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ATM
Asynchronous Transfer Mode A standard for high-speed transmission of data,
text, voice, and video, widely used within the Internet.
ATM utilizes virtual
channels instead of dedicated circuits to carry data in fixed-length cells (1 cell =
53 bytes) over a broadband network with the corresponding data rates ranging
from 45 Mbps to 2.5 Gbps.
Attenuation
The reduction in amplitude and intensity of a signal as a consequence of its
transmission over a medium.
It is usually measured in decibels (dB) and the
greater the distance from the modem to the local telephone exchange, the
higher this value is likely to be.
Authentication
The process of verifying a user’s identity, such as by prompting for a password.
Auto-MDIX
Automatic Medium-Dependent Interface Crossover A technology that automat-
ically detects the required cable connection type (straight or crossover) and
configures the connection appropriately.
Bandwidth
1. The information carrying capacity of a channel. Expressed in hertz (e.g., kHz
or MHz) for analog transmission media and in bits per second (e.g. kbps, Mbps)
for digital transmission media.
Beacon Interval
The duration between beacon packets. Access Points broadcast Beacons in
order to synchronize wireless networks.
In a "noisy" environment - one with
much interference - decreasing the Beacon Interval may improve network
performance. In very remote locations (with few wireless nodes) this value may
be increased.
BER
Bit Error Rate
BER is the percentage of bits received with errors divided by the total number of
bits that have been received over a given time period.
Binary
The "base-two" system of numbers that uses only two digits, 0 and 1, to represent
all numbers.
In binary, the number 1 is written as 1, 2 as 10, 3 as 11, 4
as 100, etc.
Although expressed as decimal numbers for convenience, IP
addresses in actual use are binary numbers; e.g., the IP address 209.191.4.240 is
11010001.10111111.00000100.11110000 in binary.
See Bit, IP Address, Network Mask.
Bit
Short for "binary digit", a bit is a number that can have two values, 0 or 1.
See Binary.
Bit-swap
Bit-swapping is the essential adaptive hand-shaking mechanism used by DMT
modems to adapt to line changes (ADSL line noise increases).
Black-list
A list of numbers that are blocked from calling the local phone lines. Whenever,
a call originating from these numbers is received, it is automatically rejected.
Bps
Bits per second
BRAS
Broadband Remote Access Server
The BRAS sits at the core of an ISP’s network, and aggregates user sessions from
the access network. Beyond aggregation it is also the injection point for policy
management and IP QoS.
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Bridged EoA
Bridged EoA connections enable an ADSL CPE to bridge Ethernet frames
between the LAN and the WAN just like a normal Ethernet switch, the only
difference being that WAN Ethernet frames are encapsulated into AAL5 using
RFC 1483/2684 bridging.
See EoA.
Bridging
Passing data from your network to your ISP and vice versa using the hardware
addresses of the devices at each location. Bridging contrasts with routing which
can add more intelligence to data transfers by using network addresses instead.
The OxyGEN miniOffice can perform both routing and bridging.
See Routing.
Broadband
A telecommunications technology that can send different types of data over the
same medium using multiple frequencies, which can be divided into frequency
channels.
This apparently leads into an increase of the effective rate of
transmission, since multiple pieces of data are sent simultaneously.
DSL is a
broadband technology.
Broadcast
To send data to all computers on a network.
Broadcast SSID
The routinely transmission of the Wi-Fi network name (SSID) into open air by
wireless access points and routers. Disabling SSID broadcasts, makes the WiFi
network invisible unless a user already knows the SSID value.
See SSID.
CAP
Carrier-less Amplitude/Phase
In CAP modulation;
incoming data modulates a single carrier that is then
transmitted down a telephone line.
The carrier itself is suppressed before
transmission (it contains no information, and can be reconstructed at the
receiver), hence the adjective "carrier-less." CAP and DMT are two modulation
systems on the market for ADSL.
CBR
Constant Bit Rate
A service category defined by the ATM Forum for applications and services
which have very stringent cell loss, delay and delay variation requirements.
