algorithm
A specific procedure used to modify a signal. For example, the
key to a digital compression system is the algorithm that eliminates
redundancy.
American
National Standards Institute (ANSI) An official body
within the United States delegated with the responsibility of defining
standards.
American
Standard Code for Information Interchange (ASCII) Assigns
specific letters, numbers, and control codes to the 256 different
combinations of 0s and 1s in a byte.
American
wire gauge (AWG) A measurement of wire diameter - the
lower the AWG number, the larger the wire diameter. Copper phone
wiring usually comes in 24 or 26 AWG.
analog A continuously varying signal or wave. As with all waves, analog
waves are susceptible to interference which can change the character
of the wave.
asymmetric
digital subscriber line (ADSL) A group of DSL technologies
that reserve more bandwidth in one direction than the other, which
is advantageous for users that do not need equal bandwidth in both
directions. See DSL.
asynchronous Occurring at different times. For example, electronic mail is asynchronous
communication because it does not require the sender and receiver
to be connected at the same time.
Asynchronous Transfer Mode (ATM)
The Asynchronous Transfer Mode (ATM) composes a protocol suite which establishes a mechanism to carry all traffic on a stream of fixed 53-byte packets (cells). A fixed-size packet can ensure that the switching and multiplexing function could be carried out quickly and easily. ATM is a connection-oriented technology, i.e.; two systems on the network should inform all intermediate switches about their service requirements and traffic parameters in order to establish communication.
The ATM reference model, which has two forms - one for the user-to-network interface (UNI) and the other for the network-to-node interface (NNI), is divided into three layers: the ATM adaptation layer (AAL), the ATM layer, and the physical layer. The AAL interfaces the higher layer protocols to the ATM Layer, which relays ATM cells both from the upper layers to the ATM Layer and vice versa. When relaying information received from the higher layers, the AAL segments the data into ATM cells. When relaying information received from the ATM Layer, the AAL must reassemble the payloads into a format the higher layers can understand. This is called Segmentation and Reassembly (SAR). Different AALs are defined in supporting different types of traffic or service expected to be used on ATM networks.
The ATM layer is responsible for relaying cells from the AAL to the physical layer for transmission and from the physical layer to the AAL for use at the end systems, it determines where the incoming cells should be forwarded to, resets the corresponding connection identifiers and forwards the cells to the next link, as well as buffers cells, and handles various traffic management functions such as cell loss priority marking, congestion indication, and generic flow control access. It also monitors the transmission rate and conformance to the service contract (traffic policing).
The physical layer of ATM defines the bit timing and other characteristics for encoding and decoding the data into suitable electrical/optical waveforms for transmission and reception on the specific physical media used. In addition, it also provides frame adaptation function, which includes cell delineation, header error check (HEC) generation and processing, performance monitoring, and payload rate matching of the different transport formats used at this layer. SONET, DS3, Fiber, twisted-pair are few media often used at the physical layer.
audio
on demand A type of media that delivers sound programs
in their entirety whenever a listener requests the delivery.
backbone The part of a communications network that handles the major traffic
using the highest-speed, and often longest, paths in the network.
bandwidth A measure of capacity of communications media. Greater bandwidth
allows communication of more information in a given period of time.
Bandwidth is generally described either in terms of analog signals
in units of Hertz (Hz), which describes the maximum number of cycles
per second, or in terms of digital signals in units of bits per
second.
basic
rate ISDN (BRI-ISDN) The basic rate ISDN interface provides
two 64 Kb/s channels (called B channels) to carry voice or data
and one 16 Kb/s signaling channel (the D channel) for call information.
bit A single unit of data, either a one or a zero, used in digital
data communications. When discussing digital data a small "b"
refers to bits, and a capital "B" refers to bytes.
broadband An adjective used to describe large-capacity networks that are
able to carry several services at the same time, such as data, voice,
and video.
broadband
integrated services digital network (BISDN) A second-generation
ISDN technology that uses fiber optics for a network that can transmit
data at speeds of 155 megabits per second and higher.
byte A compilation of bits, seven bits in accordance with ASCII standards
and eight bits in accordance with EBCDIC standards.
Call Forwarding Busy Line
Provides for calls (T) terminating to a subscriber's busy directory number to be forwarded to another telephone number on a premises other than the provisioned premises.
