Band Width
In computer networking, the term "bandwidth" refers to the data rate supported by anetwork interface. Bandwidth represents the capacity of a network connection for supporting data transfers. Higher network bandwidth often translates to better performance, although overall performance also depends on other factors.
The term derives from the field of electrical engineering, where bandwidth represents the total distance or range between the highest and lowest signals on a communication channel (band).
Measuring Network Bandwidth
Computer network bandwidth is measured in units of bits per second (bps). Most modern network devices support data rates of thousands and often millions or even billions of bps (units of Kbps, Mbps, and Gbps).
Network devices each possess a bandwidth rating according to the maximum data rate they are physically capable of supporting. The network protocol technology a device uses determines its max data rate. Protocol designers and device makers measure and assign bandwidth ratings to their devices accordingly. For example, old V.90 dial-up modems were rated as 56 Kbps devices. 802.11g Wi-Fi devices as 54 Mbps and Fast Ethernet links as 100 Mbps.
Measuring Throughput versus Bandwidth
People sometimes use the terms "throughput" and "bandwidth" interchangeably. Technically, throughput represents the actual amount of useful data transferred over a network connection compared to bandwidth that measures a theoretical maximum.
Due to network communication overheads (packing and unpacking of messages, collisions, errors, and retries), throughput typically rates significantly lower than bandwidth. Internet speed tests measure the throughput of a client's Internet connection. Various utility programs measure throughput on local networks, including ttcp.
Attenuation
Attenuation is a telecommunications term that refers to a reduction in signal strength commonly occurring while transmitting analog or digital signals over long distances.
Attenuation is historically measured in dB but it can also be measured in terms of voltage.
Attenuation can relate to both hard-wired connections and to wireless transmissions.
There are many instances of attenuation in telecommunications and digital network circuitry.
Inherent attenuation can be caused by a number of signaling issues including:
- Transmission medium - All electrical signals transmitted down electrical conductors cause an electromagnetic field around the transmission. This field causes energy loss down the cable and gets worse depending upon the frequency and length of the cable run. Losses due to
- Crosstalk from adjacent cabling causes attenuation in copper or other conductive metal cabling.
- Conductors and connectors - Attenuation can occur as a signal passes across different conductive mediums and mated connector surfaces.
Repeaters are used in attenuating circuits to boost the signal through amplification (the opposite of attenuation). When using copper conductors, the higher the frequency signal, the more attenuation is caused along a cable length. Modern communications use high frequencies so other mediums which have a flat attenuation across all frequencies, such as fiber optics are used instead of traditional copper circuits.
Different types of attenuation include:
- Deliberate attenuation can occur for example where a volume control is used to lower the sound level on consumer electronics.
- Automatic attenuation is a common feature of televisions and other audio equipment to prevent sound distortion by automatic level sensing that triggers attenuation circuits.
- Environmental attenuation relates to signal power loss due to the transmission medium, whether that be wireless, copper wired or fiber optic connected.
Bitrate
Bitrate, as the name implies, describes the rate at which bits are transferred from one location to another. In other words, it measures how much data is transmitted in a given amount of time. Bitrate is commonly measured in bits per second (bps), kilobits per second (Kbps), or megabits per second (Mbps). For example, a DSL connection may be able to download data at 768 kbps, while a Firewire 800 connection can transfer data up to 800 Mbps.
Bitrate can also describe the quality of an audio or video file. For example, an MP3 audio file that is compressed at 192 Kbps will have a greater dynamic range and may sound slightly more clear than the same audio file compressed at 128 Kbps. This is because more bits are used to represent the audio data for each second of playback. Similarly, a video file that is compressed at 3000 Kbps will look better than the same file compressed at 1000 Kbps. Just like the quality of an image is measured in resolution, the quality of an audio or video file is measured by the bitrate.
baud rate
baud, baud rate A baud is the number of signaling elements per second sent by a communications device such as a modem, In theory, a modem with a high baud rate means fast transmission. The baud rate is therefore equal to the bit rate only if each signal element represents one bit of information.
Unfortunately, in much of today's literature, the terms "baud" and "bits per second" are used synonymously. This is correct in cases where pure two-state signaling is used, but is incorrect in general. For this reason, the term "baud" is gradually being replaced by "bits per second," since the latter is independent of the coding method and truly represents the information rate.
When you use a modem to send information from one computer to another over the phone lines, the information moves at a certain speed. This speed is measured in bits per second, a bit being one electronic unit of information. This bits-per-second rate is also commonly called thebaud rate (pronounced "bod"). It's a measure of how fast your modem can send and receive information. Modems most typically send at 1200, 2400, or 9600 baud.
Now, I do have to warn you that even though the masses (that's us) often use the term "baud" to mean the same thing as "bits per second," this is technically incorrect, and someday someone will surely scold you. One baud is actually one "modulation change" or one "signal event" per second on a communications channel. It's only at 300 baud that one signal event equals one bit per second. A modem operating at 1200bits per second needs only one signal event to send 2 bits, so if you want to be persnickety you should call it a 600 baud modem. See bps for a discussion of common communications speeds and how they translate into speed ratings you can relate to.
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