JPH09214541A - Optical subscriber transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase a transmission capacity selectively and stepwise while utilizing an existing optical transmission line and an ONU resource by including type information of an optical network unit into a frame sent/received by a framer. SOLUTION: A subscriber station equipment 2 has N-sets of framers and is configured to be a single star using the framers independently of each ONU. A frame sent/received by each framer is made up of a common OAM cell, an individual information cell and a dummy cell. Bits not in use for a PON system in the common OAM cell are used for type identification of the ONU. When the connected ONU is recognized as existing ONUs 11 and so on for the conventional PON system, a frame interchangeable with a frame of the PON system is sent/received by using part of a payload. When the connected ONU is recognized as broad band ONUs 21-2M located newly, a frame consisting the common OAM cell and the individual information cell.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical subscriber transmission system using a star type topology, and particularly to an existing P
Regarding the transition from narrowband services to wideband services by the ON system.

[0002]

2. Description of the Related Art PON (Passiv) is used as an optical subscriber transmission system for economically providing a narrow band service such as a telephone.
An e-Optical Network) system has been proposed, and development for practical use is being actively conducted. In the PON system, as shown in FIG. 6, the subscriber terminal device 1 and N optical network units ONU 11 to 1 are used.
Passive double star (Passive) for distributing / multiplexing a 1-to-N optical transmission system between N (Optical Network Units) via a passive splitter 10.
It has a Double Star (PDS) configuration and downlink signals are time division multiplexed (Time Division Mul).
time-division multiple access (TDM), and upstream signals are time division multiple access (TDM).
Access: TDMA) to perform user multiplexing. Thus, by sharing the optical transmission line between the station building / splitter and the optical transmitter in the station building among the N ONUs 11 to 1N, economicization can be achieved. However, in recent years, there has been a tendency to install a splitter inside the station building.
Optical A at T's Telecom 95
It is written in the exhibition material of ccess Networks.

FIG. 5 shows an example of a frame structure in a PON system. In the PON system shown in the figure, time-axis compression bidirectional multiplexing (Ti
meCompression Multiplexin
g: TCM). The first half of one frame is for downlink transmission, and is composed of a common OAM cell which is downlink information common to all ONUs and downlink individual information cells to ONUs 1 to N. An ONU is placed between the individual information cell and the end of the frame.
Dummy cells are inserted in order to avoid a decrease in clock extraction capability in 1 to N. The latter half of one frame is for upstream transmission, and is composed of a common OAM cell that is the upstream information common to all ONUs and the upstream individual information cells from ONUs 1 to N. In upstream transmission, a dummy cell is not used because highly accurate clock extraction from a data signal is unnecessary.

Since the PON system is compatible with narrow band services such as telephone calls, it is necessary to increase the transmission capacity per ONU in order to support wide band services such as images.

Conventionally, as a method of increasing the transmission capacity of a PON system, a method of using transit length multiplexing and a method of increasing time division multiplexing have been proposed. The former allocates a wavelength to each ONU or each service by using the high-density wavelength division multiplexing in the wavelength band not used for the narrow band service. The latter is a method in which low-speed bursts for narrow-band services are mixed with high-clock-rate bursts for wide-band services as shown in FIGS. 7 and 8, and the 5th Conference on Opti is used.
ca1 / Hybrid Access Network
s Lecture No. 6.03 and 6th Interna
regional Worthshop on Optica
l Access Networks talk number 2.4.

[0006]

However, if an attempt is made to provide a broadband service stepwise by adding wavelength division multiplexing to an existing PON system, a large amount of expensive light sources and wavelength selection elements for wavelength division multiplexing are required. It must be used while performing temperature control that requires power consumption, which makes the subscriber line terminal equipment and ONU very expensive and large.

When high-speed bursts are mixed in low-speed bursts for transmission, the number of parts of the downlink frame that can be received by the existing ONUs in the downstream frame decreases, so that the existing low-speed ONUs are reduced. The clock extraction capability at the point of time deteriorates. Further, in the upstream line, it is necessary to speed up the burst-compatible optical receiver whose reception sensitivity deteriorates as compared with the receiver for continuous signals, and practically sufficient reception sensitivity is obtained in the subscriber line terminal equipment. Becomes difficult.