Call Forwarding Don't Answer
Provides for calls terminating to a subscriber's idle directory number to be forwarded, after a customer preselected interval, to another telephone number.
Call Forwarding Variable
Provides for transferring incoming calls to another telephone number by dialing a code and the telephone number of the service to which calls are to be transferred.
Call Waiting
By means of a tone signal a customer who is using his telephone is alerted when another caller is trying to reach that station. Permits putting first call on hold so that second call can be answered. Before a Call Waiting subscriber initiates a call, the subscriber may activate the cancel feature and Call Waiting is then made inoperative on the first call initiated by the subscriber immediately following activation of the cancel feature. The cancel feature may also be activated after a call is established if the customer subscribes to a service that allows flash-hook privileges such as Three-Way Calling. Call Waiting is restored automatically on termination of such a call. During the time the cancel feature is activated, incoming callers receive a busy tone.
carrier an electromagnetic wave or alternating current which is modulated
to carry signals in radio, telephonic, or telegraphic transmission.
carrierless
amplitude phase (CAP) A type of quadrature amplitude
modulation, used for some types of DSL, that stores pieces of a
modulated message signal in memory and then reassembles the parts
in the modulated wave.
central
office (CO) A telephone company facility that handles
the switching of telephone calls on the public switched telephone
network (PSTN) for a small regional area.
central
processing unit (CPU) The "brains" of a computer,
which uses a stored program to manipulate information.
circuit-switched
network A type of network in which a continuous link
is established between a source and a receiver. Circuit switching
is used for voice and video to ensure that individual parts of a
signal are received in the correct order by the destination site.
common
carrier A business, including telephone and railroads,
which is required by law to provide service to any paying customer
on a first-come, first-serve basis.
competitive
local exchange carrier (CLEC) An American term for a
telephone company that was created after the Telecommunications
Act of 1996 made it legal for companies to compete with the ILECs.
Contrast with ILEC.
compression The process of reducing the amount of information necessary to
transmit a specific audio, video, or data signal. core network -
The combination of telephone switching offices and transmission
plant connecting switching offices together. In the U.S. local exchange
network, core networks are linked by several competing Interexchange
networks; in the rest of the world the core network extends to national
boundaries.
Core / Backbone Network and Technologies
Core network and backbone network typically refer to the high capacity communication facilities that connect primary nodes. Core/backbone network provides path for the exchange of information between different sub-networks. In the world of Enterprises, the term backbone is more used, while for Service Providers, the term core network is more used.
In the U.S. local exchange Core Networks are linked by several competing Interexchange networks; in the rest of the world (now) the Core Network extends to national boundaries.
Core/backbone network usually has a mesh topology that provides any-to-any connections among devices on the network. Many main service providers in the world have their own core/backbone networks, that are interconnected. Some large enterprises have their own core/backbone network, which are typically connected to the public networks.
The devices and facilities in the core / backbone networks are switches and routers. The trend is to push the intelligence and decision making into access and edge devices and keep the core devices ¡°dump and fast¡±. As a result, switches are more and more often used in the core/backbone network facilities. The technologies used in the core and backbone facilities are data link layer and network layer technologies such as SONET, DWDM, ATM, IP, etc. For enterprise backbone network, gigabit Ethernet or 10 gigabit Ethernet technologies are also often used.
Core/Backbone Network and Technologies
crosstalk Interference from an adjacent channel.
customer
premises equipment (CPE) Any piece of equipment in a
communication system that resides within the home or office. Examples
include modems, television set-top boxes, telephones and televisions.
dedicated
connection A communication link that operates constantly.
Delay Dial
Same as Wink Start except signals are not used. Delayed time intervals are used in place of signals to perform the identification process (rarely used).
dial-up
connection A data communication link that is established
when the communication equipment dials a phone number and negotiates
a connection with the equipment on the other end of the link.
DID
Direct Inward Dialing (DID) is an inward, designed trunk-side service which enables customers to have fewer DID trunks than telephone numbers. Calls are sent to the desired station without the assistance of an attendant. Some providers offer DID / OD (out dial) services on the same trunk.
