Ethernet Tutorial - Part I: Networking Basics
Computer networking has
become an integral part of business today. Individuals, professionals
and academics have also learned to rely on computer networks for
capabilities such
as electronic mail and access to remote databases for research and
communication purposes. Networking has thus become an increasingly
pervasive, worldwide reality because it is fast,
efficient, reliable and effective. Just how all this information is
transmitted, stored, categorized and accessed remains a mystery to the
average computer user.
This tutorial will explain the basics of some of the most popular
technologies used in networking, and will include the following:
- Types of Networks - including LANs, WANs and WLANs
- The Internet and Beyond
- The Internet and its contributions to intranets and extranets
- Types of LAN Technology
- including Ethernet, Fast Ethernet, Gigabit Ethernet, 10 Gigabit Ethernet,
ATM, PoE and Token Ring
- Networking and Ethernet Basics
- including standard code, media, topographies, collisions and CSMA/CD
- Ethernet Products
- including transceivers, network interface cards, hubs and repeaters
Types of Networks
In describing the basics of networking technology, it will be helpful to explain the different types of networks in use.
Local Area Networks (LANs)
A network is any collection of independent computers that exchange
information with each other over a shared communication medium. Local
Area Networks or LANs are usually confined
to a limited geographic area, such as a single building or a college
campus. LANs can be small, linking as few as three computers, but can
often link hundreds of computers used by
thousands of people. The development of standard networking protocols
and media has resulted in worldwide proliferation of LANs throughout
business and educational organizations.
Wide Area Networks (WANs)
Often elements of a network are widely separated physically. Wide
area networking combines multiple LANs that are geographically separate.
This is accomplished by connecting the
several LANs with dedicated leased lines such as a T1 or a T3, by
dial-up phone lines (both synchronous and asynchronous), by satellite
links and by data packet carrier services.
WANs can be as simple as a modem and a remote access server for
employees to dial into, or it can be as complex as hundreds of branch
offices globally linked. Special routing protocols
and filters minimize the expense of sending data over vast distances.
Wireless Local Area Networks (WLANs)
Wireless LANs, or WLANs, use radio frequency (RF) technology to
transmit and receive data over the air. This minimizes the need for
wired connections. WLANs give users mobility
as they allow connection to a local area network without having to be
physically connected by a cable. This freedom means users can access
shared resources without looking for a
place to plug in cables, provided that their terminals are mobile and
within the designated network coverage area. With mobility, WLANs give
flexibility and increased productivity,
appealing to both entrepreneurs and to home users. WLANs may also
enable network administrators to connect devices that may be physically
difficult to reach with a cable.
The Institute for Electrical and Electronic Engineers (IEEE)
developed the 802.11 specification for wireless LAN technology. 802.11
specifies over-the-air interface between a wireless
client and a base station, or between two wireless clients. WLAN
802.11 standards also have security protocols that were developed to
provide the same level of security as that of
a wired LAN.
The first of these protocols is Wired Equivalent Privacy (WEP). WEP
provides security by encrypting data sent over radio waves from end
point to end point.
The second WLAN security protocol is Wi-Fi Protected Access (WPA).
WPA was developed as an upgrade to the security features of WEP. It
works with existing products that are WEP-enabled
but provides two key improvements: improved data encryption through
the temporal key integrity protocol (TKIP) which scrambles the keys
using a hashing algorithm. It has means for
integrity-checking to ensure that keys have not been tampered with.
WPA also provides user authentication with the extensible authentication
protocol (EAP).
Wireless Protocols
| Specification |
Data Rate |
Modulation Scheme |
Security |
| 802.11 |
1 or 2 Mbps in the 2.4 GHz band |
FHSS, DSSS |
WEP and WPA |
| 802.11a |
54 Mbps in the 5 GHz band |
OFDM |
WEP and WPA |
| 802.11b/High Rate/Wi-Fi |
11 Mbps (with a fallback to 5.5, 2, and 1 Mbps) in the 2.4 GHz band |
DSSS with CCK |
WEP and WPA |
| 802.11g/Wi-Fi |
54 Mbps in the 2.4 GHz band |
OFDM when above 20Mbps, DSSS with CCK when below 20Mbps |
WEP and WPA |
The Internet and Beyond
More than just a technology, the Internet has become a way of life
for many people, and it has spurred a revolution of sorts for both
public and private sharing of information.
