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||bandwidth is the amount of data that can be carried in a given time period over a network.
More technically, bandwidth is the width of the range of frequencies that an electronic signal occupies on a given transmission medium. In digital systems, bandwidth is usually expressed as bps (bits per second), Kbps (Kilobits/second or Mbps (Megabits / second). In analog systems, it's the number of cycles of change per second, or hertz.
||baud is essentially the rate at which bits are transmitted over a communication link. Baud is the number of transitions (used to encode bits) that take place in one second.
However, since such single state change can involve more than a single bit of data, the term bps (bits per second) has replaced baud as a better expression of data transmission speed.
||The Bandwidth*Delay Product, or BDP for short determines the amount of data that can be in transit in the network. It is the product of the available bandwidth and the latency, or RTT. BDP is a very important concept in a Window based protocol such as TCP. It plays an especially important role in high-speed / high-latency networks, such as most broadband internet connections. It is one of the most important factors of tweaking TCP in order to tune systems to the type of network used.
The BDP simply states that:
BDP (bits) = total_available_bandwidth (bits/sec) x round_trip_time (sec)
or, since RWIN/BDP is usually in bytes, and latency is measured in milliseconds:
BDP (bytes) = total_available_bandwidth (KBytes/sec) x round_trip_time (ms)
What does it all mean? The TCP Window is a buffer that determines how much data can be transferred before the server waits for acknowledgement. It is in essence bound by the BDP. If the BDP (or RWIN) is lower than the product of the latency and available bandwidth, we can't fill the line since the client can't send acknowledgements back fast enough. A transmission can't exceed the (RWIN / latency) value, so RWIN needs to be large enough to fit the maximum_available_bandwidth x maximum_anticipated_delay.
||beamforming is a signal processing technique used in wireless communications, sonars and radars for directional signal tramsmission and reception. Beamforming is achieved by combining elements in a transmitter/antenna array in a way where signals at particular angles experience constructive interference, while others experience destrictive interference. The improvement compared with an omnidirectional reception/transmission is known as the receive/transmit gain (or loss).
There are two different methods as applicable to Wi-Fi: on-chip and on-antenna beamforming.
On-chip beamforming works by not only boosting total power gain by having multiple antennas in play, but also phasing the antenna signals so that a higher signal "beam" is cast in the receiver's direction while less energy can be expended in other directions.
On-antenna beamforming uses a number of antennas and analyzes trasmitted packets to asses signal perfomance. The access point monitors connections in real-time and modifies beams on the fly to fit dynamic conditions. Antennas that need signal boosting get boosted while those that don't are attenuated.
||BGP (Border Gateway Protocol) is a routing protocol that enables groups of routers (called autonomous systems) to communicate and share routing information establishing efficient, loop-free routes while using their own internal routing policies. BGP is commonly used within and between Internet Service Providers (ISPs). For customers, BGP allows for using unique routing policies internally, as well as connecting to multiple ISPs. The protocol is defined in RFC 1771.
||BIOS (Basic Input/Output System) is the program which starts up your computer and communicates between the devices (such as your hard drive, keyboard, video card) and the system. BIOS is normally stored in an EPROM (Eraseable Programmable Read Only Memory) chip.
||bit shift is a binady number operation, that moves (shifts) the bits in a number to the left or right.
Each bit shifted increases/decreases the value by a power of two. Eg a shift of 1 to the left will double the value, a shift to 2 to the right will quarter it.
||Building-focused Local Exchange Carrier
||blog (short for short for weblog) simply refers to a frequent, chronological publication of personal thoughts and web links.
The term can be used to describe a type of a publicly accessible personal journal, or some type of discusison community about particular issues (where there can be more than one author). In either case, it is a regularly updated online journal of information and opinions.
The activity of updating a blog is referred to as "blogging," and someone who keeps a blog is a "blogger."
||Bluetooth (BT) is a short-range wireless technology that connects two devices with radio signals. Unlike WiFi, it is primarily designed for short range (up to 30 feet). Bluetooth basic rate speeds are ~720Kbps.
Common uses include connecting Bluetooth-enabled phones to headsets, PDA wireless networking, automobile interface with a phone for hands-free operation, wireless mice/keyboards, etc.
Bluetooth 1.x - basic rate bluetooth, max data rate 1Mbps
Bluetooth 2.x - basic rate + EDR(optional), max data rate with EDR 3Mbps, better pairing.
Bluetooth 3.x - basic rate + EDR(optional) + HS(optional), further speed improvements using 802.11 protocol adaptation layer.
Bluetooth 4.x - basic rate + EDR(optional) + HS(optional) + LE(optional). Low energy devices support for lower power consumption, a.k.a. Bluetooth Smart.
||BoD (Bandwidth on Demand) is a technique used in data communication to temporarily boost the capacity of a link. The technique is commonly used in wide area networks. Instead of explicitly allocating capacity during construction of the network, BoD enables network capacity to be increased on-demand and immediately reduced when the need has been addressed. This best suits applications with fluctuating bandwidth needs.
