KR20150144280A

KR20150144280A - Wavelength tuning sequences in time and wavelength division multiplexing - passive optical network

Info

Publication number: KR20150144280A
Application number: KR1020150082701A
Authority: KR
Inventors: 이한협; 두경환; 김광옥; 이상수
Original assignee: 한국전자통신연구원
Priority date: 2014-06-16
Filing date: 2015-06-11
Publication date: 2015-12-24
Also published as: KR102017882B1

Abstract

A wavelength tuning method in a time and wavelength division multiple-passive optical network (TWDM-PON) with a plurality of operable channels is refined. First, after the second channel is added as an operation channel in the TWDM-PON in which at least the first channel is operated, the OLT providing the service to the ONU through the first channel requests the change to the second channel. Then, the ONU determines whether a downstream wavelength of the second channel is recorded. As a result of the determination, the ONU transmits a wavelength tunable message indicating that the wavelength tunable message can be transmitted to the OLT, initiates wavelength tuning to the second channel, or transmits a wavelength tunable non-tunable message to the OLT.

Description

[0001] Wavelength tuning sequences in time and wavelength division multiplexing [

The present invention relates to a time and wavelength division multiplexing-passive optical network (TWDM-PON), and more particularly, to a wavelength tuning procedure for adding a channel operating in a TWDM- .

Passive optical network (PON) is a subscriber network that connects domestic and subscribers in a point-to-multipoint manner, and is economically superior because it can reduce the required national system and optical cable compared to a one-to-one connection structure.

(Time Division Multiplexing - Passive Optical Network (TDM-PON)) such as EPON (Ethernet Passive Optical Network) and GPON (Gigabit capable PON) It is characterized by the use of an optical splitter that does not require power for connecting subscribers, especially for connection between subscribers and the national government. Because of this feature, TDM-PON has been widely deployed and successfully deployed around the world. Dual GPONs were distributed in North America and Europe. In 2010, ITU-T issued the G.987 XG-PON standard recommendation, which is 10G-GPON. FSAN (Full Service Access Network), a group consisting of major telecommunication carriers and equipment manufacturers related to optical subscriber network technology, is a pre-standardization group of ITU-T SG15 Q2 group. Recently, it has developed a next generation passive optical network (NG- (PON) is adopted as the main technology of the ITU-T, and the G.989.x standard recommendation is discussed in ITU-T.

1 is a block diagram of a conventional passive optical network (TDM-PON) (corresponding to an optical line terminal (OLT) and an XGPON OLT in FIG. 1) and a P-to- (Corresponding to an optical time domain reflectometer), and an RF video overlay (corresponding to the RF Video HE of FIG. 1), can be accommodated in one network. In the system configuration of Fig. 1, NG-PON2 (corresponding to NG-PON2 OLT port-1, ..., NG-PON2 OLT port-n in Fig. 1) has a hybrid configuration combining TDM and WDM. NG-PON2 is a structure that accommodates a plurality of same services or heterogeneous service links using optical signals of various wavelengths. It can expand the transmission capacity in proportion to the number of optical wavelength channels without changing the optical distribution network used in the existing TDM network There are advantages to be able to.

Referring to FIG. 1, the TWDM-PON network indicated as NG-PON2 is a hybrid passive optical network that accommodates the national office system including n OLTs using different wavelengths. Assuming that each national office system accommodates one PON link, one optical distribution network accommodates n identical or heterogeneous networks, and each service is divided into wavelength bands of signals to be used. At this time, the TWDM-PON ONU (NG-PON2 ONU) receives wavelength multiplexed downlink optical signals transmitted from a plurality of TWDM-PON OLTs. Also, in order to communicate with a specific TWDM-PON OLT, it is necessary to be able to select the wavelength of the upstream signal corresponding thereto. Therefore, the ONU should be equipped with a wavelength selectable transceiver, that is, a tunable transceiver. A tunable transceiver includes a tunable laser and a tunable receiver.

FIG. 2 is a conceptual diagram of a TWDM-PON, which is a main technique of a next generation passive optical network. In FIG. 2, there are n optical line terminals (OLTs) having different wavelengths to be used. Each OLT receives a single PON link . One optical distribution network accommodates n TDM-PON networks, and each TDM-PON link can be distinguished according to the individual wavelengths used.

One or more optical network units (ONUs), for example, ONU A using the same wavelength (downward? _D1 , upward? _U1 ) in the system of FIG. 2 are in communication with OLT # 1 using the same wavelength, Can be connected to the OLT # 2. The upstream signal is transmitted to the OLT using a wavelength matched to the downstream signal selected by each ONU or a wavelength indicated by the wavelength allocation information received from the OLT. Upstream signals transmitted by the plurality of ONUs are separated by wavelengths by a demultiplexer To the corresponding OLT.

