KR20160024782A

KR20160024782A - network synchronization apparatus and method on passive optical access network

Info

Publication number: KR20160024782A
Application number: KR1020150117886A
Authority: KR
Inventors: 김경수; 마상수
Original assignee: (주)텔리언
Priority date: 2014-08-26
Filing date: 2015-08-21
Publication date: 2016-03-07

Abstract

The present invention relates to an apparatus and method for network synchronization in a passive optical network for frequency synchronization and time synchronization of a network clock signal. In a passive optical network, a passive optical network OLT includes a PTP packet (ONT), and the ONU synchronizes the original reference clock with the time information using the synchronization signal, offset, and delay information, and transmits the synchronized signal to the lower passive optical network ONU .
Due to the upward burst traffic and the multiplexing property, the passive optical network has a large packet transmission time displacement. Therefore, it is difficult to apply the point-to-point IEEE P1588 network synchronization protocol because of this problem, and the present invention can overcome this problem.

Description

Technical Field [0001] The present invention relates to a network synchronization apparatus and method for a passive optical network,

The present invention relates to a network synchronization transmitting apparatus and method in a passive optical network, and more particularly, to a network synchronization transmitting apparatus and method for transmitting frequency and time synchronization signals using an IEEE 1588 PTP (Precision Time Protocol) .

In general, in the network and the system that constitutes it, the visual information provides a reference for adjusting the timing of the sampling and triggering of measurement instants, providing the time interval used for measurements over a period of time, and used in the derivation of the inductance. In addition, the time information provides a criterion for determining the order of events, provides a criterion for determining the aging time (elapsed time, etc.) of the data items, and includes an operation time Of the standard. For this reason, in general, visual information is important in a network and a system constituting the network.

In order to exchange data using this time information, exchange timing slots of a transmission terminal, separate insertion of a multiplexed line, distribution of a line, and the like, a digital communication network is a network synchronization device that synchronizes the frequencies of nodes / Network Synchronization) is required. Generally, a transceiver means synchronizing all digital devices constituting a network with one reference clock (PRC), and also a method, a method, and a method for distributing (supplying) accurate timing information to the entire network System.

Plesiochronous Synchronization is a network synchronization method in which each system has a separate independent clock source and is synchronized by its independent clock source. It is mainly used for international gateway in the case of international digital transmission. Method.

As another network synchronization method, Master Slave Synchronization means a network synchronization method in which a master station is a master station, a slave station is a slave station, and a slave supplies and receives a master clock, to be. As one of the dependent synchronization methods, there is a hierarchical master slave (HMS). The hierarchical slave synchronous method is a method in which the master station is the master station and the slave station is the slave station, while the slave station is operated as the master of the other slave station that is subordinate to the slave station. More specifically, as shown in FIG. 1, the upper boundary station (PSN) 23 operates as a master, the lower boundary clock 24 operates as a slave, and the boundary clock 24 Which is operated as a master, and its subsidiary station, the Odineri clock 25 or the PSN 26, is operated as a slave. This hierarchical sub-synchronous scheme is advantageous in that it is suitable for a mesh network since the network configuration is simple.

1, the grand master 22 obtains time information synchronized with UTC (Universal Time Coordinated) by using a satellite navigation system such as a Global Positioning System (GPS) Layered synchronous mode is the most effective way to generate and share synchronized time and frequency signals over a certain level at two remote locations or a wide area.

On the other hand, the grand master 22 should maintain stable network synchronization even when the time information and the signal are disconnected by a jamming signal or the like. Therefore, by combining a frequency signal using an oven-controlled crystal oscillator (OCXO), rubidium, etc. and a visual signal of a satellite navigation system using a phase-locked loop (PLL) The grand master 22 is configured so that it can be tracked in comparison. Such a synchronizing device that maintains stable synchronization is called a GPS Disciplined Clock or a GPS Disciplined Oscillator. Currently, the mobile communication network maintains synchronization using the GPS clock.

Meanwhile, the wired network and the wireless network are used separately. In order to unify them into one access network, the network synchronization method must be integrated. However, there is a problem in that it is not possible to use an Ethernet communication-based device for precise synchronization of a remote location in the network.

Hereinafter, the IEEE 1588 PTP will be described.