With Direct Inward Dial (DID) service, each direct dialed PBX station is assigned a 7 -digit exchange telephone number. When a DID number is dialed, the central office equipment:
Determines the signaling needed by the PBX
Determines the number of digits to send
Determines the trunks for sending the message
Routes incoming calls to a trunk
Passes dialed digit information to the customer's PBX for direct routing
There are three types of signaling - Wink Start, Delay Start, or Immediate Start.
Wink Start
The PBX equipment can identify the first three or four digits of the station number being accessed. In order to identify the last three or four digits, the central office must signal back to the PBX to prepare to accept these digits. The PBX signals (winks) the central office to send the digits.
Immediate Start
As soon as the central office seizes a trunk, the central office machine sends the called station digits back to the waiting PBX for decoding.
Delay Dial
Same as Wink Start except signals are not used. Delayed time intervals are used in place of signals to perform the identification process (rarely used).
digital
signal A signal that takes on only two values, off or
on, typically represented by "0" or "1." Digital
signals require less power but (typically) more bandwidth than analog,
and copies of digital signals can be made exactly like the original.
digital
subscriber line (DSL) A data communications technology
that transmits information over the copper wires that make up the
local loop of the public switched telephone network (See local loop).)
It bypasses the circuit-switched lines that make up that network
and yields much faster data transmission rates than analog modem
technologies
digital
subscriber line access multiplexor (DSLAM) A device found
in telephone company central offices that takes a number of DSL
subscriber lines and concentrates these onto a single ATM line.
direct
broadcast satellite (DBS) A broadcast technology that
uses satellites orbiting the Earth to broadcast television or data
signals to an 18" dish antenna.
discrete
multi-tone modulation (DMT) A method of transmitting
data on copper phone wires that divides the available frequency
range into 256 sub-channels or tones, and which is used for some
types of DSL.v discrete
wavelet multitone (DWMT) A variation of DMT modulation
that improves performance by using wavelets rather than tones to
provide additional isolation of sub-channels.
DNS domain name system (DNS) - The protocol
used for assigning text addresses (such as www.2wire.com) for specific
computers and computer accounts on the Internet.
DWDM: Dense Wavelength Division Multiplex and Multiplexer
Dense Wavelength Division Multiplexing (DWDM) is a technique that multiple signals are carried together as separate wavelengths (color) of light in a multiplexed signal. DWDM is a variation of Wavelength Division Multiplex (WDM) but with much higher bandwidth and density. Using DWDM, up to 80 (and theoretically more) separate wavelengths or channels of data can be multiplexed into a lightstream transmitted on a single optical fiber. Each channel carries a time division multiplexed (TDM) signal. Each channel can carry up to 2.5 Gbps, there fore up to 200 billion bits per second can be delivered by the optical fiber simultaneously.
Another important feature of the DWDM system is that different data formats can be transmitted at different data rates can be transmitted together. Specifically, Internet (IP) data, Synchronous Optical Network data (SONET), and asynchronous transfer mode (ATM) data can all be travelling at the same time within the optical fiber. At the end of the transmission, each channel is demultiplexed back into the original source. Hence carriers can quickly introduce ATM or IP without having to deploy an overlay network for multiplexing. DWDM is a crucial component in today¡¯s optical network and widely deployed by Service Providers in their backbone network
DWDM: Dense Wavelength Division Multiplex and Multiplexer
E-1 A dedicated digital communication link provided by a European
telephone company that offers 2.048 megabits per second of bandwidth,
commonly used for carrying traffic to and from private business
networks and Internet service providers
echo
cancellation The elimination of reflected signals ("echoes")
in a two-way transmission created by some types of telephone equipment,
used in data transmission to improve the bandwidth of the line.
FDM See frequency division multiplexing. fiber optics. Thin strands
of ultrapure glass or plastic that can be used to carry light waves
from one location to another.
fiber-to-the-cabinet
(FTTCab) network architecture where an optical fiber
connects the telephone switch to a street-side cabinet where the
signal is converted to feed the subscriber over a twisted copper
pair.
fiber-to-the-curb
(FTTC) The deployment of fiber optic cable from a central
office to a platform serving numerous homes. The home is linked
to this platform with coaxial cable or twisted pair (copper wire).