An object of the present invention is to provide an optical subscriber transmission system capable of selectively and gradually increasing the transmission capacity while utilizing the existing optical transmission line and ONU assets as a PON system.

[0009]

A subscriber line terminal equipment having N framers mounted thereon, and N optical network units connected in a one-to-one correspondence with each of the N framers, An optical subscriber transmission system is configured by including the type information of the optical network unit in the frame transmitted and received by the framer.

Part of the optical network unit is an existing one for the PON system, and the rest is a new one.
The existing optical network unit and the newly added new optical network unit can operate at the same clock speed.

In the present invention, since the framer is not a PON that is shared by all ONUs but a single star configuration that is used independently for each ONU, the transmission capacity per ONU is large. Since the frame structure used in the PON can be used as it is, a user who does not want to increase the transmission capacity can utilize the existing ONU as it is.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an explanatory diagram showing a frame structure in a first embodiment of an optical subscriber transmission system of the present invention,
FIG. 2 is a block diagram showing a network configuration in the second embodiment of the optical transmission system of the present invention.

PO using the TCM shown in FIGS. 5 and 6.
ONU1 with N system already installed and connected
Some of the 1 to 1N require increased transmission capacity. The system configuration shown in FIG. 2 is obtained by performing the following replacements in the system.

The existing subscriber line terminal equipment 1 is replaced with the subscriber line terminal equipment 2 of the present invention. Since the subscriber line terminal equipment 2 accommodates N optical transmitters / receivers, the splitter 1 is abolished, and N optical fiber cables connected to the N ONUs and the subscriber line terminal equipment 2 Each of the N optical transmitters / receivers is connected to each other in a one-to-one manner to form a single star configuration. For ONUs that require increased transmission capacity,
Replace with broadband ONUs 21 to 2M. The transmission rate of frames transmitted and received by the subscriber line terminal device 2 and the broadband ONUs 21 to 2N is the same as that of the existing subscriber line terminal device 1 and ON.
It is the same as that of U11 to 1N.

The operation after replacement will be described with reference to FIG. The subscriber terminal device 2 has N framers. As a result of the replacement, the framer has a single-star configuration that uses each frame independently for each ONU.
The payload that can be occupied by the platform has increased almost N times.
As shown in FIG. 1, the frame transmitted / received by each framer is composed of a common OAM cell, an individual information cell, and a dummy cell. The common OAM cell in FIG. 1 is compatible with the common OAM cell in the PON system shown in FIG. 3, but an unused bit for the PON system in the common OAM cell is used to identify the type of the connected ONU. To use.

When the connected ONUs are recognized as the existing ONUs 11 to 1N for the conventional PON system, as shown in FIG. Send and receive frames that are compatible with PON system frames.

When the connected ONU is recognized as the newly installed broadband ONUs 21 to 2N, the common O
Send and receive new frames consisting of AM cells and wideband individual information cells.

Thus, in the optical subscriber transmission system described in the first embodiment, by applying the present invention, the existing optical transmission line and ON as a PON system are applied.
While utilizing U assets, the transmission capacity is being selectively and gradually increased.

Next, a second embodiment of the present invention will be described. FIG. 3 is an explanatory diagram showing a frame structure in the first embodiment of the optical subscriber transmission system of the present invention, and FIG. 4 is a block diagram showing a network structure in the second embodiment of the optical transmission system of the present invention. is there.

Although a two-core ATM-PON system using independent fibers for downlink signal transmission and uplink signal transmission has been already installed, some of the connected ONUs 11 to 1N require an increase in transmission capacity. Therefore, the system configuration shown in FIG. 4 is obtained by performing the same replacement as in the first embodiment.

That is, the subscriber line terminal equipment 2 is the subscriber line terminal equipment of the present invention, and accommodates N optical transceivers. The optical transmitters / receivers in the N ONUs are connected to the optical transmitters / receivers in the subscriber line terminal equipment 2 in a one-to-one correspondence by N pairs of optical fiber cables, and have a single star configuration. . The ONUs 21 to 2M are newly connected broadband ONUs. The transmission rate of frames transmitted and received by the subscriber line terminal device 2 and the broadband ONUs 21 to 2N is the same as that of the existing subscriber line terminal device 1 and the ONUs 11 to 11.
It is the same as that of 1N.

