CN100384123C - A Gigabit Passive Optical Network System - Google Patents

Abstract

The invention discloses a gigabit passive optical network system, which includes an optical network line terminal, and a plurality of optical network units or optical network terminals, wherein the optical receiving module in the optical network line terminal, and the optical network unit or The optical sending module in the optical network terminal adopts an optical module whose burst time is less than 512ns; send time. The invention requires low cost and simpler system implementation.

Description

A Gigabit Passive Optical Network System

technical field

The present invention relates to a passive optical network system (PON, Passive Optical Network), more specifically, the present invention relates to a kind of Gigabit passive optical network (GPON, Gigabit PON) system.

Background technique

PON technology is an optical access technology developed to support point-to-multipoint applications. Generally, a PON system consists of an optical line terminal (OLT, Optical Line Termination), an optical network unit/optical network terminal (ONU/ONT, Optical Network Unit/Optical Network Termination) and Optical Distribution Network (ODN, Optical Distribution Network). Its essential feature is that the ODN is all composed of passive components. The passive feature makes network deployment more flexible, without the need for equipment rooms and power supplies; the feature of shared optical fiber can save a lot of optical fiber resources, making the cost of access network lines lower; and The structure of pure optical media and transparent optical fiber broadband network make it possible to maintain technical security for future business expansion.

Since its birth, PON technology has been divided into APON (based on ATM), BPON (based on ATM), GPON (based on ATM and GEM), and GEPON (based on Ethernet) according to different data link layer protocols. Among them, APON technology is the most mature. However, the service provision capability is limited and the cost performance is low, which cannot meet the long-term development, and only meets the current access needs of some specific areas; the advantages of EPON/GEPON are simplicity, high speed, low cost, and wide range of users, and the technology and products are relatively GPON To be mature, the problem that needs to be solved is to improve the technical maturity and further reduce the cost; the advantages of GPON are transparent transmission, high speed and high efficiency, and carrier-class service, which is the trend of technological development.

In the existing GPON system, when the optical module transmits from no optical signal to optical signal, the operating point of the optical drive circuit takes a certain time to establish due to factors such as circuit capacitance; at the same time, it takes time to turn off the laser. The normal circuit set-up and turn-off time is on the order of mS, and the improved circuit reaches the order of uS. In order to achieve nS level of work, higher difficulty is required, and some new control technologies need to be adopted. Therefore, every time the index requirement is raised, the technology and cost will be higher.

The burst reception of the optical burst receiving module is even more difficult. In addition to the similar reasons for the above-mentioned burst transmission, it is also more difficult to achieve burst reception due to the large dynamic range of optical reception. In the case of scope, its burst time indicator takes more time.

In addition, reception in the OLT requires fast clock recovery from the data, such as obtaining a recovered clock within a few bits of data. Burst clock recovery (BCDR, Burst CDR) requires the use of complex new technologies and high technical costs. For example, it requires a higher-speed chip process and a new implementation method. Currently, there are no commercial products that meet the requirements. This fast BCDR can only be achieved by designing with some higher-priced, high-performance devices.

In summary, due to the high requirements on the optical burst time and optical reception establishment time of the optical transmission and reception optical modules, for example, when transmitting 1.24416Gbit/s signals, the ONU/ONT fall time is required to be less than 12ns; the OLT end burst reception Settling time is less than 36ns. The cost of the GPON system realized at present is relatively high, and the system design is relatively difficult.

Contents of the invention

The technical problem solved by the invention is to provide a gigabit passive optical network system to reduce the cost of GPON system implementation and the difficulty of system design.

In order to solve the above problems, the gigabit passive optical network system of the present invention includes an optical network line terminal, and a plurality of optical network units or optical network terminals, wherein the optical receiving module in the optical network line terminal, and The optical transmission module in the optical network unit or optical network terminal adopts an optical module with a burst time less than 512ns; and

The preamble of the data frame encapsulated by the optical network unit or the optical network terminal is configured with a predetermined length to adapt to the burst time of the optical module.

Optimally, the optical module is an optical module of an Ethernet passive optical network EPON.

Optionally, the preamble of the optical network unit or optical network terminal is configured to a predetermined length in the following manner:

The optical network line terminal sets the preamble of the uplink frame data of the optical network unit or the optical network terminal to a predetermined length through its control management channel OMCI to the optical network unit or the optical network terminal; or

The optical network unit or the optical network terminal fixedly configures the preamble with a predetermined length; or

The optical network line terminal sets the preamble of the uplink frame data of the optical network unit or the optical network terminal to a predetermined length through the service channel; or

Optionally, the optical line terminal, optical network unit or optical network terminal configures the predetermined length of the preamble through software.