The most popular source of information about almost anything, the
Internet is used daily by technical and non-technical users alike.
The Internet: The Largest Network of All
With the meteoric rise in demand for connectivity, the Internet has
become a major communications highway for millions of users. It is a
decentralized system of linked networks
that are worldwide in scope. It facilitates data communication
services such as remote log-in, file transfer, electronic mail, the
World Wide Web and newsgroups. It consists of independent
hosts of computers that can designate which Internet services to use
and which of their local services to make available to the global
community.
Initially restricted to military and academic institutions, the
Internet now operates on a three-level hierarchy composed of backbone
networks, mid-level networks and stub networks.
It is a full-fledged conduit for any and all forms of information and
commerce. Internet websites now provide personal, educational,
political and economic resources to virtually
any point on the planet.
Intranet: A Secure Internet-like Network for Organizations
With advancements in browser-based software for the Internet, many private organizations have implemented
intranets.
An intranet is a private network utilizing Internet-type
tools, but available only within that organization. For large
organizations, an intranet provides easy access to corporate information
for designated employees.
Extranet: A Secure Means for Sharing Information with Partners
While an intranet is used to disseminate confidential information
within a corporation, an
extranet
is commonly used by companies to share data in a secure fashion
with their business partners. Internet-type tools are used by content
providers to update the extranet. Encryption and user authentication
means are provided to protect the information,
and to ensure that designated people with the proper access
privileges are allowed to view it.
Types of LAN Technology
Ethernet
Ethernet is the most popular physical layer LAN technology in use
today. It defines the number of conductors that are required for a
connection, the performance thresholds that
can be expected, and provides the framework for data transmission. A
standard Ethernet network can transmit data at a rate up to 10 Megabits
per second (10 Mbps). Other LAN types
include Token Ring, Fast Ethernet, Gigabit Ethernet, 10 Gigabit
Ethernet, Fiber Distributed Data Interface (FDDI), Asynchronous Transfer
Mode (ATM) and LocalTalk.
Ethernet is popular because it strikes a good balance between speed,
cost and ease of installation. These benefits, combined with wide
acceptance in the computer marketplace and
the ability to support virtually all popular network protocols, make
Ethernet an ideal networking technology for most computer users today.
The Institute for Electrical and Electronic Engineers developed an
Ethernet standard known as IEEE Standard 802.3. This standard defines
rules for configuring an Ethernet network
and also specifies how the elements in an Ethernet network interact
with one another. By adhering to the IEEE standard, network equipment
and network protocols can communicate efficiently.
Fast Ethernet
The Fast Ethernet standard (IEEE 802.3u) has been established for
Ethernet networks that need higher transmission speeds. This standard
raises the Ethernet speed limit from 10 Mbps
to 100 Mbps with only minimal changes to the existing cable
structure. Fast Ethernet provides faster throughput for video,
multimedia, graphics, Internet surfing and stronger error
detection and correction.
There are three types of Fast Ethernet: 100BASE-TX for use with
level 5 UTP cable; 100BASE-FX for use with fiber-optic cable; and
100BASE-T4 which utilizes an extra two wires for
use with level 3 UTP cable. The 100BASE-TX standard has become the
most popular due to its close compatibility with the 10BASE-T Ethernet
standard.
Network managers who want to incorporate Fast Ethernet into an
existing configuration are required to make many decisions. The number
of users in each site on the network that need
the higher throughput must be determined; which segments of the
backbone need to be reconfigured specifically for 100BASE-T; plus what
hardware is necessary in order to connect the
100BASE-T segments with existing 10BASE-T segments. Gigabit Ethernet
is a future technology that promises a migration path beyond Fast
Ethernet so the next generation of networks
will support even higher data transfer speeds.
