Optical transmission system constructing method and system

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical transmission method and system for carrying data transmission with use of optical fiber. More particularly, it concerns an optical transmission method and system preferable in high-speed data transmission to a long distance.

2. Description of the Prior Art

Prior arts related to the optical transmission system include, for example, the technique disclosed in the Japanese Patent Application Laid-Open 3-296334.

However, it is demanded to accomplish an optical transmission system operating at further higher speed since development of the modern information society has increased long-distance communication traffic in recent years. Also, it is desired that the optical transmission system can transmit data to further longer distance without repeat in view of reliability and cost of the system.

Furthermore, the number of fields to which an optical transmission system is applied has been increased with the recent development of the information society. For the reason, it is needed to accomplish the optical transmission system having a variety of functions and capacities to satisfy specific requirements.

SUMMARY OF THE INVENTION

In view of the foregoing, it is an object of the present invention to provide an optical transmission system constructing method capable of easily constructing an optical transmission method and system depending on required functions and capacities.

Briefly, the foregoing object is accomplished in accordance with aspects of the present invention by an optical transmission system. The optical transmission system is characterized in constructing a line terminal having multiplexing means for multiplexing signals and demultiplexing means for demultiplexing the multiplexed signal so that to serve as a transmitter, the line terminal is selectively capable of implementing either a first combination of an electric-to-optic converter circuit for converting the electric signal multiplexed by the multiplexing means to a transmission light with an optical fiber amplifier for amplifying the transmitting light before feeding into an optical transmission medium or electric-to-optic converting means having a semiconductor optical amplifier for converting the electric signal multiplexed by the multiplexing means to a transmission light before feeding an optical transmission line. The optical transmission system also is characterized in constructing the line terminal so that to serve as a receiver, the line terminal is selectively capable of implementing either a second combination of an optical fiber amplifier for amplifying a receiving light from an optical transmission medium with an optic-to-electric converter circuit for converting the amplified receiving light to electric signal before feeding to the demultiplexing means or an optic-to-electric converting means for converting the received light from the optical transmission medium to electric signal before feeding to the demultiplexing means with an avalanche photodiode used as light receiver.

Also, the optical transmission system is characterized in constructing the optical transmission system for use as a longdistance optical transmission system, a plurality of the line terminals having the first combination to serve as the transmitter and the second combination to serve as the receiver implemented therein each are connected to the optical transmission medium through a single or a plurality of repeaters inserted in the optical transmission medium for multiplying the optical light signal on the optical transmission medium.

Further, the optical transmission system is characterized in constructing the optical transmission system for use as a shortdistance optical transmission system, the plurality of the line terminals having the electric-to-optic converting means having a semiconductor optical amplifier therein to serve as the transmitter and the optic-to-electric converting means having the avalanche photodiode used as the light receiver to serve as the receiver implemented therein each are directly connected to the optical transmission line.

The optical transmission system constructing method of the present invention enable an easy construction of any of the long-distance an short-distance optical transmission system only by selecting desired types of the transmitters and receivers to be implemented to change the combinations of the units. This is because the line terminal is constructed so that to serve as the transmitter, the line terminal is selectively capable of implementing either the first combination of an electric-to-optic converter circuit for converting the electric signal multiplexed by the multiplexing means to the transmission light with an optical fiber amplifier for amplifying the transmitting light before feeding into an optical transmission medium or electric-to-optic converting means having the semiconductor optical amplifier for converting the electric signal multiplexed by the multiplexing means to the transmission light before feeding an optical transmission line, and that to serve as the receiver, the line terminal is selectively capable of implementing either the second combination of an optical fiber amplifier for amplifying the receiving light from an optical transmission medium with an optic-to-electric converter circuit for converting the amplified receiving light to electric signal before feeding to the demultiplexing means or an optic-to-electric converting means for converting the received light from the optical transmission medium to electric signal before feeding to the demultiplexing means with an avalanche photodiode used as light receiver.

The foregoing and other objects, advantages, manner of operation and novel features of the present invention will be understood from the following detailed description when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1

is a block diagram for a functional construction of a optical transmission system of an embodiment of the present invention.

FIG. 2

is an overall configuration for a network system related to the embodiment.

FIG. 3

is a configuration for a network among a large-scale switching nodes extracted from the network system.

FIG. 4

is a configuration for a network among a small-scale switching nodes and among a small-scale switching nodes and the large scale switching node extracted from the network system.

FIG. 5

is a configuration for a network for a metropolitan area extracted from the network system.

FIG. 6

is block diagrams for a functional construction of a node.

FIG. 7

is a hierarchical construction of a network system.

FIG. 8

is a frame construction for a multiplexing frame used in the network system.

FIG. 9

is logical positions of path groups.

FIG. 10

is a bit allocation of overhead of the path groups.

FIG. 11

is an example of setting the path group in a ring.

FIG. 12

is path group switching procedures at failure.

FIG. 13

is a typical sequence of switching requests.

FIG. 14

is a block diagram for a configuration of the network system related to the embodiment.

FIG. 15

is a sequence diagram for transfer of alarms in the network system.

FIG. 16

is a block diagram for the optical transmission system for a long distance system.

FIG. 17

is a block diagram for the optical transmission system for a short distance system.

FIG. 18

is a block diagram for a clock transit system for the optical transmission system.

FIG. 19

is bytes to be scrambled of an overhead in a STM-64 section.

FIG. 20

is a block diagram for the 1R-REP.

FIG. 21

is a block diagram for a board construction of the 1RREP.

FIG. 22

is a format for a surveillance and control signal for use in the surveillance and control of the 1R-REP.

FIG. 23

is a block diagram for an inter-office transmission line interface of the LT-MUX.

FIG. 24

is a block diagram for the intra-office transmission line interface of the LT-MUX.

FIG. 25

is a relationship of multiplex and demultiplex between a STM-64 frame and a STM-1×64 supported by the LT-MUX.

FIG. 26

is a block diagram for a transmitter of the LT-MUX forming the long distance system.

FIG. 27

is a block diagram for the transmitter of the LT-MUX forming the short distance system.

FIG. 28

is a block diagram for a receiver of the LT-MUX forming the long distance system.

FIG. 29

is a block diagram for the receiver of the LT-MUX forming the short distance system.

FIG. 30

is a block diagram for a node having LT-MUXes and an ADM switch used.

FIG. 31

is a block diagram for extracted parts serving to the surveillance and control system for the LT-MUX.

FIG. 32

lists features of the functional blocks of the surveillance and control system.

FIG. 33

is a block diagram for a redundancy configuration of a transmitting system in the LT-MUX.

FIG. 34

is a block diagram for the redundancy configuration of a receiving system in the LT-MUX.

FIG. 35

is a block diagram for construction of a hitless switching process feature section for transmission line.

FIG. 36

is a block diagram for a construction of a 3R-REP.

FIG. 37

is a front view for an implementation of the 1R-REP.

FIG. 38

is structures of a optical preamplifier and optical booster amplifier forming a single 1R-REP system.

FIG. 39

is a front view for an implementation of the LT-MUX.

FIG. 40

is a front view for an implementation of two systems of the LT-MUX in a single rack without the line redundancy configuration.

FIG. 41

is a front view for an implementation of the LT-MUX for constructing the small scale switching node with a 40G switch unit built in as shown in

FIG. 6

b.

FIG. 42

is a structural view for a 40G switch.

FIG. 43

is a front view for an implementation of the LT-MUX for constructing the large scale switching node.

FIG. 44

is a front view for an implementation of the 3R-REP.

DETAILED DESCRIPTION OF THE INVENTION

The following describes an embodiment according to the present invention for the optical transmission system by reference to the accompanying drawings.

1. General Description

First, this section outlines the optical transmission system of the embodiment.

FIG. 1

is a block diagram for the functional construction of the optical transmission system of the embodiment.

The optical transmission system, as shown in

FIG. 1

a

, is an ultralong distance transmission system for making optical transmission between line terminals with multiplexers (hereinafter referred to as the LT-MUX 1) or between the LT-MUX 1 and a regenerator (hereinafter referred to as the 3R-REP 3) with use of an optical amplifier repeater (hereinafter referred to as the 1R-REP 2). The system can send the data at 10 Gb/sec through an optical fiber 40 up to 320 km by the 3R-REP 3 at the longest intervals of 80 km by the 1R-REP 2.

The LT-MUX 1 makes a multiplex and section-termination-process (

12

) of the data received by an intra-office interface

11

provided therein, and converts them to optical signal (

13

). An optical booster amplifier

14

magnifies the optical signal before feeding it into an optical transmission medium. On the contrary, the data received from the optical transmission medium is magnified by an optical preamplifier

15

before being converted to electrical signal (

16

). The signal then is demultiplexed and section-termination-processed (

12

) before being distributed to the intra-office interfaces

11

. The 1R-PEP 2 repeats the optical signal in a way that any of optical fiber amplifiers

21

and

22

magnifies the optical signal received from the optical transmission medium before feeding it out. The 3R-REP 3 regenerates the data to repeat in a way that the data received from the optical transmission medium are magnified by an optical preamplifier

35

before being converted to electrical signal (

36

). The electrical signal then is demultiplexed and section-termination-processed (

32

) and is multiplexed and section-termination-processed (

32

) again. It further is converted to optical signal (

33

) and magnified by an optical booster amplifier

34

before being fed into the optical transmission medium. The interface of any equipment with the optical transmission medium (hereinafter referred to as the inter-office interface) is equivalent to the CCITT recommended synchronous transport modulelevel N (STM-N) where N=64, and uses a scrambled binary NRZ (non-return to zero) as transmission line code. A spectrum broading is used to prevent a stimulated Brillouin scattering due to a higher power output.

