Patent Application
20070264016
The foregoing will be apparent from the following more particular description of example embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating embodiments of the present invention.
A description of example embodiments of the invention follows.
1. An occurrence of an ONT sending a continuous light signal (modulated or un-modulated) up a fiber prior to an OLT attempting to establish communications with any ONTs on the ODN.
2. An occurrence of an ONT sending an un-modulated light signal up the fiber to an OLT at an inappropriate time while attempting to establish communications or after having established communications with any ONTs on the ODN.
During standard ranging, a receiver (not shown) of an OLT is reset at a time that corresponds to a closest distance the ONT can be from the OLT (e.g., a time corresponding to a real distance of 1 kilometer (km) or an “ideal” distance of Okm). In contrast, when using a rogue tolerant ranging method according to an embodiment of the present invention, resetting of the receiver of the OLT is delayed by a time delay, such as an equalization delay (Te) stored for each ONT. In this way, resetting of the receiver is delayed (e.g., by delaying when a reset signal is sent) until just before a ranging response from the ONT is expected to be received. In other words, a time to reset a receiver of an OLT may be delayed until just before a ranging response from an ONT is expected to be received.
The time to reset the receiver of the OLT may be based on a previous successful ranging attempt, presumably before a rogue ONT was added to the ODN. Such a time may be incremented in an iterative manner, for example, from minus 20 bit-times to plus 20 bit-times before or after the time to allow for variations. Each bit-time may be, for example, 6 nanoseconds at 155 Megahertz (MHz). In other words, a time to reset a receiver may be changed to allow correct communication to an ONT when a rogue ONT is also present on the ODN.
When standard ranging fails to establish communication with an ONT, the rogue tolerant ranging method according to an embodiment of the present invention may be used. If the rogue tolerant ranging method succeeds (i.e., an ONT is successfully ranged), this indicates to an operator that one or more rogue ONTs are present and affecting the ODN. Such rogue ONTs can be identified and removed at a later time without further loss of service to other ONTs on the ODN. The rogue tolerant ranging method allows all ONTs on the ODN, including a rogue ONT, to communicate with the OLT, even in the presence of the rogue ONT.
The rogue tolerant ranging method, unlike existing error detection techniques (e.g., those described in the various PON protocols), detects and identifies the aforementioned rogue ONT malfunctions. Moreover, no specialized test equipment is used to overcome these malfunctions; the OLT can be configured in hardware, software, or combination thereof, to test and adjust for the rogue ONT(s).
Whether a ranging attempt is successful is determined by the determining unit 210. The determining unit 210 determines whether ranging is successful by, for example, measuring a no-input signal power level on a communications pathway.
The transmitted power level versus time plot 300b indicates that the no-input signal power level 303 may be constant during the ranging window 320, where the constant level may be a normal low level (e.g., −40 dBm) or a faulty high level (e.g., between −30 dBm and −25 dBm, or higher). The integrated no-input signal power level 305 ramps up from an integrated no-input signal power level at time tinitial 3310 to an integrated no-input signal power level at time tfinal 315, over the ranging window 320.
In operation, while the no-input signal power level 303 is being integrated over the ranging window 320, the OLT 301 sends a ranging grant 325 to the ONT 302. The ONT 302, in turn, responds with a ranging response 330. The OLT 301, having sent the ranging grant 325, receives the ranging response 330 from the ONT 302 during the ranging window 320 or it reports a ranging error.
Typically, the receiver of the OLT 301 is reset between adjacent upstream timeslots to accommodate power levels which vary from ONT to ONT. During ONT ranging, however, an upstream timeslot is effectively enlarged to accommodate variability in supported fiber lengths, i.e., more than one upstream timeslot is used for the ranging window 320. For example, the ONT 302 may be located up to 20 kilometers away from the OLT 301. To accommodate this distance, the duration of the ranging window 320 is set sufficiently long enough to allow the ONT 302 located 20 kilometers away from the OLT 301 to receive the ranging grant 325 and the OLT 301 to receive the ranging response 330.