The operation of the second embodiment will be described with reference to FIG. The subscriber terminal device 2 has N framers. As shown in FIG. 1, the frame transmitted and received by each framer is composed of a common OAM cell, an individual information cell, and a dummy cell for downlink, and each unit cell has the same structure as an ATM cell. The upstream frame is composed of a common OAM cell and an individual information cell, and each unit cell is an ATM cell to which a guard bit for collision prevention, a preamble for bit synchronization, and a delimiter for burst frame synchronization are added. Is. Common O
The AM cell is compatible with the common OAM cell in the PON system that has been traditionally installed, but it is not possible to use an unused bit for the PON system in the common OAM cell for identifying the type of the connected ONU. This is similar to the first embodiment.

When the connected ONU is recognized as the ONUs 11 to 1N already installed for the old PON system, as shown in FIG. 3 (a), the old ONUs are installed by using a part of the payload. Send and receive frames that are compatible with PON system frames.

When the connected ONUs are recognized as newly installed broadband ONUs 21 to 2N, common O
Send and receive new frames consisting of AM cells and wideband individual information cells.

Thus, also in the optical subscriber transmission system described in the second embodiment, by applying the present invention, the existing optical transmission line and ON as the PON system are applied.
While utilizing U assets, the transmission capacity is being selectively and gradually increased.

In the first embodiment, TCM is used to multiplex upstream and downstream signals, and in the second embodiment spatial multiplexing using two optical fibers is used. Other multiplexing means such as wavelength multiplexing using different wavelength bands may be used.

The first embodiment is intended for a TCM non-ATM-PON system as an existing PON system, and the second embodiment is intended for a spatially multiplexed ATM-PON system as an existing PON system. The present invention can also be applied to an ATM-PON system of TCM and a non-ATM-PON by spatial multiplexing or wavelength multiplexing.

[0028]

As described above, according to the present invention, it is possible to increase the transmission capacity without using an expensive large-scale device and without lowering the clock extraction capability or the receiving sensitivity. it can. That is, it is possible to provide an optical subscriber transmission system capable of selectively and gradually increasing the transmission capacity while utilizing the existing optical transmission line and ONU assets as the PON system, which is extremely useful.

[Brief description of drawings]

FIG. 1 is a frame structure in a first embodiment of an optical subscriber transmission system of the present invention.

FIG. 2 is a network configuration diagram in the first embodiment of the optical subscriber transmission system of the present invention.

FIG. 3 is a frame structure in the second embodiment of the optical subscriber transmission system of the present invention.

FIG. 4 is a network configuration diagram in the second embodiment of the optical subscriber transmission system of the present invention.

FIG. 5 is a frame structure of an existing PON system.

FIG. 6 is a network configuration diagram of an existing PON system.

FIG. 7 is a conventional frame structure.

FIG. 8 is a network configuration diagram of a conventional example.

[Explanation of symbols]

1 subscriber line terminal equipment in existing PON system 2 subscriber line terminal equipment of the present invention 8 high-speed frame compatible subscriber line terminal equipment 10 splitter ONU11 to 1N optical network unit in existing PON system ONU21 to 2M existing PON system Wideband optical network unit with the same clock speed ONU31-3M Optical network unit supporting high-speed frames

Claims (7)

[Claims] 1. A subscriber line terminal device equipped with N framers, and N optical network units connected to each of said N framers in a one-to-one correspondence, for transmitting and receiving said framers. An optical subscriber transmission system characterized in that the frame contains type information of the optical network unit. 2. An optical network unit according to claim 1, wherein a part of the optical network unit is an existing one for a PON system and the rest is a new one, and the existing optical network unit and the new optical network unit operate at the same clock speed. Optical subscriber transmission system characterized by being possible. 3. The optical subscriber transmission system according to claim 1, wherein the downlink frame is a burst signal. 4. The optical subscriber transmission system according to claim 1, wherein the downlink frame is a continuous signal. 5. The optical subscriber transmission system according to claim 4, wherein the upstream frame is a burst signal. 6. The optical subscriber transmission system according to claim 4, wherein the upstream frame is a continuous signal. 7. The optical transmitter / receiver in the subscriber line terminal equipment according to claim 1, wherein an array optical transmitter / receiver in which a plurality of optical transmitters are integrated in one module or a plurality of optical receivers is provided. Any of the array optical receiver integrated in the module of
The optical subscriber transmission system according to claim 1, wherein both of them are used.