In the SONET / SDH / PDH system, it has evolved from a synchronous optical network (SONET) / synchronous digital hierarchy (SDH) / pleisiochronous digital hierarchy (PDH) Ethernet-based network synchronization technology is required because the high-level clock synchronous medium provided is eliminated. The Synchronous Ethernet function synchronizes the frequency by recovering the clock from the receiving frame in the Ethernet physical layer. The IEEE 1588 PTP, also called IEEE 1588 (2002), synchronizes the time by message exchange.

The IEEE 1588 PTP provides the device with a protocol that enables the most precise and accurate clock utilization on the network. Although there is a separate accurate clock source in each configuration of the device, there is a time difference due to a circuit change occurring between nanosecond and microsecond, and a delay due to network connection, that is, jitter occurs. To address this problem, device manufacturers include IEEE 1588 PTP functionality in their products. Thus, a device equipped with the IEEE 1588 PTP function can track a synchronized clock in a range of several tens of nanoseconds to several microseconds, thereby solving the above problems.

IEEE 1588 PTP has been standardized in the past few years to be suitable for network structure such as mobile network which requires precise time. However, in addition to mobile network, IEEE 1588 PTP is used for AVB (Audio Video Bridge) To synchronize the time between the industrial automation device and the measurement network device connected to the dedicated high-speed Ethernet LAN segment.

Generally, to process the IEEE 1588 PTP, a server, a client, and switch hardware that capture a time stamp when an Ethernet frame passes through the physical layer are provided. In a network sharing environment, a grandmaster operates mainly in a synchronous mode using a broadcast mode or a unicast mode. The protocol used in these modes is referred to as a PTP On-Wire Protocol, Each client exchanges messages of a separate client / server and operates in a master / slave mode synchronized with the grand master.

The time scales used by the IEEE 1588 PTP are in seconds and nanoseconds. The IEEE 1588 PTP is generally based on January 1, 1970. The accuracy of the synchronous clock of the IEEE 1588 PTP is determined by the resolution and stability of the dedicated clock oscillator and counter, which is approximately 100 nanoseconds accuracy. In a network using IEEE 1588 PTP, the time synchronization interval is usually several seconds, and there is little network overhead problem.

The IEEE 1588 PTP improves the accuracy as well as the best master clock (BMC) algorithm that selects the optimal path to the grand master by measuring various quality parameters such as the number of hops of the network, Use a sophisticated algorithm to select the best path.

The PTP server and client use an on-wire protocol that exchanges timestamps to synchronize the client clock to the server clock. PTP uses two timestamps to calculate the clock offset and the relative round-trip latency between the server and the client. A normal PTP timestamp is captured by an Ethernet network interface card (NIC) when a start of frame (SOF) passes through the input and output frame data streams. The timestamps are captured relative to the Media Independent Interface (MII) between the MAC layer and the physical layer through dedicated oscillators and counters. Some IEEE 1588 Ethernet drivers have a dedicated input or output frame buffer for storing other related data, a timestamp field, and a PTP protocol data unit (PDU). The IEEE 1588 Ethernet driver may monitor the frame data stream and modify the on-fly time stamp field using a field programmable gate array (FPGA). After the frame is transmitted, the IEEE 1588 Ethernet driver updates the output timestamp field. After the frame is received, the IEEE 1588 Ethernet driver updates the input timestamp field. When the timestamp field is updated, the IEEE 1588 Ethernet driver recalculates the UDP checksum before the frame is passed to the upper layer protocol.

The on-wire protocol used for PTP is to synchronize the server with the grandmaster or client. In most applications, message transmission is performed periodically with intervals of a few seconds. The PTP protocol can operate in a point-to-point master-slave mode or in a point-to-multipoint multicast mode.

As shown in FIG. 2A, first, after A (client) sends a client message to B (server), B (server) sends a server message to A (client). This process is called a round, and there are four timestamps in one round. T1 (Origin Timestamp) is used when A (Client) sends a client message, T2 (Receive Timestamp) is B (Server) receives a client message, T3 (Transmit Timestamp) When transmitting, and T4 (destination timestamp), A means when receiving a server message, respectively.

At this time, the clock offset? Is calculated using the following equation (1).