On the other hand, since the downlink signals are multiplexed by the wavelength multiplexer, downlink signals of all downlink wavelengths are input to the respective ONUs, and each ONU utilizes only downlink signals of specific wavelengths among all input downlink wavelengths. To do this, the ONU needs to select the wavelength of the downlink signal, and it is also necessary to synchronize the wavelength tunable receiver with the downlink signal of the selected wavelength. The wavelength tuning process of the ONU is being standardized in ITU-T G.989.3, which is an international standard. The ONU receives a downlink signal through synchronization with a selected downlink signal, and based on the received downlink signal, It is possible to establish and communicate with the OLT.

In the TWDM-PON system, it is possible to increase or decrease the number of operating channels, that is, a pair of downstream wavelengths and upstream wavelengths, for load balancing or efficient system management in each channel. For example, in the case of a large number of service users in the TWDM-PON, all four channels are used. However, if the number of service users decreases or the amount of required traffic decreases after that, The number can be reduced.

Fig. 3 is an example schematically showing such a scenario. ₃ , a service is provided through downstream wavelengths (λ ₁ , λ ₂ , λ ₃ ,..., Λ _n ) of all channels in a normal stage. However, in a power saving stage, The downstream wavelengths (? ₂ ,? ₃ , ...,? _N ) of the channel are discontinued and the service is provided only through the downstream wavelength? ₁ of the remaining channels. By turning off the power of the optical transceiver of the OLT (NG-PON2 OLT Port-2, NG-PON2 OLT Port-3, ..., NG-PON2 OLT Port-n in FIG. 3) for the unused channel, Power consumption can be reduced.

As another example, in the case of the TWDM-PON, only a small number of channels are used at first, but if the number of service users increases or the amount of required traffic increases thereafter, the number of channels used for ensuring quality of service is added It is possible. That is, a telecommunication service provider providing Internet service using the TWDM-PON can initially increase the number of channels to use only one channel but gradually operate in order to reduce the system operation cost. Fig. 4 is an example schematically showing such a scenario. Referring to FIG. 4, in an initial stage, a service is provided through a downward wavelength (λ ₁ ) of one channel. In the intermediate stage, a downward wavelength (λ ₁ , λ ₂ ) Service is provided and finally the service is provided through downstream wavelengths (λ ₁ , λ ₂ , λ ₃ , ..., λ _n ) of all channels in the final stage.

However, as in the initial stage or intermediate stage of FIG. 4, only ONUs newly activated in the TWDM-PON in which only a part of the channels are operated recognize and record only the downstream wavelength currently being serviced in the activation stage. Then, the ONU transmits the upstream signal to the OLT using the upstream wavelength corresponding to the recognized downstream wavelength. Since the number of subscribers increases or traffic increases, the OLT increases the number of channels for providing services and also performs wavelength change or wavelength tuning with a newly added channel to some or all of the ONUs Command or request.

FIG. 5 is a block diagram of the proposed ITU-T Recommendation G.989.3 (for Consent, 4), which is a draft of the current ITU-T G.989.3 draft, more specifically G.989.3, which is being standardized in the ITU- April 2014). &Lt; / RTI > The wavelength tuning procedure shown in Fig. 5 is performed in the first channel lambda 1, u allocated to the OLT port 1 (OLT-port1) to the second channel lambda 2d, u allocated to the OLT port 2 (OLT- When the channel is changed. Referring to FIG. 5, the OLT, more specifically, the OLT-port 1 sends a wavelength tuning request message, for example, a Tuning Control (Request) PLOAM message requesting a change to the second channel (λ 2 d, u) to the ONU 1. Here, the second channel lambda 2d, u is a newly added channel as an operating channel after the ONU 1 is activated in the TWDM-PON.

The ONU 1, which has received the request message through the downstream wavelength lambda 1d of the first channel lambda 1 d, u, determines whether or not the wavelength can be changed and transmits a response message including the determination result to the first channel lambda 1 d, To the OLT-port1 through the wavelength lambda 1u. Typically, when the ONU 1 can perform a wavelength change request, it responds with a wavelength tunable message, for example, a Tuning_Response (ACK) PLOAM message. If the wavelength change request can not be performed, a wavelength tunable message such as Tuning_Response ) Reply with PLOAM message. However, in the above-described situation, the ONU 1 which is requested to change the channel can not transmit a tunable non-tunable message, for example, a Tuning_Response (NACK) PLOAM message to the OLT-port1 (S11). In the activation step of establishing the link through the first channel lambda 1 d, u, the ONU 1 recognizes and records information on the downward wavelength of the channel being served at that time, but the newly added channel, , u) are not recorded. As a result, according to the existing wavelength tuning procedure, when the number of channels served by the system is added, the ONU that has been receiving the service can not change to the added channel.

A problem to be solved by the present invention is that, in a system in which multiple channels can be operated, such as a TWDM-PON system, an ONU establishing a link to a specific channel transmits a downward wavelength different from the downward wavelength And to provide a wavelength tuning procedure that can be changed to an added channel even when the channel is further operated.

