1. Growing the Network © 2004 Cisco Systems, Inc. All rights reserved. Understanding the Challenges of Shared LANs INTRO v2.0—3-1

2. © 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—3-2 Outline Overview Early Local Area Networks Ethernet LAN Segments Extending a LAN Segment Collisions Collision Domains Summary Lab Exercise 3-1: Creating an Ethernet Hub-Connected Network

3. © 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—3-3 Early Local Area Networks

4. © 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—3-4 Signals degrade with transmission distance. Each Ethernet type has a maximum segment length. LAN Segment Limitations

5. © 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—3-5 Extending LAN Segments Bandwidth is shared Extends cable distances Repeats or amplifies signal

6. © 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—3-6 Collisions

7. © 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—3-7 Multiple Collision Domains

8. © 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—3-8 Summary The early version of Ethernet was called thick Ethernet and was large, expensive, difficult to install, limited to 500 meters before a repeater was required, limited in the number and placement of stations, relatively difficult in adding new users, and provided 10 Mbps of bandwidth. The later version of Ethernet, thin Ethernet, was smaller, limited to 185 meters before a repeater was required, limited in the number and placement of stations, easier in adding new users, and provided 10 Mbps of bandwidth.

9. © 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—3-9 Summary (Cont.) A segment is a network connection made by a single unbroken network cable. Ethernet cables and segments can only span a limited physical distance after which transmissions will become degraded. A hub extends network segments by receiving incoming bits, amplifying the electrical signal, and transmitting these bits through all of its ports to the other devices on the network. If two or more stations on a segment transmit at the same time, a collision results.

10. © 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—3-10 Summary (Cont.) The network segments that share the same bandwidth are called collision domains because when two or more devices communicate at the same time, collisions may occur within that segment. It is possible to use other network devices operating at Layer 2 (or above) of the OSI model to divide network segments to reduce the number of devices that are competing for bandwidth on a given segment and to provide more bandwidth to the devices in the segment.