Optical communication set

In an optical communication set a local transmission equipment, in which a call switch is previously pressed, becomes a master side. The local transmission equipment at the other side automatically becomes a slave side in response to a burst digital signal transmitted from the master side. The master side equipment supervises the transmitting signal and the receiving signal, adds a signal for deciding a sync state in the transmitting signal, and transmits it to the slave side equipment. The slave side equipment detects the sync signal, controls the timing of its transmitting signal, and transmits the signal to the master side equipment, thereby making a communication state of two-way time division optical communication having a predetermined sync relationship. When the transmission call of either side is made, the relationship between the master side and the slave side is established. Since the equipment of the slave side controls its transmitting timing on the basis of the sync information from the master side equipment, two-way time division optical communication can be performed by the same equipments for an optical line having any length, and optimal values of the transmitting level can be set to one another.

BACKGROUND OF THE INVENTION 
This invention relates to an optical communication set and, more 
particularly, to an optical communication set employing the same devices 
and equipments at the transmission and reception sides adapted, for 
example, for a communication by using temporarily laid optical fiber lines 
or for a test communication utilizing laid optical fiber cables. 
An encountering speech test or an announce call order speech test is 
necessary in installation and maintenance of optical fiber used as 
transmission media of optical communication. 
As shown in FIG. 1, assume that optical cables C.sub.A and C.sub.B are laid 
in adjacent blocks A and B and the optical fibers F.sub.1, F.sub.1 of the 
cables C.sub.A and C.sub.B are connected at the contacts in both blocks to 
each other. A laser light source LD is connected to the optical fiber 
F.sub.1 of the optical cable C.sub.A at the transmission terminal in the 
block A. Similarly, an optical power meter PM is connected to the optical 
fiber F.sub.1 of the optical cable C.sub.B at the reception terminal of 
the block B. The optical fibers F.sub.1, F.sub.1 of the cables C.sub.A and 
C.sub.B are connected so that the quantity of light from the source LD 
reaches the maximum value on the power meter PM. 
In such a connecting work, at least three people must work at the 
transmission, reception terminals and connecting place, and they must be 
enabled to communicate. 
Conventionally, these persons can communicate by connecting metallic line 
pairs (not shown) provided in the cables C.sub.A and C.sub.B to a 
telephone set. However, the metallic line pairs, which are not necessary 
except for the test speech, tend to be omitted from the optical cables 
from an economic viewpoint. 
Thus, in case of other optical fibers in the cables C.sub.A and C.sub.B in 
this laying work such as, for example, as shown in FIG. 1, it is requested 
to communicate test speech or test data exchange by connecting optical 
speech transceiver T/R to the optical fiber F.sub.3. 
A ping-pong transmission system is known as a transmission system for 
communicating in two ways through an optical line. 
This system is in general a system for alternatively transmitting and 
receiving pieces of block information D.sub.A, D.sub.B compressed in time 
base at transmission and reception sides as shown in FIG. 2. This system 
is excellent at the point of eliminating the influence of near-end 
crosstalk. However, since the information to be transmitted is divided 
into blocks and transmitted, the longer the transmission line is, the more 
the delay time Td increases, and the more transmission interval Ti 
increases. Thus, this system has such a disadvantage that memory having 
large storage capacity is required. Further, this system has drawbacks 
that transmission equipment increases in size and becomes expensive. 
A digital two-way transmission system employing the existing telephone 
line, i.e., two metallic lines, has been proposed. 
The digital two-way transmission system has a pair of exclusive 
transmission lines at both transmission and reception sides. This system 
is set to such timing relation that pieces of information D.sub.A, D.sub.B 
to be transmitted in a burst state at a predetermined interval T.sub.1 are 
not superposed at the transmission and reception terminals. 
However, the conventional technique is limited to the metallic line pair, 
and in order to take timing of pieces of information D.sub.A, D.sub.B to 
be transmitted, one channel unit (at telephone station side) is designated 
as master side, and the other is secured to a speech unit (subscriber's 
side) at the slave side. However, no actual technique for performing an 
optical communication system using the same optical communication 
equipments at both master and slave sides on both transmission and 
reception sides has been provided. Particularly, no technique for 
eliminating problems arising from the use of one optical line (not the 
metallic line pair), such as deterioration of information due to 
reflection occurring in the optical line or variation in transmission 
level due to optical lengths, has been invented. 