And the round trip delay [delta] is calculated using the following equation (2).

FIG. 2B is a diagram illustrating a process of synchronizing time between a master and a slave by applying the PTP protocol.

The master time 31 indicates the time progressed by the master, and the slave time 32 indicates the time progressed by the slave. In PTP, two messages are used to carry broadcast timestamps. This protocol starts with a synchronization message (sync) 33 at t1 in Figure 2b. The broadcast client records t2 (receive timestamp). At t3, a subsequent message including a data field t1, i.e., a delay time request (Delay_Req) 35 message, is transmitted. If it is received at time t4 and t4 is recorded as a time stamp in the delay response (Delay_Resp) message (36), the slave can calculate offset and delay time using the following equation (3).

The PTP uses two messages, the Sync message 33 and the Follow-up message 34, and uses the Delay_Req message 35 and the Delay_Resp 36 message for the same purpose.

Upon receiving the Sync message 33, the slave calculates the modified time based on the master's time using the following equation (4).

PTP defines two kinds of clock operation, one is a one-step clock and the other is a two-step clock. Once in the clock, the correct timestamp is sent directly to the Sync message 33, and at this two clocks, the Follow_Up message 34 is used to send the correct timestamp that matches the Sync message 33.

The Follow_Up message 34 is developed to improve the accuracy of the time stamp and to facilitate timestamping at the hardware level. The use of the message means that the master does not change the timestamp value in the Sync message 33 when transmitting a packet. However, individually, non-time-critical packets can be transmitted. If the master once uses the clocking scheme, the number of PTP messages to be transmitted can be reduced. However, due to some security mechanisms or architectural features, the master may require a two-clock approach. Thus, once the clock and two-phase clocks are allowed in the profile, a PTP master compatible with these profiles can use either a clock, a two-end clock, or both. Therefore, slaves must be able to accept both clocks and two-phase clocks.

FIG. 3 shows a method of synchronizing the phase of the synchronous clock signal between the master and the slave. The slave calculates the period of the two Sync messages based on the correct time. Then, the cycle of the two Sync messages is calculated based on the slave timestamp. The proportional factor is calculated using two cycles.

And the slave adjusts the clock frequency using Equation (5) below.

From here,

Indicates the time at which the Kth Sync message is transmitted from the master,

Indicates the time when the Kth Sync message arrives at the slave.

As described above, the PTP protocol synchronizes the frequency and the phase while communicating with each other using the on-wire protocol between the master and the slave. However, in order to apply the same PTP protocol to a passive optical network, it is necessary to understand the attributes of the passive optical network.

Hereinafter, a passive optical network will be described.

With the expansion of smart devices such as smart phones and the explosive increase in demand for broadband multimedia such as IPTV, the upgrading of the subscriber network is becoming the biggest issue in the telecom industry.

In order to upgrade the existing xDSL-based subscriber network, it is necessary to construct a fiber to the home (FTTH) that replaces the existing copper wire with an optical fiber. Alternative technologies are needed to overcome the difference between communication demand and supply during FTTH construction. Among these technologies, passive optical network (PON) is one of the most economical optical network configuration methods.

4 is a diagram illustrating a structure of a general passive optical network. As shown in FIG. 4, the passive optical network (PON) includes a passive splitter 2 such that a plurality of subscribers use one optical fiber (Feeder Fiber) And has a point-to-multipoint network structure utilizing a passive element to branch to multiple optical fibers (9). An optical line termination (PON) system 1 is located at the network end point of the optical distribution network (ODN), and an optical network termination (ONT) is located at the subscriber end point. The ONTs 4 to 8 shown in FIG. 1 refer to a single subscriber. An ONU (Optical Network Unit) 3 is installed in an inlet of a dense subscriber such as an apartment and accommodates a function of collecting a plurality of subscriber lines , Which is configured in the form of various L2 switching devices that accommodate existing xDSL subscriber lines or Ethernet subscriber lines before a full FTTH transition.

