Rick Graziani Chapter 8 – LAN Technologies and Network Topology Computer Networks and Internets by Douglas Comer CST 311 Introduction to Telecommunications Instructor: Rick Graziani August 1, 2002 Includes material from Cisco Networking Academy CCNA Semester 1 University transferable option of CIS 181 at Cabrillo College

Rick Graziani, Organization Part I: Sections 8.1 through 8.6 Covered with Cisco Chapter 3 Part II: Sections 8.7 through 8.13 Covered with Cisco Chapter 7

Rick Graziani Part I: Sections 8.1 through 8.6 Covered with Cisco Chapter 3

Rick Graziani, Direct Point-to-Point Communications The total number of connections grows more rapidly than the total number of connections. Full mesh formula: Connections = (N 2 -N)/2 Could you imagine 8,128 separate connections for 128 PC LAN! Nodes Connections , ,128

Rick Graziani, Direct Point-to-Point Communications

Rick Graziani, Shared Communication Channels LAN networks allow multiple computers to share a communcations medium, used for local communications. Point-to-point connections are used for long-distance and a few other special cases.

Rick Graziani, Shared Communication Channels Why are shared networks used only for LANs? Technically: Shared networks require coordination and having timing restrictions (later). Economically: Much more expensive over long distances.

Rick Graziani, Shared Communication Channels LANs operate under the principle of locality of reference. Locality of Reference: Computer communication follows two distinct patterns: First, a computer is more likely to communicate with computers that are physically nearby than with computers that are far away. We will see this later with Ethernet frame sizes and cable distances. Second, a computer is more likely to communicate with the same set of computers repeatedly. (Temporal Locality of Reference) We will see this later with ARP tables.

Rick Graziani, Topologies

Rick Graziani, Topologies

Rick Graziani, Topologies

Rick Graziani, History of Ethernet Bob Metcalfe Developed at Xerox PARC (Palo Alto Research Center) in early 1970’s. One of three technologies Steve Jobs saw before developing the MacIntosh (Ethernet, OOP, and GUI), Bob Metcalfe, founder of 3Com, was one of the developers Digitial Equipment Corporation, Intel and Xerox later produced the DIX standard. IEEE now controls Ethernet standards, IEEE Volume 2

Rick Graziani, Ethernet Transmissions and Manchester Encoding Ethernet frames are sent out using Manchester Encoding. Note: Token Ring uses Differential Manchester Encoding.

Rick Graziani, Ethernet Transmissions and Manchester Encoding A digital encoding technique in which each bit period is divided into two complementary halves to provide timing information. A negative-to-positive voltage (0-to-1) transition in the middle of the bit period designates a binary “1” while a positive-to-negative transition represents a “0.” (Newton) The data is included in the direction of the transition.

Rick Graziani, Ethernet Transmissions and Manchester Encoding Rick’s Coding method (no standard – can go other direction) draw lines in the middle of the bit cell make a up arrow for a one bit make an down arrow for a zero bit connect the lines and make transition when necessary (i.e. consecutive 1’s or 0’s)

Rick Graziani, Sharing on an Ethernet

Rick Graziani, Carrier Sense Multi-Access/Collision Detect No additional information

Rick Graziani Part I: Sections 8.7 through 8.13 Covered with Cisco Chapter 7