Description
BACKGROUND
1. Field of the Invention
The invention relates generally to Passive Optical Network (PON) communication system and more particularly to data acquisition and tracking in PON..
2. Related Art
A Passive Optical Network (PON) in general refers to a bi-directional point-to- multipoint communication system implemented over optical fiber as communication medium. One or more optical splitters/combiners are incorporated to form a desired optical network. In PON, often an Optical Line Terminal (OLT) analogous to the point is connected to several Optical Network Units/terminals (ONU/ONT) analogous to multipoint by optical fiber. Passive splitters are generally employed to connect (deliver signals) PON network devices (OLT and corresponding ONUs).
Since multiple network devices share common optical fiber channel, the communication between OLT and ONUs is often performed using/implementing one of several standards (for example APON, EPON, GPON as well known in the field of art). Typically, several network parameters (for example, device ID, physical location, type of service, etc.,) are used to control and (or) enhance the efficiency of the communication on the shared fiber optic PON. Often a network device may determine/compute/ measure/ assign one or more network parameters.
Such network parameters are often used for efficient communication on PON. Typically, the standards often define technique for computing/measuring and employing desired parameter for efficient communication. Accordingly, the OLT and ONUs are implemented in conjunction with the corresponding protocol and standards. Thus, data acquisition and (or) tracking signal transportation on PON may require computation/use of network parameters and the (standard) guidelines adapted by the respective PON.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be described with reference to the following accompanying drawings.
The present invention will be described with reference to the following accompanying drawings.
Figure 1 is a block diagram illustrating an example environment in which various aspect of the present invention may be implemented.
Figure 2 is a flowchart illustrating example set of procedures of OLT.
Figure 3 is an illustrative fi-ame structure depicting the portion of the downlink frame.
Figure 4 is an illustrative frame structure depicting the portion of the uplink frame.
Figure 5 is a flowchart illustrating the data extraction according to an aspect of the present
invention.
Figure 6 is a block diagram of a PON in an embodiment of the present invention.
Figure 7 is a graph illustrating the manner in which various transmission parameters may be captured in one embodiment of the present invention.
Figure 8 is a graph depicting estimation of time of arrival of data packet with sample numerical values according to various aspect of the present invention. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the corresponding reference number.
DETAILED DESCRIPTION
1. Overview
According to an aspect of the present invention, information transmitted on a PON network is extracted at a arbitrary location on PON by monitoring signal and determining network parameter at the arbitrary location. In one embodiment, signals are monitored to capture time at which a Ranging request was received, time at which ranging response were received from a desired ONU. The captured parameters are used to determine a silent window width, at the arbitrary location. Various other parameters such as equalization delay (EqD.x), start time of upstream frame, time at which a downstream frame was received at said first location, and time difference between RresTS.x, and RreqTS.x are determined to estimate the time of arrival of up stream burst from the desired ONU.
According to another aspect of the present invention, multiple monitoring devices are connected to the desired paths on the GPON network to extract the data corresponding to desired ONUs connected to the GPON, the extracted data is then used to control the ONUs and detect the mal function. Thus, malfiinctioning ONUs are detected/controlled (switched off) without having to perform ranging operation from OLT.
Several aspects of the invention are described below with reference to examples for illustration. It should be understood that numerous specific details, relationships, and methods are set forth to provide a fiill imderstanding of the invention. One skilled in the relevant art, however, will readily recognize that the invention can be practiced without one or more of the specific details, or with other methods. In other instances, well-known structures or operations are not shovm in detail to avoid obscuring the features of the invention.
2. Example Environment
Figure 1 is a block diagram illustrating an example environment in which various aspect of the present invention may be implemented. The block diagram is shown containing Optical Line Terminal (OLT) 110, splitters 120A- 120C, 130 and 140, Optical Network Units/terminals (ONU) 150, 160, 170, 175, 180, and 190. Each block is described below in further detail.
Splitters 120A- 120C, 130 and 140 splits optical signal received in one direction and provides on the multiple path. Similarly combines the multiple optical signals received in other direction on to a single path. For example, splitter 120A splits the optical signal received on optical path (fiber) 112 and provides the split optical signal on paths (fibers) 121A and 12IB. Similarly, splitter 120A combines the optical signals received on paths 121A and 121B and provides the combined signal on path 112. In one embodiment, splitters 120A-120C, 130 and 140 may represent passive splitters as well known in the art.
