Multiplex communications – Channel assignment techniques – Combining or distributing information via time channels...
Reexamination Certificate
1998-10-29
2002-02-12
Yao, Kwang B (Department: 2664)
Multiplex communications
Channel assignment techniques
Combining or distributing information via time channels...
C370S509000
Reexamination Certificate
active
06347092
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a time division multiple access communication system based upon a communication mode or method, called TDMA communication, a signal receiving method to be taken for the time division multiple access communication system, and a center unit to be employed for the time division multiple access communication system.
(2) Description of the Related Art
FIG. 43
is a block diagram showing one example of two-way (bidirectional) CATV (CAble TeleVision) system involving a TDMA communication mode. This two-way CATV system
1
′ shown in
FIG. 43
is basically composed of a plurality of subscriber's units (that is, CAUs: Communication Access Units)
4
-
1
to
4
-N (N denotes a natural number not less than 2) each being a home-use device and including terminals, such as a telephone set
5
, a personal computer
6
and/or others, and a center unit (that is, CAM: Communication Access Master)
2
′ accommodating these CAUs
4
-i (where i=1 to N) through a head end (HE) unit
7
and a necessary transmission line
8
such as a coaxial cable to execute centralized control of a TDMA communication protocol between the switching node
3
side and the CAU
4
-i side.
In some cases, as indicated by a broken line in
FIG. 43
, in place of the telephone set
5
, a personal computer
6
′ different from the aforesaid personal computer
6
is connected through a modem
6
a
to the foregoing CAU
4
-i. In addition, when necessary, a desired communication network (in this case, a packet communication network dealing with packet data) such as a LAN (Local Area Network)
9
can be connected through a LAN transmission line
13
to the foregoing CAM
2
′. Moreover, according to circumstances, in addition to a router
10
and a server
11
for the LAN
9
, a maintenance console (MC)
12
which monitors the operating status of the CAM
2
′ and the CAU
4
-i or the like is connected to the LAN transmission line
13
.
Furthermore, as shown in
FIG. 43
, the CAM
2
′ comprises an interface section (PRI: Primary Rate Interface)
20
including a plurality of ISDN trunk cards
21
, a network (NW) circuit
22
, a frame assembling section (FRMA
1
: FRaMe Assemble
1
)
23
, a modulation section (MOD
1
)
24
, demodulation sections (DEM
1
)
25
, a frame disassembling section (FRMD
1
: FRaMe Disassemble
1
)
26
′, a central processing unit (CPU
1
)
27
, a non-volatile memory
27
A, a volatile memory
27
B, a LAN controller (LANC)
28
, and other units. Further, each of CAUs
4
-i is made up of a multiplexing and demultiplexing unit (WD)
41
, a demodulation section (DEM
2
)
42
, a frame disassembling section (FRMD
2
)
43
, a single line interface (SLI) section
44
, a frame assembling section (FRMA
2
)
45
, a modulation section (MOD
2
)
46
, a central processing section (CPU
2
)
47
, a non-volatile memory
47
A, a volatile memory
47
B, a data communication control unit
48
, and others.
In the CAM
2
′, each of the trunk cards
21
constituting the interface section
20
is for interfacing with the switching node
3
side by converting a protocol (format) of a signal transmitted or received between the switching node
3
side and the CAM
2
′ side into a protocol suitable for each side, and the network circuit
22
is for conducting a switching operation of voice data (or personal computer data) between the switching node
3
and the telephone set
5
(or the personal computer
6
), and is under control of the CPU
27
.
The frame assembling section
23
assembles voice data (B channel) transmitted from each of the trunk cards
21
through the network circuit
22
, a control signal (M channel, D channel) produced in the CPU
27
and packet data (C channel) transmitted from the LAN
9
through the LAN controller
28
into a TDMA signal (down-frame) having a frame format shown in FIG.
45
.
This down-frame shown in
FIG. 45
is made to be transmitted in the order from the left and upper side (time slot (TS) number=00, frame number=00) to the rightward direction (the direction that the TS number becomes higher) and the downward direction (the direction that the frame number becomes higher). In this case, a channel (data) corresponding to one frame [128 time slots (0 to 127) (1 time slot=8 bits)] is transmitted for 125 &mgr;s, and a channel corresponding to 1 multiframe (32 frames) is sent for 4 ms (=125 &mgr;s×32), thus providing a frame configuration with a transmission rate of 128 (TS)×8 (bits)×32 (frames)÷4 ms=8.192 Mbps.
Incidentally, in
FIG. 45
, F represents a frame bit showing a bit pattern indicative of the head of each frame, while MF designates a multiframe bit showing a bit-pattern representative of the head of a multiframe. The CAU
4
-i establishes the bit synchronization with the CAM
2
′ on the basis of this down-frame, and synchronizes in multiframe on the basis of the MF.
Furthermore, an M channel (which will sometimes be referred hereinafter to as an Mch) primarily serves as a control channel to be used for when the CAM
2
′ measures the distance from the CAU
4
-i and establishes the communication synchronization with the CAU
4
-i. Concretely, when the transmission or reception of an M channel takes place with respect to a CAU
4
-i which is not in the synchronized relation, the CAM
2
′ measures the delay of the transmission and reception timing (time-difference information) in the M channel occurring in accordance with the distance from the CAU
4
-i (the length of the transmission line
8
), and informs the CAU
4
-i of that delay through the M channel, so that the CAU
4
-i corrects its own signal transmission timing to establish the communication synchronization with the CAM
2
′. As will be described herein later, the M channel is additionally used for a C-channel transmission halt request to the registered CAU
4
-i or a periodical inquiry about the status (the turning-on/off of a power supply or the like) to the CAU
4
-i.
Still further, a D channel (which will sometimes be referred hereinafter to as a Dch) serves as a calling process control channel between the switching node
3
and the CAM
2
′, and exchanges such as the transmission/reception about the telephone set
5
(or the personal computer
6
) and the notification of an available B channel are done through this D channel. Further, a C channel (which will sometimes be referred hereinafter to as a Cch) acts as a packet communication channel, and is put to use for the transmission of packet data between the LAN
9
connected to the CAM
2
′ and the personal computer
6
connected to the CAU
4
-i.
Moreover, a B channel (which will sometimes be referred hereinafter to as a Bch) is a channel for voice (sound) or data communication, and is put to use for the transmission of the voice (sound) data of the telephone set
5
(or the data of the personal computer
6
′) through the CAU
4
-i. In this case, the B channel assuming 64 kbps (=8 bits÷125 &mgr;s) per frame (125 &mgr;s) is transmittable by a quantity corresponding to 95 channels (B
0
to B
94
), which allows a maximum of 95 CAUs
4
-i to simultaneously perform the communication. However, in the case of the ordinary communication, the simultaneous communication by the 95 CAUs
4
-i is not very liable, and a free B channel is used properly. Accordingly, in this case, the CAM
2
′ can accommodate about 1000 CAUs
4
-i.
Besides, the CPU
27
is made to give an ID (identification information) on the CAU
4
-i, being the other party in the communication, to each of the aforesaid M channel, D channel and C channel, and as will be mentioned herein later, the CAU
4
-i refers to each of the M channel, the D channel and the C channel it receives, and, when being addressed to its own, takes the channel data thereof and communicates it to the CPU
47
.
Referring again to
FIG. 43
, the modulation section
24
m
Ogawa Takayuki
Serikawa Atsuo
Yamamoto Takaya
Fujitsu Limited
Rosenman & Colin LLP
Yao Kwang B
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