Various transmission schemes are used for information exchange between the OLT and the ONU / ONT. However, according to the circumstances of each communication service provider, most of them are a gigabit ethernet passive optical network (GE-PON) scheme of the IEEE 802.3ah standard or ITU- .984 use the international standard gigabit-capable passive optical network (G-PON). G-PON technology provides downlink 2.5Gbps / uplink 1.25Gbps transmission rate and supports variable length IP service and time division multiplexing (TDM) service using newly defined GEM (G-PON Encapsulation Method) frame structure. Can be provided efficiently. In addition, the G-PON technology can transmit an ATM (asynchronous transfer mode) protocol used in a mobile communication network without additional overhead. The G-PON is capable of efficiently providing voice services through a frame transmission control of 125usec (8kHz), and is known as an efficient system with relatively low overhead due to NRZ (non-return-to-zero) coding.

On the other hand, the downlink data of the PON is broadcast and transmitted to the ONT devices of all the subscribers, while the upstream data of the PON is transmitted at the time allocated to the ONT device, and the burst mode mode. For this reason, the uplink packet severely experiences a displacement of the propagation delay, and the displacement of the message transmission / reception time stamp between the master and the slave exceeds a certain standard, which makes it difficult to apply the PTP protocol to the PON.

Meanwhile, a fourth generation (4G) wireless network such as LTE (Long Term Evolution), which is currently being introduced and operated, provides a relatively broadband service using a reduced-size service cell. To this end, we have evolved from the third generation wireless network to the fourth generation wireless network, and constructed the entire network as an IP network. The fourth generation wireless network is a carrier Ethernet (CE) or packet transport network (PTN) with a low-cost Ethernet technology, operation and maintenance (OAM) functions of highly reliable transport networks such as synchronous digital hierarchy (SDH) : Packet Transfer Network). However, there is a problem that the cost of network investment increases when 1: 1 connection of the subdivided equipment such as femtocell is done.

Currently, the PON subscriber network is an access network for high-speed Internet. However, if a network synchronization function and a network synchronization distribution function are added to the PON network and a function of transmitting time information such as TOD (Time of Day) is added, It is possible to build a mobile backhaul network.

However, in the PON network, uplink and downlink communications are performed using two different wavelengths through one optical fiber. In particular, traffic to the upstream is multiplexed by time division multiplexing (TDM) It is necessary to output the optical signal only to the time slot of the time slot. For this reason, there is a problem in applying the PTP protocol because the mutual propagation delay in bi-directional communication does not converge within a predetermined value and the displacement exceeds a predetermined level.

Accordingly, it is an object of the present invention to provide a network synchronization transmitting apparatus and a method thereof for applying a PTP network synchronization technique to a passive optical network.

That is, according to the present invention, the PTP protocol is terminated in the OLT system, and a time-of-day (TOD) signal and a 1 pulse per second (PPS) signal synchronized by the 1588 protocol from the higher- A network synchronization transmitting apparatus and a method thereof in a passive optical network, which transmits an OAM packet including time and frequency information synchronized with a GPON frame every microsecond to reproduce a necessary timing signal in each ONT, There is a purpose.

The objects of the present invention are not limited to the above-mentioned objects, and other objects and advantages of the present invention which are not mentioned can be understood by the following description, and will be more clearly understood by the embodiments of the present invention. It will also be readily apparent that the objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.

According to another aspect of the present invention, there is provided an apparatus comprising: a network side line card for processing a PTP packet from an upper network to generate a timing signal synchronized with an upper network by processing a PTP protocol; A PON synchronous master unit for calculating an offset of the pulse, and a PON MAC processor for transmitting a superframe count, a timing signal generated in the network side line card, and an offset calculated in the PON synchronization master unit to the lower network.

According to another aspect of the present invention, there is provided an apparatus for receiving a super frame count, a timing signal, and an offset received by an ONU transceiver and an ONU transceiver that receives a super frame count, a timing signal, and an offset from an upper network, And a PON synchronization slave unit for generating a timing signal synchronized with the upper network using a super frame count, a timing signal, and an offset and a total delay previously known.

According to another aspect of the present invention, there is provided a method for generating a timing signal synchronized with an upper network by processing a PTP protocol from a PTP packet received from an upper network, And transmitting the superframe count, the generated timing signal and the calculated offset to the subnetwork.

