Patent Application
20100208747
The present invention relates generally to telecommunications systems and in particular to methods and systems for improving upstream transmission efficiency in passive optical networks.
Communications technologies and uses have greatly changed over the last few decades. In the fairly recent past, copper wire technologies were the primary mechanism used for transmitting voice communications over long distances. As computers were introduced the exchange of data between remote sites became desirable for many business, individual and educational purposes. The introduction of cable television provided additional options for increasing communications and data delivery from businesses to the public. As technology continued to move forward, digital subscriber line (DSL) transmission equipment was introduced which allowed for faster data transmissions over the existing copper phone wire infrastructure. Additionally, two way exchanges of information over the cable infrastructure became available to businesses and the public. These advances have promoted growth in service options available for use, which in turn increases the need to continue to improve the available bandwidth for delivering these services, particularly as the quality of video and overall amount of content available for delivery increases.
One promising technology that has been introduced is the use of optical fibers for telecommunication purposes. Optical fiber network standards, such as synchronous optical networks (SONET) and the synchronous digital hierarchy (SDH) over optical transport (OTN), have been in existence since the 1980s and allow for the possibility to use the high capacity and low attenuation of optical fibers for long haul transport of aggregated network traffic. These standards have been improved upon and today, using OC-768/STM-256 (versions of the SONET and SDH standards respectively), a line rate of 40 gigabits/second is achievable using dense wave division multiplexing (DWDM) on standard optical fibers.
In the access domain, information regarding optical networking can be found in Ethernet in the First Mile (EFM) standards supporting data transport over point-to-point (p2p) and point-to-multipoint (p2mp) optical fiber based access network structures. Additionally the International Telecommunications Union (ITU) has standards for p2mp relating to the use of optical access networking, e.g., ITU-T G.984. Networks of particular interest for this specification are passive optical networks (PONs). Three PONs are, e.g., Ethernet PONs (EPONs), Broadband PONs (BPONs) and Gigabit capable PONs (GPONs), characteristics of which are displayed below for comparison in Table 1.
PON efficiency can be affected by numerous factors, for example, transmit power, distance, traffic volume, quality of equipment, quiet windows, etc. While there is often a tradeoff between cost and efficiency, efficiency improvements can reduce the overall cost of a system, particularly when considered over time. Another factor that can affect PON efficiency is the number of optical network units (ONUs) supported by each optical line termination (OLT) in the PON. The more ONUs per OLT in a PON, the more splitting of the optical signal (which increases the link budget) and the more control signaling that is typically required, which leads to more inefficiencies in the desired data transfers. As this technology matures, PONs could scale from 32 ONUs per OLT to possibly, 64, 128 or more per OLT, particularly if these ONUs are located relatively close to their OLT e.g., within 20 kilometers. As such, it would be desirable to decrease inefficiencies in PONs.
According to one exemplary embodiment a method for communications in a passive optical network having an optical line terminal (OLT) unit connected to a plurality of optical network units (ONUs), the method includes: optically transmitting at least one data packet from each of the plurality of ONUs toward the OLT during each of a plurality of ONU cycles, wherein at least one of said ONU cycles has a time duration of a plurality of Media Access Control (MAC) frame periods.
According to another exemplary embodiment a method for communications in a passive optical network having an optical line terminal (OLT) unit connected to a plurality of optical network units (ONUs), the method includes: optically transmitting, by the OLT, a first bandwidth allocation message during a dynamic bandwidth allocation (DBA) cycle; receiving, at the OLT, a first number of data packets from one of the plurality of ONUs associated with a first ONU cycle within the DBA cycle, which first number is based upon the first bandwidth allocation message; optically transmitting, by the OLT, a second bandwidth allocation message during the DBA cycle; and receiving, at the OLT, a second number of data packets from the one of the ONUs associated with a second ONU cycle within the DBA cycle, which second number is based upon the second bandwidth allocation message, the second number of data packets being different from the first number of data packets.
According to yet another exemplary embodiment, a communications node in a passive optical network includes a processor for executing instructions, and a. communications interface which transmits at least one data packet toward an optical line termination (OLT) during each of a plurality of optical network unit (ONU) cycles, wherein at least one of said ONU cycles has a time duration of a plurality of Media Access Control (MAC) frame periods.