Gigabit Ethernet
Gigabit Ethernet was developed to meet the need for faster
communication networks with applications such as multimedia and Voice
over IP (VoIP). Also known as "gigabit-Ethernet-over-copper" or
1000Base-T, GigE is a version of Ethernet that runs at speeds 10
times faster than 100Base-T. It is defined in the IEEE 802.3 standard
and is currently used as an enterprise backbone.
Existing Ethernet LANs with 10 and 100 Mbps cards can feed into a
Gigabit Ethernet backbone to interconnect high performance switches,
routers and servers.
From the data link layer of the OSI model upward, the look and
implementation of Gigabit Ethernet is identical to that of Ethernet. The
most important differences between Gigabit
Ethernet and Fast Ethernet include the additional support of full
duplex operation in the MAC layer and the data rates.
10 Gigabit Ethernet
10 Gigabit Ethernet is the fastest and most recent of the Ethernet
standards. IEEE 802.3ae defines a version of Ethernet with a nominal
rate of 10Gbits/s that makes it 10 times
faster than Gigabit Ethernet.
Unlike other Ethernet systems, 10 Gigabit Ethernet is based entirely
on the use of optical fiber connections. This developing standard is
moving away from a LAN design that broadcasts
to all nodes, toward a system which includes some elements of wide
area routing. As it is still very new, which of the standards will gain
commercial acceptance has yet to be determined.
Asynchronous Transfer Mode (ATM)
ATM is a cell-based fast-packet communication technique that can
support data-transfer rates from sub-T1 speeds to 10 Gbps. ATM achieves
its high speeds in part by transmitting
data in fixed-size cells and dispensing with error-correction
protocols. It relies on the inherent integrity of digital lines to
ensure data integrity.
ATM can be integrated into an existing network as needed without
having to update the entire network. Its fixed-length cell-relay
operation is the signaling technology of the future
and offers more predictable performance than variable length frames.
Networks are extremely versatile and an ATM network can connect points
in a building, or across the country,
and still be treated as a single network.
Power over Ethernet (PoE)
PoE is a solution in which an electrical current is run to
networking hardware over the Ethernet Category 5 cable or higher. This
solution does not require an extra AC power cord
at the product location. This minimizes the amount of cable needed as
well as eliminates the difficulties and cost of installing extra
outlets.
LAN Technology Specifications
| Name |
IEEE Standard |
Data Rate |
Media Type |
Maximum Distance |
| Ethernet |
802.3 |
10 Mbps |
10Base-T |
100 meters |
Fast Ethernet/
100Base-T |
802.3u |
100 Mbps |
100Base-TX
100Base-FX |
100 meters
2000 meters |
Gigabit Ethernet/
GigE |
802.3z |
1000 Mbps |
1000Base-T
1000Base-SX
1000Base-LX |
100 meters
275/550 meters
550/5000 meters |
| 10 Gigabit Ethernet |
IEEE 802.3ae |
10 Gbps |
10GBase-SR
10GBase-LX4
10GBase-LR/ER
10GBase-SW/LW/EW |
300 meters
300m MMF/ 10km SMF
10km/40km
300m/10km/40km |
Token Ring
Token Ring is another form of network configuration. It differs from
Ethernet in that all messages are transferred in one direction along
the ring at all times. Token Ring networks
sequentially pass a “token” to each connected device. When the token
arrives at a particular computer (or device), the recipient is allowed
to transmit data onto the
network. Since only one device may be transmitting at any given time,
no data collisions occur. Access to the network is guaranteed, and
time-sensitive applications can be supported.
However, these benefits come at a price. Component costs are usually
higher, and the networks themselves are considered to be more complex
and difficult to implement. Various PC
vendors have been proponents of Token Ring networks.
Networking and Ethernet Basics
Protocols
After a physical connection has been established, network protocols
define the standards that allow computers to communicate. A protocol
establishes the rules and encoding specifications
for sending data. This defines how computers identify one another on a
network, the form that the data should take in transit, and how this
information is processed once it reaches
its final destination. Protocols also define procedures for
determining the type of error checking that will be used, the data
compression method, if one is needed, how the sending
device will indicate that it has finished sending a message, how the
receiving device will indicate that it has received a message, and the
handling of lost or damaged transmissions
or "packets".