The intra-office interface

11

of the LT-MUX 1 can contain a series of STM-1 (150 Mb/sec) by 64 or a series of STM-4 (600 Mb/sec) by 16. Note that the series of STM-4 (600 Mb/sec) by 1 can be compatible with the series of STM-1 by 4.

The optical transmission system can be configured in another way that instead of the 1R-REP 2 shown in

FIG. 1

a

, the LT-MUXes 1 are directly connected together or the LT-MUX 1 is directly connected with the 3R-REP 3. In this case, the transmission distance is up to 120 km without repeater.

Also, the optical transmission system can be configured in still another way as that shown in

FIG. 1

b

, the 1R-REP 2, the optical booster amplifier

14

, and the optical preamplifier

15

are omitted, but LT-MUXes 1 having an opto-electric converter

2000

and an electro-optic converter

2010

which are different in the characteristics from those of the LT-MUX 1 in

FIG. 1

a

are directly connected together. In this case, the output level is around +6 dBm, and the transmission distance is up to 80 km without repeater.

The optical transmission system having the LT-MUX 1, the 3R-REP 3, the optical booster amplifier

14

, and optical preamplifier

15

is called the long-distance system below; and the optical transmission system having no optical booster amplifier

14

and optical preamplifier

15

in the LT-MUX 1 and 3R-REP 3 is called the short distance system below.

2. Overall System Configuration

In turn, this section describes a network system having the optical transmission system of the embodiment.

FIG. 2

is an overall configuration for a network system related to the embodiment.

In the figure are indicated a large scale switching node

110

having the LT-MUX 1 of the embodiment and a small scale switching node

120

having the LT-MUX 1 of the embodiment.

The large-scale switching nodes

110

in the network system related to the embodiment, as shown in the figure, are directly connected therebetween in a ladder-shaped structure with use of the 1R-REP 2 and the 3R-REP 3. The network system has routes diversed therein and the CCITT recommended VC-¾ path protection switch in the meshed network, thereby increasing reliability of the network. The small-scale switching nodes

120

are ringstructured, and the small-scale switching nodes

120

and the large scale switching nodes

110

are also ring-structured. This does not only provide a multiplexing effect that allows efficient use of the large-capacity transmission medium, but also keeps two routes that can increase the reliability. In addition, a metropolitan area has a multiple of rings that can increase the reliability in, an area of relatively narrow, but large, facial extending traffic.

FIG. 3

is a configuration for a network among the large-scale switching nodes

130

extracted from the network system.

The large-scale switching nodes

130

, as shown in the figure, are directly connected thereamong with use of the 1R-REPs 2 and the 3R-REPs 3 without switching through an intermediate node, thereby decreasing the line cost. A distance between the 1R-REPs 2 is up to 80 km in view of the S/N design, and the one between the 3RREPs 3 is up to 320 km in view of the nonlinear distortion of the fiber.

FIG. 4

is a configuration for a network among the small-scale switching nodes

120

and among the small-scale switching nodes

120

and the large scale switching nodes

110

extracted from the network system.

If a distance between the small-scale switching nodes

120

is shorter than 120 km, as shown in the figure, no repeaters are used, but direct connection is made between any two of the smallscale switching nodes

120

. If the distance exceeds 120 km, the 1R-REP 2 is used to make the long distance system as mentioned previously. If the distance is shorter than 80 km, as will be described in detail later, the 10 Gb/sec transmitter is replaced by the one made up of a semiconductor optical amplifier and an APD (avalanche photodiode) to form a further economic short distance system (

FIG. 1

b

).

FIG. 5

is a configuration for a network for the metropolitan area extracted from the network system.

The metropolitan area, as shown in the figure, has a plurality of adjoining rings formed of the transmission media connecting the nodes in a meshed network, thereby accomplishing efficient multiplex operation and high reliability. It should be noted that there will be a greater number of the shorter node distances than 80 km. Then, as described above, the short distance system is made up of the semiconductor optical amplifier and the APD to form the network at low cost.

FIG. 6

is block diagrams for the functional construction of the node.

The large scale switching node

110

, as shown in

FIG. 6

a

, has two LT-MUXes 1 and a VC-¾ cross-connection switch

111

for path switching and setting at the VC-¾ level in the synchronous digital hierarchy (SDH). The two LT-MUXes 1 are connected by a high-speed interface which will be described later, but not any intra-office interface. The large scale switching node

110

also has the STM-1 interface and the STM-4 interface as the intraoffice interfaces. These interfaces can connect a line repeater terminal

5000

for transmission between a 600 Mb/sec or 2.4 Gb/sec offices, a cross-connection equipment

5100

for terminating the intra-office interface

111

, and an ATM cross-connection switch

5200

. The ATM cross-connection switch

5200

, if used, can accomplish lower cost and decrease cell delay as the 600 Mb/sec intra-office interface is used. Note that the large scale switching node

110

can be alternatively made up of the two LTMUXes 1 and a cross-connect equipment

111

.

The small scale switching node

120

is the same as the large scale switching node

110

or as shown in

FIG. 1

b

, has the LT-MUX 1 and an VC-¾ add-drop multiplex (ADM) switch. The small scale switching node

120

also, like the large scale switching node

110

, has the STM-1 interface and the STM-4 interface as the intraoffice interfaces, which can connect the line repeater terminal

5000

for transmission between a 600 Mb/sec or 2.4 Gb/sec offices, the cross-connection equipment

5100

for terminating the intraoffice interface

111

, and the ATM cross-connection switch

5200

.

The intra-office interface

11

of the LT-MUX 1 is used for the STM-1 interface and the STM-4 interface for each node.

Table 1 shows a hierarchy of the network system and terminals at the respective hierarchy level.

TABLE 1

NO.

LEVEL

TERMINAL

OVERHEAD

1

VC-¾

VC-½ processors, and

VC-¾ POH

ATM unit

2

VC-¾ path

VC-¾ cross-connector

Z3 byte of

group

(virtual ring branch -

representing

(VC-¾ PG)

insertion point)

VC-¾ POH

3

STM-64 section

LT-MUX

MSOH

section

4

Regenerator

3R-REP and LT-MUX

RSOH

section

5

Linear repeater

1R-REP, 3R-REP, LT-MUX

Wavelength

section

multiplexed

management

signal

As shown in the table, the present embodiment defines the new VC¾ path group to accomplish easy path switching at failure of any transmission medium.

FIG. 8

is a frame construction for an STM-64 which is an inter-office interface.

The overhead for the VC-¾ path group, as shown in the figure, is the Z3 byte of the representing VC-¾ POH forming the VC-¾ path group.

The following describes the path switching with use of the path group at failure of any transmission medium.

The term “path group” as used herein denotes a set of parts within a ring of the VC-¾ path that a point of insertion into a virtual ring is equal to each other and a point of branch from the virtual ring is equal to each other. The term “virtual ring” as used herein denotes a ring extracted from the network as a part which can virtually form a ring-like path. It should be noted that as shown in

FIG. 9

, the path group is positioned between section and path layer in view of the network layer structure.

The embodiment switches the path group when the path group is at failure. The path group is managed with use of the Z3 byte of the representing VC-¾ path overhead within the path group.

FIG. 10

is a bit allocation of the Z3 byte. The path group failure is detected by a path group alarm indication signal (PGAIS) defined in the Z3 byte.

Table 2 shows path switching features in the embodiment.

TABLE 2

NO.

ITEM

DESCRIPTION

1

Switching unit

VC-¾ path group (set of VC-¾ paths

in same route within ring)

2

Switching net-

Virtual ring (on VC-¾

work topology

path mesh)

3

Protection form

1 + 1 bidirectional switching

(Working path group and protection group

are turned reversely on ring.)

4

Switching control

Autonomous switching to ground office

method

in ring by APS control for path group

5

APS byte

b1 to b4 of Z3 byte path group

representing VC-¾

6

APS protocol

Conform to 1 + 1 switching protocol of

section APS

7

Switching trigger

Path group AIS reception at path group

terminal point

(Path group AIS bit in Z4 type = 1)

8

Switching

VC-¾ cross-connection switch (LT-MUX

equipment

with XC and LT-MUX with ADM)

9

Switch control

Switching ACM* meshed network in units

method

of VC.

*ACM = address control memory which is a memory for controlling switches in cross-connection unit and the like.

As shown in Table 2 above, the embodiment uses an alternative meshed network switching to increase the reliability. Controlling the mesh switching in the embodiment is the autonomous switching in units of the VC-¾ path group virtual ring, which conforms to the section APS recommended by CCITT.

FIG. 11

is an example of setting the path group in the ring. The protection path group is extended in the direction reverse to the working one.

FIG. 12

is path group switching procedures at failure.

