Embed Size (px)
Citation preview
Rick GrazianiRick Graziani [email protected]@cabrillo.edu [email protected][email protected]
Chapter 8 – LAN Technologies and Network
TopologyComputer 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, [email protected] Graziani, [email protected]
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 GrazianiRick Graziani [email protected]@cabrillo.edu [email protected][email protected]
Part I: Sections 8.1 through 8.6Covered with Cisco Chapter 3
Rick Graziani, [email protected] Graziani, [email protected]
Direct Point-to-Point Communications
The total number of connections grows more rapidly than the total number of connections.
Full mesh formula: Connections = (N2-N)/2 Could you imagine 8,128 separate connections for 128 PC LAN!
Nodes Connections 2 1 4 6 8 28 16 120 32 496 64 2,016 128 8,128
Rick Graziani, [email protected] Graziani, [email protected]
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, [email protected] Graziani, [email protected]
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, [email protected] Graziani, [email protected]
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, [email protected] Graziani, [email protected]
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 802.3
Volume 2
Rick Graziani, [email protected] Graziani, [email protected]
Ethernet Transmissions and Manchester Encoding
Ethernet frames are sent out using Manchester Encoding. Note: Token Ring uses Differential Manchester Encoding.
Rick Graziani, [email protected] Graziani, [email protected]
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, [email protected] Graziani, [email protected]
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, [email protected] Graziani, [email protected]
Carrier Sense Multi-Access/Collision Detect
No additional information
Rick GrazianiRick Graziani [email protected]@cabrillo.edu [email protected][email protected]
Part I: Sections 8.7 through 8.13Covered with Cisco Chapter 7