The main types of network protocols in use today are: TCP/IP (for
UNIX, Windows NT, Windows 95 and other platforms); IPX (for Novell
NetWare); DECnet (for networking Digital Equipment
Corp. computers); AppleTalk (for Macintosh computers), and
NetBIOS/NetBEUI (for LAN Manager and Windows NT networks).
Although each network protocol is different, they all share the same
physical cabling. This common method of accessing the physical network
allows multiple protocols to peacefully
coexist over the network media, and allows the builder of a network
to use common hardware for a variety of protocols. This concept is known
as "protocol independence," which
means that devices which are compatible at the physical and data link
layers allow the user to run many different protocols over the same
medium.
The Open System Interconnection Model
The Open System Interconnection (OSI) model specifies how dissimilar
computing devices such as Network Interface Cards (NICs), bridges and
routers exchange data over a network by
offering a networking framework for implementing protocols in seven
layers. Beginning at the application layer, control is passed from one
layer to the next. The following describes
the seven layers as defined by the OSI model, shown in the order they
occur whenever a user transmits information.
- Layer 7: Application
- This layer supports the application and end-user processes.
Within this layer, user privacy is considered and communication
partners, service and constraints are all identified.
File transfers, email, Telnet and FTP applications are all
provided within this layer.
- Layer 6: Presentation (Syntax)
- Within this layer, information is translated back and forth
between application and network formats. This translation transforms
the information into data the application layer
and network recognize regardless of encryption and formatting.
- Layer 5: Session
- Within this layer, connections between applications are made,
managed and terminated as needed to allow for data exchanges between
applications at each end of a dialogue.
- Layer 4: Transport
- Complete data transfer is ensured as information is transferred
transparently between systems in this layer. The transport layer also
assures appropriate flow control and end-to-end
error recovery.
- Layer 3: Network
- Using switching and routing technologies, this layer is
responsible for creating virtual circuits to transmit information from
node to node. Other functions include routing, forwarding,
addressing, internetworking, error and congestion control, and
packet sequencing.
- Layer 2: Data Link
- Information in data packets are encoded and decoded into bits
within this layer. Errors from the physical layer flow control and frame
synchronization are corrected here utilizing
transmission protocol knowledge and management. This layer
consists of two sub layers: the Media Access Control (MAC) layer, which
controls the way networked computers gain access
to data and transmit it, and the Logical Link Control (LLC)
layer, which controls frame synchronization, flow control and error
checking.
- Layer 1: Physical
- This layer enables hardware to send and receive data over a
carrier such as cabling, a card or other physical means. It conveys the
bitstream through the network at the electrical
and mechanical level. Fast Ethernet, RS232, and ATM are all
protocols with physical layer components.
This order is then reversed as information is received, so that the
physical layer is the first and application layer is the final layer
that information passes through.
Standard Ethernet Code
In order to understand standard Ethernet code, one must understand what each digit means. Following is a guide:
Guide to Ethernet Coding
| 10 |
at the beginning means the network operates at 10Mbps. |
| BASE |
means the type of signaling used is baseband. |
| 2 or 5 |
at the end indicates the maximum cable length in meters. |
| T |
the end stands for twisted-pair cable. |
| X |
at the end stands for full duplex-capable cable. |
| FL |
at the end stands for fiber optic cable. |
For example: 100BASE-TX indicates a Fast Ethernet connection (100 Mbps) that uses a
twisted pair cable capable of full-duplex transmissions.
Media
An important part of designing and installing an Ethernet is
selecting the appropriate Ethernet medium. There are four major types of
media in use today: Thickwire for 10BASE5
networks; thin coax for 10BASE2 networks; unshielded twisted pair
(UTP) for 10BASE-T networks; and fiber optic for 10BASE-FL or
Fiber-Optic Inter-Repeater Link (FOIRL) networks.
This wide variety of media reflects the evolution of Ethernet and
also points to the technology's flexibility. Thickwire was one of the
first cabling systems used in Ethernet, but
it was expensive and difficult to use. This evolved to thin coax,
which is easier to work with and less expensive. It is important to note
that each type of Ethernet, Fast Ethernet,
Gigabit Ethernet, 10 Gigabit Ethernet, has its own preferred media
types.