Cell
The basic unit of information transfer in the ATM network. The cell is comprised
of 53 bytes, with five of the bytes making up the header field and the remaining
48 bytes forming the user information field.
See ATM.
Certificate
An electronic document which incorporates a digital signature to bind together
a public key with an identity. The public key is used to encrypt information and
a private key is used to decrypt it.
Certificate Authority
A certificate authority issues digital certificates and once queried verifies if a
certificate presented is genuine or not.
Channel
A transmission path between two points. The term channel usually refers to a
one-way path, but when paths in the two directions of transmission are always
associated, the term channel can refer to this two-way path.
CIFS
Common Internet File System
See SMB/CIFS.
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Codec
COder-DECoder
A device or program capable of encoding and/or decoding a digital data
stream or signal. In VoIP codec represents the encoding method used for the
voice stream data.
Coding Gain
The increase in efficiency that a coded signal provides over an uncoded signal.
Expressed in decibels (dB), it is the measure in the difference between the SNR
levels of the uncoded and coded systems required to reach the same BER levels.
An improvement in coding gain can provide the option of achieving the same
efficiency over a link with reduced transmission power or bandwidth.
CPE
Customer Premises Equipment
Any equipment provided by the customer at their premises.
CRC
Cyclic Redundancy Check
CRC is a method of checking for errors in data transmitted. Using this technique,
the transmitter appends an extra field to every frame of data. This field holds
redundant information about the frame that helps the receiver detect errors in
the frame.
Crossover Ethernet Cable
A type of Ethernet cable that is used to interconnect two computers by "crossing
over" (reversing) their respective PIN contacts.
Crosstalk
Crosstalk is an undesired coupling from one telecommunication circuit or medium
to another. It is caused by the electric or magnetic fields of one signal affecting
a signal in an adjacent circuit. For example, in a telephone circuit, crosstalk can
result in your hearing part of a voice conversation from another circuit.
Decibel (dB)
A measure of signal intensity. It’s a logarithmic unit, so an increase in 3dB is equal
to double the original intensity.
DECT
Digital Enhanced Cordless Telecommunications
An ETSI standard for digital portable phones (cordless home telephones), com-
monly used for domestic or corporate purposes.
Default Route
The network route used when no other known route exists for a given IP packet’s
destination IP address.
DHCP
Dynamic Host Configuration Protocol
DHCP automates address assignment and management.
When a computer
connects to the LAN, DHCP assigns it an IP address from a shared pool of IP
addresses; after a specified time limit, DHCP returns the address to the pool.
DHCP Lease
Dynamic Host Configuration Protocol Lease
The automatic assignment of network settings using the DHCP protocol. Each
DHCP lease can be static (permanent) or dynamic.
In the latter case, it is
characterized by a lease time, which determines the validity period of the lease.
DHCP Relay
Dynamic Host Configuration Protocol Relay
A DHCP relay is a computer that forwards DHCP data between computers that
request IP addresses and the DHCP server that assigns the addresses. Each of
the OxyGEN miniOffice’s interfaces can be configured as a DHCP relay.
See DHCP.
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DHCP Server
Dynamic Host Configuration Protocol Server
A DHCP server is a computer that is responsible for assigning IP addresses to the
computers on a LAN.
See DHCP.
DHCPv6
DHCPv6 is the version of the Dynamic Host Configuration Protocol (DHCP) for
Internet Protocol Version 6 (IPv6) networks.
In addition to stateless address
autoconfiguration in IPv6, DHCPv6 provides an alternate solution to assign
addresses, nameservers and other configuration information in a manner similar
to DHCP for IPv4. A notable case is Domain Name System servers used on a
network.
Dial Plan
A set of rules defined at a voice endpoint or switch, which controls the exact
action that is going to be performed when a number is dialed. The dial plan is
usually closely related to the defined numbering plan, controlling the way calls
belonging to different categories are going to be routed.
DiffServ
Differentiated Services
A QoS model for IP networks. It is based on the TOS byte of the IP header and
differentiates the relative priority of each IP packet on a per-hop basis.