Optionally, the optical line terminal sends data to the optical network unit or the optical network terminal in a broadcast manner.

Optionally, the optical network unit or optical network terminal determines and processes the received data through address matching.

Optionally, the optical network unit or optical network terminal transmits data to the optical line terminal using a time division multiple access protocol.

Compared with the prior art, the present invention has the following beneficial effects:

In the present invention, an optical module with a large dynamic range (optical burst time<512ns) can be used in the OLT and ONU/ONT to transmit and receive data, and at the same time, the optical network unit/optical network terminal (that is, the optical network unit/optical network terminal, down The same) the preamble of the encapsulated data frame is configured as a predetermined length to adapt to the burst time of the optical module, which can ensure that the data is sent and received correctly, compatible with high-cost and low-cost optical modules, and the system implementation is simpler;

In addition, in the preferred embodiment of the present invention, the optical module of Ethernet Passive Optical Network (EPON, Ethemet Passive Optical Network) can be used in the GPON system, which can meet the burst time requirements of the GPON system for the optical module. The cost of the optical module of the network is lower, and the system realization technology is more mature. Compared with the prior art, the system realization cost of the present invention is lower, and the system design is simpler.

Description of drawings

Fig. 1 is the composition schematic diagram of GPON system of the present invention;

Fig. 2 is a GPON system data frame structure;

Figure 3 is the internal data frame structure of the uplink T-CONT of the GPON system;

Fig. 4 is a schematic diagram of the principle of increasing the length of the preamble Preamble to ensure data reception in the present invention.

Detailed ways

Referring to FIG. 1 , this figure is a schematic diagram of the composition of the GPON system of the present invention.

As shown in the figure, the GPON system consists of an OLT located at the central office and a group of associated ONU/ONT located at the client end. The ONU/ONT is located at the user end (the difference is that the ONT is directly located at the user end, and there are other network such as Ethernet). Between them is an ODN composed of optical fibers and passive optical splitters or connectors. The direction from OLT to ONU/ONT is the downlink direction, and vice versa is the uplink direction. As shown in Figure 1, the transmission and processing process of the downstream data flow and the upstream data flow in the GPON system are different. The downstream data is broadcast from the OLT to each ONU/ONT, and each ONU/ONT is determined by the address matching in the data packet/data unit. Process relevant data. Due to the sharing feature of the ODN, the processing of the upstream data flow is more complicated. In order to prevent collisions, it is necessary to coordinate the transmission flow from each ONU/ONT to the OLT. The uplink data is transmitted according to the control mechanism in the ONU/OLT, and the time division multiple access protocol is adopted. This protocol allocates dedicated transmission time slots to each ONU/ONT. These time slots are synchronized, so the data streams from different ONTs will not Collision occurs.

In the present embodiment, the optical receiving module of OLT and the optical transmitting module of ONU/OLT have all adopted the optical module of EPON network, and promptly burst time is greater than 12ns, but the burst optical module less than 512ns, when concrete implementation, in the present invention Optical modules with other indicators can also be selected, so I won’t go into details here. Table 1 shows the burst time indicators of optical modules in the existing EPON and GPON standards:

Table I

Ordinary optical module Achievable Low Cost Burst Module EPON standard GPON standard Ton/Toff(ns) >1000 40～500 <512 <12

In order to adapt to the burst time requirement of the optical module (in this embodiment, it is the optical module burst time of the Ethernet passive optical network), the data encapsulated by the optical network unit/optical network terminal in the present invention The preamble of frame is configured as predetermined length, guarantees that data can be sent and received correctly in GPON system, during concrete realization, the present invention makes Preamble length be greater than system intrinsic burst time (EPON burst sends and is set up and closes by increasing the length of preamble Preamble) Time + EPON burst receiving time + BCDR recovery time), the data can be sent and received correctly to ensure the normal operation of the system.

The details will be described below with reference to FIG. 2 , FIG. 3 and FIG. 4 .

Referring to Fig. 2, the figure shows the data frame structure of the GPON system.

OLT sends continuous data stream Downstream to ONT/ONU, and each ONU receives data in different time slots; ONU sends upstream data stream Upstream to OLT. When sending data, each ONU uses a different time segment, through time division multiplexing send;

T-CONT1, T-CONT2, etc. are the upstream data streams sent by each ONU/ONT to the OLT; the data in each T-CONT is the data of the same ONU/ONT; the ONU/ONT can occupy multiple T-CONT data packets; each Keep a certain interval between T-CONT;

The US BWMap field in the downstream data stream contains the start and end positions of each T-CONT of the upstream data stream in the slot segment in the upstream data stream.

