As companies rely on
applications like electronic mail and database management for core
business operations, computer networking becomes increasingly more
important. This tutorial helps to explain Ethernet and Fast Ethernet,
which are two of the most popular technologies used in networking.
LANs (Local Area Networks)
A network is any collection
of independent computers that communicate with one another over a shared
network medium. LANs are networks usually confined to a geographic area,
such as a single building or a college campus. LANs can be small,
linking as few as three computers, but 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.
WANs (Wide Area Networks)
Often a network is located
in multiple physical places. Wide area networking combines multiple LANs
that are geographically separate. This is accomplished by connecting the
different LANs using services such as dedicated leased phone lines,
dial-up phone lines (both synchronous and asynchronous), satellite
links, and data packet carrier services. Wide area networking can be as
simple as a modem and remote access server for employees to dial into,
or it can be as complex as hundreds of branch offices globally linked
using special routing protocols and filters to minimize the expense of
sending data sent over vast distances.
Internet
The Internet is a system of linked networks that are worldwide in scope
and facilitate data communication services such as remote login, file
transfer, electronic mail, the World Wide Web and newsgroups.
With the meteoric rise in demand for connectivity, the Internet has
become a communications highway for millions of users. The Internet was
initially restricted to military and academic institutions, but now 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 every corner of the planet.
Intranet
With the advancements made in browser-based software for the Internet,
many private organizations are implementing intranets. An intranet is a
private network utilizing Internet-type tools, but available only within
that organization. For large organizations, an intranet provides an easy
access mode to corporate information for employees.
Ethernet
Ethernet is the most popular physical layer LAN technology in use today.
Other LAN types include Token Ring, Fast 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 (IEEE) defines the Ethernet standard
as IEEE Standard 802.3. This standard defines rules for configuring an
Ethernet network as well as specifying how 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
For Ethernet networks that
need higher transmission speeds, the Fast Ethernet standard (IEEE
802.3u) has been established. This standard raises the Ethernet speed
limit from 10 Megabits per second (Mbps) to 100 Mbps with only minimal
changes to the existing cable structure. 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. For the network manager, the incorporation of Fast Ethernet
into an existing configuration presents a host of decisions. Managers
must determine the number of users in each site on the network that need
the higher throughput, decide which segments of the backbone need to be
reconfigured specifically for 100BASE-T and then choose the necessary
hardware 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.
Token Ring
Token Ring is another form
of network configuration which differs from Ethernet in that all
messages are transferred in a unidirectional manner along the ring at
all times. Data is transmitted in tokens, which are passed along the
ring and viewed by each device. When a device sees a message addressed
to it, that device copies the message and then marks that message as
being read. As the message makes its way along the ring, it eventually
gets back to the sender who now notes that the message was received by
the intended device. The sender can then remove the message and free
that token for use by others.
Various PC vendors have
been proponents of Token Ring networks at different times and thus these
types of networks have been implemented in many organizations.
Protocols
Network protocols are
standards that allow computers to communicate. A protocol 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
handling lost or damaged transmissions or "packets." 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) are the main types of network protocols in use
today.
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 that are compatible at the physical and data link layers allow
the user to run many different protocols over the same medium.
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 was expensive and difficult to use. This
evolved to thin coax, which is easier to work with and less expensive.
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
cable, 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 for situations
where electronic emissions and environmental hazards are a concern.
Fiber-optic cable is often used in interbuilding 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 large amounts of electromagnetic
interference are present, such as on a factory floor. The Ethernet
standard allows for fiber-optic cable segments up to 2 kilometers long,
making fiber optic Ethernet perfect for connecting nodes and buildings
that are otherwise not reachable with copper media.
A
network topology is the geometric arrangement of nodes and cable links in a LAN, and is used
in two general configurations: bus and star. These two topologies define
how nodes are connected to one another.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.
10BASE-T Ethernet and Fast
Ethernet use a star topology, in which 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. 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 nonexistent.
Collisions
Ethernet is a shared media, so there are rules for sending packets of
data to avoid conflicts and protect data integrity. Nodes determine when
the network is available for sending packets. It is possible that two
nodes at different locations attempt to send data at the same time. When
both PCs are transferring a packet to the network at the same time, a
collision will result.
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, which results in a lot of contention for network
bandwidth. This can slow the performance of the network from the user's
point of view. Segmenting the network, where a network is divided into
different pieces joined together logically with a bridge or switch, is
one way of reducing an overcrowded network.
Ethernet
Products
The standards and technology that have just been discussed help define
the specific products that network managers use to build Ethernet
networks. The following text discusses the key products needed to build
an Ethernet LAN.
Transceivers
Transceivers 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, allowing them to be connected directly to
Ethernet without requiring an external transceiver. Many Ethernet
devices provide an AUI connector to allow the user to connect to any
media type 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. Thickwire (10BASE5) cables also use transceivers to
allow connections.
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 master 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.
Many NIC adapters comply with Plug-n-Play specifications. On these
systems, NICs are automatically configured without user intervention,
while on non-Plug-n-Play systems, configuration is done manually through
a setup program and/or DIP switches.
Cards are available to support almost all networking standards,
including the latest Fast Ethernet environment. Fast Ethernet NICs are
often 10/100 capable, and will automatically set to the appropriate
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 media type. 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 takes any incoming signal and repeats it out 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). This
means that individual members of a shared network will only get a
percentage of the available network bandwidth.
Next: Ethernet
Tutorial Part 2: Adding Speed