According to still another exemplary embodiment, a communications node in a passive optical network includes a memory for storing program instructions associated with a dynamic bandwidth allocation (DBA) algorithm, a processor for executing the program instructions associated with the DBA algorithm which results in generation of a plurality of different bandwidth maps which describe a DBA cycle associated with upstream transmissions, and a communications interface for transmitting the plurality of different bandwidth maps in downstream frames during the DBA cycle.
The accompanying drawings illustrate exemplary embodiments, wherein:
a)-(c) show various parts of a downstream GPON Transmission Convergence (GTC) frame;
a) depicts two optical network units (ONUs) with associated transmission containers (T-CONTs) in a GPON;
b) illustrates a relationship between various transmission cycles used to transmit upstream data;
The following detailed description of the exemplary embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. Also, the following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims.
According to exemplary embodiments it is desirable to provide mechanisms and methods that improve the efficiency of passive optical networks (PON). In order to provide some context for this discussion, an exemplary Gigabit-capable PON (GPON) is shown in
According to exemplary embodiments, GPON 100 in
It will be understood by those skilled in the art that this purely illustrative GPON 100 can be implemented in various ways, e.g., with modifications where different functions are combined or performed in a different manner. For example the multiplexers (108, 110 and 116) typically are duplexers, but if an additional signal is being transmitted, e.g., a cable-television signal in a GPON 100, they can act as triplexers. Additionally in the upstream direction, the optical signal would typically have a different wavelength from the downstream signal and use the same multiplexers 106, 110 and 116, which have bidirectional capabilities.
In the downstream direction, the OLT 210 transmits a 125 μs long frame 212 which is composed of a GPON transmission convergence (GTC) header and a GTC payload. The GTC payload typically contains a sequence of GPON encapsulation method (GEM) headers and GEM payloads, with the GEM header containing information identifying the destination ONU, e.g., the ONU-ID, and the GEM payload containing the desired data. In
As described above,
The DBA algorithm, which can be stored in the format of executable program instructions, is executed periodically on the OLT 210 by polling the active ONUs 202, 206 for traffic utilization data and calculating an upstream bandwidth map, which is then transmitted to all of the ONUs. The periodicity with which the DBA algorithm is executed to generate new upstream bandwidth maps is referred to herein as a “DBA cycle” and is described in more detail below with respect to
As described above, a GPON 100 typically includes various ONUs 202, 206 each of which may, in turn, include one or more T-CONTs which serve as logical queues for transmitting data. An illustration of this is shown in
Illustrating the relationship between some of the transmission cycles used below and their corresponding structures will hopefully render more easily understood the further discussion of the exemplary embodiments. As shown in
The conventional DBA algorithm 504 uses these inputs to allocate a certain amount of bandwidth to each transmit queue or data stream of each ONU in each GTC frame. Thus, upstream data to be transmitted by the ONUs is parceled out to each MAC frame, e.g., each GTC frame 506, according to the bandwidth map generated by the conventional DBA algorithm 504 in a repeating format as shown by the data chunks 508 (which are the same for each GTC frame in a conventional DBA cycle) over the DBA cycle 510. Again, cylinders are used in the figure to represent the number and size (by thickness) of the bandwidth allocations. Each data chunk 508 includes data from each ONU 502, 512, 514, 516, 518, i.e., each ONU 502, 512, 514, 516, 518 transmits during each GTC frame 506 at their respective allocation window which repeats during DBA cycle 510. For example, the same amount of data 520 from ONU 502, data 522 from ONU 512, data 524 from ONU 514, data 526 from ONU 516 and data 528 from ONU 518 are transmitted in accordance with the same pattern/bandwidth allocation in each GTC frame 508. However using a conventional DBA algorithm, e.g., wherein each ONU transmits in each GTC frame using the same bandwidth, it is anticipated that, as the number of ONUs in a PON grows from 32 to 128 or more, communications inefficiencies will increase.