SUMMARY OF THE INVENTION 
It is, therefore, an object of the present invention to provide a new and 
improved optical communication set which can perform the use of the same 
equipment at both transmission and reception sides and remedy problems 
arising when commonly using one optical line. 
According to the present invention, there is provided an optical 
communication set comprising: 
an optical transmission medium set in an arbitrary optical transmission 
path length; 
a first optical communication terminal station coupled with one end of said 
optical transmission medium; 
a second optical communication terminal station coupled with the other end 
of said optical transmission medium; 
each terminal station comprising: 
master-slave designating means for generating designating information for 
designating self-terminal station to master side and opponent terminal 
station to slave side at communication starting time at any of said first 
and second optical communication terminal stations; 
transmitting information input means for inputting information to be 
transmitted to become the master or slave side; 
transmitting time setting means for generating first transmitting time 
setting information at the master side and second transmitting time 
setting information at the slave side in response to the designating 
information; 
sync supervision information outputting means for outputting sync 
supervision information indicating whether the first transmitting time 
setting information of the master side and the second transmitting time 
setting information of the slave side have a predetermined synchronizing 
relationship or not in response to the designating information; 
composition means for outputting a transmission burst signal of the master 
or slave side by combining the transmitting information of the master or 
slave side with the designating information, the first or second 
transmitting time setting information and the sync supervision 
information; 
optical transmitting and receiving means for converting the transmission 
burst signal of the master or slave side into an optical signal to 
transmit the signal to the optical transmission medium, and for converting 
transmission burst signal due to the optical signal of the slave or master 
side into an electric signal by receiving the transmission burst signal; 
decomposition means for separating the designating information, the 
transmitting information, the first or second transmitting time setting 
information and the sync supervision signal contained in the received 
transmission burst signal of the slave or master side; 
first control means for locking the slave-master designating means to a 
slave state in response to the separated designating information at the 
slave side; 
second control means for varying the second transmitting time setting 
information of the slave side during a period indicating that the sync 
supervision information separated at the slave side does not have the 
predetermined synchronizing relationship; 
third control means for judging whether the first transmitting time setting 
information and the second transmitting time setting information separated 
at the master side have a predetermined synchronizing relationship ship or 
not, and for supplying the judged result as the sync supervision 
information to the sync supervision information outputting means; and 
receiving information outputting means for outputting the separated 
transmitting information as a receiving information of the master or slave 
side.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
In FIG. 4, reference numeral 100 designates an optical fiber line as an 
optical transmission medium having a predetermined length. A pair of 
two-way time division optical communication local transmission equipments 
200, 200 constructed in the same configuration are respectively coupled 
with both ends of the optical fiber line 100. 
The details of the local transmission equipments 200, 200 will be described 
later. Master or slave side is decided according to which of call switches 
CS provided in both the local transmission equipments is previously 
operated. Thus, two-way time division optical communication can be 
performed between both the local transmission equipments in the state that 
one optical fiber line 100 is commonly provided as will be described. 
FIG. 5 is a block diagram showing the details of the two-way time division 
optical communication local transmission equipments 200, 200, wherein both 
the equipments have the same construction, and only one is accordingly 
shown. 
In FIG. 5, reference numeral 1 surrounded by a dotted chain line designates 
a signal processor for processing a signal to be transmitted or received. 
The processor 1 has a transmitting input circuit 1a, a call signal 
generator 1b, a receiving output circuit 1c and a call switch CS. 
The input circuit 1a (see FIG. 9) has a plurality of input terminals. The 
input circuit 1a has an encoder (CODIC IC, e.g., HD44238 made by Hitachi 
Limited) 1a1 for coding an analog signal (for voice) from a microphone 
line input to the first input terminal into a PCM signal B, and a 
multiplexing circuit 1a2 including a shift register (e.g., 74HC164 widely 
known as 74H-series CMOS logic IC, and similary referred to below) for 
combining the PCM signal B and digital data F from an external digital 
equipment line input to the second input terminal, with a predetermined 
timing relationship as transmitting information B, F, and a multiplexer 
(e.g., 74HC151), as shown in FIG. 9. 
