Reference
Exchange line service
An “exchange line service” is a communication service that is capable of connecting to an unspecified host. The connection is established by dialing for every communications session, using a device called an exchanger. This service
uses a telephone line.
Reference
Leased line service
A “leased line service” is a communication service that is permanently connected to the specified host that the
user has subscribed to.
Reference
ISDN
Abbreviation for “Integrated Services
Digital Network.”
Reference
Packet switching
“Packet switching” is a method for data
communication that sends data by dividing it into packets.
Reference
Packet
(1)Types of communication services
The main types of communication services are summarized below.
●Telephone line
A “telephone line” is a communication service whose main purpose is for
voice communications using a common telephone line (analog line). The
transmission speed is slow at a maximum speed of around 56kbps. Since a
telephone line is an analog line, a “modem” is required to convert digital
data into analog data, and connect to a computer that processes the digital
data.
●ISDN (Integrated Services Digital Network) line
“ISDN” is a digital communication service that supports a wide variety of
data communication including voice, image, and fax communications.
Certain equipment is necessary in order to use ISDN such as a DSU, terminal adapter, and dial-up router.
A typical ISDN service is “BRI (Basic Rate Interface),” also called
“2B+D.” BRI is comprised of a pair of information channels (B channels)
and one control channel (D channel) for each subscriber line. Each of the
two information channels can be used respectively for data communication
or voice communications, making it possible for one computer to use the
Internet while simultaneously talking on the same line using telephone
equipment. The control channel mainly sends control information such as
the telephone number of the other communicating party. Data communication using packet switching can also be performed.
Basic rate interface (2B+D)
A “packet” is a unit of measurement for
data transfer, which is derived by dividing data into blocks that do not exceed
a fixed length.
Reference
IP phone
An “IP phone” is a telephone service
that is provided by using the “IP (Internet Protocol)” over the Internet. Voice
calling is accomplished by converting
voice data into digital data, which is divided into packets and sent to the called
party over an IP network.
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Capable of simultaneous calling and
data communication using one line
Channel B
Channel B
Channel D
64kbps
64kbps
16kbps
TA
DSU