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- Bandwidth – is the average number of bits that can be transmitted from the source to a destination over the network in one second.
- Latency – (AKA “lag”) is the amount of time it takes a packet of data to move across a network connection. When a packet is being sent, there is “latent” time, when the computer that sent the packet waits for confirmation that the packet has been received. Latency and bandwidth are the two factors that determine your network connection speed. Latency in a packet-switched network is measured either one-way (the time from the source sending a packet to the destination receiving it), or round-trip (the one-way latency from source to destination plus the one-way latency from the destination back to the source). Round-trip latency is more often quoted, because it can be measured from a single point. Note that round trip latency excludes the amount of time that a destination system spends processing the packet. Many software platforms provide a service called ping that can be used to measure round-trip latency. Ping performs no packet processing; it merely sends a response back when it receives a packet (i.e. performs a no-op), thus it is a relatively accurate way of measuring latency.Where precision is important, one-way latency for a link can be more strictly defined as the time from the start of packet transmission to the start of packet reception. The time from the start of packet transmission to the end of packet transmission at the near end is measured separately and called serialization delay. This definition of latency depends on the throughput of the link and the size of the packet, and is the time required by the system to signal the full packet to the wire.Some applications, protocols, and processes are sensitive to the time it takes for their requests and results to be transmitted over the network. This is known as latency sensitivity. Examples of latency sensitive applications include VOIP, video conferencing, and online games. In a VOIP deployment, high latency can mean an annoying and counterproductive delay between a speaker’s words and the listener’s reception of those words. Network management techniques such as QoS, load balancing, traffic shaping, and caching can be used individually or combined to optimize the network and reduce latency for sensitive applications. By regularly testing for latency and monitoring those devices that are susceptible to latency issues, you can provide a higher level of service to end users.
- Jitter – Jitter is the deviation in or displacement of some aspect of the pulses in a high-frequency digital signal. As the name suggests, jitter can be thought of as shaky pulses. The deviation can be in terms of amplitude, phase timing, or the width of the signal pulse. Another definition is that it is “the period frequency displacement of the signal from its ideal location.” Among the causes of jitter are electromagnetic interference (EMI) and crosstalk with other signals. Jitter can cause a display monitor to flicker; affect the ability of the processor in a personal computer to perform as intended; introduce clicks or other undesired effects in audio signals, and loss of transmitted data between network devices. The amount of allowable jitter depends greatly on the application.
- Packet Loss – is the failure of one or more transmitted packets to arrive at their destination. This event can cause noticeable effects in all types of digital communications.The effects of packet loss:
- In text and data, packet loss produces errors.
- In videoconference environments it can create jitter.
- In pure audio communications, such as VoIP, it can cause jitter and frequent gaps in received speech.
- In the worst cases, packet loss can cause severe mutilation of received data, broken-up images, unintelligible speech or even the complete absence of a received signal.
The causes of packet loss include inadequate signal strength at the destination, natural or human-made interference, excessive system noise, hardware failure, software corruption or overburdened network nodes. Often more than one of these factors is involved. In a case where the cause cannot be remedied, concealment may be used to minimize the effects of lost packets.
- Echo – is when portions of the transmission are repeated. Echoes can occur during many locations along the route. Splices and improper termination in the network can cause a transmission packet to reflect back to the source, which causes the sound of an echo. To correct for echo, network technicians can introduce an echo canceller to the network design. This will cancel out the energy being reflected.
- High Bandwidth Applications – A high bandwidth application is a software package or program that tends to require large amounts of bandwidth in order to fulfill a request. As demand for these applications continues to increase, bandwidth issues will become more frequent, resulting in degradation of a network system. One way to combat the effects of these applications on a network is to manage the amount of bandwidth allocated to them. This allows users to still use the applications without degrading the QoS of network services.Examples:
- Thin Clients
- Voice over IP
- Real Time Video
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