The output circuit 1c (see FIG. 10) has a demultiplexing circuit 1c 1 
including a shift register (e.g., 74HC164) for separating the received 
digital signal into a voice PCM signal and digital data (including a call 
signal) with a predetermined timing relationship, and an AND gate (e.g., 
74HC08) and a D flip-flop (e.g., 74HC074), and a decoder (CODIC IC such as 
HD44238 made by Hitachi Limited) 1c2 for decoding the separated PCM signal 
into an analog signal (for voice), as shown in FIG. 10. 
The output circuit 1c has a plurality of output terminals, and outputs the 
decoded analog signal (for voice) from the first output terminal to an 
earphone line, the separated digital data from the second output terminal 
to an external digital equipment line, and the call signal from the third 
output terminal to a buzzer line. 
The call signal generator 1b has an OR gate (e.g., 74HC032) for generating 
a call signal C when the call switch CS is depressed before the other 
local transmission equipment for the purpose of setting the associated 
local transmission-equipment to a master side. 
Reference numeral 2 surrounded by a dotted chain line designates a 
master-slave state setter. The setter 2 has D type flip-flops (hereinbelow 
referred to as "D-F/F") 2a, 2b for setting the local equipment to a master 
state and the other equipment to a slave state to be described later, by 
setting in the state that the call switch CS is pressed as described 
above, and AND circuits 2c, 2d. The D F/F 2a, 2b outputs master-slave set 
signals D, D' which become 1, 0 when the local equipment is in the master 
state, 0, 1 when in the slave state, and 0, 0 when in the reset state. 
A composition circuit 3 has a shift register (e.g., 74HC164) for combining 
the transmitted information B, F from the input circuit 1 with various 
types of pieces of control information (including the call signal C from 
the call signal generator lb and master-slave set signals D, D' from the 
setter 2) to be described later with a predetermined timing relationship 
and outputting the combined information as a transmission burst signal 
having a predetermined interval, and a multiplexer (e.g., 74HC151). The 
interval of the digital burst signals is set to three times or more of the 
time occupied by the digital burst signal to be described later. 
Reference numeral 4 surrounded by a dotted chain line designates an optical 
transceiver. The transceiver 4 has an electro/optical modulator 
(hereinbelow referred to as "E/O", e.g., a laser diode) 4a for converting 
the digital transmission burst signal from the composition circuit 3 into 
an optical signal to transmit the optical signal to the optical fiber line 
100, and an optical directional coupler (e.g., a beam splitter) 4c. 
Further, the transceiver 4 has an opto/electrical demodulator (e.g., a 
photodiode, hereinbelow referred to as "O/E") 4b for receiving the optical 
signal transmitted through the line 100 from the other equipment through 
the coupler 4c to convert the signal into an electric signal. 
The first switch circuit 5 has an analog switch (e.g., 74HC4066) for 
inhibiting a reception signal from the O/E 4b set to OFF state on the 
basis of the output from the composition circuit 3, i.e., when the digital 
transmission burst signal of the associated local equipment is 
transmitted. 
Reference numeral 6 designates an input level detector for detecting the 
level of a reception signal input when the switch circuit 5 is in an ON 
state. 
Reference numeral 7 designates an output level controller for controlling 
the E/O 4a and O/E 4b to regulate the transmission output of the local 
equipment in response to the detected output from the detector 6. 
Reference numeral 8 surrounded by a dotted chain line designates a 
reception signal processor. The processor 8 separates transmission 
information and various pieces of control information, from a received 
digital burst signal from the other equipment as supplied through the 
switch circuit 5. The processor 8 has an AGC amplifier 8a for amplifying 
the reception signal to a predetermined level, a clock extract circuit 8b 
for extracting a clock signal from the output of the amplifier 8a, a D-F/F 
(e.g., 74HC074) to act as a decider 8c for deciding the reception signal 
on the basis of the clock signal from the extract circuit 8b, and a 
decomposition circuit 8d for separating the output from the decider 8c 
into the respective signals on the basis of a predetermined timing. The 
decomposition circuit 8d has a JK-type F/F (e.g., 74HC107), an AND gate 
(e.g., 74HC008) and a shift register (e.g., 74HC164). 
A transmission time set circuit 9 has a first counter (e.g., 74HC161) for 
setting the transmitting timing of the digital transmission burst signal 
to be described later on the basis of a synchronizing signal separated by 
the decomposition circuit 8d to be described later and the clock signal 
extracted by the extract circuit 8b, and a second counter (e.g., 74HC193). 