FIG. 13

is a typical sequence of switching requests. The switching sequence, as shown in

FIG. 13

, conforms to the usual 1+1 section APS. Finally, Table 3 shows priorities of the switching requests and coding of the Z3 byte, and Table 4 shows coding of the path group status.

TABLE 3

TYPE OF

z3 BYTE

PRIOR-

SWITCHING

b1, b2,

ITY

REQUEST

DESCRIPTION

b3, b4

1

Lockout

Inhibit all switchings by any

—

of following switching

requests, with working state

held.

2

Forced

Make switching if protection

1 1 1 0

switching

path group is normal.

(FS)

3

Signal

Make switching if protection

1 1 0 0

failure

path group is normal after

(SF)

results of surveillance of

working path group AIS and

units are triggered for

failure. Path group AIS is

generated by LOS, LOF, and

severed MER.

4

Manual

Make switching if protection

1 0 0 0

switching

path group is normal.

5

Wait to

Do not release from switched

0 1 1 0

restore

state during the waiting

period even if the working

path group is restored

while the automatic switching

SF or SD is made.

6

Exerciser

Test switching control system.

0 1 0 0

7

Reverse

Respond operation of switching

0 0 1 0

request

to requesting source after

receiving request for forced

switching or signal failure

or wait to restore.

8

No bridge

Inhibit all switchings by any

0 0 0 0

required

of the following switching

requests, with the working

state held.

TABLE 4

z3 BYTE

b7, b8

DESCRIPTION

0

0

Normal state

1

1

PG-AIS*

1

0

PG-FERF

*PG-AIS = path group AIS.

3. Surveillance and Control System

This section describes a surveillance and control system for the network system related to the embodiment.

FIG. 14

is a block diagram for a configuration of the network system related to the embodiment.

Each of the LT-MUXes and the 1R-REPs 2 has a surveillance and control function

1001

and an OpS-IF

1002

for connection with an OpS (operation system)

1000

. The surveillance and control are made under control of the OpS

1000

which governs the surveillance and control of the system.

The embodiment makes a wavelength multiplex of a surveillance and control signal with a main signal on the STM-64 interface before transmitting the multiplexed signal to monitor and control the 1R/3R-REPs 3 having no OpS IF

1002

remotely. That is, the OpS

1000

gives a direction signal to the equipment having the OpS IF

1002

to make the equipment superimpose the direction signal onto the surveillance and control signal, or makes the 1R/3R-REP having no OpS IF

1002

transfer an alarm detected or generated by the 1R/3R-REP to the equipment having the OpS IF

1002

. Alternatively, it can be made that the 1R/3R-REP should have the OpS IF

1002

to allow the OpS

1000

to monitor and control the 1R/3R-REP directly.

In turn, the surveillance and control signal of 384 kb/sec is transferred by a light of the same 1.48 μm wavelength as that of a pumping light source of the 1R-REP 2. The surveillance and control signal, as shown in

FIG. 22

, also has a 48 byte frame length for a 1 msec frame period, 24 bytes (192 kb/sec) of which are allocated to a DCC (data communication channel) for the remote control, 8 bytes (64 kb/sec) for an order wire, and 6 bytes (48 kb/sec) for the alarm transfer. The surveillance and control signal allows each of the 1R/3R-REPs 2 to inform the state and alarm. That is, each of the 1R/3R-REPs can generate its own monitoring information and repeat the surveillance and control signal generated by the preceding 1R/3P-REP as well. The state monitoring is made at intervals of 1 sec so that an access collision cannot happen even if number of the 1R/3RREPs is around 100.

Also the surveillance and control signal has 1 byte allocated there to as the 1R-REP section has a feature equivalent to that of the usual AIS. The 1R/3R-REP having detected a fatal failure, such as loss of the main signal, transfers its own ID to the succeeding repeater using the one byte. This 1R/3R-REP 2 repeats the one byte to the LT-MUX 1. This allows informing of the 1R/3R-REP section AIS at intervals of 1 msec. If it is used, the 3R-REP converts it to an S-AIS (section alarm indication signal).

The features of the surveillance and control system are charted in Tables 5 and 6. Surveillance and control items are charted in Table 7.

TABLE 5

ITEM

DESCRIPTION

NOTE

Surveillance

(1)

LT-MUX

1R/3R-REP

and control

Has OpS-IF and is started by

can have

equipment

direction by OpS.

OpS-IF.

(2)

1R-REP

Has RMT-IFs, such as DCC-IF and

ALARM-IF, and is started by direc-

tion by surveillance and control

signal.

(3)

3R-REP

Same as 1R-REP.

Surveillance

(1)

Physical characteristics

Frame

and control

Frame length: 48 bytes.

synchro-

signal

Frame period: 1 msec.

nization

Rate: 384 kb/sec.

by CMI

Wavelength: 1.48 μm.

code rule

Line code: CMI.

violation.

(2)

Generation method

To increase

Generation by LT-MUX and 1R/3R-

reliability.

REP.

(3)

Transfer method

Is wavelength-multiplexed with the

main signal before being transferred.

1R/3R-REP determines either repeat

or reception with destination ID

added on surveillance and control

signal. For repeat, 1R/3R-REP stores

it in the reception buffer before

transmission.

(4)

Access to 1R/3R-REP

Access can be made from either west

or east.

Monitoring

(1)

Amount of information:

Equivalent

method

4 bytes of surveillance and control

to feature

signal.

of SONET F1

(2)

Monitoring Interval/alarm transfer

byte.

interval: 1 sec.

However, if fatal failure, such as

loss of signal, is detected,

1R/3R-REP section AIS is transferred

at intervals of 1 msec.

(3)

Transference can be made to either

west and east.

TABLE 6

ITEM

DESCRIPTION

NOTE

Control

(1)

Surveillance and control signal

Setting can

method

has DCC area of 24 bytes

be made also

(equivalent to 192 kb/sec)

from OpS if

provided therein for setting

necessary.

surveillance and control items.

(2)

Surveillance and control signal

has order wire area of 8 bytes

(equivalent to 64 kb/sec)

provided therein. This allows

maintenance communication.

(3)

Access can be made from either

west or east.

(4)

Response is made after

execution of instruction.

TABLE 7

Monitoring items

Monitoring items

Monitoring items

1R section

Optical fiber

Optical fiber

Optical fiber

monitoring

disconnection (LOS)

disconnection

disconnection (LOS)

items

Loss of main signal

Loss of main signal

Loss of main signal

(Preceding REP

(Preceding REP

(Preceding REP

failure)

failure)

failure)

Loss of surveilance

Loss of surveilance

Loss of surveilance

and control signal

and control signal

and control signal

(Preceding REP

(Preceding REP

(Preceding REP

failure)

failure)

failure)

Surveilance and

Surveilance and

Surveilance and

control signal LOF

control signal LOF

control signal LOF

(CMI)

(CMI)

(CMI)

Surveilance and

Surveilance and

Surveilance and

control signal FCS

control signal FCS

control signal FCS

error

error

error

3R section

Main signal LOF

Main signal LOF

monitoring

Error rate

Error rate

items

degradation (B1)

degradation (B1)

F1 byte process

F1 byte process

S-AI5 detection,

S-AI5 detection,

generation, and

generation, and

transfer

transfer

Others

Equiptment failure

Equiptment failure

Other SDH features

Input, intermediate,

Input, intermediate,

Equiptment failure

and output signal

and output signal

Input, intermediate,

levels

levels

and output signal

LD temperature

LS temperature

levels

LD biases

LD biases

LD temperatures

Gains

Gains

LD biases

Gains

Control items

Control items

Control items

Year and date

Year and date

Year and date

setting

setting

setting

Output halt or release

Output halt or release

Output halt or release

Soft strap setting

Soft strap setting

and reading related

and reading related

to SDH

to SDH

Example:

Example:

B1 error rate-

B1 error rate-

degradation threshold

degradation threshold

value

value

Order wire of

Order wire of

Order wire of

64 kb/sec

64 kb/sec

64 kb/sec

DCC of 192 kb/sec

DCC of 192 kb/sec

DCC of 192 kb/sec

As shown in

FIG. 7

, if any of the monitoring items is at failure, the equipment transfers the alarm. The alarm detection and transfer are made for the four layers, including the 1R section layer, the 3R section layer, the LT section layer, and the path layer.

The 1R section layer deals with any of the alarms detected by the 1R-REP 2. The alarm is transferred by the surveillance and control signal. The 1R section layer processes the following items.

(a) Optical fiber disconnection: The main signal input and the surveillance and control signal input are disconnected by an optical fiber disconnection.

(b) Loss of main signal: The main signal input is lost by a preceding 1R/3R-REP stage failure.

(c) Loss of surveillance and control signal: The main signal input is lost by a preceding 1R/3R-REP stage failure.

(d) Surveillance and control signal LOF (loss of frame): The frame synchronization surveillance and control signal is lost.

(e) Surveillance and control signal FCS (frame check sequence) error: A code error is detected by checking the FCS of the surveillance and control signal.

(f) 1R section failure REP identification: The 1R-REP having detected a fatal failure writes its own ID into a predetermined byte provided in the surveillance and control signal before generating the surveillance and control signal. This accomplishes the feature of F1 byte for the SDH recommended by the CCITT.