When the duration of the ranging window 320 is set for a long period of time, the receiver of the OLT 301 is not reset during this period of time. As a result, a no-input signal power level, such as power level of rogue ONT on the ODN, have more time to be integrated by the receiver of the OLT 301, thus increasing the integrated no-input signal power level 305.
As the received power level versus time plot 300c illustrates, integrating the no-input signal power 303 over a long period of time causes the integrated no-input signal power level 305 to ramp (or increase). Consequently, over time, it may be more difficult to distinguish a zero-bit input signal (i.e., a zero bit) from a one-bit input signal (i.e., a one bit) possibly causing ranging errors and/or may lead to upstream communications problem(s)
Rather than using a typical ranging window, such as the ranging window 320, to determine when to reset a receiver of an OLT, in one embodiment of the present invention, the receiver is reset at about a time a ranging response from an ONT is expected to be received. Changing the time the receiver is reset may be referred to as a “dynamic reset.” Through the use of the dynamic reset, the amount of time a power level of rogue ONT is integrated may be limited, thereby reducing the adverse effects associated with integrating such a power level. In this way, the ranging techniques according to this and other embodiments of the present invention tolerate a fault condition otherwise affecting ranging of an ONT.
In some instances, however, resetting a receiver at about a time a ranging response from an ONT is expected to be received by an OLT does not result in successful ranging of the ONT. For example, a time between a time a ranging response from an ONT is expected to be received by an OLT and a time a ranging response from an ONT is actually received is large, possibly in terms of a time window or relative to a sensitivity of a particular receiver with respect to an amount of power a rogue ONT adds to an optical fiber link. Consequently, despite resetting the receiver at about the time the ranging response from the ONT is expected to be received, a power level is integrated sufficiently long enough to affect ONT ranging adversely.
In another example, a time a ranging response from an ONT is actually received occurs before a time a ranging response from the ONT is expected to be received. Again, despite resetting the receiver at about the time the ranging response from the ONT is expected to be received, a power level is integrated sufficiently long enough to affect ONT ranging adversely. In such instances, a time to reset a receiver is changed (described later in greater detail).
Additional techniques for determining whether ranging is successful are described in a U.S. patent application Ser. No. 11/515,504, entitled, “Methods and Apparatus for Identifying a Passive Optical Network Failure,” filed on Sep. 1, 2006 and assigned to Tellabs Petaluma, Inc., which is hereby incorporated by reference in its entirety.
Returning to
In one embodiment, the time delay changing unit 215 is configured with an adder (not shown) adapted to add a delay to the time when a ranging response from an ONT is expected to be received by an OLT. In another embodiment, the time delay changing unit 215 is configured with a subtracter (not shown) adapted to subtract a delay from the time when a ranging response from an ONT is expected to be received by an OLT. In yet another embodiment, the time delay changing unit 215 is configured with an incrementer (not shown) adapted to increment a delay in an iterative manner within a range of delays to delay the time to reset the receiver of the OLT and to compensate for variations in an equalization delay due to physical conditions expected to be experienced by an optical distribution network. In this way, the time to reset the receiver of the OLT is changed by the delay.
At the time to reset the receiver on the OLT, the resetting unit 220 resets the OLT receiver 205, such as via a reset signal 221.
In
In one embodiment, a receiver is reset at a time Treset and disabled at a time Tdisabled. Between the time Treset and the time Tdisabled is an expected ranging response time Tranging response, which is typically at least as long as a ranging response message or signal. Disabling the receiver at Tdisabled limits the effects of post-integration by an integrator (not shown) which may interfere with ONT ranging and/or may lead to upstream communications problem(s).
In this example, rather than at the time Texpected 425, the OLT actually receives the ranging response 430 at a time Tactual 435. Between the time Texpected 425 and the time Tactual 435, in a typical optical receiver manner, the receiver of the OLT integrates a power level of a rogue ONT for a time Tintegrate 440, which may extend further along the OLT time line 405 to an upper bound of a typical ranging window (e.g., a time equivalent to ranging an ONT 20 kilometers from the OLT). By not resetting the receiver of the OLT at the time Tinitial 415, but at about the time Texpected 425 (e.g., at the time Treset 445), in some embodiments, the amount of time the receiver integrates is limited or otherwise shortened to the time Tintegrate 440.