Each fiber carries signals for more than one residence, lowering
the cost of installing the network versus fiber to the home.
fiber-to-the-home
(FTTH) The deployment of fiber optic cable from a central
office to an individual home. This is the most expensive broadband
network design, with every home needing a separate fiber optic cable
to link it with the central office.
frame
relay A high-speed packet switching protocol used in
wide area networks (WANs), often to connect local area networks
(LANs) to each other, with a maximum bandwidth of 44.725 megabits
per second.
frequency The number of oscillations in an alternating current that occur
within one second, measured in Hertz (Hz).
frequency
division multiplexing (FDM) The transmission of multiple
signals simultaneously over a single transmission path by dividing
the available bandwidth into multiple channels that each cover a
different range of frequencies.
full-motion
video The projection of 20 or more frames (or still images)
per second to give the eye the perception of movement. Broadcast
video in the United States uses 30 frames per second, and most film
technologies use 24 frames per second.
G.dmt A kind of asymmetric DSL technology, based on DMT modulation,
that offers up to 8 megabits per second downstream bandwidth, 1.544
Megabits per second upstream bandwidth. "G.dmt" is actually
a nickname for the standard officially known as ITU-T Recommendation
G.992.1. (See International Telecommunications Union.)
G.lite
[pronounced "G-dot-light"] A kind of asymmetric
DSL technology, based on DMT modulation, that offers up to 1.5 megabits
per second downstream bandwidth, 384 Kilobits per second upstream,
does not usually require a splitter and is easier to install than
other types of DSL. "G.lite" is a nickname for the standard
officially known as G.992.2. (See International Telecommunications
Union.)
graphical
user interface (GUI) A computer operating system that
is based upon icons and visual relationships rather than text. Windows
and the Macintosh computer use GUIs because they are more user friendly.
hybrid
fiber/coax (HFC) A type of network that includes coaxial
cables to distribute signals to a group of individual locations
(typically 500 or more), and a fiber optic backbone to connect these
groups.
high
bit rate digital subscriber line (HDSL) A symmetric DSL
technology that provides a maximum bandwidth of 1.5 megabits per
second in each direction over two phone lines, or 2 Megabits per
second over three phone lines.
high
bit rate digital subscriber line II (HDSL II) A descendant
of HDSL which offers the same performance over a single phone line.
high-definition
television (HDTV) Any television system that provides
a significant improvement in picture quality over existing television
systems. Most HDTV systems offer more than 1,000 scan lines, in
a wider aspect ratio, with superior color and sound fidelity.
hypertext Documents or other information with embedded links that enable
a reader to access tangential information at specific points in
the text.
hypertext
markup language (HTML) The computer language used to
create hypertext documents, allowing connections from one document
or Internet page to numerous others. HTML is the primary language
used to create pages on the World Wide Web.
hypertext
transfer protocol (HTTP) The first part of an address
(URL) of a site on the Internet, signifying a document written in
Hypertext Markup Language (HTML).
Immediate Start
As soon as the central office seizes a trunk, the central office machine sends the called station digits back to the waiting PBX for decoding.
incumbent
local exchange carrier (ILEC) A large telephone company
that has been providing local telephone service in the United States
since the divestiture of the AT&T telephone monopoly in 1982.
Institute
of Electrical and Electronics Engineers (IEEE) A membership
organization comprised of engineers, scientists and students that
sets standards for computers and communications.
integrated
services digital network (ISDN) A circuit-switched communication
network, closely associated with the public switched telephone network,
that allows dial-up digital communication at speeds up to 128 kilobits
per second.
inter-exchange
carrier (IXC) A long-distance telephone carrier.
International
Organization of Standardization (ISO) Develops, coordinates,
and promulgates international standards that facilitate world trade.
International
Telecommunication Union (ITU) A United Nations organization
that coordinates use of the electromagnetic spectrum and creation
of technical standards for telecommunication and radio communication
equipment.
International
Telecommunication Union/Telecommunication Standardization Sector
(ITU-T) The branch of the ITU that is responsible for
telecommunication standardization.
Internet
Engineering Task Force (IETF) The standards organization
that standardizes most Internet communication protocols, including
Internet protocol (IP) and hypertext transfer protocol (HTTP).