The 3R section layer performs processes about an RSOH (regenerator section overhead) of the STM frame.

(a) Main signal LOF: Loss of frame of the main signal is detected with A1 and A2 bytes.

(b) Error rate degradation: MER and ERR MON are generated with use of B1 byte.

(c) F1 byte process: If it detects a fatal failure, the 3R-REP writes its own ID into the F1 byte of the sending STM frame. Also, if it receives the surveillance and control signal indicating that the preceding the 1R-REP is at failure, the 3RREP writes the ID in a predetermined byte into the F1 byte of the sending STM frame.

(d) S-AIS detection, generation, and transfer: S-AIS process is made.

The LT section layer performs processes about an MSOH (multiplex section overhead) of the STM frame.

The path layer performs processes about a VC-¾ POH (path overhead) of the STM frame.

In turn, the alarm of the 1R section is sent to the LT-MUX through 1R-REP and 3R-REP by the surveillance and control signal.

For any of the fatal failures, such as loss of the main signal, if the alarm is transferred through the 3R-REP, then the 3R-REP converts it to S-AIS.

FIG. 15

is a sequence diagram for transfer of the alarm in the network system.

4. Optical Transmission System

This section describes an optical transmission method for the optical transmission system related to the embodiment.

FIG. 16

is a block diagram for the optical transmission system for the long distance system.

As shown in the figure, the embodiment includes a modulator integrated light source module

200

of 1552 nm wavelength having little chirping as a sending light source for the LT-MUX 1 and the 3RREP 3. To suppress an SBS (stimulated Brilloiun scattering) caused in the optical fiber, the embodiment uses the spectrum broading that a signal of a low-frequency oscillator

201

is applied to a laser section of the modulator integrated light source module

200

to make a light frequency modulation. Optical booster amplifiers

14

and

34

use a bidirection pumping method for which a pumping light source of 1480 nm wavelength is used. The transmission power and chirping quantities of a modulator are optimized to accomplish the longest regeneration distance of 320 km.

To transmit the supervisory signal, a supervision light source

202

of 1480 nm wavelength range provided in the light booster amplifier is used. The supervisory signal is wavelengthmultiplexed with the main signal before being transmitted to a downstream. To prevent output of the light booster from decreasing, a WDM (wave division multiplex) coupler

203

for wavelength multiplex of the surveillance and control signal with the main signal is made to also serve as WDM coupler for laser pumping.

A forward pumping optical preamplifier

35

having a pumping source of 1480 nm range accomplishes highly sensitive reception.

On the other hand, to receive the supervisory signal, a WDM coupler

210

for pumping Erbium-doped fiber is used to draw the supervisory signal, which is received by an exclusive receiver. This minimizes degradation of the NF (noise figure). With the use of the light booster amplifiers

13

and

34

and light preamplifiers

5

and

35

, the distance between the LT-MUX 1 and the 3R-REP 3 can be made 120 km if they are directly connected together.

The 1R-REP 2 has two Erbium-doped fibers

211

and

216

and pumping light sources of 1480 nm wavelength range used therein. The former laser pumping stage

212

pumps forward, and the latter three laser pumping stages

213

,

214

, and

215

pump bidirectionally. This accomplishes both lower NF and higher output power. For reception of the supervisory signal by the 1RREP 2, a WDM coupler

217

for pumping the first Erbium-doped fiber

211

stage is used to draw the supervisory signal before an exclusive receiver

218

. This minimizes degradation of the NF below 0.2 dB to accomplish an optimum reception of the supervisory signal.

For transmission of the supervisory signal by the 1R-REP 2, a light source

219

of 1480 nm wavelength range for the supervisory signal is used to wavelength-multiplex with the main signal before being transmitted to a downstream. Wavelength multiplexing of the supervisory signal with the main signal is made by using a WDM coupler

220

which also serves to pump the latter Erbium-doped fiber

216

.

To prevent output of the light booster from decreasing, the WDM (wave division multiplex) coupler

203

for wavelength multiplex of the surveillance and control signal with the main signal is made to also serve as the WDM coupler for laser pumping. In such a way as described above, with the surveillance and control signal demultiplexed and multiplexed at the input and the output of the 1R-REP 2 respectively, an inter-office cable connected to the equipment can be used to inform a failure to the downstream even if the failure is the input signal disconnection or in the transmission medium within the 1R-REP 2.

FIG. 17

is a block diagram for the optical transmission system for the short distance system.

The short distance system, as shown in the figure, like the long distance system, uses a modulator integrated light source module

200

of 1552 nm wavelength for a transmitting light source. The short distance system is different from the long distance system in that a transmitter of the short distance system uses a semiconductor light amplifier

230

as an optical booster to make the transmitter small, and a receiver uses an optical receiver

231

of small size and low power consumption having a superlattice APD of low noise and wide frequency response.

If it has a high optical power input thereto, the optical fiber has an SBS caused, resulting in degradation of the transmission characteristics. For the CW light, the SBS is caused with the optical fiber input power higher than +6 dBm. In modulation, the SBS is caused by blight-line spectra contained in the signal light. It is generated at a light power level higher than the one for the CW light.

To suppress the SBS, the embodiment uses a way that the generated laser light is modulated with a low frequency signal to broaden the light spectra equivalently. The suppression of the SBS by broadening the light spectra is described in an article entitled “Suppression of Stimulated Brilloiun scattering and Brilloiun Crosstalk by Frequency Sweeping Spread-Spectrum Scheme,” Journal Optical Communications, Vol. 12, No. 3, pp. 82-85 (1991), A. Hirose, Y. Takushima, and T. Okoshi.

FIG. 18

is a block diagram for a clock transit system for the optical transmission system.

A clock for process of section overhead of transit signals in the LT-MUX 1 and 3R-REP 3, as shown in the figure, is an extracted clock smoothed by a PLL. The PLL has a time constant which is set in an order of msec that can almost completely suppress random jitters superimposed through the transmission circuit and line. A low-speed wander of the transmission clock is transferred by a pointer justification feature of the section overhead. With these, the 3R-REP 3 can make the repeat without accumulation of the jitters, so that it is free of the jitter accumulation due to continuation of an identical code.

In transmission of the SDH section overhead, all the section overhead bytes except parts of the first line are scrambled. (

FIG. 19

shows the parts of the first line, including 4 bytes containing the last 2 A1 bytes and first 2 A2 bytes, 64 C1 bytes, and succeeding 2×64 fixed bytes.) This prevents repetition of a fixed pattern as much as hundreds of bytes, reduces a pattern jitter, and averages output of a timing filter. If a 4-byte synchronous pattern is used, a frame synchronization protection is longer than 10 years in average misframe interval for five consecutive forward protection, and is lower than 1% in misframe probability and rehunting probability for two consecutive backward protection.

5. Description of 1R-REP

This section describes the 1R-REP 2.

FIG. 20

is a block diagram for the 1R-REP. Table 8 charts major features of the 1R-REP 2.

TABLE 8

ITEM

DESCRIPTION

Main signal

Signal wavelength

1.552 μm ± 0.001 μm

interface

Mean light output

+10 to +12 dBm

Input light level

−18 to 0 dBm

Noise figure

Lower than 7 dB

Pumping method

Bidirectional pumping of

Erbium-doped fiber, with

1.48 μm pumping lasers.

Surveillance and control

Transference of surveillance

method

and control signal by 1.48 μm

wavelength multiplex.

Implementation of

surveillance and control

section in main signal unit.

Physical implementation

300 mm high × 3 shelves per

method

bay (1800 × 795 × 600 mm)

Cooling method

Natural convection, with

convection guiding plate of

100 mm high.

Accommodation of systems

Two systems per shelf (one

system contains both east and

west systems)

Environmental conditions

Temperature: 10 to 40° C.

Humidity: 20 to 80%

Input power condition

−42 to −53 V

As shown in

FIG. 20

, the 1R-REP optical transmission system consists of two amplifier stages, including an optical preamplifier

301

for magnification with a low noise and an optical booster amplifier

320

for high power magnification. An output of the optical preamplifier

301

is connected to an input of the optical booster amplifier

320

. This accomplishes a lownoise, high power output characteristic in a wide dynamic range.

Description of the preamplifiers is ignored here as it was already made previously by reference to FIG.

16

.

The 1R-REP 2 can monitor light outputs and intermediate signal powers and detect opening of the outputs so that it can control and monitor a gain of each optical amplifier stage. As described previously, the 1R-REP 2 also can receive and transmit the surveillance and control signal of 1.48 μm wavelength. The monitor and control and processing the surveillance and control signal are made by an surveillance signal processor/automatic power control circuit

310

.

FIG. 21

is a block diagram for a package construction of the 1R-REP 2. The main signal system of the 1R-REP 2, as shown in the figure, comprises two packages, including a preamplifier package having the low-noise optical preamplifier

301

and a booster amplifier package having the high-power optical booster amplifier

320

. As will be described later, a single bay having a plurality of shelves, each of which has two systems and the OpS IF as a common section.

The ground 1R-REP 2, like the LT-MUX 1 and the 3R-REP 3, has features of preventive maintenance, failure identification, and workability increase.