Splitters 120A- 120C, 130 and 140 together with optical fibers 112, 121 A, 121B, 123-126, 135, 137, 148 and 149 represent an example optical fiber network. The flow of optical signal (in one direction) from OLT 110 to ONUs 150,160, 170,175,180, and 190 is often referred to as downlink, while the and the flow of signal in the (other direction) from ONUs to OLT is referred to as uplink. Splitters and optical fibers may be arranged in different topology as well known in the field of art.
ONUs 150, 160, 170, 175, 180 and 190 transmit/receive optical signal to/from OLT 110. ONUs may operate to provide interfaces to connect to PON through other network/devices (for example Ethernet/signal processing device). Accordingly, ONUs may convert optical signals to desired other signal/format (compatible to be transmitted on the other network) and visa versa. ONUs 150, 160, 170, 175, 180, and 190 are implemented to operate in conjunction with OLT 110. Accordingly, ONUs may receive commands or instructions for transmitting the signal on the PON to OLT and Vise versa. ONUs, 160, 170, 175,180, and 190 are often located near user/customer premises.
OLT 110 transmit/receive optical signals (through PON) to and fi-om ONUs 150, 160, 170, 175, 180, and 190. OLT 110 also operates to control and/or manage communication to and from ONUs 150, 160, 170, 175, 180, and 190. In general, OLT broadcasts information (downlink) through the optical fiber network (PON) to all ONUs connected OLT 110. The Broadcast information may contain commands and instruction for ONUs for transmitting the information to OLT (uplink transmission).
OLT 110 may also operate to provide connectivity to other electronic devices or other network devices. For example, OLT 110 may provide connectivity to devices such as voice gateways, IP routers, (Gigabit) Ethernet interfaces, and video-to-telephone network interfaces etc., as well known in the field of art. OLT 110 is usually located at the central office (CO).
OLT 110 may be implemented according to several standards such as EPON GPON etc. Accordingly, OLT 110 may adapt the corresponding protocol for controlling and/or managing communication to and from ONUs. The operation of OLT 110 and ONUs 150, 160, 170, 175, 180, and 190 is described below in an example embodiment merely for illustration.
3. Example Implementation OLT and GNU.
In an example embodiment, OLT 110 and ONUs 150, 160, 170, 175, 180, and 190 are implemented according to "ITU-T G.984 recommendations" (hereafter referred to as "GPON recommendation"). The details of the recommendation are provided/available at http://www.itu.int/rec/T-REC-G/e and are incorporated in entirety herein by reference. However, operation of OLT in the example embodiment is briefly described below with reference Figure 2, 3 and 4 for continuity and completeness.
Figure 2 is a flowchart illustrating example set of procedures of OLT 110. The flowchart is described with reference to Figure 1 merely for illustration. The flowchart begins in step 201 and control passes to step 210.
In step 210, OLT 110 performs range and delay measurement. Typically, each ONU 150, 160, 170, 175, 180, and 190 is located at a different distance from the OLT 110. Thus OLT 110 measures the distance (ranging) of each ONU in the PON. Further, OLT 110 performs measurement of various delays such as propagation delay, transmission delay, roundtrip delay (RTD) etc. An equalization delay (for example equalization roundtrip delay) is computed for each ONU 150, 160, 170, 175, 180, and 190 based on the measured delays.
The process of performing range and delay measurements is often referred as "ranging". OLT 110 may perform all procedures or some of the procedures during the operation. For example, OLT may perform delay measurement with the prior knowledge of the distance obtained during earlier iteration. OLT 110 may perform ranging during various network events. For example, OLT may performing range measurement while initializing the network, when new ONU is connected to network, serial number acquisition or may periodically perform ranging to initialize new ONUs.
The ranging process typically includes: 1. OLT 110 halts active ONUs to avoid collision of data from the active ONUs while ranging is being performed. OLT 110 may wait for a predetermined time period for all ONUs to stop transmitting uplink from the issue of halt command. 2. OLT 110 opens a ranging window. Generally a ranging request is transmitted downlink to ONUs (or to desired ONU). 3. ONUs 150, 160, 170, 175, 180, and 190 transmits ranging data on the uplink (for example, serial number and random delay for ranging response transmission). 4. OLT 110 receives ranging data from ONUs (from desired ONU) and determines the ranging parameters such as round trip delay and equalization delay.
In step 230, OLT 110 assigns an ONU-ID and equalization delay. Each ONUs in the PON is provided with an ONU-ID that uniquely identifies each ONU in the PON. The ONU-ID is assigned to each ONU (desired ONU) during the ranging process. OLT 110 computes equalization delay for each ONU (or desired ONU).