In
In this example, despite resetting the receiver at about the time Texpected 525 in a first ranging attempt, ranging is unsuccessful. In a second ranging attempt, the time to reset the receiver is changed by adding a delay 540 to the time Texpected 525. With the delay 540 added, the receiver is reset at a time Treset 545, and ranging is successful. With the ONT successfully ranged, the time Treset 545 may be optionally stored. In others words, in an event ranging is successful, the time Treset 545 is stored. As such, the receiver of the OLT in subsequent ranging attempts is not reset at the time Texpected 525, but at the time Treset 545.
In an alternative embodiment, resetting a receiver of an OLT at about a time a ranging response is expected to be received is based on a time which resulted in a successful ranging attempt previously.
In
In this example, despite resetting the receiver at about the time Texpected 525b in a first ranging attempt, ranging is unsuccessful. In a second ranging attempt, the time to reset the receiver is changed by subtracting a delay 540b from the time Texpected 525b. With the delay 540b subtracted, the receiver is reset at a time Treset 545b, and ranging is successful. With the ONT successfully ranged, the time Treset 545b may be optionally stored. In others words, in an event ranging is successful, the time Treset 545b is stored. As such, the receiver of the OLT in subsequent ranging attempts is not reset at the time Texpected 525b, but at the time Treset 545b.
In an alternative embodiment, resetting a receiver of an OLT at about a time a ranging response is expected to be received is based on a time which resulted in a successful ranging attempt previously.
To ensure upstream communications sent from an ONT is received by the OLT in a correct time slot, relative to upstream communications from other ONTs, data is delayed at least for an equalization delay before being sent. Equalization delays are assigned to ONTs to equalize logical distances between the OLT and ONTs, making every ONT appear equidistant from the OLT. Since physical distances from the OLT vary from ONT to ONT, the equalization delays also vary from ONT to ONT.
Based on an equalization delay assigned to a given ONT, a time a ranging response from the given ONT is expected to be received can be calculated or otherwise determined. As such, resetting a receiver about the time the ranging response from the ONT is expected to be received may be based on the equalization delay for the given ONT.
However, an equalization delay for a given ONT varies, for example, as physical conditions experienced (or expected to be experienced) by an Optical Distribution Network (ODN) change. For example, temperature variations cause fiber optic cables to lengthen and shorten, effectively causing the ONT to be further away from or closer to an OLT in optical path distance. Accordingly, to ensure the OLT receives upstream communications in the correct time slot, an equalization delay for a given ONT may be updated with some periodicity. Consequently, a time a ranging response from an ONT is expected to be received by an OLT and a time a ranging response from an ONT is actually received by the OLT may differ throughout a day or from season to season. Generally speaking, to accommodate such variations, a time to reset a receiver of an OLT may be delayed (or advanced) in increments.
In
In another embodiment, a size (or duration) of the delay increments 650 depends on an overall system tolerance window. For example, the overall system tolerance window may be defined or otherwise configured to be plus or minus 100 nanoseconds. Accordingly, a duration of each delay increment is some portion of the plus or minus 100 nanoseconds.
Continuing to refer to
In
In a first ranging attempt, resetting a receiver of the OLT is advanced by n number of delay increments from the time Texpected 720a, and the receiver is reset at a time Treset 725a-1. In this example, the first ranging attempt is unsuccessful, i.e., the ranging the ONT is unsuccessful. In an event ranging is unsuccessful in a next ranging attempt, the time to reset the receiver of the OLT is incremented (i.e., a time at which the receiver of the OLT is reset is incremented).
In a second ranging attempt, a time at which the receiver of the OLT is reset is advanced (not shown) by n−1 number of delay increments from the time Texpected 720a. In this example, the second ranging attempt is unsuccessful. In a third ranging attempt, a time at which the receiver of the OLT is reset is advanced by n−2 delay increments from the time Texpected 720a and the receiver is reset at a time Treset 725a-2. In this example, the third ranging attempt is successful.