These features facilitate troubleshooting for each 1R repeater section. As for the 1R repeater section overhead providing a feature of a surveillance and control communication channel between offices having the 1R-REP 2, as described previously, it uses the surveillance and control light of 1.48 μm wavelength.

The following describes monitor of the 1R repeater section and process of the 1.48 μm surveillance and control signal in detail. It should be noted that the surveillance and control made by the 1R-REP 2 are similarly made by the LT-MUX 1 and the forward pumping optical preamplifier

35

and the optical booster amplifier

34

of the 3R-REP 3.

Table 9 lists surveillance and control items of the 1R-REP 2.

TABLE 9

Surveil-

Alarm

Signal

Optical fiber disconnection

lance

failure

Main signal (Preceding REP

failure)

Loss of surveillance and

control signal (Preceding REP

failure)

Surveillance and control

signal LOF (CMI)

Surveillance and control

signal FCS (frame check

sequence) error

Equipment

Output open

failure

Main signal transmit failure

Surveillance and control

signal transmit failure

Optical amplifier equipment

failure

Surveillance and control

equipment failure

Power source system failure

Monitor

Input signal level

Intermediate signal level

Output signal level

Pumping LD temperature

Pumping LD bias

Surveillance and control LD temperature

Surveillance and control LD bias

Gain

Control

Year and date setting and reading

Output halt and release

Failure section determination

As shown in

FIG. 9

, the 1R-REP 2 provides the following processes with use of surveillance lights and control signals marked with an encircled number in FIG.

20

.

Number {circle around (

1

)} in

FIG. 20

denotes a surveillance light signal which is taken by a PF-WDM out of the input light having been composed of the main signal light of 1552 nm wavelength and the surveillance and control light signal of 1480 nm wavelength. The surveillance light signal is 3R-processed to convert to electrical signal by a supervisory signal receiver. The surveillance light signal is used by the automatic power control circuit surveillance signal processor

310

to detect the supervisory signal input disconnection.

Number {circle around (

2

)} in

FIG. 20

denotes a monitor light branched from a light output of the low-noise amplifier section by a CPL. The monitor light is used by the automatic power control circuit surveillance signal processor

310

to control the gain, to monitor the input state, and to monitor the intermediate power.

Number {circle around (

3

)} in

FIG. 20

denotes another monitor light branched from a light output of the high-power output amplifier section by another CPL. This monitor light is taken out through a BPF. The monitor light is used by the automatic power control circuit surveillance signal processor

310

to control the gain and to monitor the output state.

Number {circle around (

4

)} in

FIG. 20

denotes still another monitor light branched through the CPL from a light reflected from the output end. This monitor light is used by the automatic power control circuit surveillance signal processor

310

to detect opening of the output.

Number {circle around (

5

)} in

FIG. 20

denotes control signals used by the automatic power control circuit surveillance signal processor

310

to stabilization-control the output of the pumping source and to monitor LD states.

Number {circle around (

6

)} in

FIG. 20

denotes the surveillance and control signal sent from the automatic power control circuit surveillance signal processor

310

. The surveillance and control signal is converted to an optical signal by the surveillance and control light source of 1480 μm wavelength. The optical signal is composed with the light output of the high-power output amplifier by the BB-WDM. The surveillance and control signal is used to monitor the surveillance light source LD state and to detect the supervisory signal transmit failure.

It is needed for the 1R-REP 2 that depending on the surveillance results and the like of the surveillance items, as described above, identification should be made for the transmission line alarms as to loss of the main signal, transmit failure of the main signal, loss of the supervisory signal, the input fiber disconnection, and the like. Such failure points can be identified by a judgement logic comprehended of the surveillance items {circle around (

1

)}, {circle around (

2

)}, and {circle around (

3

)}. Also, the 1R-REP 2 can detect the equipment failures of the optical amplifier repeater section for preventive maintenance of equipment. Further, the 1R-REP 2 has external control features of output shutdown for safe work.

Furthermore, the 1R-REP 2, as described above, can not only send the surveillance and control information to the downstream equipment depending on the surveillance results of the surveillance and control items, but can also repeat to transfer to the downstream equipment the surveillance and control information received from the upstream equipment.

Still furthermore, the embodiment does not only inform any of the failures of the 1R-REP 2 to the downstream, but also facilitates judgement of a failure point in each of the 1R repeater section and also maintains on the inter-office fiber the surveillance and control communication channel between the office having the 1RREP 2. To do these, the surveillance and control signal light is terminated once for each 1R-REP 2 before being repeated to the downstream through automatic power control circuit surveillance signal processor

310

to transfer. This has the advantage that the surveillance information can be transfered by a single wavelength even if the number of repeaters is increased.

In turn, if the wavelength used for the supervisory signal is out of the range of the optical amplifier, this will not cause saturation in the optical amplifier, and thus will not affect the main signal. For this reason, the light of 1.48 μm is used as described above. This light provides as little a transmission line fiber loss as the main signal waveform, and allows using a WDM (wave division multiplex) coupler to compose and divide the pumping light in common.

The CMI code is used to send the surveillance and control signal. With the CMI code used, a dc component and zero continuation can be suppressed. Also, a frame synchronizing circuit can be made up of relatively few components by a frame synchronization method of code violation.

FIG. 22

is a format for the surveillance and control signal for use in the surveillance and control of the 1R-REP 2.

The embodiment accomplishes the feature of remote control in a way as that shown in

FIG. 22

, the surveillance and control signal used is of a 48 byte-long frame for period of 1 msec at a rate of 384 kb/sec, and the DCC of 192 kb/sec is maintained within the surveillance and control signal. The frame has 1 byte for information of severe failures every period of 1 msec. This accomplishes the feature equivalent to the F1 byte of the SDH.

6. Description of LT-MUX

This section describes the LT-MUX 1 in detail.

FIGS. 23 and 24

are block diagrams for hardware constructions of the long distance system related to the embodiment. Table 10 charts major features of the LT-MUX 1. As for differences of the hardware construction of the LT-MUX 1 for use in the short distance system from those of the long distance system, they will be described below as necessary.

TABLE 10

DESCRIPTION

FOR

FOR

LONG-

SHORT-

DISTANCE

DISTANCE

ITEM

SYSTEM

SYSTEM

Intra-

Transmission rate

155.52 Mb/sec (STM-1) ×

office

64 series or 622.08 Mb/sec

inter-

(STM-4) × 16 series.

face

Transmission line code

Scrambled binary NRZ.

Error rate

Lower than 10

−11

Light source wavelength

1.31 μm +0.05 μm to

−0.04 μm (STM-1);

1.31 μm +0.05 μm to −0.05 μm

(STM-4)

Average light output

−17 to −11 dBm (STM-1);

−15 to −8 dBm (STM-4)

Maximum detectable power

Higher than −8 dBm

Minimum detectable power

Lower than −24 dBm (STM-1):

Lower than −23 dBm (STM-4)

Redundancy configuration

1 + 1 dual

Inter-

Transmission rate

9953.28 Mb/sec (equivalent

office

to STM-64)

inter-

Transmission line code

Scrambled binary NRZ (non-return

face

to zero)

Error rate

Lower than 10

−11

Light source wavelength

1.552 ± 0.001 μm, with chirping

parameter a being 1.0 ± 0.2

Average light output

+10 to +12 dBm

+5.6 to

Direct LT connection:

+6.6 dBm

+15 to +16 dBm

Maximum detectable power

Higher than −7 dBm

Higher

than −10

dBm

Minimum detectable power

Lower than −27 dBm

Lower

than −23

dBm

Redundancy configuration

Mesh switching using

virtual ring at VC-¾

level

Surveillance and control method

Surveillance control by OpS inter-

face. 1R-REP surveillance and

control by 1.48 μm wavelength

multiplex.

Physical implementation method

300 mm high with 4 shelves

(1800 × 395 × 600 mm)

Cooling method

Push-pull type forced air cooling,

with large fan.

Accommodation of systems

Two systems per rack.

Environmental conditions

Temperature: 10 to 40° C.

Humidity: 20 to 80%

Input power condition

−42 to −53 V

FIG. 23

is for the inter-office transmission line of the LT-MUX 1.

FIG. 24

is for the intra-office transmission line of the LTMUX 1. The LT-MUX 1, as shown in the figures, comprises a high-speed IF shelf

600

, a low-speed IF shelf

700

, a supervisory control/OpS

650

, an OH IF

660

, and a clock section

670

.

The high-speed IF shelf

600

comprises an OPTAMP S

601

having features as the optical booster amplifier

14

of the transmitting system, an OPTAMP R

603

having features as the optical preamplifier

15

of the receiving system, a 10G IF S

602

, a 10G IF S

604

, and a plurality of S

0

H

605

boards. The lowspeed IF shelf

700

comprises a plurality of SELs

701

, and a plurality of intra-office IF

702

packages. The high-speed IF shelf

600

and the low-speed IF shelf

700

are connected together by an intra-equipment interface of 155 Mb/sec rate.

The embodiment has a high-speed interface

600

-

1

, an SEL

701

-

1

, and an intra-office interface

702

-

1

to have a redundancy feature of 1+1 section switching type. These blocks are not needed if the section switching is not made.

Tables 11 and 12 chart the features of the LT-MUX 1.