According to another aspect of the present invention, there is provided a method for receiving a superframe count, a timing signal, and an offset from a network, the method including receiving a superframe count, a timing signal and an offset from the network, Lt; / RTI > timing signal.

The current mobile backhaul network and high-speed Internet network are separated. In order to accommodate the busy traffic due to the spread of smartphones, the mobile backhaul network is switched to the All-IP network, and a point-to-point network structure using synchronous Ethernet technology with enhanced OAM function is used. And for high-speed Internet networks, FTTH technology using the most economical passive optical network (PON) technology is applied.

On the other hand, the integration of subscriber networks is necessary because the subscriber network of globalized network operators is diverged and the maintenance and repair costs are increasing. However, the biggest obstacle to integrate them is the network synchronization function required in the mobile network. For the mobile network, it is essential to apply the network synchronization using the PTP protocol such as 1588.

The present invention also provides frequency accuracy and time information accuracy of a clock signal required in a mobile network in a passive optical network.

By providing frequency accuracy of a clock signal and accuracy of time information, an infrastructure for accommodating a small-sized cell structure such as a femtocell which is required in the future in a subscriber network can be integrated. As a result, It is possible to reduce the installation cost and the operation maintenance cost.

1 shows a synchronous clock scheme of a packet network;
FIG. 2A shows a master slave mode; FIG.
Figure 2B illustrates a PTP on-wire protocol;
FIG. 3 illustrates a PTP phase adjustment scheme; FIG.
FIG. 4 illustrates a general PON network configuration; FIG.
5 illustrates an OLT system and an ONU system according to an embodiment of the present invention;
6 is a diagram showing the timing relationship of IRIG timing signals; And
7 is a diagram showing an offset calculation and a delay calculation method.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings, It can be easily carried out. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.

And throughout the specification, when a part is referred to as being "connected" to another part, it includes not only "directly connected" but also "electrically connected" with another part in between. Also, when a component is referred to as " comprising "or" comprising ", it does not exclude other components unless specifically stated to the contrary . In addition, in the description of the entire specification, it should be understood that the description of some elements in a singular form does not limit the present invention, and that a plurality of the constituent elements may be formed.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

5 is a diagram illustrating an OLT system and an ONU system according to an embodiment of the present invention.

As shown in FIG. 5, the OLT system according to an embodiment of the present invention includes a grand master 41 (hereinafter, referred to as " master ") that receives an GPS signal and performs on-wire IEEE 1588 PTP master function through time information included in the signal (IRIG_CLK, IRIG_DATA, and 1PPS) synchronized with the upper network by performing the IEEE 1588 PTP slave function through the PSN 42, And a system clock signal for synchronizing with the IRIG timing signal (or a dedicated timing signal) to generate a system clock for driving the switch fabric 44, the PON MAC processing units 47 and 48, A PON synchronizing master unit 45 for calculating the offset of the PON synchronizing pulse signals PON_REF_PULSE 1 to N and a PON synchronizing pulse signal for PON transmission frame synchronizing and transmitting them to the PON synchronizing master unit 45 And a super-high frame count, and the timing signal PON MAC processing unit 47 for transmitting PON transmission frame including the offset in the PON Optical Distribution Networks 51 via an OLT transceiver (49 and 50).

5, the ONU system according to an embodiment of the present invention includes an ONU transceiver 52 that receives a PON transmission frame from the PON optical distribution network 51 and a PON 52 that is received by the ONU transceiver 52. [ A PON synchronization slave unit 54 that receives the super frame count, timing signal, and offset included in the transmission frame through the PON MAC processing unit 53, restores the timing signal synchronized with the OLT system, and distributes the signal to the gateway 55, Respectively.

First, an OLT system according to an embodiment of the present invention will be described, and an ONU system according to an embodiment of the present invention will be described.

The network side line card 43 receives the PTP packet from the grand master 41 via the PSN 42 and processes the PTP protocol to synchronize with the time of the grandmaster 41, IRIG timing signals (IRIG_CLK, IRIG_DATA, 1PPS) are generated using the recovered clock signal using the time information and the synchronous Ethernet function.

