King Fahd University of Petroleum & Minerals
College of Computer Science & Engineering
COMPUTER ENGINEERING DEPARTMENT
COE 341 – Data & Computer Communications
Semester 2007/2008 (Term 071)
Dr. Radwan E. Abdel-Aal
Saleh Al-Ghamdi 243160
Abdullah Al-Yabis 231817
uthman Al-Amoudi 246754
Table of Contents
INTRODUCTION …………………………………………………… 1
I. ETHERNET ………………………………….…... 2
II. Ethernet Network Elements ……………….. 3
III. Ethernet Standards ………………………........... 3
IV. How it Works ………………………………… 5
V. Ethernet Network Topologies and Structures … 6
VI. Ethernet Hubs ………………………………………. 7
VII. Switched Ethernet ……………………………… 8
VIII. Ethernet Products ……………………………… 9
Sources …………………………………………………. 12
In information technology, a network is a series of points or nodes
connected by communication paths. Networks can interconnect with
other networks to make sub-networks. Computer networking technologies
are the glue that binds these elements together.
Networking allows one computer to send information or receive
information from another computer. We can classify network technologies
as belonging to one of two basic groups. Local area network (LAN)
technologies that connect many devices that is relatively close to each
other, usually in the same building ( e.g. KFUPM campus ). The second
type is the Wide area network (WAN) technologies that connect a smaller
number of devices which can be many kilometers apart.
There are many different types of LANs, Ethernet being the most
common for PCs. And because of its simplicity and widespread support
among manufacturers, Ethernet has adapted over the years to grow and
survive, running on newer devices and network media. You can now run
an Ethernet network on wired media such as coaxial cable, twisted-pair
wiring (shielded and unshielded), and fiber-optic cabling.
Ethernet networks can also be wireless. Rather than using Ethernet
cables to connect the computers, wireless NICs use radio waves for two-
way communication with a wireless switch or hub. In lieu of Ethernet ports,
wireless Nicks, switches and hubs each feature a small antenna. Wireless
networks can be more flexible to use, but also require extra care in
Ethernet was originally developed at Xerox PARC (Palo Alto Research
Center) Laboratories in the 1970s. Robert Metcalfe was charged with the
responsibility of networking a group of computers that could all use a new
laser printer that Xerox had developed. Xerox also had just developed
what was probably the first personal workstation, and had a need to
network more than the usual two or three computers that you would find
in a single building during that time.
The original Ethernet standard was developed over the next few years,
and this resulted in a paper, "Ethernet: Distributed Packet-Switching for
Local Computer Networks," written by Metcalfe and David Boggs. In this
first Ethernet experimental network described in the paper, the network
covered a distance of 1 kilometer, ran at 3Mbps, and had 256 stations
connected to it.
Later, a consortium of three companies Digital Equipment Corporation,
Intel, and Xerox took the original specifications and developed the Ethernet II
standard which has a speed of 10 Mbps using coaxial cable.
The Institute of Electrical and Electronics Engineers, Inc (IEEE) is responsible
for a wide range of standards that allow vendors to create hardware
which could interoperate. In 1985, the IEEE standard 802.3 "Carrier Sense
Multiple Access with Collision Detection (CSMA/CD) Access Method and
Physical Layer Specifications" was published. Since then, a number of
supplements to the standard have been defined to take advantage of
improvements in the technologies and to support additional network
media and higher data rate capabilities.
The IEEE committee is made up of various working groups. The IEEE 802.3,
for example, is the working group for standard Ethernet CSMA/CD
technology, while IEEE 802.3z is the standard for Gigabit Ethernet, which is
an updated, faster version of the original 802.3.
Ethernet evolved into the complex networking technology that today
underlies most LANs. The coaxial cable was replaced with point-to-point
links connected by hubs or switches to reduce installation costs and
increase the reliability and enable point-to-point management and
troubleshooting. Starling was the first step in the evolution of Ethernet from
a coaxial cable bus to a hub, twisted-pair network. The advantage of
twisted-pair wiring dramatically lowered installation costs relative to
competing technologies, including the older Ethernet technologies.
II. Ethernet Network Elements
Ethernet LANs consist of network nodes and interconnecting media. The
network nodes fall into two major classes:
• Data terminal equipment (DTE) is devices that are either the source or
the destination of data frames. DTEs are typically devices such as PCs,
workstations, file servers, or print servers that, as a group, are all often
referred to as end stations.
