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| 3.1 |  | Characteristics of Physical Layer Failure Problems |
| 3.1.2 |  | Critical characteristics – upper layer component operation |

With the exception of Layer 1, each layer of the OSI model depends on the layer below it for communication to work. In the event of a Layer 1 connectivity problem, no component above the physical layer will be operational. For example, name resolutions, ARP requests, and DHCP requests all rely on Layer 1 for connectivity.

An example of upper layer protocol failure would be a corporate user attempting to access a file server from a workstation. Depending on the location of the fault, the following types of communication components may fail:

- All pings to external devices would timeout.
- The user would not be able to telnet into any other device.
- The user would not be able to access network drives.
- E-mail messages would not be sent or received and there may be an undeliverable message to this effect when attempting to send.
- “Page cannot be displayed” messages occur when attempting to gain intranet or Internet access.