BoD is a tailored product for customers who require Internet Access in varied amounts at varying times. It caters additional bandwidth needs when required by the customer. When more capacity is needed, routers that provide bandwidth-on-demand can establish links on demand and then bring the line down when traffic demand is lower, allowing for a more cost-effective solution.
||Bonding combines two or more physical circuits into one logical circuit, for example, two T1s (1.54 Mbps each) can be combined to form a 3Mbps circuit. Bonding can be accomplished on the physical level through multiplexing or through hardware such as Tiara equipment.
||Boot - to start a device and cause it to start executing instructions.
||BPI (Baseline Privacy Interface)
DOCSIS required encryption standard used to protect users and their data. BPI uses a public/private key exchange system to encrypt data that is transmitted between the cable modem and the CMTS.
Also: Bits Per Inch - A measurement of the recording density of a disk or tape.
Also: British Phonographic Industry
||BPL (Broadband over Power Lines) is an emerging internet access technology that utilizes existing power lines to transport data at broadband speeds.
The IEEE 1901 (1901-2010) standard replaced a number of previous powerline specifications. It prevents interference when the different BPL implementations are operated within close proximity.
Related: IEEE 1905.1 heterogeneous networking, IEEE P1909.1 smart grid standards
||bits per second, as oposed to Bps (Bytes per seccond).
||bricked - when used in reference to electronics, "brick" describes a device that connot function in any capacity (such as a device with damaged firmware). This usage derives from teh fact that many electronic devices are vaguely brick-shaped, and would be useful only as bricks if they do not function.
Bricking implies that a software error has rendered the device completely useless without some hardware replacement, or a complex procedure, often requiring dificult to obtain cables, software, shipping it back to the manufacturer, etc.
||broadband is a term that is being used interchangeably with high-speed. More specifically, it desctibes a wideband high-speed data transmission that employs only one wire, which is able to carry multiple channels at once (as opposed to narrowband, or baseband which transmits one channel at a time).
Various definitions of broadband assign a different minimum data rate to the term, however it is generally agreed that DSL and Cable are broadband services in the downstream direction.
||BSOD (Blue Screen of Death) - This term is closely related to the older Black Screen of Death but much more common (many non-hackers have picked it up). Due to the extreme fragility and bugginess of MS Windows, misbehaving applications can crash the OS. The Blue Screen of Death, sometimes decorated with hex error codes, is what you get when this happens.
||Bufferbloat is the undesirable increase in latency caused by a router or other network equipment buffering too much data.
Bufferbloat can also refer to an increase in latency (measure of round trip delay) when an internet connection is fully utilized.
Note that a bufferbloat has an effect only when that particular buffer is actually filled. In other words, oversized buffers have a damaging effect only when the link they buffer becomes a bottleneck.
||CAIDA (Cooperative Association for Internet Data Analysis) provides tools and analyses promoting the engineering and maintenance of a robust, scalable global Internet infrastructure. It is a collaborative undertaking among commercial, government, and research organizations with a strong interest in keeping primary Internet capacity and usage efficiency in line with ever-increasing demand.
||Cantenna - yagi antenna design for 802.11b wireless applications, constructed from Pringles, or other type of cans :) Yes, they work too, you can make a 12db gain cantenna in 30 min.
||CAT5 (Category 5 ethernet cable) is an widely used EIA/TIA Ethernet cable standard. CAT5 cables contain 4 twisted pairs of copper wire and support 100 Mbps Fast Ethernet. CAT5 cable runs are limited to a maximum recommended length of 100m (328 feet).
||CAT5e (Category 5 enhanced) is a CAT5 variation that supports short-run Gigabit Ethernet (1000 Mbps) networking by utilizing all four wire pairs in a CAT5 cable, and is backward-compatible with ordinary CAT5.
||CAT6 (Category 6) is the 6th generation of twisted pair Ethernet cabling. It is a standard superseeding CAT5e in its support for Gigabit Ethernet. Unlike CAT5, it utilizes all four twisted pairs. CAT6 supports communications at more than twice the speed of CAT5e, the other popular standard for Gigabit Ethernet cabling.
||CAT7 (Category 7) is the new generation of cabling that is still in the works. Generally when CAT6 was introduced there were actually two proposals, 200MHz and 600MHz one. When study began on those two proposals, a decision was made to develop both generations in parallel. The CAT7 standard is not yet finalized, besides at some point it might be cheaper to use fiber than to "stretch" the UTP copper any further.
||CCCM (CPE Controlled Cable Modem) is a project covered under the DOCSIS CMCI Specification.
It provides an architectural overview of a CPE Controlled Cable Modem (CCCM), introducing the basic functions residing in both the CCCM hardware and the CCCM software running on the host CPE.
||CCMP (Counter-Mode Cipher Block Chaining Message Authentication Code Protocol). It is a specific mode of AES which is implemented in the 802.11i standard and WPA2.
||Code-Division Multiple Access - a digital cellular technology, that uses spread spectrum techniques. Each channel in CDMA uses the full spectrum (unlike comppeting technologies, such as GSM or TDMA), and individual conversations are encoded with a random digital sequence.
||cellular refers to a communicatins system that divides geographic regions into sections called cells. The purpose of this division is to make the most out of a limited number of transmission frequencies (total of ~1000) required by each separate call. Cellular systems allocate a set number of frequencies to each cell, and such frequencies can only be reused by other non-adjacent cells.