According to exemplary embodiments, on the other hand, a DBA algorithm can generate multiple, different bandwidth maps for use by the ONUs over a single DBA cycle. A conceptual diagram according to exemplary embodiments is shown in
More specifically, according to this exemplary embodiment the upstream data is parceled out in each GTC frame according to the plurality of different bandwidth maps created and transmitted by the DBA algorithm 604. In this purely illustrative example, a different map is being used for each GTC frame 608, 612 and 614 as shown by the different data transmission patterns of representative cylinder sets 606, 610 and 616, respectively. However, it will be appreciated that the present invention is not limited to using a different bandwidth map for each MAC or GTC frame and that, more generally, exemplary embodiments contemplate using two or more different bandwidth maps per DBA cycle. Returning to
For example, as will be appreciated by those skilled in the art, different bandwidth maps and different numbers of bandwidth maps (than those shown in
The characteristic of spreading out ONU transmissions over multiple GTC frames can reduce overhead transmissions. For example, a DBA algorithm can create a desired bandwidth mapping for the ONUs and T-CONTs by optimizing desired performance parameters such as DBA response time and jitter for different queues and traffic classes and by not restricting a single ONU cycle to one GTC frame. This allows for the accommodation of various sizes and types of traffic to be transmitted as desired in a more efficient manner. For example, traffic which is sensitive to longer response times may be scheduled earlier in the DBA cycle 602, i.e., in one of the first ONU cycles. For another example, voice traffic from a single ONU which tends to be jitter sensitive, i.e., variation of delay sensitive, can be put in relatively smaller chunks more frequently throughout a DBA cycle 602. Moreover, traffic with fixed bandwidth, as well as best-effort bandwidth, may be scheduled towards the end of the DBA cycle 602.
Using multiple bandwidth map messages per DBA cycle according to these exemplary embodiments, traffic can be scheduled on a per queue basis as compared to being scheduled purely based on traffic requirements associated with the various traffic classes, since each queue is often associated with several traffic classes. Also, a DBA scheme can be created according to exemplary embodiments where traffic requirements are also directly associated with queues which can simplify the upstream scheduling algorithm.
To better understand these features of the exemplary embodiments, a more detailed example of upstream scheduling and multiple bandwidth maps during a DBA cycle will now be described with respect to
Numerous variations on the foregoing exemplary embodiments are contemplated. For example, while traffic classes 810 are shown in
The DBA algorithm then determines how the different queues 808 of the various ONUs are to be scheduled during the assigned transmission time points for each ONU. If there are several ONU cycles in a DBA cycle 602, the DBA algorithm may schedule the transmission of different queues in different ONU cycles. The transmission of queues with jitter sensitive traffic classes may occur during each ONU cycle, whereas the transmission of response sensitive traffic can be scheduled in the earlier ONU cycles and transmission of best-effort type traffic in the later ONU cycles. Thus, according to exemplary embodiments, using the DBA algorithm, bandwidth maps can be generated and implemented over the course of a DBA cycle 602 which minimize overhead by using the largest ONU cycle which respects the system requirements, e.g., jitter requirements, the desire for the DBA cycle to be a multiple of the ONU cycle and whereby the ONU cycle roughly determines the transmission slots of each ONU.
The exemplary embodiments described above provide methods and systems for improving the upstream transmission efficiency in PONs, e.g., a GPON 100, which include various communications nodes, an example of which is shown in
Utilizing the above-described exemplary systems according to exemplary embodiments, a method for communications in a PON is shown in the flowchart of
Utilizing the above-described exemplary systems according to exemplary embodiments, another method for communications in a PON is shown in the flowchart of
The above-described exemplary embodiments are intended to be illustrative in all respects, rather than restrictive, of the present invention. All such variations and modifications are considered to be within the scope and spirit of the present invention as defined by the following claims. For example, the DBA algorithm could generate a single bandwidth map or at least three different bandwidth maps for use over a single DBA cycle. Also overhead for static bandwidth allocation (SBA) can be reduced by scheduling all of the ONUs over multiple GTC frames by using exemplary embodiments as described above. In the case of SBA, exemplary embodiments can generate a sequence of US BWmaps, that would not have to be recalculated every DBA cycle, since it is static. Moreover, for exemplary embodiments employing DBA, there exist two types of DBA: those with status reporting, and those without status reporting. Status reporting means that the ONUs report their queue buffer occupancy periodically, while in the non-reporting case, the DBA algorithm estimates the traffic needs for each ONU's T-CONT-based queue. Additionally, improvements similar to those as described in the exemplary embodiments herein could be used in other types of PONs. No element, act, or instruction used in the description of the present application should be construed as critical or essential to the invention unless explicitly described as such. Also, as used herein, the article “a” is intended to include one or more items.
