© 2007 Cisco Systems, Inc. All rights reserved.ICND1 v1.0—1-1  A network is a connected collection of devices (computers, interconnections, routers, and switches) that can communicate with each other, providing the means for users to share both hardware and applications.  Today’s network must be secured from both physical and network attacks.  Ethernet is the most common type of LAN, and it has its own unique characteristics. Standards specify cabling and signaling for Ethernet LANs at both the physical and data link layers of the OSI model.  Bits that are transmitted over an Ethernet LAN are organized into frames. Ethernet LANs manage the signals on a network by a process called CSMA/CD. Module Summary

© 2007 Cisco Systems, Inc. All rights reserved.ICND1 v1.0—1-2 Module Summary (Cont.)  Host-to-host communications are governed by OSI and TCP/IP.  The OSI reference model defines the network functions that occur at each layer and facilitates an understanding of how information travels throughout a network.  TCP/IP defines a 21-bit address that is represented by 4 octets separated by a period.  A host address may be manually configured or obtained from a DHCP server.

© 2007 Cisco Systems, Inc. All rights reserved.ICND1 v1.0—1-3