In
In a first ranging attempt, resetting a receiver of the OLT is advanced by zero number of delay increments from the time Texpected 720b and the receiver is reset at a time Treset 725b-1. In this example, the first ranging attempt is unsuccessful, i.e., the ranging the ONT is unsuccessful. In an event ranging is unsuccessful in a next ranging attempt the time to reset the receiver of the OLT is incremented.
In a second and a third ranging attempt, the time to reset the receiver of the OLT is advanced (not shown) by 1 and 2 number of delay increments from the time Texpected 720, respective. In this example, the second and the third ranging attempt are unsuccessful. In a fourth ranging attempt, the time to reset the receiver of the OLT is advanced by 3 delay increments from the time Texpected 720b and the receiver is reset at a time Treset 725b-2. In this example, the fourth ranging attempt is successful. With the ONT successfully ranged, the time Treset 725b-2 may be optionally stored. In others words, in an event ranging is successful, the time Treset 725b-2 is stored. As such, the receiver of the OLT in subsequent ranging attempts is not reset at the time Texpected 720, but at the time Treset 725b-2.
In an alternative embodiment, resetting a receiver of an OLT at about a time a ranging response is expected to be received is based on a time which resulted in a successful ranging attempt previously.
In contrast to
In
For purposes of describing this and other embodiments, delay increments advancing a time to reset a receiver of an OLT (Treset) so that that the time (Treset) occurs in time before a time a ranging response from an ONT is expected to be received (Texpected) are referred to hereinafter as “negative” delay increments. Conversely, delay increments delaying a time to reset a receiver of an OLT (Treset) so that the time Treset occurs in time after the time Texpected are referred to hereinafter as “positive” delay increments. One skilled the art will readily acknowledge the choice of labels is arbitrary and is not intended to be limiting.
Continuing to refer to
In an nth ranging attempt, the time to reset the receiver of the OLT is advanced by zero number of negative delay increments from the time Texpected 820, and the receiver is reset at a time Treset 825-2. In this instance, resetting the receiver at about the time the ranging response is expected to be received does not result in successful ranging.
In (n+2)th ranging attempt, the time to reset the receiver of the OLT is delayed by 2 positive delay increments from the time Texpected 820, and the receiver is reset at a time Treset 825-3. In this example, the third ranging attempt is successful. With the ONT successfully ranged, the time Treset 825-3 may be optionally stored. In others words, in an event ranging is successful, the time Treset 825-3 is stored. As such, the receiver of the OLT in subsequent ranging attempts is not reset at the time Texpected 820, but at the time Treset 825-3.
In an alternative embodiment, resetting a receiver of an OLT at about a time a ranging response is expected to be received is based on a time which resulted in a successful ranging attempt previously.
For example, in a first ranging attempt, a time to reset a receiver of an OLT is delayed by n number delay increments from a time a ranging response from an ONT is expected to be received (Texpected). In a second ranging attempt, resetting the receiver is delayed by n−1 number of delay increments from the time Texpected, and so on. With each successive ranging attempt, a time to reset a receiver (Treset) occurs earlier in time. That is to say, a time to reset a receiver is changed in a “backwards” direction in time relative to the time Texpected in successive ranging attempts.
In another example, in a first ranging attempt, a time to reset a receiver of an OLT is delayed by n number of delay increments from a time a ranging response from an ONT is expected to be received (Texpected). In the case of n being equal to zero, the receiver is reset at about the time the ranging response from the ONT is expected to be received. In a second ranging attempt, resetting the receiver is delayed by n number of delay increments in one direction in time. In a third ranging attempt, resetting the receiver is delayed by n number of delay increments in the other direction in time, and so on. With each successive ranging attempt, a time to reset a receiver (Treset) occurs either earlier or later in time. That is to say, a time to reset a receiver starts at a “middle time” and can be shifted relative to the middle time in either directions in time in successive ranging attempts.
In yet another example, in a first ranging attempt, a time to reset a receiver of an OLT is delayed by n delay increments from a time a ranging response from an ONT is expected to be received (Texpected). In a second ranging attempt, resetting the receiver is delayed by n/2 delay increments from the time Texpected, and so on. With each successive ranging attempt, a time to reset a receiver (Treset) is halved.
