RU2537965C2 - Windband passive optical network with wave division - Google Patents

Abstract

FIELD: physics, communication.

SUBSTANCE: invention relates to communication equipment and may be used in telecommunication technologies. For this purpose it is suggested to realise effective system-network solutions in optical networks of access to wideband multimedia services during transition to communication networks of the next generation (NGN - IMS). The optical network comprises a central unit, subscriber nodes with transmitters and receivers, a switch of information packets. The invention makes it possible to double network capacity (number of connected subscribers) in respect to conventional WDM-systems due to application of division of transmission directions along directions of light flux propagation. Besides, it will make it possible to increase maximum radius of passive optical network coverage.

EFFECT: technical result consists in increased reliability and throughput capacity of passive networks.

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Description

The present invention relates to telecommunication technologies.

With its help, it is proposed to implement effective system-network solutions in access networks to broadband multimedia services when switching to next-generation packet networks NGN - IMS (Next Generation Network - Internet Multimedia Subsystem - next-generation communication networks - Internet multimedia subsystems). The application of this invention will significantly increase the maximum throughput of a single-fiber passive network infrastructure - PON tree (Passive Optical Network - passive optical network).

Using this invention will provide symmetry of maximum throughputs in the downstream and upstream directions of transmission in the access network. With its help, it will be possible to increase the capacity at the subscriber level and the quality of service indicators of the transmitted schedule due to the monopolization of the allocated channel resource by the subscribers ensured as a result of its use. It will significantly increase the efficiency of using fiber optic passive network infrastructure PON. When using it, the total maximum transmission speed in the fiber will be at least N times higher than in the traditional segments of the used PON networks, where N is the number of wavelengths used in the proposed network (number of subscribers).

In addition, this invention will double, in relation to traditional WDM systems, the capacity (number of connected subscribers) in the passive optical network segment by using the separation of upstream and downstream transmission directions not by wavelengths, as in traditional WDM systems, but by directions of light distribution. It will allow building networks with an increased coverage radius (up to 60-80 km).

These advantages are achieved due to the use of a significant number of N wavelengths in the proposed network, one wavelength per subscriber, and not two wavelength ranges (1.3 and 1.55 μm) for separating the upstream and downstream directions and the temporary separation of the common channel a resource between subscribers (using TDMA - Time Division Multiplexing Access), as in traditional PON networks (for example, in GPON).

The traditional PON network (GPON), described in the book: R. Freeman “Fiber-optic communication systems”, was chosen as a prototype. 3rd revised edition. - M .: Technosphere, 2006. - 496 p. (Translated from English) ISBN 5-94836-010-5.

The prototype is the GPON network (Gigabit PON - PON network operating at gigabit speeds) can support a symmetric bit rate in the tree up to 2.5 Gbit / s in each direction. However, the GFP protocol used in this network (Generic framing protocol - general frame protocol) performs a temporary separation of the total channel resource of the mono channel between all subscribers included in the network segment when transmitting the graph in the upstream direction, i.e. uses a variety of TDMA procedures with flexible separation. The bandwidth of such a 2.5 Gbit / s network is shared between all subscribers included in the PON tree (the maximum number of such subscribers can reach 64), which leads to a significant limitation of the channel resource allocated to each subscriber.

In addition, the implementation of the GFP protocol, which requires measuring the propagation delays from the central node to each subscriber (phase ranking) in the equipment used, followed by these delays when assigning access intervals to subscribers (which means storing their base throughout the PON tree in the memory of the central node) , controlling the power of the transmitters (ranking by power), providing clock and loop synchronization, flexible separation of the channel resource and other complex procedures, significantly complicates the equipment of the cent the OLT (Optical Line Termination) node and the ONU (Optical Network Unit) peripheral nodes, which means it reduces their reliability. In addition, short-term malfunctions in the GPON system (for example, interruption of the OLT power supply) lead to the transition to the initialization mode, which blocks the transmission of data for the initialization time and reduces the quality of service of the traffic transmitted in the network.

Thus, the prototype under consideration has the following significant disadvantages:

- low efficiency of the use of optical fiber in the passive optical infrastructure of the PON tree - maximum total speed of up to 5 Gb / s;

- dividing the channel resource of the common channel (mono channel) between all subscribers, which means reducing the maximum speed at the subscriber level, reducing the quality of service for broadband subscriber traffic (increasing delays and their variations);

- high complexity of active terminal equipment, low reliability, lack of full logical transparency;

- the presence of intervals for blocking the transmitted schedule when switching to the initialization mode, the dependence of the capacity at the subscriber level on the total number of subscribers in the network segment and on the variation in the length of subscriber lines;

- limited (up to 20 km) network coverage radius.