TABLE 11

BLOCK

ITEM

NAME

FEATURE

NOTE

1

10G IF-S

(1)

Optical booster amplification

OPTAMP-S

(2)

1R repeater surveillance and

control signal light transmission

(3)

STM-64 signal E/O conversion

(4)

10 GHz PLL

(5)

STM-64 RSOH transmission

(6)

Physical rate conversion of

155 Mb/sec to 10 Gb/sec

2

10G IF-R

(1)

Optical preamplification

OPTAMP-R

(2)

1R repeater surveillance and

control signal light reception

(3)

STM-64 signal D/E conversion and

clock extraction

(4)

STM-64 RSOH termination

(5)

Physical rate conversion of

10 Mb/sec to 155 Gb/sec

3

SOH

(1)

STM-64 MSOH process

(2)

Pointer conversion of AU-3, AU-4,

and AU-4-4c

(3)

POH monitor of VC-3, VC-4, and

VC-4-4c and line test

4

SEL

(1)

System 0/system 1 selection of

STM-1/STM-4

intra-office transmission line

(2)

System 0/system 1 phase matching

of VC-3, VC-4, and VC-4-4c

(hitless switching)

(3)

APS protocol control for

intra-office transmission

line switching

5

Intra-IF

STM-1 or STM-4 intra-office

transmission line termination

(1)

E/O and O/E conversions

(2)

SOH process

(3)

Pointer conversion of AU-3, AU-4,

and AU-4-4c

(4)

POH monitor of VC-3, VC-4, and

VC-4-4c and line test

Number of accommodated lines is

STM-1 × 8 or STM-4 × 2 per

board.

6

SVCONT

(1)

Information collection in

(LIF)

low-speed IF shelf,

operation of performance

surveillance information,

and event made of alarm data

Intra-office section

AU pathbus

Surveillance in equipment

(2)

Alarm priority processing and

failure determination

(3)

Distribution and status reading of

control information in shelf

Software strap of intra-office

section

AU line test

Selected status of redundancy

system

TABLE 12

BLOCK

ITEM

NAME

FEATURE

NOTE

7

SVCONT

(1)

10G high-speed transmission IF,

(HIF)

surveillance information collection of

submarine repeater, operation of

performance surveillance

information, and event made

of alarm data

IR repeater section

Multiplex section

AU path

Surveillance in equipment

(2)

Alarm priority processing and failure

determination

(3)

Distribution and status reading of

10G high-speed transmission line

IF and repeater control

information

Software strap

AU line continuity check

Control and status reading of repeater

8

SEMF

(1)

OpS message conversion

(2)

Time management and history

processing

(3)

Emergency start-up of

backup memory

(4)

Switching control of clock

section and SVCONT

(5)

Processing of common system

alarm

9

OpS IF

(1)

OpS message communication

processing

10

RMT IF

(1)

Remote surveillance and

control communication by

DCC of multiples section

overhead (MSOH)

11

CREC

(1)

B/U conversion of 64 kHz +

8 kHz clock

12

CDIS

(1)

Clock generation (PLL) and

distribution in equipment

13

CSEND

(1)

Transmission of extracted clock

14

OH IF

(1)

Input/output of overhead signal

outside equipment

(2)

OAM processing by overhead signal

FIG. 25

is a relationship of multiplex and demultiplex between the STM-64 frame and the STM-1×64 supported by the LT-MUX.

A 10G E/O

610

of a 10G IF S

602

and an OPTAMP S

601

the transmitter of the LT-MUX 1, and a 10G O/E

611

of a 10G IF R

604

and an OPTAMP R

603

form the receiver of the LT-MUX 1.

The following describes the transmitter and the receiver mentioned above.

FIG. 26

is a block diagram for the transmitter of the LT-MUX 1 forming the long distance system.

The transmitter, as described previously, comprises the 10G E/O S

610

having the high-speed multiplex circuit

682

for converting a 622 Mb/sec, 16-parallel signal to 9.95 Gb/sec signal in a way of a 16-bit multiplex (STM-64) and the electro-optic converter

681

and the OPTAMP S

601

which is an optical amplifier.

As shown in the figure, the embodiment uses an external modulation of electric field absorption type for electro-optic conversion. The OPTAMP S

601

is formed of an optical fiber amplifier. The optical fiber amplifier is separately implemented in its respective package in view of its occupying area and consumption power. The transmitter further has a temperature control circuit

683

and an optical output control circuit

684

so that the long-distance transmission can be made even if environmental conditions around the electro-optic converter

681

and the OPTAMP S

601

change. Description of the transmission operation is ignored as it was already made by reference to FIG.

16

.

FIG. 27

is a block diagram for the transmitter of the LT-MUX 1 forming the short distance system.

The transmitter of the LT-MUX 1 forming the short distance system, as described in the figure, has no OPTAMP S

603

. The 10G IF S

602

, unlike that of the long distance system, uses a semiconductor optical amplifier of preferably smaller size and lower power consumption for optical amplification in the 80-km transmission. The semiconductor optical amplifier can be made to occupy as narrow an area as the modulator with LD, and can be implemented in the 10G IF S

602

shelf. The embodiment, as shown in the figure, uses a modulator of an electric field absorption type for the external modulator. The electric field absorption type modulator is integrated to a module of small size as electric field absorption type device are structurally practical to integrate with the laser diode for the light source.

FIG. 28

is a block diagram for the receiver of the LT-MUX 1 forming the long distance system.

The receiver comprises the OPTAMP R

603

which is an optical amplifier and the 10G O/E

611

having an opto-electric converter

693

and a high-speed demultiplex circuit

692

. The OPTAMP R

630

, as shown in the figure, is made up of an optical fiber amplifier having an optical preamplifier feature, and is separately implemented in its respective board. The opto-electric converter

693

is made up of a front module, an amplifier, a timing extractor, and an dicision circuit. The highspeed demultiplex circuit

692

converts the 9.95 Gb/sec signal to 622 Mb/sec in a way of parallel demultiplex. Description of the reception operation is ignored as it was already made by reference to FIG.

16

.

FIG. 29

is a block diagram for the receiver of the LT-MUX 1 forming the short distance system.

The short distance system is different from the long distance system in that the short distance system has no OPTAMP R

603

and uses an APD

694

for opto-electric conversion. As its APD

694

is capable of higher sensitive reception than Pln-PD, the short distance system needs no optical amplifier, thus resulting in a smaller system.

In turn, if the LT-MUX 1 and the ADM switch are combined to form the small scale switching node

120

as in

FIG. 6

, the high-speed IF shelf, the low-speed IF shelf

700

, and a 40G switch shelf are combined as shown in FIG.

30

. The 40G switch shelf comprises multiplexing circuits

901

for multiplexing the input signals to feed to time-division switches

903

, the time-division switches

903

, and demultiplexing circuits

902

for demultiplexing the signals from the time-division switches

903

. An interface of the multiplexing circuits

901

and the demultiplexing circuit

902

is the intra-equipment interface.

In turn, the signal from the transmission line is processed by the high-speed IF shelf

600

before being directly input to the switch without the low-speed IF shelf

700

. The signal to be dropped into the office, is connected to the low-speed IF shelf

700

. As for the signal to be passed to the another node, it is connected to the high-speed IF shelf

700

before being fed out to another node. That is, the signal from the transmission line is not converted as to interface by the lowspeed interface before being connected to the switch, as usual.

But, the high-speed IF shelf

600

is directly connected with the switch. This can make the equipment smaller.

If the small scale switching node

120

or the large scale switching node

110

is constructed to have the cross-connection switch feature, the 40G switch in

FIG. 30

is replaced by a multi-stage switch configured of a plurality of 40G switch shelves.

As described above, the embodiment can appropriately combine the high-speed IF shelves

600

, the low-speed IF shelves

700

, and the 40G switch shelves

900

in the building block way. This allows accomplishment of a desired equipment with use of the common shelves in a minimized construction. Also, the embodiment allows accomplishment of the 3R-REP 3 by combination of the boards of the high-speed IF shelf

600

as will be described later.

The following describes the surveillance and control system for the LT-MUX 1.

FIG. 31

is a block diagram for extracted parts serving to the surveillance and control system for the LT-MUX 1.

FIG. 32

lists features of the functional blocks.

FIGS. 13

,

14

,

15

, and

16

chart features of the surveillance and control system.

In

FIGS. 31 and 32

, the SVCONT

703

is installed for each low-speed IF shelf. The SEMF

651

, the OpS IF

652

, and RMT IF

653

are equipped in the common a shelf as will be described later.

TABLE 13

FEATURE

DESCRIPTION

NOTE

1

Path setting

(1)

Switch control memory

Control system

is updated to set path

according to the control

message from the operation

system outside equipment.

(2)

Path setting units include:

a. Units of VC-3

b. Units of VC-4

c. Units of VC-4c

(600 M at max)

(3)

This feature is an option for

implementation of cross-

connection feature

2

Software strap

(1)

Control register of each

Control system

setting

section in equipment is

NOTE 1:

updated to set operation

Upon use of

mode (software strap)

section

according to control

protection

message from operation

feature

system outside equipment.