Digital
Representation of data, having a form based on discrete values expressed as
binary numbers (0’s and 1’s). The data component in DSL is a digital signal.
See Analog.
DMT
Discrete Multi-Tone (DMT) multicarrier modulation uses 256 QAM modulation
tones simultaneously to create the ADSL signal. DMT is the basis of ANSI Standard
T1.413, and has the support of other world standards bodies. CAP and DMT are
two modulation systems for ADSL.
DMZ Host
DeMilitarized Zone Host
A host put outside the router firewall, since all incoming connection attempts
from the Internet are automatically forwarded to it.
DNS
Domain Name System
The DNS maps domain names into IP addresses. DNS information is distributed
hierarchically throughout the Internet among computers called DNS servers.
For example, www.yahoo.com is the domain name associated with IP address
216.115.108.243. When you start to access a web site, a DNS server looks up
the requested domain name to find its corresponding IP address.
If the DNS
server cannot find the IP address, it communicates with higher-level DNS servers
to determine the IP address.
See Domain Name.
Domain Name
A domain name is a user-friendly name used in place of its associated IP address.
Domain names must be unique; their assignment is controlled by the Internet
Corporation for Assigned Names and Numbers (ICANN). Domain names are a
key element of URLs, which identify a specific file at a web site.
See DNS.
Download
To transfer data in the downstream direction, i.e., from the Internet to the user.
Downstream
Downstream refers to "host to end-user" (receive, download) direction.
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DSCP
Differentiated Services Code Point
A QoS model defined in RFC 2474 which is based on six bits of the TOS byte of
the IP header. Each DSCP value specifies a particular per-hop behavior that is
applied to the IP packet.
DSL
Digital Subscriber Line
A technology that allows both digital data and analog voice signals to travel
over existing copper telephone lines.
DSL Modem
Short for MOdulator-DEModulator, this hardware device converts ATM cells to
Ethernet packets and visa-versa in the use of DSL.
DSLAM
Digital Subscriber Line Access Multiplexer
A device which takes a number of ADSL subscriber lines and concentrates these
to the core network of the ISP.
DTMF
Dual-Tone MultiFrequency
DTMFs are a series of tones used for telephone signaling over the telephony lines.
DTMFs are mainly used as a signaling system used for dialing telephone numbers
using a numeric keypad (tone-dialing), instead of using the spinning dial on
old telephones (pulse-dialing). They are also used, however, for other signaling
applications like the passing of commands to voice-mail systems or to IVRs.
Dual Stack
It is a transition mechanism that allows the coexistence and independence of
IPv4 and IPv6 traffic flows in the same device.
Dual Stack Lite
Because of IPv4 address exhaustion, Dual-Stack Lite was designed to let an
Internet service provider omit the deployment of any IPv4 address to a CPE.
Instead, only global IPv6 addresses are provided. The CPE distributes private IPv4
addresses for the LAN clients, the same as a NAT device. The subnet information
is arbitrarily chosen by the customer, identically to the NAT model. However,
instead of performing the NAT itself, the CPE encapsulates the IPv4 packet inside
an IPv6 packet. The CPE uses its global IPv6 connection to deliver the packet
to the ISP’s Carrier-grade NAT (CGN), which has a global IPv4 address. The IPv6
packet is decapsulated, restoring the original IPv4 packet.
NAT is performed
upon the IPv4 packet and is routed to the public IPv4 Internet. The CGN uniquely
identifies traffic flows by recording the CPE public IPv6 address, the private IPv4
address, and TCP or UDP port number as a session.
Duplex
The mode of operation of an Ethernet link, determining if data can be transmitted
in both directions at the same time or in one direction at a time.
See Full Duplex and Half Duplex.
Dynamic DNS
A service allowing the use of domain names in conjunction with dynamic IP
addresses. The service relies on notifications from the device bearing the domain
name towards a server controlling the Dynamic DNS service, with the current
value of the dynamic IP address.
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