packet
TCP Header
DATA
IP Datagram
HELLO THERE
Trailers
23
The Basic Ethernet Frame Format
contains the following seven fields

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
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Preamble (PRE)—Consists of 7 bytes and is an alternating
pattern of ones and zeros that tells the receiving stations that a
frame is coming.
Start-of-frame delimiter (SOF)—Consists of 1 byte.
Destination address (DA)—Consists of 6 bytes and identifies
which station should receive the frame.
Source addresses (SA)—Consists of 6 bytes and it identifies
the sending station.
Length/Type—Consists of 4 bytes and indicates the number
of MAC-client data bytes.
Data—Is a sequence of 1500 bytes maximum.
Frame check sequence (FCS)—Consists of 4 bytes and this
sequence contains a 32-bit cyclic redundancy check (CRC).
24
Basic MAC Data Frame Format
Transmission order, left to right, bit serial.
D
25
Configuring a Network Interface Card


This involves three settings:
 Interrupt Request line (IRQ)
 Base Input/Output (I/O) port
 Base memory address
In older computers, the user needed to supply the
IRQ and base I/O port. Currently Plug and Play
operating systems have automated this task and
default values are normally assigned.
26
Driver Software for the NIC



This is a small specialized program that manages
communications between the operating system
and the NIC.
Earlier, each NIC vendor built its own driver.
Now, operating system vendors define drivers for
NICs.
27
Network Layout Design


The Physical Topology refers to physical layout
including computers, cables, and other resources
on the network.
The Logical topology refers to how data travels
between computers on the network.
28
Today’s network designs are based on three
topologies:



Ring which connects computers to form a
continuous circular loop.
Bus which consists of a series of computers
connected along a single cable segment.
Star which connects computers via a central
connection point known as a hub or switching
hub.
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Ring Topology
30
Bus Topology
31
Two Types of Coaxial Cable used as a Bus



Thin Ethernet (also called thinnet) designated by
the Institute of Electrical and Electronics
Engineers (IEEE) as 10Base2
Thick Ethernet (also called thicknet) designated
by IEEE as 10Base5
Each of these types of cables is terminated with
BNC connectors.
32
Understanding IEEE Cable Designations

10Base2, for example, refers to a total bandwidth
of 10 Mbps, baseband signaling, and the
maximum cable segment length as designated in
hundreds of meters.

10Base2 means 200 meters including patch cables

10Base5 means 500 meters
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Star Topology




This is the most common topology in today’s
networks.
It connects computers to a central hub that
receives and transmits signals to all devices on the
network.
Data is addressed and sent in packets to a specific
MAC address found inside the computer’s
Network Interface Card.
There is ease in troubleshooting because the
failure of a single computer or cable does not
affect the entire network.
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Star Topology
35

Unshielded Twisted-Pair (UTP) wire is the most
common cable used in a Star topology

IEEE specifies that the most popular form of LAN
cabling is 10BaseT and 100BaseT
T means Twisted-Pair wire.
Normally 4 sets of twisted-pairs = 8 wires.
The maximum length of a 10BaseT or a 100BaseT
segment is 100 meters or 328 feet. This is called
the channel link and includes the necessary patch
cable at each end of the basic link.
Twisted-Pair wire is also used for telephone
systems.

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

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Twisted-Pair Wire Categories





Category 1 or 2: carries voice and low speed data
Category 3: has a bandwidth up to 10 Mbps. It’s
used with older networks such as 10BaseT
Ethernet. It’s still commonly used for telephone
networks today.
Category 4: has a bandwidth up to 16 Mbps and
was formally used for 16 Mbps token ring
networks.
Category 5: has a bandwidth up to 100 Mbps and
is used with 100BaseT Ethernet.
Category 5e or 6: is used for Gigabit Ethernet
known as 1000BaseT.
37
Twisted-Pair Connectors