The aim of this invention is the creation of such a passive optical network (PON), which will provide a significant increase in the efficiency of use of optical fiber in the PON tree (increase the total maximum speed in the fiber). In addition, the created passive network should ensure for each of the subscribers connected to the network, the symmetry of the maximum transmission speeds of the subscriber traffic in the downstream (forward) and upstream (reverse) flows, and these speeds should not depend on the number of connected subscribers (network capacity) . In the created network, each of the subscribers of the entire resource should be monopolized, organized at the wavelengths allocated to the subscribers, which will inevitably provide an improvement in the quality of service of subscriber traffic in such a network. The maximum total transfer rate in the fiber of such a network should be at least N times higher than in the GPON network selected as a prototype.

The capacity of the network created as a result of achieving the objective of this invention should be increased in 2 times with respect to traditional WDM systems, with the number of wavelengths being used unchanged, by applying the principle of separation of downward (forward) and upward (reverse) transmission directions in directions propagation of the light flux, carried out through the use of special separation devices, and not due to separation by the wavelength ranges selected in various transparency windows of the optical fiber, as in the prototype e (GPON), or by wavelengths, as in traditional WDM systems.

In addition, the aim of the invention is to create a simple, complex procedures, logically transparent and reliable passive optical network, focused on the use of domestic electronic component base (ECB) of fiber optic systems (VOS), minimizing the likelihood of undeclared functionality (bookmarks) -spyware in imported VLSI), which provides increased information security of the proposed network. Another objective of this invention is the creation of a network with an increased (up to 60-80 km) coverage radius that does not have a dependency on the capacity at the subscriber level on the number of subscribers included in the network and on the variation in the length of subscriber lines.

To achieve this goal, it is proposed to supplement the prototype (see the diagram of the upper part of Fig. E.3.2. "The main elements of the PON architecture and the principle of operation" on page 473 of the above book) in the OLT part: by receivers and transmitters for N wavelengths (in number of connected subscribers), devices for separating propagation directions, connected instead of WDM 1310/1550 gf, an optical multiplexer-demultiplexer for N wavelengths, in addition, include an Ethernet switch in the OLT, and in the part of the passive node it is proposed to replace the passive splitter JZ 131 0, 1550 nm (see Fig. 1.3.2. In the book) with an optical multiplexer for N wavelengths, in addition, in the subscriber unit ONU, replace WDM 1310/1550 with a device for separating propagation directions, install transmitters configured on ie in ONU ie the wavelengths allocated to the corresponding i-th subscribers and enter the Ethernet subscriber switch into the ONU.

It is proposed that a broadband optical access network is performed as follows:

- build OLT and ONU networks on the basis of standard Ethernet switches, introduce N transceivers into the OLT network at the wavelengths allocated to subscribers (one wavelength per subscriber), introduce N devices for separating the directions of the light flux propagation in the OLT network, and an optical multiplexer a demultiplexer for N wavelengths, and use an optical multiplexer-demultiplexer for N wavelengths as a passive network node, in each ONU introduce one device for separating the directions of propagation of the light flux (instead of WDM 1310/1550 nm), O NU build on the basis of a standard Ethernet switch, in each ONU install a transmitter (Tx) on the λi wavelength allocated to this subscriber, and in OLT the optical ports of the receivers and transmitters must be connected to the separated ports of the separation devices, and the combined ports of these devices are connected to the corresponding ports component signals of the optical multiplexer-demultiplexer, the combined port of this multiplexer-demultiplexer is connected via the trunk optical line to the same port of the multiplexer-demult plexor of the passive node, while the ports of the component streams of the passive node multiplexer-demultiplexer are connected via optical subscriber lines to the ONU subscriber nodes, in which are connected to the combined ports of the separation devices, and the receivers and transmitters installed in the subscriber switches are connected to the divided ports of these devices each of the subscriber transmitters is tuned to the corresponding i-th wavelength.

Based on the proposed passive optical network, broadband access networks for services, including multimedia, in the next-generation packet networks NGN - IMS can be implemented, focused on the use in FTTB and FTTH class solutions (Fiber to the Bilding - bringing fiber to the building and Fiber to the Home - bringing fiber to the subscriber's premises).

In addition, the proposed passive network can find application in the construction of high-speed local area networks with a large coverage area (large enterprises, residential complexes, campuses). Also, the passive infrastructure of the proposed network can be used to deploy distributed systems of optical sensors, and can also be used, for example, in the construction of phased array antennas and in a wide class of other distributed systems with a large (up to 60-80 km) coverage radius.

The coverage radius in this case will be determined by the optical power budget of the applied transceiver modules.