In a time and wavelength division multi-passive optical network (TWDM-PON) having a plurality of operable channels, a wavelength tuning method according to an embodiment of the present invention includes: (a) Transmitting to the ONU a wavelength tuning request message in which an OLT providing a service to the ONU through the first channel requests a change to the second channel after the two channels are added as an operation channel; The ONU receiving the tuning request message may determine whether a downward wavelength of the second channel is recorded and the ONU may perform a wavelength change when it is determined that the downward wavelength of the second channel is recorded A wavelength tunable message is transmitted to the OLT and a wavelength change to the second channel is started or a downstream wavelength of the second channel is not recorded If it is determined that the ONU can not perform the wavelength change, the ONU transmits a wavelength tunable message to the OLT.

According to an aspect of the embodiment, the wavelength tunable non-message message may include a wavelength tunable non-tunable code indicating a reason why the ONU can not change the wavelength. And the wavelength tunable code may indicate one in the group consisting of unready status, out of transmit wavelength range, out of receive wavelength range, out of transmit and receive wavelength range, and lack of wavelength channel calibration information.

According to another aspect of the present invention, the wavelength tuning request message may include a new indicator code indicating whether the second channel is a channel to be newly added to the operation channel.

According to still another aspect of the present invention, if it is determined that the downstream wavelength of the second channel is not recorded in the step (b) before the step (c), the ONU transmits the reception wavelength of the wavelength tunable receiver And (e) the ONU may record the detected downstream wavelength.

According to another aspect of the present invention, before transmitting the wavelength tuning request message of the step (a), the OLT transmits a wavelength re-search request message to the ONU requesting the OLT to search for the downstream wavelength again And (g) transmitting the wavelength re-search completion message to the OLT after the ONU having received the wavelength re-search request message performs the re-search for the downward wavelength.

According to still another aspect of the present invention, after the step (c), (h) the OLT that has received the wavelength tunable message transmits to the ONU a wavelength re-search request message requesting a redraw of the downstream wavelength (I) the ONU having received the wavelength re-search request message performs a re-search for a downstream wavelength, and then transmits a wavelength re-search complete message to the OLT; and (j) And transmitting to the ONU a wavelength tuning request message in which one OLT requests a change to the second channel. In this case, the step (h) includes the steps of (k) transmitting to the ONU a wavelength information request message requesting the wavelength information in which the OLT having received the wavelength tunable message is received, and (l) Transmitting the wavelength information response message including the wavelength information recorded in response to the wavelength information request message to the OLT.

According to still another aspect of the present invention, after the step (c), (m) transmitting, from the OLT having received the wavelength tunable message, a reactivation request message requesting the ONU to perform the activation procedure again (n) transmitting an activation completion message to the OLT after the ONU having received the reactivation request message performs an activation procedure, and (o) when the OLT having received the activation completion message changes to the second channel And transmitting the wavelength tuning request message to the ONU again. In this case, (p) transmitting to the ONU a wavelength information request message requesting the wavelength information in which the OLT having received the wavelength tunable non-receipt message before the step (m) Transmitting the wavelength information response message including the wavelength information recorded in response to the wavelength information request message to the OLT.

According to the embodiment of the present invention described above, in a system in which multiple channels can be operated, such as a TWDM-PON system, an ONU establishing a link to a specific channel is different from a downstream wavelength It is possible to change to an added channel even if the downstream wavelength channel is further operated. Therefore, when additional channels are operated in the TWDM-PON system, the existing ONUs can be serviced by the added channels, thereby enabling efficient system operation such as traffic distribution.

FIG. 1 is a diagram illustrating a configuration of an optical subscriber network capable of accommodating a plurality of heterogeneous services into one network by applying a wavelength multiplexing scheme to a conventional passive optical network.
2 is a diagram showing an example of the configuration of the TWDM-PON system.
3 is a diagram schematically illustrating an example of a scenario in which the number of channels used decreases with time in the TWDM-PON system.
4 is a diagram schematically illustrating an example of a scenario in which the number of channels used gradually increases with time in the TWDM-PON system.
FIG. 5 is a flowchart showing a part of an existing wavelength tuning procedure that can occur in the scenario of FIG.
6 is a flowchart showing a wavelength tuning procedure according to an embodiment of the present invention in a TWDM-PON.
7 is a diagram showing an example of the configuration of a Tuning_Response (NACK) PLOAM message, which is an example of a wavelength tunable message.
8 is a diagram showing an example of the configuration of a Tuning Control (Request) PLOAM message, which is an example of a wavelength tuning request message.
9 is a flowchart showing a wavelength tuning method according to the first embodiment.
10 is a state diagram of an ONU showing an activation procedure of an ONU including an operation and a tuning block.
11 is a diagram for explaining a search process for a downward wavelength in an operation step.
12 is a flowchart illustrating a wavelength tuning method according to the second embodiment.
13 is a diagram showing a configuration of a calibration request PLOAM message.
14 is a flowchart illustrating a wavelength tuning method according to the third embodiment.
15 is a flowchart illustrating a wavelength tuning method according to the fourth embodiment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The terms used in this specification are terms selected in consideration of functions in the embodiments, and the meaning of the terms may vary depending on the user, the intention or custom of the operator, and the like. Therefore, the meaning of the terms used in the following embodiments is defined according to the definition when specifically defined in this specification, and unless otherwise defined, it should be interpreted in a sense generally recognized by those skilled in the art. In the following description, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the technical concept of the present invention unnecessarily obscure.

