Telephonic communications – Diagnostic testing – malfunction indication – or electrical... – Of trunk or long line
Reexamination Certificate
1999-03-16
2002-08-13
Kuntz, Curtis (Department: 2643)
Telephonic communications
Diagnostic testing, malfunction indication, or electrical...
Of trunk or long line
C379S323000, C379S390010, C379S022000, C379S032020
Reexamination Certificate
active
06434220
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a long-distance transmission system and a device applicable thereto, and more particularly to an LT-NT long-distance transmission system in which a two-wire metallic subscriber line is used to mutually connect a network terminal (NT) which accommodates terminal equipment (TE)and a line terminal (LT).
The basic services of the ISDN (Integrated Services Digital Network) in Japan are designed and developed so that a two-wire metallic subscriber line used in the conventional analog telephone transmission is applied without any modification and high-transmission-rate data transmission is realized using such a subscriber line. At the initial stage of the development, it was planned to accommodate 99% of the total number of subscribers through digital transmission lines. After that, however, it was found that some areas accommodated in the analog system could not be accommodated in the digital system for various reasons. For example, there was a limitation resulting from loss of the main signal caused during the propagation of the main signal through the subscriber line. Further, there was a restriction concerning a feed of electricity to the NT (including TE). In addition, there has recently been an unexpected increase in the number of subscribers located at a long distance from the office facility (LT). Under the above situations, it is required to efficiently provide subscribers located in areas as described above with services.
2. Description of the Related Art
FIGS. 1
,
2
and
3
show prior art. More particularly,
FIG. 1
shows a network structure which conforms with the TTC standard (JT-G961) defined by the Telecommunication Technology Committee in Japan and which is provided by NTT (Nippon Telegraph and Telephone Corporation). The network shown in
FIG. 1
includes a central office
100
, a switch
6
, a line terminal (LT)
50
accommodating network equipment (NT), a metallic subscriber line
1
, a user's house
200
a
, a network terminal (NT
1
)
30
, ISDN standard terminal equipment (TE)
10
, an existing analog telephone set (TEL)
5
, a terminal adapter (TA)
4
, an office building
200
b
, a network terminal (NT
2
)
60
, a user's house
200
c
located a long distance away from the central office
100
, a central office terminal (CT)
61
, a remote terminal (RT)
62
, and an optical fiber cable
2
. The network terminal (NT
1
)
30
has the functions of terminating the subscriber line
1
, establishing a phase synchronization (frame synchronization and bit synchronization), changing the data transmission rate, and testing and protecting the system from an excessive voltage. The network terminal
30
can also be called a digital service unit (DSU). The terminal adapter (TA)
4
is equipped with functions of converting the protocol and changing the data transmission rate in order to connect the telephone set
5
to the network terminal
30
. The network terminal (NT
2
)
60
has a PBX (Private Branch Exchange) function including a line connection control, switching and selection and a protocol processing function in order to accommodate the terminal equipment
10
and implement switching therebetween.
The central office
100
and the user's house
200
a
are connected by a two-wire metallic subscriber line
1
a
as in the case of the conventional analog system. The possible transmission distance in the existing facility specification is 7 km without any repeater. The network terminal
30
and a plurality of terminal equipment
10
are connected by a four-wire metallic cable
3
(which is 100-200 m long) in a bus system. Symbols R, S, T and U denote reference points. The connection between the central office
100
and the user's home
200
c
located a long distance away will be described later.
FIG. 2
schematically shows the line terminal
50
, the network terminal
30
and the terminal equipment
10
and connections therebetween.
The line terminal
50
is configured as follows. A signal processing part
51
establishes a phase synchronization of the main signal and changes the transmission rate. A signal transmission circuit
52
sends a signal to the subscriber line
1
. A signal reception circuit
53
receives a signal from the subscriber line
1
, and includes the function of equalizing the main signal. A symbol T
2
denotes a main signal transformer, and C
2
is a capacitor for DC isolation. The capacitor C
2
is not limited to the position shown in FIG.
2
. An office feed part
54
remote-feeds electricity to the network terminal
30
. A normal/reverse switch
55
switches the polarity in feeding. A power separation filter PSF
2
is formed of a coil or the like, and realizes AC isolation.
The network terminal
30
is configured as follows. A symbol T
1
denotes a main signal transformer, and C
1
denotes a capacitance for DC isolation. The capacitor C
1
is not limited to the position shown in
FIG. 2. A
board
31
has a main signal circuit part. A signal processing part
32
has the functions of establishing the phase synchronization of the main signal and changing the data transmission rate. A signal transmission circuit
33
sends a signal to the subscriber line
1
. A variable equalizer
36
amplifies a signal received from the subscriber line
1
and compensates for (or equalizes) a deterioration of the received signal due to the characteristics of the transmission line (the amplitude characteristic, the phase characteristic and so on) which depend on the distance thereof. A symbol R denotes a reception circuit to the bus line
3
, and a symbol T denotes a transmission circuit from the bus line
3
. A symbol PSF
1
denotes a power separation filter for AC isolation. A standby circuit
44
feeds DC electricity to the terminal equipment
10
when a call issued by the terminal equipment
10
is detected or the normal feeding of electricity to the network terminal
30
is performed. A call detection part
45
detects a call from the terminal equipment
10
. A DC power source (SRG)
46
is a series regulation generator. A symbol DN denotes a diode which is connected in normal-connection fashion and implements the normal feed to the DC power source
46
. A DC/DC converter
47
supplies DC electricity to the board (main signal circuit part)
31
and the terminal equipment
10
at the time of the reverse feed to the NT
30
. A symbol DR denotes a diode which is connected in the reverse connection fashion and implements the reverse feed to the DC/DC converter
47
. A terminal feed circuit
48
carries out the remote feed from the network terminal
30
to the terminal equipment
10
.
The terminal equipment
10
is configured as follows. A symbol T denotes a transmission circuit which sends a signal to the bus line
3
, and a symbol R denotes a reception circuit which receives a signal from the bus line
3
. A signal processing part
11
processes the main signal. A DC/DC converter
12
receives the remote feed of electricity from the network terminal
30
and supplies the DC electricity to the terminal equipment
10
.
AMI (Alternate Mark Inversion) code is applied to data communications between the terminal equipment
10
and the network terminal
30
and between the network terminal
30
and the line terminal
50
. The AMI code is characterized in that the required bandwidth can be reduced and the DC component can be suppressed. The main signal level between the terminal equipment
10
and the network terminal
30
is equal to ±0.75 V and the main signal level between the network terminal
30
and the line terminal
50
is equal to ±0.6 V.
The channel bit rate supported by the ISDN basic services is such that 2B+D=144 kbps, and is formatted to the frame signal of a bit rate of 48 bits per frame (including various control bits) between the terminal equipment
10
and the network terminal
30
. Hence, it takes 250 &mgr;s to transmit one frame. Thus, the line bit rate between the terminal equipment
10
and the network terminal
Barnie Rexford N
Fujitsu Limited
Katten Muchin Zavis & Rosenman
Kuntz Curtis
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