The most popular wiring schemes are 10BASE-T and 100BASE-TX, which
use unshielded twisted pair (UTP) cable. This is similar to telephone
cable and comes in a variety of grades,
with each higher grade offering better performance. Level 5 cable is
the highest, most expensive grade, offering support for transmission
rates of up to 100 Mbps. Level 4 and level
3 cable are less expensive, but cannot support the same data
throughput speeds; level 4 cable can support speeds of up to 20 Mbps;
level 3 up to 16 Mbps. The 100BASE-T4 standard
allows for support of 100 Mbps Ethernet over level 3 cables, but at
the expense of adding another pair of wires (4 pair instead of the 2
pair used for 10BASE-T). For most users,
this is an awkward scheme and therefore 100BASE-T4 has seen little
popularity. Level 2 and level 1 cables are not used in the design of
10BASE-T networks.
For specialized applications, fiber-optic, or 10BASE-FL, Ethernet
segments are popular. Fiber-optic cable is more expensive, but it is
invaluable in situations where electronic
emissions and environmental hazards are a concern. Fiber-optic cable
is often used in inter-building applications to insulate networking
equipment from electrical damage caused
by lightning. Because it does not conduct electricity, fiber-optic
cable can also be useful in areas where heavy electromagnetic
interference is present, such as on a factory floor.
The Ethernet standard allows for fiber-optic cable segments up to
two kilometers long, making fiber-optic Ethernet perfect for connecting
nodes and buildings that are otherwise
not reachable with copper media.
Cable Grade Capabilities
| Cable Name |
Makeup |
Frequency Support |
Data Rate |
Network Compatibility |
| Cat-5 |
4 twisted pairs of copper wire -- terminated by RJ45 connectors |
100 MHz |
Up to 1000Mbps |
ATM, Token Ring,1000Base-T, 100Base-TX, 10Base-T |
| Cat-5e |
4 twisted pairs of copper wire -- terminated by RJ45 connectors |
100 MHz |
Up to 1000Mbps |
10Base-T, 100Base-TX, 1000Base-T |
| Cat-6 |
4 twisted pairs of copper wire -- terminated by RJ45 connectors |
250 MHz |
1000Mbps |
10Base-T, 100Base-TX, 1000Base-T |
Topologies
Network topology is the geometric arrangement of nodes and cable
links in a LAN. Two general configurations are used, bus and star. These
two topologies define how nodes are connected
to one another in a communication network. A node is an active
device connected to the network, such as a computer or a printer. A node
can also be a piece of networking equipment
such as a hub, switch or a router.
A bus topology consists of nodes linked together in a series with
each node connected to a long cable or bus. Many nodes can tap into the
bus and begin communication with all other
nodes on that cable segment. A break anywhere in the cable will
usually cause the entire segment to be inoperable until the break is
repaired. Examples of bus topology include 10BASE2
and 10BASE5.
General Topology Configurations
10BASE-T Ethernet and Fast Ethernet use a star topology where
access is controlled by a central computer. Generally a computer is
located at one end of the segment, and the other
end is terminated in central location with a hub or a switch.
Because UTP is often run in conjunction with telephone cabling, this
central location can be a telephone closet or
other area where it is convenient to connect the UTP segment to a
backbone. The primary advantage of this type of network is reliability,
for if one of these 'point-to-point' segments
has a break; it will only affect the two nodes on that link. Other
computer users on the network continue to operate as if that segment
were non-existent.
Collisions
Ethernet is a shared medium, so there are rules for sending packets
of data to avoid conflicts and to protect data integrity. Nodes
determine when the network is available for
sending packets. It is possible that two or more nodes at different
locations will attempt to send data at the same time. When this happens,
a packet collision occurs.
Minimizing collisions is a crucial element in the design and
operation of networks. Increased collisions are often the result of too
many users on the network. This leads to competition
for network bandwidth and can slow the performance of the network
from the user's point of view. Segmenting the network is one way of
reducing an overcrowded network, i.e., by dividing
it into different pieces logically joined together with a bridge or
switch.