6 is a flowchart showing a wavelength tuning procedure according to an embodiment of the present invention in a TWDM-PON. In FIG. 6, the TWDM has a plurality of operable channels. At present, at least the first channel is operated but the second channel is not operated. In this case, the ONU is connected to the PON and activated. In the activation process, the ONU searches for downstream wavelengths of the channels operating in the TWDM-PON. Therefore, the ONU recognizes and records the downstream wavelength of the channel operating in the TWDM-PON including the first channel through the search, but the downward wavelength of the channel that is not operated including the second channel is detected through the search I can not do it, and I do not record it as a result.

Referring to FIG. 6, a second channel is added as an operation channel to a TWDM-PON in which at least a first channel is operated (S10). According to the present embodiment, there is no particular limitation on the reason why two channels are added as an operation channel. For example, the number of subscribers may increase and / or the amount of traffic required may increase, thereby adding a channel that the OLT services. To add a channel, the OLT can either install a new line card or use a method to supply power to the optical transceiver of a channel that is already installed but is not being used.

Then, the OLT transmits a wavelength tuning request message to the ONU requesting the change from the first channel to the newly added second channel to the ONU (S11). For example, the wavelength tuning request message includes the current ITU-T G.989.3 draft, more specifically the draft of G.989.3, which is being standardized in ITU-T Study Group 15 (Title: Draft new recommendation ITU-T G Tuning_Control (Request) PLOAM (Physical Layer Operation Administration and Management) message described in IEEE 802.3 (for Consent, 4 April 2014) can be used. The wavelength tuning request message may include information for identifying a channel to be changed, that is, a second channel. Whether or not the message is sent to an ONU can be specified by the ONU-ID included in the wavelength tuning request message.

Subsequently, the ONU that has received the wavelength tuning request message from the OLT determines whether the downstream wavelength of the second channel is recorded in itself (S12). Normally, the ONU records only the downstream wavelength recognized in the previous activation process, so that the downward wavelength of the newly added channel in the TWDM-PON is not recorded. Accordingly, in this case, the ONU determines that the downstream wavelength of the second channel is not recorded and transmits a wavelength tunable non-tunable message to the OLT that wavelength tuning is not possible (S13). The Tuning_Response (NACK) PLOAM message described in the above G.989.3 draft can be used as the wavelength tunable message.

However, in some cases, the ONU may have an opportunity to rediscover the downstream wavelengths of the channels operating in the TWDM-PON after the second channel is added to the TWDM-PON as an operating channel. For example, the ONU may perform a rediscovery in response to an explicit rediscovery request from the OLT, or a rediscovery of the downstream wavelength in the process of reactivating in response to a request to reactivate from the OLT. Such a re-search request or a reactivation request may be performed after the addition of the operation channel in step S10 or after receiving the wavelength tunable message of step S13. As another example, if the ONU performs a periodic / aperiodic re-search according to an internal algorithm, or if it is determined in step S12 that the downstream wavelength of the second channel is not recorded, the wavelength tunable non- It is also possible to perform the re-search without transmitting. An implementation for performing the rediscovery of such a downstream wavelength will be described later in detail.

Subsequently, when it is determined in step S12 that the downstream wavelength of the second channel is recorded, the ONU transmits a wavelength tunable message to the OLT (S14). As the wavelength tunable message, the Tuning_Response (ACK) PLOAM message described in the above G.989.3 draft can be used. Then, the ONU starts a procedure for changing the wavelength to the second channel according to a predetermined procedure (for example, the procedure described in the above-mentioned G.989.3) (S15).

According to an aspect of the present embodiment, the wavelength tuning disable message transmitted to the OLT by the ONU in step S13 may include information indicating the reason why the wavelength of the ONU can not be changed. For example, a wavelength tunable message may include a wavelength tunable code. The wavelength tunable non-transmission message transmitted to the step S13 may include a wavelength tunable non-tunable code indicating that the wavelength can not be changed because the wavelength information of the channel requested by the OLT is not included in the wavelength information recorded in the ONU have. For example, the ONU may include a wavelength tunable non-tunable code meaning "NACK by lacking calibration information" in the wavelength tunable non-tunable message.

7 is a diagram showing an example of the configuration of a Tuning_Response (NACK) PLOAM message, which is an example of a wavelength tunable message. 7, a Tuning Response (NACK) PLOAM message includes an ONU-ID field octet 1-2, a message type field octet 3, a sequence number field octet 4, an operation code field octet 5, Field octet 6, a wavelength tuning result field octet 7, a target wavelength field octet 8, a padding field octet 9-40, and a MIC (Message Integrity Check) field octet 41-48.