• Data communication equipment (DCE), Intermediate network
devices that receive and forward frames across the network. DCEs may
be either standalone devices such as repeaters, network switches, and
routers, or communications interface units such as interface cards and
The current Ethernet media options include two general types of copper
cable: unshielded twisted-pair (UTP) and shielded twisted-pair (STP), plus
several types of optical fiber cable. (2)
III. Ethernet Standards
There are a variety of different Ethernet implementations defined within
the 802.3 specification. Some examples include Ethernet, Fast Ethernet,
Gigabit Ethernet, and 10Gigabit Ethernet. These implementations differ
according to the type of media used, the speed of the network, and the
maximum cable length.
10Base-2 and 10Base-5 are some of the old Ethernet standards which are
rarely implanted now. They use a coaxial cable for transmission with a
speed of 10Mbps.The term "Base" refers to the technology used, which is
Baseband, while the last number indicates the maximum length allowed
for any segment (200m for 10Base-2 & 500m for 10Base-5).
The following table shows and compares some of the most common
Category Standard Bandwidth Cable Type
10 Mbps (half
duplex) Twisted pair
10BaseT 100 meters
20 Mbps (full (Cat3, 4, or 5)
1,000 to 2,000
10BaseFL (multimode Fiber optic
100 Mbps (half Twisted pair
duplex) (Cat5 or
100BaseT4 100 meters
200 Mbps (full higher) Uses 4
Fast duplex) pairs of wires
100BaseFX (multimode Fiber optic 412 meters
1000BaseT Twisted pair
(short copper) Special 25 meters, used
1000BaseSX copper (150 within wiring
1,000 Mbps ohm) closets
Gigabit (short) (half duplex)
Ethernet 2,000 Mbps 220 to 550 meters
(full duplex) depending on
1000BaseLX cable quality
(long) 550 (multimode)
10 Km (single-
10 GBaseSR 2 to 300 meters
10 G 10 Gaps (full
10 Basel Fiber optic 2 to 10 kilometers
Ethernet duplex only)
10 Baser 2 to 40 kilometers
IV. How it Works
A. Media Access Method
Ethernet networking uses Carrier Sense Multiple Access with Collision
Detection (CSMA/CD) for access to the physical medium. The CSMA/CD is a
protocol that helps devices share the bandwidth evenly without having
two devices transmit at the same time on the network medium. CSMA/CD
keeps devices on the network from interfering with one another when trying to
transmit; if they do, a collision occurs. The way that CSMA/CD works is the
1. All devices have equal access (multiple access) to the transmission
media, so when a device has data to send it first listens to the
transmission medium to determine if it is free (carrier sense).
2. If it is not free, the device waits a random time and listens again to
the transmission medium. When it is free, the device transmits its
3. If two devices transmit at the same time, a collision occurs. The
sending devices detect the collision (collision detection) and send
a jam signal to notify all other hosts that a collision has occurred.
4. Both devices wait a random length of time before attempting to
resend the original message (called back off).
CSMA/CD doesn’t stop collisions from happening, but it helps manage the
situations when they do occur. When switches are used on an Ethernet
network, collisions disappear. Most devices can detect this and will turn off
collision detection and use full-duplex communication.
B. Half- and Full-Duplex Ethernet
The early Ethernet standard defined in the original 802.3 Ethernet used
half-duplex mode of transmission where one pair of wire is used to send
digital signals in both directions on the wire. It also uses the CSMA/CD
protocol to help prevent collisions and to permit retransmitting if a collision
does occur. Half-duplex Ethernet are not that efficient since the collisions
still occur which reduces the overall efficiency.
On the other hand, full-duplex Ethernet uses two pairs of wires instead of
one wire pair like half duplex. And full duplex uses a point-to-point
connection between the transmitter of the transmitting device and the
receiver of the receiving device. This means that with full-duplex you get a
faster data transfer compared to half duplex. And most importantly,
because the transmitted data is sent on a different set of wires than the
received data, no collisions will occur. Full-duplex Ethernet can be
implemented with just about any device except a hub.
V. Ethernet Network Topologies and Structures
LANs take on many topological configurations, but regardless of their
size or complexity, all will be a combination of only three basic
interconnection structures or network building blocks.
The simplest structure is the point-to-point interconnection, shown in
Figure 1-1. Only two network units are involved, and the connection may
be DTE-to-DTE, DTE-to-DCE, or DCE-to-DCE. The cable in point-to-point
interconnections is known as a network link. The maximum allowable
length of the link depends on the type of cable and the transmission
method that is used.
Figure 1-1 Example Point-to-Point Interconnection
The original Ethernet networks were implemented with a coaxial bus
structure, as shown in Figure 1-2. Segment lengths were limited to 500
meters, and up to 100 stations could be connected to a single segment.
Individual segments could be interconnected with repeaters, as long as
multiple paths did not exist between any two stations on the network and
the number of DTEs did not exceed 1024. The total path distance
between the most-distant pair of stations was also not allowed to exceed
a maximum prescribed value.
