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| 3.2 |  | Characteristics of Physical Layer Optimization Problems |
| 3.2.1 |  | Performance lower than baseline |

If there is a problem with sub-optimal operation at the physical layer, the network will be operational, but performance will be consistently or intermittently lower than the level specified in the baseline.

If performance is unsatisfactory all the time, then the problem is probably related to a poor configuration, inadequate capacity somewhere, or some other systemic problem. If performance varies and is not always unsatisfactory, then the problem is probably related to an error condition or is being affected by traffic from other sources:

- Unstable routing due to a marginal port or link somewhere beyond the broadcast domain, possibly the result of a bad cable
- Excessive traffic across a low speed LAN or WAN link, possibly causing traffic to be discarded or buffer capacity to be exceeded
- Overloaded server or service

A physical layer optimization problem occurs when the physical properties of the connection are substandard, causing data to be transferred at a rate that is constantly less than the rate of data flow established in the baseline.

A number of factors can be involved in decreasing the rate at which data is transmitted across media. Major causes of networks performing below baseline are:

- Exceeding the design limits of the media in terms of cabling distance or of network devices
- Large collision domains in shared media networks such as CSMA/CD Ethernet
- Electromagnetic Interference (EMI) effects
- Faulty media or hardware