7 is a specific example of the response code field (octet 6). In the conventional Tuning Response (NACK) PLOAM message, a wavelength tunable code is included to indicate a specific reason why wavelength change is not possible. Message See the draft of ITU-T G.989.3 above). More specifically, the wavelength tunable non-tunable code may be a NACK by not ready yet, a NACK by out of supported TX tuning range, a NACK by out of supported RX tuning range, The NACK may be directed to one of either the supported TX and RX tuning range and the NACK by lacking wavelength channel (calibration information).

According to another aspect of the present invention, the wavelength tuning request message to which the OOL is transmitted to the ONU in step S11 may include information on the new wavelength added in step S10. As described above, the wavelength tuning request message includes information for identifying a channel to be changed, that is, a second channel. The wavelength tuning request message may also include information indicating whether the second channel is a channel to be newly added to the operation channel, for example, a new instruction code. The new instruction code may have a value consisting of a predetermined number of bits or bytes.

8 is a diagram showing an example of the configuration of a Tuning Control (Request) PLOAM message, which is an example of a wavelength tuning request message. 8, the Tuning Control (Request) PLOAM message includes an ONU-ID field octet 1-2, a message type field octet 3, a sequence number field octet 4, an operation code field octet 5, The counted fields octet 7-8, the rollback field octet 9, the target downward wavelength field octet 10-12, the target upward wavelength field octet 13-15, the new instruction code field octet 16, octet 17-40, and a Message Integrity Check (MIC) field (octets 41-48).

The Tuning Control (Request) PLOAM message shown in FIG. 8 differs from the existing Tuning Control (Request) PLOAM message (see the above-mentioned ITU-T G.989.3 draft) in that it includes a new indication code. More specifically, the new indication code may indicate a normal channel tuning request, or may direct a channel tuning request (calibrate the target channel first and tune to the target channel). If the new indication code indicates a normal channel tuning request, the ONU transmits a wavelength tunable message to the OLT as in step S13 when the downstream wavelength of the second channel is not recorded. On the other hand, when the new instruction code indicates the channel tuning after searching, the ONU can perform the procedure after step S12 after first searching for the downward wavelength of the second channel. These new instruction codes are exemplary only and may be represented by various values depending on the implementation.

Next, implementation examples of the wavelength tuning method according to the embodiment of the present invention described with reference to FIG. 6 will be described. Therefore, the description of the embodiment described above with reference to FIG. 6 can be applied to the matters not described in detail in the following embodiments.

9 is a flowchart showing a wavelength tuning method according to the first embodiment. In the embodiment of FIG. 9, information on the downward wavelength of the second channel added as the operation channel is not recorded in the ONU. In this case, the ONU performs a search for the downward wavelength itself.

Referring to FIG. 9, a second channel is added as an operation channel to a TWDM-PON in which at least a first channel is operated (S20). The OLT transmits a wavelength tuning request message to the ONU requesting the change from the first channel to the newly added second channel to the ONU (S21). The ONU, which has received the wavelength tuning request message from the OLT, determines whether the downstream wavelength of the second channel is recorded in itself and confirms that the downstream wavelength of the second channel is not recorded (S22).

According to this embodiment, the ONU performs the search for the downward wavelength again while changing the wavelength of the wavelength tunable receiver (S23). In the process of rediscovering the downstream wavelength, a physical synchronization is attempted by searching for a downstream signal, and the wavelength of the downstream signal is recorded. If a downward wavelength of the second channel is searched for in the rediscovery of the downstream wavelength in step S23, the ONU transmits a wavelength tunable message to the OLT in response to the response message (S24). Then, the ONU starts a procedure for changing the wavelength to the second channel according to a predetermined procedure (for example, the procedure described in the above-mentioned G.989.3) (S25). On the other hand, although not shown in the figure, if the downstream wavelength of the second channel can not be found in the rediscovery process for the downstream wavelength in step S23, the ONU transmits a wavelength tunable message to the OLT as a response message.

Thus, according to the present embodiment, the ONU performs search for the downward wavelength in step S23. In this case, the ONU can perform an operation during the activation procedure of the ONU under discussion in the standardization process of G.989.3 and a search for the downward wavelength in the tuning block (operating tuning block) to search for the downstream wavelength. 10 is a state diagram of an ONU showing an activation procedure of an ONU including such an operation and a tuning block.

As another example, the ONU may perform a search for a downward wavelength in an operation state (Operation State, O5) of an ONU activation procedure described in the aforementioned G.989.3 to search for a downward wavelength. FIG. 11 is a diagram for explaining a search process for the downward wavelength in this operation step, and the state diagram of FIG. 10 is connected to each other by symbols 1, 2 , and 3 .

Referring to FIG. 11, the ONU enters a pending state upon receiving a wavelength change request during an operating state. If the super frame counter is matched within a short period of time, it enters the tuning state (O8) and performs physical synchronization (Psync) and profile learning (profile learning).