Internet
protocol (IP) - The standard signaling method used for
all communication over the Internet
Internet
service provider (ISP) An organization offering and providing
Internet access to the public using computer servers connected directly
to the Internet.
Intranet A network serving a single organization or site that is modeled
after the Internet, allowing users access to almost any information
available on the network. Unlike the Internet, intranets are typically
limited to one organization or one site, with little or no access
to outside users.
ISDN
digital subscriber line (IDSL) A type of DSL that uses
ISDN transmission technology to deliver data at 128kbps into an
IDSL "modem bank" connected to a router.
Joint
Photographic Experts Group (JPEG) A committee formed
by the International Organization of Standardization to set standards
for digital compression of still images. Also refers to the digital
compression standard for still images created by this group.
Laser From the acronym for "Light Amplification by Stimulated Emission
of Radiation." A laser usually consists of a light-amplifying
medium placed between two mirrors. Light not perfectly aligned with
the mirrors escapes out the sides, but light perfectly aligned will
be amplified. One mirror is made partially transparent. The result
is an amplified beam of light that emerges through the partially
transparent mirror.
local
access transport area (LATA) The geographical areas defining
local telephone service. Any call within a LATA is handled by the
local telephone company, but calls between LATAs must be handled
by long-distance companies, even if the same local telephone company
provides service in both LATAs.
local
area network (LAN) A network connecting a number of computers
to each other or to a central server so that the computers can share
programs and files.
Local
exchange carrier (LEC) A local telephone company. LECs
provide telephone service for phone calls originating and terminating
within a single LATA.
local
loop The copper lines between a customer's premises and
a telephone company's central office (See central office).
Megabyte 1,000,000 bytes, or 1,000 kilobytes (see Byte).
millions
of instructions per second (MIPS) This is a common measure
of the speed of a computer processor.
modem
(MOdulator-DEModulator) A device that converts digital
data into analog signals and vice-versa for transmission over a
telephone line.
Moving
Pictures Experts Group (MPEG) A committee formed by the
ISO to set standards for digital compression of full-motion video.
Also stands for the digital compression standard created by this
committee.
MPEG-1 An international standard for the digital compression of VHS-quality,
full-motion video.
MPEG-2 An international standard for the digital compression of broadcast-quality,
full-motion video.
MPEG-3 An international standard for the digital compression of broadcast-quality,
audio.
Multicast The transmission of information over the Internet to two or more
users at the same time.
multiplexing Transmitting multiple signals over a single communications line
or computer channel. The two common multiplexing techniques are
frequency division multiplexing, which separates signals by modulating
the data onto different carrier frequencies, and time division multiplexing,
which separates signals by interleaving bits one after the other.
optical
carrier 3 (OC-3) An fiber optic line carrying 155 megabits
per second; a U.S. designation generally recognized throughout the
telecommunications community worldwide.
optical
network unit (ONU) A form of access node that converts
optical signals transmitted via fiber to electrical signals that
can be transmitted via coaxial cable or twisted pair copper wiring
to individual subscribers. (See hybrid fiber/coax.)
OSI
Open Systems Interconnection (OSI) is a standard reference model for communication between two end users in a network. The model is used in developing products and understanding networks. Also see the notes below the figure.
** Illustration republished with permission from The manual Page.
OSI divides telecommunication into seven layers. The layers are in two groups. The upper four layers are used whenever a message passes from or to a user. The lower three layers are used when any message passes through the host computer. Messages intended for this computer pass to the upper layers. Messages destined for some other host are not passed up to the upper layers but are forwarded to another host. The seven layers are:
Layer 7: The application layer...This is the layer at which communication partners are identified, quality of service is identified, user authentication and privacy are considered,
Layer 6: The presentation layer...This is a layer, usually part of an operating system, that converts incoming and outgoing data from one presentation format to another (for example, from a text stream into a popup window with the newly arrived text). Sometimes called the syntax layer.
Layer 5: The session layer...This layer sets up, coordinates, and terminates conversations, exchanges, and dialogs between the applications at each end. It deals with session and connection coordination.
Layer 4: The transport layer...This layer manages the end-to-end control (for example, determining whether all packets have arrived) and error-checking. It ensures complete data transfer.
Layer 3: The network layer...This layer handles the routing of the data (sending it in the right direction to the right destination on outgoing transmissions and receiving incoming transmissions at the packet level). The network layer does routing and forwarding.
