Network Performance Specifications and Limitations PDF

Summary

The document discusses the specifications and limitations of network links, specifically focusing on speed, throughput, distance constraints, and interference. It explains the concepts of bit rate, baud rate, latency, and signal attenuation in the context of data transmissions.

Full Transcript

2.6.1 Specification and Limitations When troubleshooting a link, you will need to compare the expected performance with the actual current performance. To do this, you must understand how to assess and distinguish speed, throughput, and distance...

2.6.1 Specification and Limitations When troubleshooting a link, you will need to compare the expected performance with the actual current performance. To do this, you must understand how to assess and distinguish speed, throughput, and distance specifications and limitations. Speed Versus Throughput At the Physical layer, a signal transmitted over a communications channel consists of a series of events referred to as symbols. A symbol could be something like a pulse of higher voltage in an electrical current or the transition between the peak and the trough in an electromagnetic wave. The number of symbols that can be transmitted per second is called the baud rate. The baud rate is measured in hertz (or MHz or GHz). At the Data Link layer, the nominal bit rate—or bandwidth—of the link is the amount of information that can be transmitted, measured in bits per second (bps), or some multiple thereof. In order to transmit information more efficiently, a signaling method might be capable of representing more than one bit per symbol. This also helps to overcome noise and detect errors. The use of these encoding methods means that the bit rate will be higher than the baud rate. In Ethernet terms, the bit rate is the expected performance of a link that has been properly installed to operate at 10 Mbps, 100 Mbps, 1 Gbps, or better. The nominal bit rate will not often be achieved in practice. Throughput is an average data transfer rate achieved over a period of time excluding encoding schemes, errors, and other losses incurred at the Physical and Data Link layers. Throughput can be adversely affected by link distance and by interference (noise). Throughput is typically measured at the Network or Transport layer. Often the term "goodput" is used to measure an averaged data transfer rate at the Application layer. This takes account of the effect of packet loss. Throughput is also sometimes measured as packets per second. As well as bandwidth or throughput and packet loss, the speed at which packets are delivered is also an important network performance characteristic. Speed is measured as a unit of time—typically milliseconds (ms)—and is also referred to as latency, or delay. The term "speed" is also used to describe how well or badly a link is performing in terms of throughput but do be aware of the distinction between bit rate and latency. Distance Limitations, Attenuation, and Interference Each type of media can consistently support a given bit rate only over a defined distance. Some media types support higher bit rates over longer distances than others. Attenuation and interference enforce distance limitations on different media types. Attenuation is the loss of signal strength, expressed in decibels (dB). dB expresses the ratio between two measurements; in this case, signal strength at origin and signal strength at destination. Interference (or noise) is anything that gets transmitted within or close to the channel that isn't the intended signal. This serves to make the signal itself difficult to distinguish, causing errors in data and forcing retransmissions. This is expressed as the signal to noise ratio (SNR). Copyright © The Computing Technology Industry Association, Inc. All rights reserved.

Use Quizgecko on...
Browser
Browser