On the other hand, if the time required for the wavelength tuning is very long, the ONU enters the intermittent LODS state (O6) since the loss of the downlink signal, that is, the loss of data signal (LODS) occurs. If the synchronization with the downstream signal is not made even after entering the intermediate signal loss state (O6) and the TO2 timer time has elapsed, the ONU returns to the initial state (Initial State, O1, see Fig. 10). That is, the entire activation procedure is performed again.

In order to solve this problem, it is necessary to know the time required to change the wavelength of the wavelength tunable transceiver of the ONU in the intermediate signal loss state (O6), and wait for this time. The wavelength change time of the wavelength tunable transceiver of the ONU is classified into Class 1, Class 2, and Class 3 according to the G.989.2 standard. Each class, namely, the transmit / The time corresponding to the channel tuning time class (Classes of Tx / Rx Wavelength Channel Tuning Time) is shown in Table 1 below.

When the tuning time class of the ONU is 1, the ONU receiving the wavelength change request enters the tuning state (Tuning State, O8). When the tuning time class of the ONU is 2 or 3, the superframe counter matching condition is not satisfied, and therefore, it enters the intermediate signal loss state (Intermittent LODS state, O6). In this case, the TO2 timer used in the intermediate signal loss state is determined in consideration of the tuning time class of the wavelength tunable transceiver of the ONU. On the other hand, the ONU can recognize the tuning time class of the wavelength tunable transceiver and adjust the time of the TO2 timer accordingly. Alternatively, it is also possible to set a new timer in addition to the existing TO2 timer.

When this tuning time class is used, it can be applied to the operation in the operation and tuning block described with reference to Fig. More specifically, the OLT and the ONU recognize the tuning time class mutually, and can take this into consideration in the operation and operation in the tuning block. In order for the OLT and the ONU to mutually recognize the tuning time class, it is possible to exchange information using a predetermined message, for example, a PLOAM message.

In the embodiment shown in FIG. 9, when the ONU performs the search for the downward wavelength of S23, there may be a disconnection of the service that is already provided through the first channel. That is, the data packet to be transmitted to the OLT due to the search for the downward wavelength, i.e., the uplink signal, can not be transmitted, and thus the service may be delayed. To prevent this, the ONU may have a memory of an appropriate size. Alternatively, the service delay may be minimized by sequentially searching for some wavelengths at predetermined time intervals without searching all the wavelengths at the time of searching for the wavelength of S23.

The above-described wavelength re-search procedure described in connection with the first embodiment can be applied to the case where the ONU searches for the downward wavelength in other embodiments described later.

12 is a flowchart illustrating a wavelength tuning method according to the second embodiment. 12 is a case in which a wavelength search request is transmitted to an ONU before a wavelength change request is made when the OLT adds a new operation channel. In this case, the ONU transmits a wavelength search request to the ONU in response to a wavelength search request, Perform a search.

Referring to FIG. 12, a second channel is added to the TWDM-PON in which at least the first channel is operated as an operation channel (S30). In step S31, the OLT informs the ONU that the second channel is newly added as the operation channel in the first channel and transmits a message requesting the OLT to perform the search for the downlink signal wavelength again, such as a wavelength search request message. Therefore, the wavelength search request message includes information on the newly added channel (at least information on the downward wavelength of the corresponding channel).

The wavelength search request message can be a message in a predetermined format, but there is no particular limitation in this embodiment. However, the wavelength search request message may indicate a wavelength search or a PLOAM message including information of this purpose may be used. The wavelength search request message may be individually transmitted to each ONU, or may be transmitted to all ONUs in a broadcast manner.

FIG. 13 is a diagram illustrating a configuration of a calibration request PLOAM message, which is an example of such a wavelength search request message. 13, the calibration request PLOAM message includes an ONU-ID field (octet 1-2), a message type field (octet 3), a sequence number field (octet 4), a vendor- 8, a bend serial number field octet 9-12, an upstream wavelength channel ID field octet 13, a correlation ID field octet 14-15, a target downlink / uplink wavelength field octet 16, a padding field octet 17, -40), and a Message Integrity Check (MIC) field (octet 41-48).

Subsequently, the ONU receiving the wavelength search request message from the OLT searches for the downstream wavelength again while changing the wavelength of the wavelength tunable receiver (S32). In the process of rediscovering the downstream wavelength, a physical synchronization is attempted by searching for a downstream signal, and the wavelength of the downstream signal is recorded. The ONU transmits a wavelength search complete message to the OLT as a response message (S33). At this time, the ONU transmits a wavelength search completion message to the OLT through the upward wavelength that has been used for the upstream communication. And the wavelength search complete message may indicate the completion of the wavelength search or a PLOAM message containing information of this purpose may be used.

Subsequently, the OLT having received the wavelength search completion message transmits a wavelength tuning request message to the ONU (S34). And the subsequent process may proceed according to the procedure of step S12 shown in Fig.