Layer 2: The data-link layer...This layer provides synchronization for the physical level and does bit-stuffing for strings of 1's in excess of 5. It furnishes transmission protocol knowledge and management.
Layer 1: The physical layer...This layer conveys the bit stream through the network at the electrical and mechanical level. It provides the hardware means of sending and receiving data on a carrier.
packet-switched
network A network that allows a message to be broken
into small "packets" of data that are sent separately
by a source to the destination. The packets may travel different
paths and arrive at different times, with the destination sites
reassembling them into the original message. Packet switching is
used in most computer networks because it allows a very large amount
of information to be transmitted through a limited bandwidth.
passive
optical network (PON) a fiber-based transmission network
containing no active electronics.
peripheral An external device that increases the capabilities of a communication
system.
plain
old telephone service (POTS) An acronym identifying the
traditional function of a telephone network to allow voice communication
between two people across a distance. In most contexts, POTS is
synonymous with the public switched telephone network (PSTN).
point
of presence (POP) The physical point of connection between
a data network and a telephone network.
Postal,
Telegraph and Telephone (PTT) The generic European name
usually used to refer to state-owned telephone companies.
POTS
splitter A device that uses filters to separate voice
from data signals when they are to be carried on the same phone
line, required for several types of DSL service.
primary-rate
ISDN (PRI-ISDN) The primary rate ISDN interface provides
23 64 Kb/s channels (called B channels) to carry voice or data and
one 16 Kb/s signaling channel (the D channel) for call information.
PSTN: Public Switched Telephone Network
PSTN, the Public Switched Telephone Network, is a circuit-switched network that is used primarily for voice communications worldwide, with more than 800 million subscribers. Originally a network of fixed-line analog telephone systems, the PSTN is now almost entirely digital and also includes mobile as well as fixed telephones.
The basic digital circuit in the PSTN is a 64-kilobit-per-second channel, known as "DS0" or Digital Signal 0. DS0's are also known as timeslots because they are multiplexed together in a time-division fashion.To carry a typical phone call from a calling party to a called party, the audio sound is digitized at an 8 kHz sample rate using 8-bit pulse code modulation.
Multiple DS0's can be multiplexed together on higher capacity circuits, such that 24 DS0's make a DS1 signa or T1 (the European equivalent is an E1, containing 32 64 kbit/s channels).
The timeslots are conveyed from the initial multiplexer to the exchange over a set of equipment collectively known as the access network. The access network and inter-exchange transport of the PSTN use synchronous optical transmission (SONET and SDH) technology, although some parts still use the older PDH technology.
For more than a hundred years, the PSTN was the only bearer network available for telephony. Today, the mobile telephone over wireless access network, which is carried through the PSTN trunking network, is becoming increasingly popular. Other bearer networks for voice transmission include integrated service digital network (ISDN), Digital Subscriber Line (DSL), Asynchronous Transfer Mode (ATM), frame relay and the Internet VOIP.
Today typical PSTN: Public Switched Telephone Network for voice and data communications with both wireless and wire line access
PSTN: Public Switched Telephone Network
PTT See Postal, Telegraph and Telephone. public switched telephone
network (PSTN) - The worldwide communications network that carries
phone calls and data.
radio
frequency (RF) Electromagnetic carrier waves upon which
audio, video, or data signals can be superimposed for transmission.
rate-adaptive
digital subscriber line (RADSL) A variation of DSL that
uses carrierless amplitude phase modulation, divides the available
frequencies into discrete sub-channels and also maximizes performance
by adjusting the transmission to the quality of the phone line while
in use.
Regional
Bell Operating Company (RBOC) One of the seven local
telephone companies formed upon the divestiture of AT&T in 1984.
The seven are: NYNEX, Bell Atlantic, BellSouth, Southwestern Bell,
U S WEST, Ameritech, and Pacific Telesis.
Router
- The central switching device in a packet-switched computer network
that directs and controls the flow of data through the network.
small
computer system interface (SCSI) [pronounced "scuzzy"]
A type of interface between computers and peripherals that allows
faster communication than most other interface standards, often
used to connect PCs to external disk drives.