The set circuit 9 operates in a state when the associated local equipment 
becomes the slave side to be described later. 
Reference numeral 10 surrounded by a dotted chain line designates a 
controller. The controller 10 has a M/S supervision circuit 11 of a NAND 
gate (e.g., 74HC00) for monitoring whether the local equipment is the 
master or slave side on the basis of the master-slave monitor signal 
(M/S)r detected by the decomposition circuit 8d and the outputs D, D' from 
the setter 2. The controller 10 further has a sync supervision circuit 12 
having a D-F/F (e.g., 74HC074) and a counter (e.g., 74HC163) for 
supervising whether the own equipment and the other equipment are in 
synchronizing state or not to be described on the basis of a frame bit 
(A)r separated by the decomposition circuit 8d. Further, the controller 10 
has second and third switch circuits 15a, 15b. The second switch circuit 
15a has an AND gate (e.g., 74HC08) equivalently controlled by the output D 
from the setter 2 to an ON state (M) for supplying the output from the 
supervision circuit 12 to the composition circuit 3 as a sync signal E. 
The third switch circuit 15b has a multiplexer (e.g., 74HC153) 
equivalently controlled to an M contact side when the output D from the 
setter 2 is "1" for supplying the output from a transmission time set 
circuit (M) 13 provided in the controller 10, or controlled to an S 
contact side when the output D is "0" for supplying the output from the 
set circuit 9 as a frame signal A to be described later to the composition 
circuit 3. The set circuit (M) 13 has a counter (e.g., 74HC163) provided 
in the controller 10 for setting the transmitting timing of the digital 
transmission burst signal on the basis of a clock from a clock generator 
14 for generating a clock to the entire system. The output of the set 
circuit (M) 13 is also applied to the sync supervision circuit 12. 
The controller 10 further has a system reset circuit 16 of an AND gate 
(e.g., 74HC08) for supplying a reset signal to all the circuit elements 
(except mere gate elements) upon reception of the output from the M/S 
supervision circuit 11 in case of the specific state to be described 
later. 
FIG. 6 shows the format of the digital burst transmission signal when 
communicating in the two-way time division optical communication system 
according to the present invention. In FIG. 6, reference character A 
designates a frame bit period showing a start signal and clock bit period 
(16 bits), reference character B designates an analog signal and a PCM bit 
period (8 bits) with a PCM signal for voice, reference character C 
designates a bit period (1 bit) of call signal, reference character D 
designates a decision bit period (1 bit) of different sign according to 
whether the local equipment is master or slave, reference character E 
designates a sync bit period (1 bit) inserted with a sync signal 
representing whether the sync state is established or not, reference 
character F designates transmitting information except the analog signal 
for voice such as data bit period (20 bits) used when there is digital 
data. 
The digital burst signal (hereinbelow referred to "a burst signal") is set 
at the transmitting time T.sub.2 (e.g., 125 .mu.sec.) by considering the 
sampling period when the analog signal for voice is used as a PCM signal, 
necessary control bit and the length of a data signal. 
More specifically, FIG. 7A to FIG. 7D show all the cases of the time 
relationship that the burst signal D.sub.S transmitted from the slave side 
arrives at the equipment of the master side with respect to the burst 
signals D.sub.m1, D.sub.m2, . . . , transmitted from the master side. 
In FIG. 7A to FIG. 7D, D.sub.m1 ', D.sub.m2 ' designate signals of the 
master side reflected at the slave side, i.e., the reflected waves, and it 
is preferred that the reflected waves D.sub.m1 ', D.sub.m2 ' are not 
superposed with the transmitting burst signal D.sub.S of the slave side. 
To this end, the transmitting burst signal D.sub.S of the slave side may be 
delayed in transmission at a time of T.sub.d from the reflected waves 
D.sub.m1 ', D.sub.m2 '. 
In this case, as shown in FIG. 7C, the case of the line length that the 
reflected wave D.sub.m1 ' exists at an intermediate point of the burst 
signals D.sub.m1, D.sub.m2 of the master side becomes the worst condition. 