(2)

Major software strap features

include:

a. Transference approval or

inhibition of transmission line

system alarm

b. Threshold of error rate

degradation

c. Protection time of

switching control (NOTE 1)

3

Path test

(1)

Test access point is set to

Control system

confirm continuity and set

quality in units of path

according to the control

message from the operation

system outside equipment.

(2)

Path testing units include:

a. Units of VC-3

b. Units of VC-4

(3)

Test pattern conforms to

CCITT Recommendation

0.151

4

Redundancy

(1)

The operation system switches

Control system

system

over functional components of

Surveillance

switching in

equipment having redundancy

system

equipment

form according to the

control message from

the operation system outside

equipment. (Forced switching)

(2)

As results of equipment

diagnosis, the operation

system switches over

to the protection side

from function component of

equipment judged at failure.

(Autonomous switching)

(3)

Operation modes of

redundancy system include:

a. Automatic mode,

allowing autonomous

switching

b. Forced selection mode

c. Lock-out mode

TABLE 14

FEATURE

DESCRIPTION

NOTE

5

Configuration

(1)

Implementation states of

Surveillance

management

functional components of

system

equipment are monitored,

and the database for con-

figuration management in the

control system is automatically

updated as needed.

(2)

When the implemented

functional component does not

logically match with the physical

implementation position, then an

alarm is issued.

(3)

Management units for functional

components of equipment

include:

a. Board

b. Board group

c. Shelf

6

Alarm

(1)

Transmission line system alarms

Surveillance

transference

are collected from line termi-

system

nation feature blocks and path

connection feature blocks to

detect generation and restoration

of alarms before transmission

line system alarms are

made into an event.

(2)

On basis of diagnosis results of

equipment failure, equipment

alarms are made into an event.

(3)

Contents of these alarms made

into a event are converted to

messages before being informed

to external surveying operation

system.

7

Performance

(1)

Performance information, such

Surveillance

management

as a bit error, are collected

system

from line termination feature

blocks and path connection

feature blocks to calculate

and generate performance

management information

for transmission lines

and paths.

(2)

The performance management

information includes:

a. CV (code violation)

b. ES (errored second)

c. SES (severely errored second)

(3)

Types of registers for history

management includes:

a. 1-sec register

b. 15-min register

c. 1-day register

TABLE 15

FEATURE

DESCRIPTION

NOTE

7

Equipment

(1)

Failure surveillance infor-

Surveillance

diagnosis

mation is collected from

system

functional components

of equipment, and a specific

functional component having

a hardware failure generated

is identified on the basis of

the failure judgement map

provided in the surveillance

and control system.

(2)

Specific functional component

having a hardware failure

generated is logically

disconnected, and the

operation system switches

over from the functional

component of redundancy

configuration to the

protection side.

(3)

Equipment information is

sent out to inform

existence of a functional

component having a failure

generated.

9

Section

(1)

If a section failure happens,

Control system

switching

section switching is controlled

Surveillance

control

on the basis of MSP protocol.

system

(2)

Switching system includes the

MPS:

Multi-

following manners:

plan

a. 1 + 1 (without switch-back)

Section

b. Bi-directional switching

Protec-

(3)

Switching is caused by

tion

include:

a. SF switching (LOS, LOF,

S-AIS, and hardware failure)

b. SD switching (MER)

c. Forced switching

(OpS command)

(4)

This feature is optional.

10

Path switching

(1)

If a path failure is detected

Control system

control

with generation of a failure

Surveillance

in the ring meshed network,

system

section switching is con-

PGP:

Path

trolled on the basis of MSP

Group

protocol.

Protec-

(2)

Switching system includes the

tion

following manners:

a. 1 + 1 (with switch-back)

b. Bilateral switching

(3)

Switching is caused by

include:

a. SF switching (LOP, P-AIS,

and hardware failure)

b. SD switching (MER)

c. forced switching

(OpS command)

(4)

This feature is optional for

implementation of cross-

connection feature.

TABLE 16

FEATURE

DESCRIPTION

NOTE

11

History

(1)

Variety of events generated

Control system

management

as to transmission line

Surveillance

received signals and

system

equipment statuses are

recorded and

managed as history

information.

(2)

History information to be

managed includes:

a. Redundancy system

switching history

b. Signal performance

history

c. APS information

changing history

12

Backup

(1)

If the operation state in

Control system

information

equipment is changed, then

NOTE 1:

management

the changed state is

With use of

automatically recorded in

cross-

nonvolatile memory as the

connection

latest information.

feature

(2)

Information to be recorded

includes:

a. Operation information of

redundancy system

b. Information of software

strap

c. Path setting information

(NOTE 1)

(3)

The following processes are

made with the control

message from the control

operation system

a. Update of backup

information

b. Comparison with statuses

in equipment

c. Initialization of backup

information

13

Emergency

(1)

If it is powered on, equip-

Control system

start-up

ment is autonomously

started up for opera-

tion on basis of backup

information.

14

Communication

(1)

Control is made on com-

Control system

control

munication with the

Surveillance

operation system outside

system

equipment.

(2)

Communication is of a

message form and has a

protocol system on

basis of the Q interface of

CCITT Recommendations.

(3)

Two independent

communication links

are provided, including

the control system

and surveillance system.

15

OpS message

(1)

Control information of

Control system

conversion

message received from

Surveillance

operation system is

system

converted to the command

form specific to equipment.

(2)

Control information and

surveillance information

of the command form

specific to equipment are

converted to information of

message form before being

sent to the operation

system.

FIG. 33

is a block diagram for the redundancy configuration of the transmitting system in the LT-MUX 1.

FIG. 34

is a block diagram for the redundancy configuration of the receiving system in the LT-MUX 1.

In general, operations including AU pointer conversion are nonhitlessly switched. To make this hitless, a hitless switching process is needed. In the embodiment, in view of the balance of the features provided in the whole equipment, the AU pointer conversion process is provided in the intra-office interface and the high-speed interface unit. In the SEL

701

between these is provided a hitless switching process feature section which will be described later. As shown in the figures, simplex sections are optical booster amplifier

601

, 10G IF-S

602

and the SOH

605

in the operation form without the 1+1 section switching in the 10 Gb/sec transmission line.

As the intra-office interface is an interface to be connected with an existing intra-office equipment, the redundance configuration follows the manner of the existing equipment. That is, the redundance configuration is made of the 1+1 section switching type of system

0

/system

1

without switch-back. The board for the intra-office interface accommodates a plurality of highways. Auto-switching at failure is made in units of transmission line. The intra-office interface board, therefore, has working highways and waiting highways mixed therein. For this reason, for interface package maintenance, a hitless forced switching is needed which will be described later.

The SEL

701

, as shown in

FIGS. 23 and 24

, is arranged so that it can be added or removed depending on the situation of transmission line accommodation. The SEL

701

, therefore, is arranged so that it can be automatically switched in units of package in the 1+1 way. Note that if the hitless forced switching which will be described later is made for the SEL

701

, this is hitlessly made by the hitless switching process section.

Now, the following describes the hitless switching process.

FIG. 35

is a block diagram for construction of the hitless switching process feature section for transmission line. Table 17 lists features of functional blocks of the hitless switching process feature section.

TABLE 17

NO.

ITEM

FEATURES

1

AU pointer

AU pointer byte and AU stuff operation

termination

are read. It is instantaneously taken in

without protection of consecutive

coincidence three times.

2

2 × 2 SEL

Selector for passing delayed system

through, but storing preceding system

into VC buffer.

3

VC buffer

FIFO memory for delaying preceding

VC-3, VC-4, and

VC-4-4c data. Adjustable distance

difference is 4 km.

4

VC buffer writing

Writing address counter for VC

control

buffer. Only VC-3, VC-4,

and VC-4-4c data of input signal are

written according to detection of AU stuff.

5

VC buffer reading

VC buffer is read in line to AU stuff of

control

the delayed system. If delay insertion

is needed to increase in

phase synchronizing pull-in course,

positive stuff is added. If it is

needed to decrease, negative stuff

is added.

6

Delay insertion

Delay insertion of FIFO is calculated

calculation

through calculation of the writing

address minus reading address.

7

Phase difference

Transmission delay difference

detection

is detected by comparison of AU

pointer values.

8

Delay insertion

Result of delay insertion calculation is

control

compared with result of phase difference

detection. If it is necessary to increase

delay insertion, positive stuff is added

on VC buffer reading side.

If it is necessary to decrease delay

insertion, negative stuff is added on the

VC buffer reading side. 2 × 2 SEL

is controlled depending on the direction

of the delay difference generation.

9

Pointer calculation

New pointer value is calculated by

comparison of the VC in-put phase of the

VC buffer with output frame phase.

10

Pointer insertion

New pointer value is written in VC buffer

output signal.

Following specific patterns are written in

predetermined positions.

(1) On generation of stuff:

Inversion of bits 1 and 0.

(2) On jump of pointer:

Sending of NDF pattern.

(3) On AU-4 or AU-4-4c:

CI concatenation indicator).

(4) On sending of P-AIS:

All 1 of all bytes.