CSMA/CD
In order to manage collisions Ethernet uses a protocol called
Carrier Sense Multiple Access/Collision Detection (CSMA/CD). CSMA/CD is a
type of contention protocol that defines
how to respond when a collision is detected, or when two devices
attempt to transmit packages simultaneously. Ethernet allows each device
to send messages at any time without having
to wait for network permission; thus, there is a high possibility
that devices may try to send messages at the same time.
After detecting a collision, each device that was transmitting a
packet delays a random amount of time before re-transmitting the packet.
If another collision occurs, the device
waits twice as long before trying to re-transmit.
Ethernet Products
The standards and technology just discussed will help define the
specific products that network managers use to build Ethernet networks.
The following presents the key products
needed to build an Ethernet LAN.
Transceivers
Transceivers are also referred to as Medium Access Units (MAUs).
They are used to connect nodes to the various Ethernet media. Most
computers and network interface cards contain
a built-in 10BASE-T or 10BASE2 transceiver which allows them to be
connected directly to Ethernet without the need for an external
transceiver.
Many Ethernet devices provide an attachment unit interface (AUI)
connector to allow the user to connect to any type of medium via an
external transceiver. The AUI connector consists
of a 15-pin D-shell type connector, female on the computer side,
male on the transceiver side.
For Fast Ethernet networks, a new interface called the MII (Media
Independent Interface) was developed to offer a flexible way to support
100 Mbps connections. The MII is a popular
way to connect 100BASE-FX links to copper-based Fast Ethernet
devices.
Network Interface Cards
Network Interface Cards, commonly referred to as NICs, are used to
connect a PC to a network. The NIC provides a physical connection
between the networking cable and the computer's
internal bus. Different computers have different bus architectures.
PCI bus slots are most commonly found on 486/Pentium PCs and ISA
expansion slots are commonly found on 386 and
older PCs. NICs come in three basic varieties: 8-bit, 16-bit, and
32-bit. The larger the number of bits that can be transferred to the
NIC, the faster the NIC can transfer data
to the network cable. Most NICs are designed for a particular type
of network, protocol, and medium, though some can serve multiple
networks.
Many NIC adapters comply with plug-and-play specifications. On
these systems, NICs are automatically configured without user
intervention, while on non-plug-and-play systems, configuration
is done manually through a set-up program and/or DIP switches.
Cards are available to support almost all networking standards.
Fast Ethernet NICs are often 10/100 capable, and will automatically set
to the appropriate speed. Gigabit Ethernet
NICs are 10/100/1000 capable with auto negotiation depending on the
user’s Ethernet speed. Full duplex networking is another option where a
dedicated connection to a switch
allows a NIC to operate at twice the speed.
Hubs/Repeaters
Hubs/repeaters are used to connect together two or more Ethernet
segments of any type of medium. In larger designs, signal quality begins
to deteriorate as segments exceed their
maximum length. Hubs provide the signal amplification required to
allow a segment to be extended a greater distance. A hub repeats any
incoming signal to all ports.
Ethernet hubs are necessary in star topologies such as 10BASE-T. A
multi-port twisted pair hub allows several point-to-point segments to be
joined into one network. One end of
the point-to-point link is attached to the hub and the other is
attached to the computer. If the hub is attached to a backbone, then all
computers at the end of the twisted pair
segments can communicate with all the hosts on the backbone. The
number and type of hubs in any one-collision domain is limited by the
Ethernet rules. These repeater rules are discussed
in more detail later.
A very important fact to note about hubs is that they only allow
users to share Ethernet. A network of hubs/repeaters is termed a "shared
Ethernet," meaning that all
members of the network are contending for transmission of data onto a
single network (collision domain). A hub/repeater propagates all
electrical signals including the invalid ones.
Therefore, if a collision or electrical interference occurs on one
segment, repeaters make it appear on all others as well. This means that
individual members of a shared network
will only get a percentage of the available network bandwidth.
Basically, the number and type of hubs in any one collision domain for 10Mbps Ethernet is limited by the following rules:
Or
from the CLI, issue these commands:
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