However, in order that the transmitting burst signal D.sub.s from the 
slave fall within the range designated by P and Q of FIG. 7C, (T.sub.2 
/2)-(T.sub.1 /2)&gt;T.sub.1. Eventually, the transmitting interval T.sub.2 in 
the equipment used in this system and the length T.sub.1 of the burst 
signal may become at least T.sub.2 &gt;3T.sub.1. 
Therefore, when the interval time T.sub.2 is, for example, set to 125 
.mu.sec., preferable two-way time division optical communication can be 
performed in response to all line length if 31.25 sec. or 1/4 of T.sub.2 
is set to the transmitting time T.sub.1. 
The transmitting and receiving timings of the two-way time division optical 
transmission system according to the present invention thus constructed as 
described above will be explained with reference to FIG. 8. 
When the burst signal time shown in FIG. 6 is set to T.sub.1 and the 
transmitting interval is set to T.sub.2, a burst signal D.sub.m of the 
period shown in FIG. 8 is transmitted from the equipment (master side) or 
calling side. This burst signal D.sub.m arrives at the equipment (slave 
side x1) or opponent side after the delay time T.sub.d1 of the optical 
fiber line 100. Therefore, when the burst signal D.sub.s1 is transmitted 
from the equipment of the slave side x1 to the equipment of master side by 
the returning after the time T.sub.s1, for example, as shown in FIG. 8, 
the burst signals (D.sub.m, D.sub.s) of transmitting and receiving sides 
are generated at a timing such that the signals are not superposed at the 
transmitting and receiving local equipments, thereby enabling the two-way 
time division optical communication. 
However, if the burst signal D.sub.s2 is returned and transmitted after the 
time T.sub.s1 in the equipment at the slave side x2 coupled at the ground 
point that the delay time of the optical fiber line becomes T.sub.d2, the 
signal collides with the transmitting burst signal D.sub.m of the master 
side as readily understood from FIG. 8. Then, in this case, if the delay 
time of the transmitting burst signal D.sub.s2 to be returned and output 
is set to T.sub.s2, it can be set so that the burst signals transmitted 
and received at both the equipments do not collide at the transmitting and 
receiving terminals in the same manner as the equipment of the slave side 
x1. 
The operation of setting the returning timing will be explained according 
to the embodiment shown in FIG. 4 and FIG. 5. 
When the call switch CS of the local transmission equipment 200 of one side 
is depressed in the state that the equipments 200 of both sides are 
connected through one optical fiber line 100, the master-slave state 
setter 2 of the equipment enters a set state. Thus, the second and third 
switch circuits 15a, 15b are respectively controlled to the M sides. Since 
a predetermined timing signal (T.sub.1 +T.sub.2) is supplied from the 
transmitting time setter (M) to the composition circuit 3 through the 
third switch circuit 15b, the pieces of transmitting information B, F from 
the input circuit 1 are input to the composition circuit 3 at the timing 
signal. At this time, a sign (sync signal bit) representing the sync state 
through the second switch circuit 15a, a sign representing that the one 
equipment is a master, and a call signal C from the call signal generator 
1b are input to the composition circuit 3 at a predetermining timing, and 
formed to a burst signal. Then, this transmission burst signal is 
transmitted to the optical fiber line 100 through the optical transceiver 
4. 
The equipment installed at the other end of the optical fiber line 100, 
i.e., the reception side receives the burst signal at the O/E 4b of the 
transceiver 4, input to the signal processor 8 through the first switch 
circuit, the decision code bit (D) to become an M/S supervision signal is 
separated by the decomposition circuit 8d, and the setter 2 is set. Thus, 
the called equipment is controlled to a slave state. (The called equipment 
cannot enter a master state until the communication is finished.) 
In the equipment which has become the slave side, the timing signal formed 
by the time set circuit (S) 9 is input to the composition circuit 3 
through the switch circuit 15b, the burst signal is returned and 
transmitted to the equipment of the master side. 
The equipment of the master side which has received the returned burst 
signal inputs the frame bit signal contained in the burst signal to the 
sync supervision circuit 12 through the decomposition circuit 8d, and 
compares it with the timing of the time set circuit (M) 13 for setting the 
timing of the master side burst signal. 
