King Fahd University of Petroleum

King Fahd University of Petroleum & Minerals

College of Computer Science & Engineering

COMPUTER ENGINEERING DEPARTMENT

COE 341 – Data & Computer Communications

Semester 2007/2008 (Term 071)

Section 02

Ethernet

Prepared for

Dr. Radwan E. Abdel-Aal

By

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 ………………………...........

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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

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INTRODUCTION

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 configuring security.

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I. ETHERNET

A. HISTORY

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.

B. DESCRIPTION

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-

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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 modems.

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

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length allowed for any segment (200m for 10Base-2 & 500m for 10Base-5).

The following table shows and compares some of the most common Ethernet implementations:

Category Standard Bandwidth Cable TypeMaximum Segment Length

Ethernet

10BaseT

10 Mbps (half duplex)20 Mbps (full duplex)

Twisted pair (Cat3, 4, or 5)

100 meters

10BaseFL10 Mbps (multimode cable)

Fiber optic1,000 to 2,000 meters

Fast Ethernet

100BaseT4

100 Mbps (half duplex)200 Mbps (full duplex)

Twisted pair (Cat5 or higher) Uses 4 pairs of wires

100 meters

100BaseFX100 Mbps (multimode cable)

Fiber optic 412 meters

Gigabit Ethernet

1000BaseT

1,000 Mbps (half duplex)2,000 Mbps (full duplex)

Twisted pair (Cat5e)

100 meters

1000BaseCX (short copper)

Special copper (150 ohm)

25 meters, used within wiring closets

1000BaseSX (short)

Fiber optic

220 to 550 meters depending on cable quality

1000BaseLX (long)

550 (multimode)10 Km (single-mode)

10 G Ethernet

10 GBaseSR

10 Gaps (full duplex only)

Fiber optic

2 to 300 meters

10 Basel2 to 10 kilometers

10 Baser2 to 40 kilometers

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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 following:

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 message.

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.

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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.

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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 still useful.

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

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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 packet collisions.

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

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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. HUB

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).

B. SWITCHES

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

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adapter hardware in the form factor of an add-in card such as a PCI or PCMCIA card.

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 (transceivers).

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.

D. ROUTERS

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 OSI model.

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.

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Sources:

1- http://en.wikipedia.org/wiki/Ethernet

2- http://www.ecapsindia.com/ethernet.html#arrival

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3- http://www.omsar.gov.lb/ICTSG/102NW/6.1_Local_Area_Networks.htm

4- http://www.domainsarefree.com/glossary/Ethernet.html

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