Both Shielded Twisted-Pair and Unshielded
Twisted-Pair wire use RJ-45 modular connectors.
These are similar to the two wire RJ-11 or four
wire RJ-14 modular connectors used for the
telephones in your house.
RJ-45 is larger and uses eight wires.
38
In a star topology, the network gear at the
center can be a hub or a switching hub.
 With a hub, data is sent from one computer to every
other computer on the hub simultaneously.
 While a switch, as it’s commonly called, maintains
address tables for each connection.
 On a switch, traffic is sent
only to the port for which
the data is destined.
HUB
 A switch allows all pairs
of stations to communicate
simultaneously at top
speed.
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Simple Router
 This router is connected to the
LAN and also has a WAN
(Internet) connection.
 One purpose for the router is
to act as a secured “gateway”
protecting your network from
intruders on the Internet. It uses
Network Address Translation
(NAT) to perform this function.
NAT simply means that the router
has it’s own IP address on your
network and also has a uniquely
different IP address on the
Internet.
Router
World
Wide
Web
40
Types of Network Interface Cards




Fiber-Optic Network Interface Cards work on a
Fiber-Optic cabled network.
Infrared networking uses infrared light to transmit
data from one device to another.
Wireless network cards with antennas operate on a
wireless network with a wireless hub.
Copper wired Network Interface Cards work on
coax cable or twisted-pair wire.
41
10Mbs Ethernet Card with an ISA Slot
Mounting
bracket
10baseT RJ45
Socket
Status LEDs
Each network card
has a unique 48 bit identifier
known as the Media Access Control
(MAC) number.
10Base2 BNC
Connector
42
Electronic Components on the
Network Interface Card






Resistors
Diodes
Capacitors
Coils
Crystals
Integrated Circuits such as the Realtek Fast
Ethernet controller chip shown next.
43
44
M
45
MAC Layer Block Diagram
46
Features of the Ethernet Controller



Scrambling: All the encoded data is passed to the data
scrambler to reduce EMI by spreading the power spectrum
using a 10-bit scrambler seed loaded at the beginning.
Equalizer and Baseline Wander: High speed signals over
unshielded (or shielded) twisted pair cable will experience
attenuation and phase shift. These effects depend on the signal
frequency, cable type, cable length and the cable connectors.
Robust circuits in the transceiver provide reliable adaptive
equalizer and baseline wander compensation for amplitude
attenuation and phase shift due to transmission line parasitics.
4B/5B encoding procedure: Each 4-bit data nibble
(representing half of a data byte) is mapped into a 5-bit binary
code-group that is transmitted bit-serial over the link.
47
Signetics Thompson Ethernet Controller STE10/100A
48
Full Duplex and Half Duplex Operation of Transceiver

The transceiver can operate in either full
duplex or half duplex network applications.
 In
full duplex, both transmission and reception
between the network interface cards can take place
simultaneously.
 In half duplex mode, only one network card can
transmit at a time.
49
System Diagram of the STE10/100A
D
50
Types of Digital to Digital Encoding


Unipolar – 1 for high, 0 for low. (common to all
students)
Polar




NRZ – Non-Return to Zero
RZ – Return to Zero
Biphase
• Manchester
• Differential Manchester
Bipolar



AMI – Alternate Mark Inversion, used on T1 lines
B8ZS – Binary Eight Zero Suppression, used on T1
HDB3
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Unipolar Encoding
Amplitude
Time
52
NRZ-L and NRZ-I Encoding
NRZ-L
NRZ-I
Transition cause next bit
is a one.
53
RZ – Return to Zero Encoding
These transitions can be used for
synchronization.
54
D
Manchester Encoding

Each bit period is divided into two equal intervals.
 Binary 1 = High then Low
 Binary 0 = Low then High
 Some network cards send the signal through an
inverter so this polarity is backwards.
55
Differential Manchester Encoding

Each bit period is divided into two equal intervals.
 Binary 1 = Lack of voltage transition from
pervious bit
 Binary 0 = Voltage transition from previous bit
56
Manchester Encoding
vs.
Differential Manchester Encoding
57
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Summary of the Network Interface Card
 Allows connectivity of one computer to another.
 Controls the communication that takes place between
computers.
 Utilizes an ethernet controller chip to encode,
scramble, send and receive data.
 Converts data from parallel to serial for transmission
to another Network Interface Card.
 Comes in a variety of forms depending on the
application or network medium.
 In other words, it’s all pretty simple, huh!
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I hope you enjoyed today’s presentation on Networks
and the Network Interface Card by
Daniel D. Kochmanski and Michael A. DiVito
To view this presentation again please go to
www.ddktele.com and click on the
Networks and the Network Interface Card link.
For other information on this subject please go
to www.wzrd.com/home/ddk/nic
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