Speed Calling
Provides for the calling of a 7- or 10-digit telephone number by dialing an abbreviated code. The two arrangements available are an eight-number capacity (8-code) and a thirty-number capacity (30-code).
Softswitch
Softswitch is the next generation voice and multimedia switch based on the IP technologies. It is design to replace the Class 5 and Class 4 switches based on the circuit switching technologies. Softswitch gets its name because typically it is a software based solution implemented on general purpose computers/servers, while the traditional Class 5 and Class 4 switches are rely on dedicated facilities for inter-connection and are designed primarily for voice communications. Sometimes Call Agent or Media Gateway Controller, a key component in the VOIP solution, is also called Softswith, though the definition of Softswith is often extend to the whole solution.
The advantages of the Softswitch vs. the traditional circuit switch are:
New services and revenue stream for service providers
Flexibility in deployment and operation
Unified messaging
Easy integration of dissimilar networks and components
Lower cost of solution deployment and total ownership
Softswitch technology enables connectivity between the Internet, wireless networks, cable networks and traditional wireline telephony network, which results a converged network.
sdsl - Symmetric
Digital Subscriber Line This technology provides the same
bandwidth in both directions, upstream and downstream. That means
whether you're uploading or downloading information, you have the
same high-quality performance. SDSL provides transmission speeds
within a T1/E1 range, of up to 1.5 Mbps at a maximum range of 12,000
- 18,000 feet from a central office, over a single-pair copper wire.
This option is ideal for small and medium sized businesses that
have an equal need to download and upload data over the Internet.
T1.413 The American National Standards Institute (ANSI) standard for
asymmetric digital subscriber line using discrete multitone modulation,
which the G.dmt standard is based on.
T-1 Also known as DS1 and T1, a T-1 is dedicated digital communication link provided by a telephone
company that offers 1.544 megabits per second of bandwidth, commonly
used for carrying traffic to and from private business networks
and Internet service providers.
T-3 Also known as DS3 and T3, a T-3 is a dedicated digital communication link provided by a telephone
company that offers 44.75 megabits per second of bandwidth, commonly
used for carrying traffic to and from private business networks
and Internet service providers.
telecommuting The practice of using telecommunication technologies to facilitate
work at a site away from the traditional office location and environment.
teleconference - Interactive, electronic communication among three
or more people at two or more sites. Includes audio-only, audio
and graphics, and video-conferencing.
terabyte 1,000,000,000,000 bytes, or 1,000 gigabytes (see Byte).
Three-Way Calling
Permits an existing call to be held, and by dialing, a second telephone call can be established and added to the connection. Normal transmission performance quality cannot be guaranteed on all calls.
time
division multiplexing (TDM) A digital data transmission
method that takes signals from multiple sources, divides them into
pieces which are then placed periodically into time slots, transmits
them down a single path and reassembles the time slots back into
multiple signals on the remote end of the transmission.
transmission
control protocol/Internet protocol (TCP/IP) A method
of packet-switched data transmission used on the Internet. The protocol
specifies the manner in which a signal is divided into parts, as
well as the manner in which "address" information is added
to each packet to ensure that it reaches its destination and can
be reassembled into the original message.
twisted
pair The set of two copper wires used to connect a telephone
customer with a switching office, loosely wrapped around each other
to minimize interference from other twisted pairs in the same bundle.
Synonymous with 2-wire line.
Uniform
Resource Locator (URL) A text-based address used to identify
specific resources on the Internet, such as web pages. URLs are
arranged in a hierarchical form that specifies the name of the server
on which a resource is located (such as www.2wire.com) and the name
of the file on that server (www.2wire.com/index.html).
Universal
ADSL Working Group (UAWG) An organization composed of
leading personal computer industry, networking and telecommunications
companies with the goal of creating an interoperable, consumer-friendly
ADSL standard titled the G.992.2 standard, and commonly referred
to as the G.lite standard.
Universal
Serial Bus (USB) A computer interface with a maximum
bandwidth of 1.5 Megabytes per second used for connecting computer
peripherals such as printers, keyboards and scanners.
universal
service provider (USP) A company that sells access to
phone, data, and entertainment services and networks.
variable
bit rate (VBR) A data transmission that can be represented
by an irregular grouping of bits or cell payloads followed by unused
bits or cell payloads.