Meanwhile, the IRIG timing signal system is a standard system for transmitting time information by outputting precise timing signals through an atomic frequency standard and a GPS receiver. In particular, the IRIG-B type is often used. The IRIG-B type displays time information such as time, date, and year using a 1-second cycle, a 100-Hz bit clock, a 10-ms bit time, Method. In addition, the IRIG-B type uses a 1PPS signal, an IRIG_CLK signal, and an IRIG-DATA signal.

6 is a diagram showing the timing relationship of the IRIG timing signals generated by the network side line card 43. In FIG.

The 1PPS signal is a synchronous pulse signal that indicates the start of a frame by repeating one pulse per second, the IRIG_CLK signal is a clock signal of 100 Hz, and the IRIG-DATA signal is information of 100 bits of time, day, Lt; / RTI > After at least five IRIG_CLK signals from the start of the 1PPS signal, the IRIG-DATA signal is initiated.

The PON synchronization master unit 45 receives the IRIG timing signals IRIG_CLK1, IRIG_DATA1 and 1PPS1 from the network side line card 43 and receives the dedicated synchronization signals IRIG_CLK0, IRIG_DATA0 and 1PPS0 of the OLT system. At this time, the PON synchronization master unit 45 selects the IRIG timing signal if the network side line card 43 is judged as normal, and when the restored signal is in the state of error or the like and it is determined that the network side line card 43 is not normal, Selects the dedicated timing signal of the system.

The PON synchronization master unit 45 generates a system clock signal (125 MHz) synchronized with the selected IRIG timing signal (or dedicated timing signal), and uses the generated system clock signal as a clock signal of the OLT system. On the other hand, in the following, only the "IRIG timing signal" is used for the sake of simplicity, but it should be noted that this expression is also alternatively included in the "dedicated timing signal ".

The PON synchronization master unit 45 calculates an offset for the IRIG timing signal of each PON synchronization pulse signals. However, since all the PON synchronization pulse signals are not synchronized at the same time, the timing of each PON synchronization pulse signal differs for each optical line depending on the initialization time. Therefore, it is necessary to accurately grasp the degree of offset of the corresponding PON synchronizing pulse signal of each optical line. Accordingly, since the OLT system is synchronized with the system clock signal, the PON synchronization master unit 45 uses a 32-bit counter (hardware counter) to count several system clock signals (8 ns clocks from the start point of the 1PPS signal to the PON synchronization pulse signal Pulse) is present and calculates an offset accurately.

The PON MAC processing unit 47 transmits the offset information to the ONU system (or the ONT system) according to the priority through the operation and management (OAM) packet.

On the other hand, the PON transmission frame in which the operation and management packet is carried includes a superframe counter, and the superframe counter includes the position information of the PON transmission frame on which the operation and management packet is carried. Therefore, when the ONU system receives the PON transmission frame carrying the operation and management packet, the ONU system can calculate the delay using the offset information and the position information. Accordingly, the corresponding ONU system receiving the PON transmission frame can know the delay information of the transmission time point of the PON MAC processing unit 47.

FIG. 7 is a diagram illustrating an offset calculation and a delay calculation method in which four system clock signals REFCLK exist from a start point T0 of a 1PPS signal to a PON synchronization pulse signal PON_REF_PULSE.

As shown in FIG. 7, since the four system clock signals REFCLK correspond to 32 ns, the offset of the PON synchronizing pulse signal PON_REF_PULSE is 32 ns. The recognizer of the super frame count corresponding to the time point T0 of the 1PPS signal is 00FE 0001. The superframe count recognizer at the time when the offset (32 ns), the superframe count (00 FE 0001), and the TOD information (IRIG_DATA and IRIG_CLK signals) of the T0-1 second are actually transferred to the ONU system (or the ONT system) is 00FE 0003 .

The transmission delay of each optical line is known in advance because it measures the round trip delay in the ONU system registration process. Therefore, it is sufficient to transmit the measured delay value when transmitting the operation and management packet.

In the ONU system, it is assumed that the delay required when recovering the clock and the PON transmission frame synchronous pulse from the PON signal (operation and management packet) converges to a hardware constant value.

Therefore, the total delay is the sum of the propagation delay (1/2 value of the PON round trip delay) in the PON network and the processing delay (hardware fixed value) in the ONU system.

