© 2005 Cisco Systems, Inc. All rights reserved.INTRO v Building a Simple Ethernet Network Understanding How an Ethernet LAN Works

© 2005 Cisco Systems, Inc. All rights reserved.INTRO v Outline Overview Ethernet Ethernet Addresses The Role of CSMA/CD in Ethernet Ethernet LAN Standards Ethernet Frames Ethernet Frame Addressing MAC Addresses and Binary-Hexadecimal Numbers Converting Numbers from Decimal to Binary Format Binary-to-Hexadecimal Number Conversion Hexadecimal-to-Binary Number Conversion Summary

© 2005 Cisco Systems, Inc. All rights reserved.INTRO v Ethernet Evolution

© 2005 Cisco Systems, Inc. All rights reserved.INTRO v MAC Address Components

© 2005 Cisco Systems, Inc. All rights reserved.INTRO v CSMA/CD

© 2005 Cisco Systems, Inc. All rights reserved.INTRO v LAN Standards

© 2005 Cisco Systems, Inc. All rights reserved.INTRO v Ethernet Frame Structure

© 2005 Cisco Systems, Inc. All rights reserved.INTRO v Communicating Within the LAN

© 2005 Cisco Systems, Inc. All rights reserved.INTRO v MAC Addresses

© 2005 Cisco Systems, Inc. All rights reserved.INTRO v Base 2 Numbering System

© 2005 Cisco Systems, Inc. All rights reserved.INTRO v Decimal-to-Binary-Conversion

© 2005 Cisco Systems, Inc. All rights reserved.INTRO v Decimal, Binary, and Hexadecimal Number Systems

© 2005 Cisco Systems, Inc. All rights reserved.INTRO v Binary and Hexadecimal Number Comparisons

© 2005 Cisco Systems, Inc. All rights reserved.INTRO v Binary-to-Hexadecimal Conversion Example

© 2005 Cisco Systems, Inc. All rights reserved.INTRO v Hexadecimal-to-Binary Number Conversion

© 2005 Cisco Systems, Inc. All rights reserved.INTRO v Hexadecimal-to-Binary Conversion Example

© 2005 Cisco Systems, Inc. All rights reserved.INTRO v Summary Ethernet, the most common type of LAN, was originally developed in the 1970s by DEC, Intel, and Xerox, and was called DIX Ethernet. When a work group of this body (referred to as IEEE 802.3) defined new standards for Ethernet in the mid-1980s to define Ethernet-like networks for public use, the standard was called Ethernet and The address used in an Ethernet LAN is the means by which data is directed to the proper receiving location. Stations on a CSMA/CD LAN can access the network at any time. Before sending data, CSMA/CD stations listen to the network to determine whether it is already in use. If it is in use, they wait. If the network is not in use, the stations transmit. A collision occurs when two stations listen for network traffic, hear none, and transmit simultaneously.

© 2005 Cisco Systems, Inc. All rights reserved.INTRO v Summary (Cont.) Ethernet LAN standards specify cabling and signaling at both the physical and data link layers of the OSI model and divide the OSI data link layer into these two separate sublayers: LLC (transitions up to the network layer) and MAC (transitions down to the physical layer). An Ethernet frame consists of fields, including preamble, start-of-frame delimiter, destination address, source address, type/length, data and pad, and frame check sequence. There are three major kinds of communications in networks: unicast, in which frame is sent from one host addressed to a specific destination; broadcast, in which a frame is sent from one address to all other addresses; and multicast, in which a destination addresses a specific group of devices.

© 2005 Cisco Systems, Inc. All rights reserved.INTRO v Summary (Cont.) The MAC sublayer handles physical addressing issues, and the physical address is a 48-bit number usually represented in hexadecimal format. Computers can recognize and process data only in a binary format. The binary number system is made up of 0s and 1s. Decimal numbers can be converted to binary numbers, and binary numbers can be converted to hexadecimal numbers (and vice versa) by following specific procedures. The hexadecimal number system is used frequently at higher levels of representation. The hexadecimal number system uses 16 symbols: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, and F.

© 2005 Cisco Systems, Inc. All rights reserved.INTRO v