Figure 1 shows one example of building a broadband passive network with wave separation, where:

1 ₁₁ -1 _i1 - ... 1 _N2 - optical transmitters;

2 ₁₁ -2 _i1 - ... 2 _N2 - optical receivers;

3 ₁ -3 ₂ - Ethernet switch of the central node;

4 ₁₁ -4 _i1 - ... 4 _N2 - devices for separating the directions of propagation of the light flux;

5 ₁ -5 ₂ - optical multiplexer;

6 - central node (OLT);

7 ₁ -7 _N - subscriber units (ONU).

Optical transmitters 1 ₁₁ -1 _i1 - ... 1 _N2 terminals of the central and subscriber units are designed to convert an electrical linear signal into an optical linear signal at the wavelength of the i-th subscriber and input power into the optical fiber of the lines.

Optical receivers 2 ₁₁ -2 _i1 - ... 2 _N2 terminals of the central and subscriber units are designed to convert an optical linear signal into an electric linear signal (at all wavelengths, without wavelength selection).

The Ethernet switch 3 of the central node is designed to switch information packets (Ethernet frames) at the level of a passive optical network to provide information transfer through the interface to the backbone network and to generate and process linear electrical signals supplied to transmitters 1 ₁₁ -1 _N1 and received from receivers 2 ₁₁ -2 _N1 .

Devices 4 ₁₁ -4 _i1 - ... 4 _{N2 for} separating the directions of propagation of the light flux are designed to separate the forward and reverse directions of transmission at the level of optical signals in the central node (OLT) and in the subscriber nodes (ONU).

Optical multiplexers 5 ₁ -5 ₂ are intended for combining component optical signals at subscriber wavelengths (total N wavelengths) into a combined multi-wave linear signal and for selecting a multi-wave linear signal for subscriber wavelengths, extracting component single-wave signals at subscriber wavelengths at corresponding spatial divided ports for the subsequent transmission of these signals on subscriber lines to the corresponding terminals (ONU) and to the ports of the switch 3 ₁ .

The central node (OLT) 6 is designed to provide the process of transmitting information through the interface towards the backbone network, to support the process of switching information packets at the segment level of the passive network, to form, transmit and process a linear multi-wave optical signal, to combine and select subscriber optical signals at the wavelengths of subscribers , separating and combining transmission directions in the directions of light flux propagation, maintaining the transformations of an electric signal - light - electric esky signal at each wavelength. Subscriber units (ONU) 7 ₁ -7 _N are designed to provide information transfer through interfaces towards local networks of subscribers, switching information packets at the level of local networks of subscribers and in a passive network, separating and combining transmission directions along the directions of light flux distribution in subscriber lines maintaining the conversion of an electrical signal - light - an electrical signal at the wavelengths of the respective subscribers.

The main advantages of the proposed passive optical network with wave separation are as follows.

1. The proposed passive network with wave separation provides a significant increase in throughput in each segment and a significant increase in the efficiency of using optical fiber in a passive optical infrastructure. When using the cheapest wave multiplexing technology CWDM (Coarse Wave Division Multiplexing - Multiplexing coarse wavelength division multiplexing), and using all the 16 wavelengths of the grid CWDM, at a speed in the forward and reverse channels (V _CAD) of each subscriber 2.5Gb / s (as in the selected prototype) the total speed in the passive network infrastructure of the proposed network V _∑ = 16 · V _channel · 2 = 80 Gbit / s (in the selected prototype this value is only 5 Gbit / s).

2. Each subscriber of the proposed network monopolizes the entire channel resource of the bandwidth of the allocated wave channel, which significantly improves the quality of service for the schedule in the proposed network. In the above example, this resource is 2.5 Gbit / s (in the prototype, this value is only (2.5 / N) Gbit / s with the number of subscribers in the PON tree N = 64, this value will be equal to only 0.039 Gbit / s, provided that sharing the channel resource between all subscribers of the PON tree, even without taking into account losses due to the assignment of guard intervals proportional to the spread of propagation delays).

3. Doubling the capacity (number of connected subscribers) in the PON network as compared to the use of traditional wave compression technologies due to the separation of transmission directions not by wavelengths (as in traditional systems), but by the directions of light flux propagation. In the case of the proposed network, for connecting each subscriber, only one wavelength is required (and not two, as in traditional WDM systems).

4. The proposed passive network provides full logical transparency in dedicated channels and does not require any additional headers to be attached to information packets (frames), as in the prototype. In addition, there is no dependence of the capacity at the subscriber level on the number of subscribers included in the network segment, and on the variation in the length of the subscriber lines.

