Content

| 3.1 |  | Characteristics of Physical Layer Failure Problems |
| 3.1.1 |  | Critical characteristics – connectivity |

Anytime that there is a physical layer failure, a loss of connectivity will be experienced. A user or a group of users affected by the problem will usually call the help desk complaining that everything is down. Less astute users may only complain that a specific service or application is not working. If a technician can log in to one of the affected devices and start gathering information, it will be evident that no component above the physical layer is operating.

Unlike network failures, all cable failures are approached in approximately the same manner, whether the link is newly installed or has failed during operation. There are many instances where a poor quality link has been in service, but due to the operating environment and influences it has stopped working. These influences include visible damage to the cable, new electrical noise sources near the cable, or accidental movement of the cables.

Most networks have converted from coaxial cable to Category 5 or Category 5e UTP links. However, there is still a surprising amount of coaxial cable in legacy network segments. Fiber-optic cable is approaching a price point where it will rival Category 6 UTP in overall cost. The overall cost of a fiber-optic cable installation includes materials, labor, and network adapters. All of these factors have become less expensive in recent years. There are different installation and maintenance issues for each cable type.

| Lab Activity Lab Exercise: Applying a Logical Layered Model to a Physical Network After completing this lab, the student will be able to understand the data flow in the classroom network based on the logical network model.