14 is a flowchart illustrating a wavelength tuning method according to the third embodiment. The embodiment of FIG. 14 is a case where the OLT transmits a wavelength search request to the ONU when the ONU transmits a wavelength tunable message to the OLT in response to the wavelength tuning request message from the OLT. Also in this case, the ONU performs a search for the downward wavelength in response to the wavelength search request from the OLT.

Referring to FIG. 14, a second channel is added as an operation channel to a TWDM-PON in which at least a first channel is operated (S40). The OLT transmits a wavelength tuning request message to the ONU requesting a change from the first channel to the newly added second channel to the ONU (S41). Then, the ONU receiving the wavelength tuning request message from the OLT judges whether the downstream wavelength of the second channel is recorded in itself, and confirms that the downstream wavelength of the second channel is not recorded (S42). The ONU transmits a wavelength tunable message to the OLT (S43).

Upon receipt of the wavelength tunable message, the OLT transmits to the ONU a message requesting to send the currently recorded wavelength information, for example, a wavelength information request message (S44). The wavelength information request message may be, for example, a message requesting wavelength information or a PLOAM message containing information of this purpose. In response to the received wavelength information request message, the ONU transmits a wavelength information response message including information on the downlink wavelength recorded by the ONU to the OLT (S45). The wavelength information response message may be a message in a predetermined format including information on the downstream wavelength, for example, a PLOAM message including such information. The process of steps S44 and S45 may be omitted as an optional process.

Then, the OLT compares the wavelength information received from the ONU with the wavelength information of the channels providing the service. If the two wavelengths do not coincide with each other, the OLT transmits a message requesting that the search for the downlink signal wavelength be performed again, for example, a wavelength search request message to the ONU (S46). The wavelength search request message can be a message in a predetermined format, but there is no particular limitation in this embodiment. However, the wavelength search request message may indicate a wavelength search or a PLOAM message including information of this purpose may be used.

Subsequently, the ONU receiving the wavelength search request message from the OLT searches for the downstream wavelength again while changing the wavelength of the wavelength tunable receiver (S47). In the process of rediscovering the downstream wavelength, a physical synchronization is attempted by searching for a downstream signal, and the wavelength of the downstream signal is recorded. The ONU transmits a wavelength search complete message to the OLT as a response message (S48). At this time, the ONU transmits a wavelength search completion message to the OLT through the upward wavelength that has been used for the upstream communication. And the wavelength search complete message may indicate the completion of the wavelength search or a PLOAM message containing information of this purpose may be used. Subsequently, the OLT having received the wavelength search completion message transmits a wavelength tuning request message to the ONU (S49). And the subsequent process may proceed according to the procedure of step S12 shown in Fig.

15 is a flowchart illustrating a wavelength tuning method according to the fourth embodiment. In the embodiment of FIG. 15, when the ONU transmits a wavelength tunable message to the OLT in response to the wavelength tuning request message from the OLT, the OLT requests the ONU to reactivate. In this case, the ONU performs a re-search for the downstream wavelength in the process of performing the reactivation procedure.

Referring to FIG. 15, a second channel is added as an operation channel to a TWDM-PON in which at least a first channel is operated (S50). Then, the OLT transmits a wavelength tuning request message to the ONU requesting the change from the first channel to the newly added second channel to the ONU (S51). Then, the ONU receiving the wavelength tuning request message from the OLT determines whether the downstream wavelength of the second channel is recorded in itself, and confirms that the downstream wavelength of the second channel is not recorded (S52). The ONU transmits a wavelength tunable message to the OLT (S53).

Then, the OLT having received the wavelength tunable message transmits to the ONU a message of requesting the ONU to perform the activation procedure again, for example, a reactivation request message to the ONU (S54). The reactivation request message may be a message of a predetermined format, but there is no particular limitation in this embodiment. However, the reactivation request message may indicate a reactivation procedure, or a PLOAM message containing information of this purpose may be used.

Subsequently, the ONU that has received the reactivation request message from the OLT performs the reactivation procedure (S55). During the reactivation procedure, the wavelength of the tunable receiver is changed in the physical synchronization process, and the search for the downstream wavelength is performed to record the wavelength of the downstream signal. The ONU transmits a reactivation completion message to the OLT as a response message (S56). At this time, the ONU can transmit the reactivation completion message to the OLT through the upward wavelength that has been used for the upstream communication. And the reactivation completion message may indicate the completion of the wavelength re-search or a PLOAM message including information of this purpose may be used. The OLT having received the wavelength search completion message transmits a wavelength tuning request message to the ONU (S57). And the subsequent process may proceed according to the procedure of step S12 shown in Fig.

According to the wavelength tuning method according to the fifth exemplary embodiment of the present invention, the OLT can periodically or optionally use an algorithm for receiving the wavelength recording status from the ONU and transmitting a wavelength tuning request message based on the received wavelength tuning status. For example, the OLT and the ONU may operate according to the following procedure.