Then, when the sync supervision circuit 12 decides that the master burst 
signal and the burst signal transmitted from the slave side are superposed 
at one time, a sync bit representing that the burst signal is not 
synchronized, e.g., "0" is inserted to the composition circuit 3 through 
the second switch circuit 15a to continue the transmission. Since the 
equipment of the slave side detects the sync bit "0" in the decomposition 
circuit 8d and supplies it to the time set circuit (S), it counts the 
output from the clock extract circuit 8b in the counter provided in the 
time set circuit (S) 9 while the sync bit "0" continues to displace the 
transmitting timing by the counted value of the counter, thereby 
displacing the transmitting timing of the burst signal of the slave side 
until a synchronization is made. 
When the equipment of the master side confirms that the master burst signal 
and the burst signal transmitted from the slave side indicate completely 
different time blocks in the sync supervision circuit 12, it decides that 
synchronization is made and alters the sync bit "0", for example, to "1". 
Then, it causes a signal "1" of the sycn completion to be transmitted to 
the equipment of the slave side. Thus, the equipment of the slave side 
stops the counting operation of the counter in the time set circuit (S) 9 
when the sycn completion signal is received, finishes the timing 
regulation of the output from the time set circuit (S) 9, holds the timing 
at that time, and enters the communication state for transmitting the 
burst signal. 
Since both equipments detect the reception level by the level detectors 6 
and control their own transmitting levels by the detection signals applied 
to the level controller 7, if the equipments set, for example, the 
transmitting level to the maximum level at the communication starting 
time, the optimum transmitting level can be set even in any line length. 
More specifically, the transmitting level is controlled, for example, in 
two stages by the level controller 7, and the level detector 6 can decide 
whether the input level is proper or not. If proper, the detector outputs 
the "0" signal, if not, the detector outputs the "1" signal to the 
controller 7. 
Therefore, the equipment of the master side sets the maximum output level 
at the communication starting time and starts transmitting. When the 
equipment of the slave side receives the burst signal transmitted from the 
master side, if the reception level is not proper, the transmitting level 
from the slave side is set to the low level by the controller 7. 
On the other hand, if the equipment of the master side cannot receive the 
burst signal from the slave side within a predetermined time, it sets the 
transmitting level to a low level by the controller 7. 
Thus, the transmitting levels of the master and slave sides are controlled 
to suitable levels by this operation, and both equipments can enter the 
sync operation. 
The M/S supervision circuit 11 initially sets the entire system by the 
system reset circuit 16 when the call buttons CS are simultaneously 
depressed at both equipments to prevent erroneous operation. 
Further, since the sign representing a transmission signal of one side is 
inserted to both the burst signals during the decision bit period D, the 
transmission signal of one side as reflected by the connector of the 
optical line is removed, for example, by the decomposition circuit 8d to 
prevent the equipment from arriving at an erroneous sync relationship by 
the reflected signal of its own transmission signal. Further, since 
near-end crosstalk can be prevented by the first switch circuit 5, the AGC 
amplifier 8a is prevented from erroneously operating due to the near-end 
crosstalk of large level from a transmission signal reflected at the 
connector of the optical line. 
When entering the communication state, both voice signals are inserted into 
the PCM bit period D as PCM signals, and when there is data to be 
transmitted, the voice signals are inserted into the data bit period F, 
and transmitted as burst signals. 
An example of the configuration of the controller 10 is shown, and the 
second and third switch circuits 15a, 15b may be, for example, analog 
switches. 
Since the M/S supervision circuit 11 and the system reset circuit 16 are 
not substantial elements, they may be omitted. Further, the time set 
circuit (M) 13 and the time set circuit (S) 9 may be formed by the same 
circuit to be used commonly. 
As described above, the two-way time division optical communication system 
of the present invention can advantageously transmit the burst signal by 
the operation of the call switch, receive the burst signal from the 
equipment to become the master side and the master side to control the 
sync relationship, can be used for any of the equipments of master and 
slave sides, and can automatically establish the relationship between the 
master side and the slave sides. Further, since the timing for setting to 
the two-way communication state can be automatically controlled and the 
level of the transmission level can be set to the optimum value, the 
optical transmission system can be advantageously useful when 
communicating through an optical line having unknown line length used as 
communication medium. 
Moreover, since the transmission burst signal has a function of deciding 
whether it is a signal originating from its own side or the opposite side 
signal, the timing is not disturbed by optical reflection signals in the 
optical line.