In still another example, in a first ranging attempt, a time to reset a receiver of an OLT (Treset) is delayed by any number of delay increments from a time a ranging response from an ONT is expected to be received (Texpected). In a second ranging attempt, the time Treset is delayed by any number delay increments from the time Texpected, and so on. That is to say, the time to reset a receiver of an OLT is randomized.
In still yet another example, a time to reset a receiver of an OLT is delayed from a time a ranging response from an ONT is expected to be received (Texpected) by a delay which has been calculated or otherwise determined.
In
In
Whether the next ranging attempt is successful is determined (1015). If determined (1015) successful, a fault condition is identified and the flow diagram 1000 ends. If determined (1015) unsuccessful, however, in a next ranging attempt, a time to reset a receiver of an OLT (Treset) is changed (1020). With the time Treset changed (1020), the receiver of the OLT is reset (1025) at the time Treset.
Whether the next ranging attempt is successful is determined (1030). If determined (1030) successful, a fault condition is identified and the flow diagram 1000 ends. If determined (1030) unsuccessful, however, the flow diagram further determines (1035) whether to continue changing the time Treset.
Whether the flow diagram 1000 determines (1035) to continue changing the time Treset may be limited by, for example, a number of instances configured or otherwise permitted. By way of example, the number of instances is limited to 20 and, as such, the time Treset is changed (1020) 20 times before the time Treset is no longer changed.
In another example, the time Treset is changed (1020) until a range of times is tried or otherwise covered. By way of example, the time Treset is changed (1020) by 1 to 100 nanoseconds. That is, the time Treset is changed (1020) by 1 nanosecond in a first ranging attempt, by 2 nanoseconds in a second ranging attempt, and so forth. The time Treset continues to change (1020) until the time Treset is changed by 100 nanoseconds.
If the flow diagram 1000 determines (1035) not to continue changing the time Treset, a fault condition is identified and the flow diagram 1000 ends. If however, the flow diagram 1000 determines (1035) to continue changing the time Treset, the time Treset is incremented (1040). The flow diagram 1000 continues and the receiver of the OLT is reset (1025) at the time Treset.
Changing (1020) the time Treset and resetting (1025) the receiver of the OLT at the time Treset in a next ranging attempt continues until the flow diagram 1000 either determines (1030) that a next ranging attempt is successful or further determines (1035) not to continue changing the time Treset. In either instance, a fault condition is identified.
In
It should be understood that elements of the block diagrams, network diagrams, and flow diagrams described above may be implemented in software, hardware, or firmware. In addition, the elements of the block diagrams and flow diagrams described above may be combined or divided in any manner in software, hardware, or firmware. If implemented in software, the software may be written in any language that can support the embodiments disclosed herein. The software may be stored on any form of computer-readable medium, such as RAM, ROM, CD-ROM, and so forth. In operation, a general purpose or application specific processor loads and executes the software in a manner well understood in the art.
Although described in reference to ranging grants and ranging responses, it should be understood that other signals may be used to determine timing between the OLT and ONTs. Further, although the examples are presented herein in reference to optical networks, such as passive optical networks, it should be understood that example embodiments of the present invention can be applied to other networks, such as wireless radio frequency (RF) networks in which timing between two wireless devices can be disrupted by a rogue device.
This application claims the benefit of Provisional Application No. 60/848,955, filed on Oct. 3, 2006, entitled “Method and Apparatus for Rogue Tolerant Ranging and Detection,” and is a continuation-in-part of U.S. application Ser. No. 11/515,504 entitled, “Methods and Apparatus for Identifying a Passive Optical Network Failure,” filed on Sep. 1, 2006, which claims the benefit of U.S. Provisional Application No. 60/793,748, filed on Apr. 21, 2006. The entire teachings of the above applications are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60793748 | Apr 2006 | US | |
| 60848955 | Oct 2006 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11515504 | Sep 2006 | US |
| Child | 11651329 | US |