The equalization delay is computed and communicated to ensure arrival of the data from each ONU in the network in synchronization (in phase) with a reference time. In other words, ONUs located at different distances from OLT 110 are made to appear to be in equal distance from the OLT. The equalization delay may further enhance bandwidth utilization and avoid data collision. The equalization delay for each ONU is determined during the ranging process.
In step 250, OLT 110 sends downlink frames. The downlink frame contains information indicating permitted locations (time slots) for upstream traffic. Downstream frame provides the common time reference for the PON, and provides the common control signaling for the upstream. Typically, numbers of transmission containers T-counts (a predetermined time slot) are assigned to each ONU dynamically through Allocation ID (alloc ID). OLT may assign multiple alloc-Ids to the same ONU. An alloc ID might be seen as analogous to a customer (multiple customers can interface to an ONU). The grants for uplink bandwidth are assigned based on an alloc ID. Thus, the downlink (downstream frame) carries the allocation ID for each ONU in PON.
Figure 3 is an illustrative frame structure depicting the portion of the downlink frame. Alloc ID field 310 through 390 corresponds to the allocation ID allocated to each ONU in the PON. Start fields 311, 321, etc., represents the start time for transmitting the upstream burst for respective Alloc IDs. Similarly end field 319, 329, etc. represents the end time for transmitting the burst.
Thus each ONUs 150, 160, 170, 175, 180, and 190 transmits the burst of information on the upstream at the reference time slot allocated in the down stream by OLT. Each ONU may compute the reference start time and end time with reference to downstream frame and equalization delay as noted above. Hence the up stream data are time multiplexed from a reference time.
In step 270, OLT 110 receives uplink frames. The received up stream frame contains the bursts of information/data from the ONUs that were assigned an allocation ID in the downlink. Figure 4 is an illustrative frame structure depicting the portion of the uplink frame. Field 410 through 490 represents the burst of transmission corresponding to Alloc ID 310 through 390. Each burst 410 through 490 are measured and identified with reference to the upstream frame pulse 401. The delay from the reference time point 401 to the start of the burst 410 through 490 are computed by each ONU based on the equalization delay assigned to it by OLT 110.
In step 290, OLT 110 extracts the data of each ONUs. OLT extracts the information corresponding to each ONU from the time reference. The flowchart ends in step 299.
From the above description it may be appreciated that, OLT 110 may not detect a ONU that may wrongly transmit the data at time slot allocated to other ONU in the PON. Also it may be desirable to extract data for monitoring and recording the network activity for various purposes at a location other than the location of OLT. Various aspect of the present invention described below overcome at least some of the disadvantages noted above.
4. Data Extraction and Monitoring at a location other than OLT
Figure 5 is a flowchart illustrating the data extraction according to an aspect of the present invention. The flowchart and the subsequent descriptions are provided with reference to Figure 1-4 and GPON recommendation described above merely for continuity and illustration. However, extending the technique to other embodiment and systems is apparent to one skilled in the art by reading the disclosure provided herein. All such system and embodiments are contemplated to be covered by the present invention. The flowchart begins in step 501 and control passes to step 510.
In step 510, a monitoring device (connected to PON network) determines network parameters at one or more desired locations other than OLT. The network parameters such as round trip delay, equalization delay etc., as noted above are determined at a desired location on the PON. The determination may be performed without transmitting any signal on the PON. For example, the downlink signals and uplink signals may be monitored to extract the network parameter. The device may be connected to PON network through a bi direction splitter (2:2 splitters) as well known in the art.
Measurement of network parameter such as equalization delay, round trip delay etc., at a desired location enable determination of arrival of uplink burst data at the desired point from a corresponding ONU.
Instep 520, the monitoring device extracts the data at the desired location based on the network parameter determined in step 510. The data corresponding to some of the ONUs located on the down stream in the PON may be extracted using the new network parameters using any known technique described above. Manner in which the monitoring devices may be connected to PON and the network activity may be monitored is described below with reference to Figure 6.
Figure 6 is a block diagram of a PON in an embodiment of the present invention. In the block diagram, blocks operating similar to the blocks in Figure 1 are retained with like reference numbers for simplicity. Thus descriptions of the like blocks are not repeated for conciseness. The block diagram is shown additionally containing monitoring devices 610, 620, 630 and 640 respectively connected to optical fiber 125, 135, 148, and 124. The connection may be performed using couplers and splitter as well known in the art.