Referring to Figure 3, this figure is the internal data frame structure of the uplink T-CONT in the GPON system.

The uplink T-CONT frame contains multiple fields, such as: physical layer overhead field PLOu, physical layer operation management and uplink data flow management PLOAMu, uplink power level sequence (PLSu), uplink data dynamic bandwidth reporting DBRu, digital payload Field Payload;

Among them, PLOu also specifically includes: preamble Preamble, delimiter Delimter, bit interleaved check BIP of uplink frame, ONU identification field ONU-ID, indication field Ind;

Referring to Fig. 4, through the analysis of the ONU/ONT upstream data transmission process, it can be seen that there will be many factors affecting the function of data transmission and reception.

First, the impact of optical burst transmission: As shown in Figure 4a, when an ONU/ONT optical module transmits data in a burst, due to the need for a certain work setup time, the front part of the transmitted data will not be correct. After the data in Figure 4b is sent, the optical data output in Figure 4c is obtained; the data in the AB section of Figure 4c will be incorrect data. Different optical modules have different AB ranges.

Secondly, the impact of optical reception: When the OLT optical module receives data in a burst, the size and time of the sending signal of each ONU/ONT are different, and it is necessary for the optical reception to respond quickly and output the correct high and low levels. Due to the limitation of the dynamic response time of the optical module and the circuit, some of the previous data received by the input will not be received correctly. As shown in Figure 4d and Figure 4e in Figure 4, the AC segment signals sent upstream by the ONU/ONT cannot be received correctly. Different optical modules receive different AC ranges.

In this way, if the lost valid data is lower than the data length of the Preamble of the preamble, the system can also receive it correctly; for the existing GPON system, due to the limited time of the required AC segment (<90bit, 1.25Gb/s), the system It is necessary to use high-cost and high-performance ONU optical transmission modules and OLT optical reception modules.

And use the optical module of EPON network in the present embodiment, preamble code is configured as predetermined length when ONU/OLT encapsulates data, makes the length of preamble code Preamble in the uplink data frame structure long enough, to adapt to described Ethernet wireless The burst time of the optical module of the source optical network, so that the data after the preamble can be received correctly. During specific implementation, those skilled in the art will know that the length of the preamble Preamble can be changed in the following ways:

1) The optical network line terminal sets the preamble of the uplink frame data of the optical network unit/optical network terminal to a predetermined length through its control management channel OMCI to the optical network unit/optical network terminal; or

2) The optical network unit/optical network terminal is fixedly configured with a preamble of a predetermined length; or

3) The optical network line terminal sets the preamble of the uplink frame data of the optical network unit/optical network terminal to a predetermined length through the service channel;

In addition, the system in the present invention can also support software configuration of the Preamble length.

The above descriptions are only preferred embodiments of the present invention, and do not constitute a limitation to the protection scope of the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the claims of the present invention.

Claims (6)

1. kilomega passive optical network system, include the optical network line terminal, and a plurality of optical network units or Optical Network Terminal, it is characterized in that, Optical Receivers in the described optical network line terminal, and the optical transmission module in optical network unit or the Optical Network Terminal adopts the optical module of burst time less than 512ns; And

The lead code of the Frame of described optical network unit or Optical Network Terminal encapsulation is configured to predetermined length, to adapt to the described optical module burst time.

2. kilomega passive optical network system according to claim 1 is characterized in that, described optical module is the optical module of Ethernet passive optical network EPON.

3. kilomega passive optical network system according to claim 1 and 2 is characterized in that, the lead code that disposes optical network unit or Optical Network Terminal by following manner is a predetermined length:

The optical network line terminal is a predetermined length by the lead code that its control and management passage OMCI to optical network unit or Optical Network Terminal is provided with the uplink frame data of optical network unit or Optical Network Terminal; Or

Optical network unit or Optical Network Terminal fixed configurations lead code are predetermined length; Or

The optical network line terminal is a predetermined length by the lead code that service channel is provided with the uplink frame data of optical network unit or Optical Network Terminal; Or

Optical line terminal, optical network unit or Optical Network Terminal are predetermined length by the software arrangements lead code.

4. the unglazed source network of gigabit according to claim 1 and 2 system is characterized in that, optical line terminal sends data with broadcast mode to optical network unit or Optical Network Terminal.

5. the unglazed source network of gigabit according to claim 4 system is characterized in that, the data that described optical network unit or Optical Network Terminal are definite by matching addresses and processing receives.

6. the unglazed source network of gigabit according to claim 1 and 2 system is characterized in that, described optical network unit or Optical Network Terminal adopt time division multiple access protocol to transmit data to described optical line terminal.

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