GSM and CDMA are some of the more popular cellular systems in use today.
||Central Office (CO) is the office of your local carrier (LEC) closest to your location. Your circuit will be terminated to the CO closest to you and then connected to the closest Point of Presence (POP) of your chosen ISP.
||checksum is a value calculated by aplying a specific algorithm to a file or datagram. The algorithm is designed so that even a single bit change in the source file/data causes a completely different checksum value.
Checksums are fixed length (32 bits for CRC32, 128 bits for MD5, etc.) regardles of the size of the file or datagram they are applied to.
See also: CRC
||CIDR (Classless Inter-Domain Routing) is an IP addressing scheme that allows network administrators to subdivide a block of IP addresses to create more usable address space. CIDR IP addresses are normally noted in the format of a normal IP address except that it ends with a slash followed by a number, called the IP network prefix: 126.96.36.199/27. In this case, /27 indicates that the first 27 bits are used to identify the unique network, and the remaining 5 bits (5 binary digits, or 32 addresses) have been allocated to the client.
CIDR addresses reduce the size of routing tables and make more IP addresses available within organizations. CIDR is also called supernetting. CIDR currently uses prefixes anywhere from 13 to 27 bits:
CIDR - # hosts (Class C equivalent)
/27 - 32 hosts (1/8th of a Class C)
/26 - 64 hosts (1/4th of a Class C)
/25 - 128 hosts (1/2 of a Class C)
/24 - 256 hosts (1 Class C )
/23 - 512 hosts (2 Class C)
/22 - 1,024 hosts (4 Class C)
/21 - 2,048 hosts (8 Class C)
/20 - 4,096 hosts (16 Class C)
/19 - 8,192 hosts (32 Class C)
/18 - 16,384 hosts (64 Class C)
/17 - 32,768 hosts (128 Class C)
/16 - 65,536 hosts (256 Class C = 1 Class B)
/15 - 131,072 hosts (512 Class C)
/14 - 262,144 hosts (1,024 Class C)
/13 - 524,288 hosts (2,048 Class C)
||block ciphers - method for encrypting plain text in chunks. Common block sizes are 64 and 128 bits.
stream ciphers - method for encrypting plain text one byte (or bit) at a time. A stream cipher can be thought of as a block cipher with a really small block size.
Generally, block ciphers are more efficient for computers than stream ciphers.
Examples: DES is a block sipher with a 64-bit block size. RSA is a block cypher with a variable block size. RC4 (WEP, WPA, TKIP) and A5 (the algorightm used to encrypt GSM) are stream ciphers.
||CIR (Committed Information Rate) is a specified amount of guaranteed bandwidth (measured in bits per second).
Typically, when purchasing a Broadband Internet service, the ISP can specify the CIR level they wish. The vendor basically guarantees that a certain bandwidth will be delivered. It's possible that additional traffic may also be delivered, but it's not guaranteed.
||In telecommunications, a circuit is a physical path between two or more points along which signals (data or voice) can be carried. It consists of one or more wires or wireless paths, and possibly intermediate switching points. It represents a persistent, dedicated connection established for transmitting information.
||CLEC (Competitive Local Exchange Carrier) is a company that competes with established local telephone business (local exchange carriers, or simply LEC) by providing its own network and switching.
The term arises from the Telecommunications Act of 1996, which was intended to promote competition among providers.
||CMTS (Cable Modem Termination System) is a system of devices located at the head-end (the local cable TV company office) that exchanges digital signals with cable modems on a cable network. All cable modems can exchange signals only with the CMTS, and not directly with other modems.
One TV channel is used for upstream signals from cable modems to the CMTS, and another channel for downstream signals from the CMTS to cable modems. The CMTS is responsible for converting received signals into IP packets, which are then sent to an IP router for transmission across the Internet. When a CMTS sends signals to a cable modem, it modulates the downstream signals for tranmission to the cable modem via coax cable.
||CODEC - a hardware device or software program that converts analog information streams into digital signals, and vice versa; generally used in audio and video communications where compression and other functions may be necessary and provided by the CODEC as well.
||CoDel (controlled delay) is a network scheduler algorithm designed to overcome bufferbloat in network links, such as routers by setting limits on the delay network packets can suffer because of buffering. It only affects congested links, and helps improve overall latency by dropping the slowest packets on links that are overloading the buffers.
CoDel improves on the performance of the RED algorithm by better recognizing bufferbloat. CoDel distinguishes between two types of packet queues, "good queues" that exibit no buffer bloat, and "bad queues" that exibit some buffer bloat (more than 5ms delay because of buffers). CoDel only comes into effect when the network buffers fill up, and the minimum delay for the TCP Window is exceeded, it then treats "bad queues" by dropping slowest packets to control link rates.
CoDel is available in the Linux kernel since version 3.5. It is also available with various open source router firmwares, such as CeroWrt, OpenWrt, dd-wrt, and AsusWrt-Merlin firmware.
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