Thus, monitoring device 610 may extract data corresponding to the ONUs connected through optical fiber 125 (in this case only one ONU 125). Similarly, monitoring device 640 may extract data corresponding to the ONUs coimected through optical fiber 124 (ONU 180 and 190).
Each monitoring device 610, 620, 630 and 640 may perform operation according to the steps described above with reference to Figure 5. Thus, data extracted from each device may be recorded/ stored for various applications. In addition, each monitoring device 610, 620, 630 and 640 may detect when the ONU connected to the respective optical fiber transmits the burst at a time slot not allocated to it. For example, monitoring device 610 may detect when ONU 150 transmits a data at a time slot not allocated to it by OLT 110. Such malfiinctioning may be detected and desired corrective measures (such as tumoff ONU 150) may be taken to avoid the data collision.
Further, monitoring device 610, 620, 630 and 640 may be connected together (not shown) using any known connectivity means to a central location for central monitoring and recording. The data hence extracted may be further provided to OLT 110 as a feedback (not shown). Thus the OLT may identify the ONUs that are malfunctioning with lesser overheads like larger laser on off times, or longer preambles.
Manner in which network parameters may be determined in an embodiment of the present invention is described below in further detail.
5. Determination of Networlc parameter
Figure 7 is a graph illustrating the manner in which various transmission parameters may be captured in one embodiment of the present invention. In the graph, X axis represents position or distance with reference to OLT and Y axis represents the time. The graph is described below in further detail.
Position/location 710 and 720 example position at which monitoring devices are connected to PON. Position 730 represents the position of an ONU. Set of lines 740 and 770 represents the transmission from other ONUs. The thick line 750 represents range request transmitted from OLT. The dashed line 760 represents the range response from the ONU. Manner in which various transmission parameter are captured is illustrated below with reference to Figure 7.
The monitoring devices (example 630 and 640) may capture and record various transmission parameters to estimate the network parameters such as roundtrip delay and equalization Delay etc., for data extraction.
In one embodiment, monitoring device 630 (at location 710) determines time at which a Ranging request was received for a particular ONUx (example 180, for Alloc-ID less than 256). The determined time stamp may be stored as Ranging Request Time Stamp (RreqTS.x). With reference to Figure 7, time t4 represents the RreqTS.x.
From RreqTS.x, monitoring device 630, determines a silent window width to unambiguously (without the upstream bursts from the other ONUs) capture the ranging response. The start of the silent window may be determined as:
SWStart = RreqTS.x + Delta + Ranging Response Start Time.
Wherein, Delta represents a minimum response time of an ONU. The Delta may be computed as: Delta = 35 us + lOxD us. Wherein, D is the distance (in km) of the nearest ONU from the monitoring device 630. Wherein, "us" represents microseconds.
With reference to Figure 7 t5-t4 represents the delta computed according to above equation. t6-t5 represents the silent window at location 710. Similarly t9-t8 represents the silent window at location 720. The time instant t6 and t9 are determined based on the time instant at which the transmission from other ONUs is received. Each monitoring device may operate with the different time scale. The time difference t3-t2 represents the silent window at OLT 110.
The "Ranging Response Start Time" in the above equation may be extracted from the BWMap (noted in the GPON recommendation) for a desired ONU using known technique.
Monitoring device 630 then captures time at which a ranging response was received from a particular ONU.x at position 710. The determined time stamp may be stored Ranging Response Time Stamp (RresTS.x). Further, Monitoring device 630 captures the entire ranging response. In one embodiment, the first response 760 received after SWStart is considered as the ranging response if ONU-ID of ranging request 750 and ranging response 760 matches.
Monitoring device 630 may determine/ capture various other transmission parameters from bandwidth map and downstream/upstream PLOAM. In one embodiment, monitoring device 630 determines EqDelay (EqD.x), StartTime.x of upstream frame (ST.x), GateRecpTS.x, and RTTx.
\^erein,
EqDelay (EqD.x) represents equalization delay assigned to a desired ONUx and the value may be extracted from the Ranging Time PLOAMd for ONU.x.
StartTime.x of upstream frame (ST.x) represents the start time of the upstream frame. The value may be exfracted from the US Bandwidth Map.
GateRecpTS.x represents time at which a downstream frame was received at the monitoring device Port. (Latched at the begirming of the BWMap).
RTTx represents time difference between RresTS.x, and RreqTS.x and may be represented as: RTT.x = (RresTS.x - RreqTS.x).
Manner in which the transmission parameters determined according to the present invention are employed to estimate time of arrival of the upstream burst from ONUs is described below in further detail.