1. First, the OLT requests the ONU to transmit the currently recorded wavelength information. For example, the US_WLCH_info PLOAM message defined in G.989.3 can be used for the transmission of wavelength information.

2. When the ONU transmits the wavelength information, the ONU compares the received wavelength information with the wavelength information of the channel on which the ONU itself provides the service.

3. If the wavelength information of the OLT and the wavelength information received from the ONU do not match, the OLT requests the ONU to search for the downstream wavelength again. For example, the calibration request PLOAM message shown in FIG. 13 may be used for a redraw request for the downstream wavelength.

According to the wavelength tuning method according to the sixth embodiment of the present invention, when the ONT transmits a wavelength tunable message in response to a wavelength tuning request message received from the OLT and the OLT receives a wavelength tunable message from the ONU, An algorithm for transmitting a search request message can be used. For example, the OLT and the ONU may operate according to the following procedure.

1. The OLT sends a wavelength tuning request to the ONU.

2. The ONU responds to the received wavelength tuning request with wavelength tuning disabled, and simultaneously transmits the recorded wavelength information to the OLT.

3. The OLT that has received the wavelength tuning disable message from the ONU transmits the wavelength search request to the ONU.

The above description is only an example of the present invention, and the technical idea of the present invention should not be interpreted as being limited by this embodiment. The technical idea of the present invention should be specified only by the invention described in the claims. Therefore, it is apparent to those skilled in the art that the above-described embodiments may be modified and embodied in various forms without departing from the technical spirit of the present invention.

Claims

A wavelength tuning method in a time and wavelength division multiple-passive optical network (TWDM-PON) having a plurality of operable channels,
(a) After a second channel is added as an operation channel in a TWDM-PON in which at least a first channel is being operated, an OLT serving the ONU through the first channel transmits a change to the second channel Transmitting a requesting wavelength tuning request message to the ONU;
(b) the ONU receiving the wavelength tuning request message determines whether a downstream wavelength of the second channel is recorded; And
(c) if it is determined that the downward wavelength of the second channel is recorded, the ONU transmits a wavelength tunable message to the OLT capable of performing wavelength change and starts changing wavelength to the second channel Or transmitting a wavelength tunable non-tunable message to the OLT that the ONU can not perform a wavelength change if it is determined that the downstream wavelength of the second channel is not recorded.

The method according to claim 1,
Wherein the wavelength tuning disable message includes a tunable non-tunable code that indicates a cause of the wavelength tunable non-change of the ONU.

3. The method of claim 2,
Wherein the wavelength tunable code indicates one of a group consisting of a non-ready state, a transmission wavelength out of range, a reception wavelength out of range, a transmission and reception wavelength out of range, and a lack of wavelength channel calibration information.

The method according to claim 1,
Wherein the wavelength tuning request message includes a new indication code indicating whether the second channel is a channel newly added to the operation channel.

2. The method of claim 1, wherein before step (c)
(d) if it is determined in the step (b) that the downward wavelength of the second channel is not recorded, the ONU searches for a downward wavelength while changing a reception wavelength of the wavelength tunable receiver; And
(e) The ONU further comprises recording the searched downstream wavelength.

The method of claim 1, further comprising: prior to transmitting the wavelength tuning request message of step (a)
(f) transmitting, to the ONU, a wavelength re-search request message requesting the OLT to search for a downward wavelength; And
(g) transmitting the wavelength re-search completion message to the OLT after the ONU having received the wavelength re-search request message performs the re-search for the downward wavelength.

2. The method of claim 1, wherein after step (c)
(h) transmitting, to the ONU, a wavelength re-search request message in which the OLT having received the wavelength tuning disable message requests a re-search for a downward wavelength;
(i) the ONU having received the wavelength re-search request message performs a re-search for a downward wavelength and then transmits a wavelength re-search complete message to the OLT; And
(j) transmitting to the ONU a wavelength tuning request message in which the OLT having received the wavelength search completion message requests to change to the second channel.

8. The method of claim 7, wherein before step (h)
(k) transmitting to the ONU a wavelength information request message requesting the wavelength information in which the OLT receives the wavelength tunable message; And
(1) The ONU transmits a wavelength information response message including wavelength information recorded in response to the wavelength information request message to the OLT.

2. The method of claim 1, wherein after step (c)
(m) transmitting a reactivation request message requesting the OLT, which has received the wavelength tuning disable message, to request the ONU to perform the activation procedure again;
(n) transmitting an activation completion message to the OLT after the ONU having received the reactivation request message performs the activation procedure; And
(o) transmitting to the ONU a wavelength tuning request message in which the OLT having received the activation completion message requests the change to the second channel.

10. The method according to claim 9, wherein before step (m)
(p) transmitting, to the ONU, a wavelength information request message for requesting wavelength information on which the OLT receives the wavelength tunable message; And
(q) transmitting, by the ONU, a wavelength information response message including wavelength information recorded in response to the wavelength information request message to the OLT.