Figure 1-2 Example of Coaxial Bus Topology
Although new networks are no longer connected in a bus
configuration, some older bus-connected networks do still exist and are
And since the early 1990s, the network configuration of choice has
been the star-connected topology, shown in Figure 1-3. The central
network unit is either a multi-port repeater (also known as a hub) or a
network switch. All connections in a star network are point-to-point links
implemented with either twisted-pair or optical fiber cable. (3)
Figure 1-3 Example of Star-Connected Topology
VI. Ethernet Hubs
The problems of a single shared transmission medium were partially
addressed by the invention of Ethernet hubs, which had a physical star
topology, with multiple devices being wired back to a hub, and the hub
then being either wired back to an original passive coax backbone, or to
a higher-level hub. Instead of a coax connection or an AUI cable,
hubbed 10BASE-T Ethernet uses Cat-3/Cat-5 cable and RJ45 connectors
to connect endpoints to hubs.
However, in spite of the physical star topology, hubbed Ethernet
networks still use CSMA/CD, with every packet being sent to every port on
the hub, and only minimal cooperation from the hub in dealing with
Ethernet as a shared medium works well when the level of traffic is
low. Since the chance of collision is proportional to the number of
transmitters and the data to be sent, the network gets extremely
congested above 50% capacity. To resolve this, Ethernet "switches" were
developed to maximize available bandwidth. (4)
VII. Switched Ethernet
Most modern Ethernet installations use Ethernet switches as
opposed to hubs. Although the wiring is identical to hubbed Ethernet,
switched Ethernet has several advantages over shared medium Ethernet
including greater bandwidth and simplified wiring. Switched networks
typically have a star topology, even though they still implement a single
Ethernet "cloud" from the viewpoint of attached machines.
Initially, Ethernet switches work like Ethernet hubs, with all traffic
being echoed to all ports. However, as the switch "learns" the end-points
associated with each port, it ceases to send non-broadcast traffic to ports
other than the intended destination. In this way, Ethernet switching can
allow the full wire speed of Ethernet to be used by any given pair of ports
on a single switch.
Since packets are typically only delivered to the port they are
intended for, traffic on a switched Ethernet is slightly less public than on
shared-medium Ethernet. However, as it is easy to subvert switched
Ethernet systems by means such as ARP spoofing and MAC flooding, as
well as for the network administrators to use monitoring functions to copy
traffic from the network, switched Ethernet should still be regarded as an
insecure network technology.
VIII. Ethernet Products
Ethernet cables are limited in their reach, and these distances (as short
as 100 meters) are insufficient to cover medium-sized and large network
installations. A repeater in Ethernet networking is a device that allows
multiple cables to be joined and greater distances to be spanned. A
bridge device can join an Ethernet to another network of a different type,
such as a wireless network.
A device that interconnects clients and servers, repeating (or amplifying)
the signals between them. Hubs act as wiring "concentrators" in networks
based on star topologies (rather than bus topologies, in which computers
are daisy-chained together).
A device that filters and forwards packets between LAN segments.
Switches operate at the data link layer (layer 2) of the OSI Reference
Model and therefore support any packet protocol. When a switch port
receives data packets, it forwards those packets only to the appropriate
port for the intended recipient. This further reduces competition for
bandwidth between the clients, servers or workgroups connected to each
switch port. Switches evolved from bridges to become the main
technology in modern Ethernet LANs.
C. Network Interface Card (NIC)
In computer networking, a NIC provides the hardware interface between
a computer and a network. A NIC technically is network adapter
hardware in the form factor of an add-in card such as a PCI or PCMCIA
Some NIC cards work with wired connections while others are
wireless. Most NICs support either wired Ethernet or WiFi wireless standards.
Ethernet NICs plug into the system bus of the PC and include jacks for
network cables, while WiFi NICs contain built-in transmitters / receivers
In new computers, many NICs are now pre-installed by the
manufacturer. All NICs feature a speed rating such as 11 Mbps, 54 Mbps
or 100 Mbps that suggest the general performance of the unit.
Routers are physical devices that join multiple wired or wireless
networks together. Technically, a wired or wireless router is a Layer 3
gateway, meaning that the wired/wireless router connects networks (as
gateways do), and that the router operates at the network layer of the
Home networkers often use an Internet Protocol (IP) wired or wireless
router, IP being the most common OSI network layer protocol. An IP router
such as a DSL or cable modem broadband router joins the home's local
area network (LAN) to the wide-area network (WAN) of the Internet.
By maintaining configuration information in a piece of storage
called the "routing table," wired or wireless routers also have the ability to
filter traffic, either incoming or outgoing, based on the IP addresses of
senders and receivers.