6. Estimation Of time of arrival Of Upstream Burst
In an embodiment of the present invention, monitoring device 630 determines Estimation Of time of arrival Of Upstream Burst ETAF.x from a particular ONU.x as:
ETAF.x = RTT.x + EqD.x + StartTime.x + GateRecpTS.x.
It may be appreciated that RTT.x and EqD.x remains constant for a given ONU.x and RTT.x + EqD.x = constant; for each values of x. The computed ETAF.x may be incremented by 125us for each successive frame. Thus, one ranging cycle is enough for the monitoring devices to find out the network parameters for all ONUs.
It may be fiirther appreciated that in GPON, the knowledge of the uplink transmission time is required to delineate the uplink frame of the ONU. This is because the OLT may assign grants with flag-bits that request different control structures and/ or payload. For example OLT may request one/ more or all of PLOAM message, DBRu message (buffer occupancy at the ONU) and/ or payload.
Figure 8 is a graph depicting estimation of time of arrival of data packet ETAF.x with sample numerical values according to various aspect of the present invention.
7. Conclusion
While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of the present invention should not be limited by any of the above described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

Claims; 1/ We claim,
I/we claim,
1. A method of extracting a first information at first location on a passive optical network (PON), wherein an OLT and plurality of ONUs are connected to said PON, said OLT controlling transmission of information from said plurality of ONUs, wherein said first information is transmitted from a first ONU comprised in said plurality of ONUs, said first location is located on the signal path connecting said first ONU and said OLT, said method comprising;
monitoring the signal at said first location;
determining network parameter at said first location; and
using said network parameter to extract said first information
2. The method of claim 1 wherein, said determining comprising;
capturing a time (RreqTS.x) at which a Ranging request was received for said first
ONU;
determining a silent window width, wherein the start of the silent window "SWStart" is determined using equation
SWStart = RreqTS.x + Delta + Ranging Response Start Time, wherein. Delta representing a minimum response time of said first ONU; and
capturing a ranging response time (RresTS.x) corresponding to said (RreqTS.x) from said first ONU.
3. The method of claim 2, wherein said determining determines at least one of an equalization delay (EqD.x), start time of upstream frame (ST.x), time at which a downstream frame was received at said first location (GateRecpTS.x), and time difference (RTTx.) between RresTS.x, and RreqTS.x
4. The method of claim 3 where in said determining determines an estimation Of time of arrival Of Upstream Burst ETAF.x from said first ONU using equation;
ETAF.x = RTT.x + EqD.x + StartTime.x + GateRecpTS.x.
5. A device for extracting a first information at first location on a passive optical network (PON), wherein an OLT and plurality of ONUs are connected to said PON, said OLT controlling transmission of information from said plurality of ONUs, wherein said first information is transmitted from a first ONU comprised in said plurality of ONUs, said first location is located on the signal path connecting said first ONU and said OLT, said device comprising;
means for monitoring the signal at said first location;
means for determining network parameter at said first location; and
means for using said network parameter to extract said first information
6. The device of claim 5 wherein, said means for determining comprising;
means capturing a time (RreqTS.x) at which a Ranging request was received for said first ONU;
means for determining a silent window width, wherein the start of the silent window "SWStart" is determined using equation
SWStart = RreqTS.x + Delta + Ranging Response Start Time, wherein, Delta representing a minimum response time of said first ONU; and
means for capturing a ranging response time (RresTS.x) corresponding to said (RreqTS.x) from said first ONU.
7. The device of claim 6, wherein said means for determining determines at least one of an equalization delay (EqD.x), start time of upstream frame (ST.x), time at which a downstream frame was received at said first location (GateRecpTS.x), and time difference (RTTx.) between RresTS.x, and RreqTS.x
8. The device of claim 7 where in said means for determining determines an estimation Of time of arrival Of Upstream Burst ETAF.x from said first ONU using equation;
ETAF.x = RTT.x + EqD.x + StartTime.x + GateRecpTS.x.
9. A system comprising;
plurality of ONUs connected to a PON network operating to transmit data over said PON network according to GPON protocol;
an OLT connected to said PON network, operating to control transmission from said plurality of ONUs according to said GPON protocol; and
first plurality of monitoring devices selectively coupled to plurality of transmission paths to extract the data transmitted from corresponding first plurality of ONUs connected to said plurality of paths.
10. The system of claim 9, frirther comprising;
a central control unit receiving data from said plurality of monitoring devices to control operation of said plurality of ONUs.