Therefore, in the ONU system, 1PPS is generated at the position offset from the calculated offset (32 ns) and the total delay value at the position of 00FE 1F41, which is the next period of 00FE 0001, using the super frame position information in which 1PPS exists on the OLT system side , The TOD information of the ONU system can be corrected to the TOD information of (T0 + 1) seconds to recover the original 1PPS signal and time (TOD) information.

The 1PPS signal and the time of day (TOD) information restored in the ONU system are used in the gateway 55 of the ONU system or in other devices requiring synchronization signals. In addition, a PTP protocol master (not shown in the figure) may be installed in the ONU system to operate as a PTP master in the home network of the ONU system.

The ONU system includes a Gigabit Ethernet physical layer processor (not shown) capable of processing the TOD information and the 1PPS signal by the IEEE 1588v2 method in order to transmit a network synchronous signal to a small base station device or a femtocell of a mobile backhaul, Can be mounted. The ONU system transmits a synchronous clock signal generated by the Gigabit Ethernet physical layer processing unit to a VOIP DSP (not shown in the figure) and a PDH frame processor (not shown in the figure).

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, Various permutations, modifications and variations are possible without departing from the spirit of the invention.

Therefore, the scope of the present invention should not be construed as being limited to the embodiments described, but should be determined by the scope of the appended claims, as well as the appended claims.

Claims

A network side line card for processing a PTP packet from an upper network to generate a timing signal synchronized with the upper network;
A PON synchronization master unit for calculating an offset of a transmission frame synchronization pulse for the timing signal generated in the network side line card; And
A PON MAC processing unit for transmitting a transmission frame including a super frame count, the timing signal generated in the network side line card, and the offset calculated in the PON synchronization master unit to a lower network,
And an optical line termination device.

The method according to claim 1,
The timing signal may include:
IRIG timing signal.

The method according to claim 1,
The PON synchronization master unit,
And generates a system clock signal synchronized with the timing signal and counts the system clock signal from a start time point of the timing signal to a start time point of the transmission frame synchronization pulse to calculate the offset.

The method of claim 3,
The PON synchronization master unit,
And counts the system clock signal using a hardware counter.

An ONU transceiver for receiving a transmission frame including a superframe count, a timing signal and an offset from an upper network; And
A PON synchronization slave unit for generating a timing signal synchronized with the upper network using the super frame count, the timing signal and the offset received by the ONU transceiver,
And an optical network terminating device.

6. The method of claim 5,
The PON synchronization slave unit,
Generating a timing signal synchronized with the upper network at a position of the next cycle of the timing signal at a position indicated by the super frame count, the offset of a position of the next cycle, .

6. The method of claim 5,
The total delay may be,
And a processing delay that is a hardware fixed value and a propagation delay that is a value of half the round trip delay.

8. The method according to any one of claims 5 to 7,
And a PON synchronization master unit for performing a PTP protocol master function using a timing signal synchronized with the upper network.

8. The method according to any one of claims 5 to 7,
A Gigabit Ethernet physical layer processing unit for processing the timing signal synchronized with the upper network in accordance with the IEEE 1588v2 method;
And an optical network terminating device.

Processing a PTP protocol from a PTP packet received from an upper network to generate a timing signal synchronized with the upper network;
Calculating an offset of a transmission frame sync pulse for the generated timing signal; And
Superframe count, transmitting the generated timing signal and the calculated offset to the subnetwork
/ RTI >

11. The method of claim 10,
The timing signal may include:
IRIG timing signal.

12. The method of claim 11,
Further comprising the step of generating a system clock signal synchronized with the timing signal,
And counting the system clock signal from a start point of the timing signal to a start point of the transmission frame sync pulse to calculate the offset.

13. The method of claim 12,
And counting the system clock signal using a hardware counter.

Receiving a superframe count, a timing signal and an offset from an upper network; And
Generating a timing signal synchronized with the upper network using the super frame count, the timing signal, the offset, and a known total delay;
Gt;

15. The method of claim 14,
Generating a timing signal synchronized with the upper network at a position of the next cycle of the timing signal at a position indicated by the super frame count, the offset of a position of the next cycle, .

15. The method of claim 14,
The total delay may be,
And a processing delay which is a hardware fixed value and a propagation delay that is a value of half the round trip delay.