As depicted in Table 17, the hitless switching process feature section makes the received data, including VC-3, VC-4, and VC-4-c data, of the system having less transmission delay of systems

0

and

1

delay in FIFO memory (VC buffer) as necessary. This makes contents of the output signals of both systems coincide. Detection of the transmission difference is made by comparison of the pointer values. Adjustment of the delay insertion of the FIFO is made with stuff operation of the AU pointer so gradually that the signal of the working system will not be hit while the phase synchronizing pull-in is made in maintaining the protection system. In writing into the VC buffer, the AU pointer is terminal once before only the VC-3, VC-4, and VC-4-c data are written in the VC buffer. In reading from the VC buffer, on the other hand, reading is made along with the operation of the AU stuff in line with that of the AU stuff in the delayed line. In a phase synchronized state, thus, the system

0

can be made to coincide with the system

1

perfectly not only in the phases of the output VC signals, but also the timings of the AU stuffs. This means that the hitless switching can be made securely even if the frequency of the AU stuff is higher.

The VC buffer is a kind of AU pointer converting circuit. At the time of output, a new AU pointer value is calculated before being inserted into the AU. The calculation principles are the same as those of the usual pointer converting circuit. As the adjustable transmission delay difference is 4 km, the process cannot only be applied to the intra-office transmission line, but also to a short or intermediate inter-office transmission line. Thus, in the SEL, the hitless switching process feature section is constructed so that it cannot be used for switching the intra-office interface, but also for switching the 10 Gb/sec transmission line interface.

7. Description of 3R-REP

FIG. 36

is a block diagram for a construction of the 3R-REP 3. Table 18 lists features of functional blocks of the 3R-REP 3.

TABLE 18

ITEM

DESCRIPTION

Main signal

Transmission rate

9953.28 Mb/sec (equivalent to

interface

STM-64)

Transmission line

Scrambled binary NRZ

code

(non-return to zero)

Error rate

Lower than 10

−11

/repeater.

Light source

1.552 μm ± 0.001 μm

wavelength

Average light

+10 to +12 dBm

output

Maximum detectable

Higher than −7 dBm

power

Minimum detectable

Lower than −27 dBm

power

Surveillance and control method

Surveillance and control

signal transference by

1.48 μm wavelength

multiplexed signal.

Implementation of

surveillance control section

in main signal unit.

Physical implementation method

300 mm high with 4 shelves per

frame (1800 × 795 × 600 mm).

Cooling method

Push-pull type forced air

cooled type, with large fan.

Accommodation of systems

One system per shelf, with one

bidirectional system of west

and east.

Environmental conditions

Temperature:

10 to 40° C.

Humidity:

20 to 80%.

Input power condition

−42 to −53 V

The 3R-REP 3 makes regeneration through its optical preamplication, O/E conversion, E/O conversion, and optical booster amplification. The 3R-REP 3 also makes the surveillance, alarm transference, and remote maintenance for the 1R repeater section and the 3R repeater section with use of the 1.48 μm surveillance and control light and the RSOH (regenerator section overhead. The boards used in the main signal system are all the same as those of the LT-MUX 1.

8. Implementation of the 1R-REP, LT-MUX, and 3R-REP

The following describes implementation of the 1R-REP 2, LT-MUX 1, and 3R-REP 3.

First, implementation of the 1R-REP 2 is described below.

FIG. 37

is a front view for an implementation of the 1R-REP 2.

A rack of the embodiment, as shown in the figure, has three shelves each of which contains two 1R-REP 2 systems, or six 1RREP 2 systems in total. Each system comprises two subsystems: the repeaters

301

and

302

. For an unattended office which needs remote monitor and control, these are implemented in the same shelf as the system to which the OpS IF

651

and the like serve. Note that a power source board

810

is for the optical preamplifier

301

and the optical booster amplifier

320

.

FIG. 38

is structures of the optical preamplifier

301

and optical booster amplifier

320

forming a single 1R-REP 2 system. The optical preamplifier

301

and the optical booster amplifier

320

, as shown in

FIG. 37

, occupy two-fold and four-fold widths in reference to a standard board width respectively, or six-fold width in total. They are naturally air-cooled. Note that a TEC drive circuit in

FIG. 38

is a circuit added to the pumping light source to control a temperature adjustment for thermoelectron cooling devices.

Implementation of the LT-MUX 1 is described below.

FIG. 39

is a front view for an implementation of the LT-MUX 1.

The construction shown is for accomplishing the transmission line 1+1 redundancy system switching. The functional boards of the high-speed IF unit

600

and the low-speed IF unit

700

, as shown in the figure, are all doubled as in a working system

0

and a waiting system

1

.

FIG. 40

is a front view for an implementation of two systems of the LT-MUX 1 in a single rack without the redundancy configuration.

The 10G IF R

604

package and the 10G IF S

602

board, as shown in the figure, are of two-fold wide as these have many components. Similarly, the OPTAMP R

603

board and the OPTAMP S

601

board are of two-fold wide.

FIG. 41

is a front view for an implementation of the LT-MUX 1 for constructing the small scale switching node

120

with the 40G switch unit built in as shown in

FIG. 6

b.

In this case, as shown in the figure, are implemented two highspeed interface units

600

, a duplexed 40G switch unit

900

, and a duplexed low-speed IF unit

700

. The 40G switch unit

900

, as shown in

FIG. 42

, is three-dimensionally constructed in view of the flow of its signals. That is, a plurality of boards MUX/DMUX containing a plurality of multiplex/demultiplex circuits

901

and

902

and a time-division switch (TSW)

903

, are three-dimensionally connected together with use of a subpanel for a time switch unit. This construction can be made small.

Implementing the 40G switch into the shelf is made in a way that the TSW

903

is put in front, the 40G switch unit

900

is put into the shelf, and the MUX/DMUX board

901

/

902

is connected with other units on the rear side of the shelf.

FIG. 43

a

is a front view for an implementation of the LT-MUX 1 for constructing the large scale switching node

110

with a multi-stage switch meshed network of a plurality of the 40G switch units built therein.

In this case, as shown in the figure, a plurality of racks have the 40G switch units, the high-speed IF units

600

, and the lowspeed IF units

700

built therein so that the high-speed IF units

600

, and the low-speed IF units

700

can be connected with the switch multi-stage network.

Finally,

FIG. 44

is a front view for an implementation of the 3RREP 3.

As shown in the figure, a single rack has four shelves each of which contains a main signal board, including OPTAMP R

603

, 10G IF R

604

, 10G IF S

602

, and OPTAMP S

601

packages, and a common section, such as an OpS IF

651

. This construction allows a single shelf to complete all the features of a single equipment. It is possible to easily increase or remove the equipment in shelf units as needed.

As described so far, the present invention can flexibly build up the optical transmission system depending on capacities and function required.

Number	Name	Date	Kind
4680776	Ikeuchi et al.	Jul 1987	A
4979234	Agrawa et al.	Dec 1990	A
5043976	Abiven et al.	Aug 1991	A
5113459	Grasso et al.	May 1992	A
5227908	Henmi	Jul 1993	A
5291326	Heidemann	Mar 1994	A
5300328	Rehfuss	Apr 1994	A
5315426	Aoki	May 1994	A
5327275	Yamane et al.	Jul 1994	A
5339187	Nelson	Aug 1994	A
5343320	Anderson	Aug 1994	A
5343464	Iino et al.	Aug 1994	A
5396360	Majima	Mar 1995	A
5440418	Ishimura et al.	Aug 1995	A
5500756	Tsushima et al.	Mar 1996	A
5535037	Yoneyama	Jul 1996	A
5546213	Suyama	Aug 1996	A
5555477	Tomooka et al.	Sep 1996	A
5668658	Hamada	Sep 1997	A
6018405	Tomooka et al.	Jan 2000	A
6266169	Tomooka et al.	Jul 2001	B1

Number	Date	Country
0 440 276	Jan 1991	EP
57-4625	Jan 1982	JP
1-7727	Jan 1989	JP
2-266245	Oct 1990	JP
2-297027	Dec 1990	JP
3-62638	Mar 1991	JP
3-214936	Sep 1991	JP
3-258038	Nov 1991	JP
3-267829	Nov 1991	JP
3-270520	Dec 1991	JP
4-29123	Jan 1992	JP

	Number	Date	Country
Parent	09/409872	Oct 1999	US
Child	09/907939		US
Parent	09/244856	Feb 1999	US
Child	09/409872		US
Parent	08/746027	Nov 1996	US
Child	09/244856		US
Parent	08/705366	Aug 1996	US
Child	08/746027		US
Parent	08/044425	Apr 1993	US
Child	08/705366		US

	Number	Date	Country
Parent	08/023546	Feb 1993	US
Child	08/044425		US

Optical transmission system constructing method and system

Information

Patent Number

Date Filed

Date Issued

Inventors

Original Assignees

Examiners

Agents

CPC

US Classifications

Field of Search

US

International Classifications

Disclaimer

Term Extension

Abstract

Description

Claims

Priority Claims (1)

Parent Case Info

US Referenced Citations (21)

Foreign Referenced Citations (11)

Non-Patent Literature Citations (2)

Continuations (5)

Continuation in Parts (1)

Entry
Saito, Prechirp Technique for Dispersion Compensation for a High-Speed Long-Span Tranmission; IEEE (1991) vol. 3, No. 1.
Kazuo Aida, et al.; IM/DD Optical Transmission Systems Using Optical Amplifiers; NTT R&D vol. 40, No. 2, 1991.