VDSL See very high bit rate digital subscriber line. very high bit rate
digital subscriber line (VDSL) - An asymmetric DSL that delivers
from 13 to 52 megabits per second downstream bandwidth and 1.5 to
2.3 megabits per second upstream.
video
on demand (VOD) A pay-per-view television service in
which a viewer can order a program from a menu and have it delivered
instantly to the television set, typically with the ability to
pause, rewind, etc.
Video conference Interactive, audiovisual communication among three or more people
at two or more sites.
Virtual
Reality Markup Language (VRML) A computer language that
provides a three-dimensional environment for traditional Internet
browsers, resulting in a simple form of virtual reality available
over the Internet.
VOIP
Voice over IP (VOIP) uses the Internet Protocol (IP) to transmit voice as packets over an IP network. Using VOIP protocols, voice communications can be achieved on any IP network regardless it is Internet, Intranets or Local Area Networks (LAN). In a VOIP enabled network, the voice signal is digitized, compressed and converted to IP packets and then transmitted over the IP network. VOIP signaling protocols are used to set up and tear down calls, carry information required to locate users and negotiate capabilities. The key benefits of Internet telephony (voice over IP) are the very low cost, the integration of data, voice and video on one network, the new services created on the converged network and simplified management of end user and terminals.
There are a few VOIP protocol stacks which are derived from various standard bodies and vendors, namely H.323, SIP, MEGACO and MGCP.
H.323 is the ITU-T's standard, which was originally developed for multimedia conferencing on LANs, but was later extended to cover Voice over IP. The standard encompasses both point to point communications and multipoint conferences. H.323 defines four logical components: Terminals, Gateways, Gatekeepers and Multipoint Control Units (MCUs). Terminals, gateways and MCUs are known as endpoints.
Session Initiation Protocol (SIP) is the IETF's standard for establishing VOIP connections. SIP is an application layer control protocol for creating, modifying and terminating sessions with one or more participants. The architecture of SIP is similar to that of HTTP (client-server protocol). Requests are generated by the client and sent to the server. The server processes the requests and then sends a response to the client. A request and the responses for that request make a transaction.
Media Gateway Control Protocol (MGCP) is a Cisco and Telcordia proposed VOIP protocol that defines communication between call control elements (Call Agents or Media Gateway) and telephony gateways. MGCP is a control protocol, allowing a central coordinator to monitor events in IP phones and gateways and instructs them to send media to specific addresses. In the MGCP architecture, The call control intelligence is located outside the gateways and is handled by the call control elements (the Call Agent). Also the call control elements (Call Agents) will synchronize with each other to send coherent commands to the gateways under their control.
The Media Gateway Control Protocol (Megaco) is a result of joint efforts of the IETF and the ITU-T (ITU-T Recommendation H.248). Megaco/H.248 is for control of elements in a physically decomposed multimedia gateway, which enables separation of call control from media conversion. Megaco/H.248 addresses the relationship between the Media Gateway (MG), which converts circuit-switched voice to packet-based traffic, and the Media Gateway Controller, which dictates the service logic of that traffic). Megaco/H.248 instructs an MG to connect streams coming from outside a packet or cell data network onto a packet or cell stream such as the Real-Time Transport Protocol (RTP). Megaco/H.248 is essentially quite similar to MGCP from an architectural standpoint and the controller-to-gateway relationship, but Megaco/H.248 supports a broader range of networks, such as ATM.
In the past few years, the VOIP industry has been working on addressing the following key issues:
Quality of voice - As IP was designed for carrying data, so it does not provide real time guarantees but only provides best effort service. For voice communications over IP to become acceptable to the users, the packet delay and getter needs to be less than a threshold value.
Interoperability - In a public network environment, products from different vendors need to operate with each other for voice over IP is to become common among users.
Security - Encryption (such as SSL) and tunneling (L2TP) technologies are developed to protect VOIP signaling and bear traffic.
wide
area network (WAN) A network that interconnects geographically-distributed
computers or LANs.
Wink Start
The PBX equipment can identify the first three or four digits of the station number being accessed. In order to identify the last three or four digits, the central office must signal back to the PBX to prepare to accept these digits. The PBX signals (winks) the central office to send the digits.