5. The proposed passive network uses wave separation and can be used commercially available domestic elements of the BOC-optical transceivers, optical multiplexers-demultiplexers, optical circulators and splitters, as well as domestic switches packet information, including those with special certificates of conformity, which passed special checks and special studies. This excludes the possibility (or minimizes the probability of these events to the minimum) of the presence of undeclared functionality in the equipment of the proposed network, which provides increased information security in the proposed network, in relation to the prototype based on imported ultra-large integrated circuits (VLSI).

6. The proposed passive network has an increased (compared to the prototype) coverage radius, which is determined by the power budget of the selected optical transceivers (transceivers). For example, when using transceivers with a maximum transmission distance in the point-to-point scheme of up to 80 km, in the experimental sample constructed at the branch of the Central Scientific Research Institute of Scientific Research, the proposed passive network, the coverage radius in the point-to-many-point scheme was not less than 40 km (at that time as in the prototype, this value is only 20 km).

7. The proposed network has increased (compared to the prototype) reliability. This is achieved, first of all, because in case of failure of a single transceiver (one of the unreliable elements) in the central node of the PON tree of the GPON prototype, there will be no communication between all the subscribers of the tree (segment) under consideration, and in the proposed network, failure of one of the transceivers in OLT will only lead to failure communication with just one of the subscribers. In addition, it can be shown by analyzing the mathematical model of reliability developed by the authors of the invention and a comparative analysis of this model with a similar model for the GPON prototype, which, due to the blocking of the graph when switching to the initialization mode in the GPON network and the absence of this phenomenon in the proposed network, an additional gain is achieved in reliability indicators of the proposed network.

The proposed broadband passive optical network with wave separation was implemented in FSUE TsNIIS (branch of LO TsNIIS) based on the following components.

Typical SFPs (Small Form factor Plug-in - small-sized interchangeable) optical modules with a power budget calculated for the line length dot were used as transmitters 1 ₁₁ -1 _i1 - ... 1 _N2 and receivers 2 ₁₁ -2 _i1 - ... 2 _N2 optical -point up to 80 km, type TBSF 15d-80-12gLC-3c at wavelengths of 1550, 1570, 1590, 1610 nm. As switches 3 ₁ -3 ₂ Ethernet of the central and subscriber nodes, layer 2 packet switches were developed and developed at the branch of the Central Scientific and Research Institute of Computer Science. Devices 4 ₁₁ -4 _i1 - ... 4 _{N2 of} separation of the directions of propagation of the light flux were implemented in three versions:

- based on serial alloyed single-mode optical couplers 1 × 2 50/50 3.0 LC / UPC manufactured by ZAO Component, St. Petersburg;

- based on serial planar single-mode optical splitters 1 × 2 50/50 3.0 3LC / UPC manufactured by LLC Prointekh, St. Petersburg;

- on the basis of serial single-mode optical circulators FBT-CR-55 (1550 nm) developed and manufactured by LLC "PKT" Svyaz Engineering ".

Optical multiplexers 5 ₁ -5 ₂ were used serial, developed and manufactured by ZAO Component, type CWDM MUX 1 × 4 1550-1610 3.0 LC / UPC 1.5 m.

The central node 6 (OLT) and subscriber nodes 7 ₁ -7 _N were designed and manufactured in the branch of the LO TsNIIS based on the above components. An optical line with a length of 40 km, 4 reels of 10 km each connected in series, single-mode Fujikura fibers wound around 4 standard reels of 10 km each, manufactured at OPTEN-CABLE LLC, Leningrad Region, was used as the main line.

Built and tested at the Leningrad Central Scientific Research Institute, in accordance with the program methodology 4a1.600.004PM for testing an experimental sample of the CWDM-PON segment (test report 4a1.600.004PI of 03.12.2013), an experimental sample of the CWDM-PON segment - Broadband passive network with wave separation was integrated into the research stand of the FSUE TsNIIS branch - LO TsNIIS for research and demonstration of elements of the hardware-software complex of emergency warning and public information (PAK KSEOIN), where it is functioning properly at present e time.

Claims (1)

Broadband passive optical network (PON) with wave separation, including a central node (OLT), subscriber nodes (ONU) with their respective transmitters (TX) and optical receivers (RX), passive optical node, trunk (AML) and subscriber optical lines, characterized in that the OLT includes a packet information switch, in which N transmitters are installed, tuned to N wavelengths and N optical receivers (N is equal to the number of subscribers in the network), as well as N devices for separation of directions the luminous flux and the first optical multiplexer-demultiplexer for N wavelengths, and a second optical multiplexer-demultiplexer for N wavelengths was used as a passive optical network node, information packet switches were inserted into the subscriber network nodes, in which the corresponding optical transmitters configured At the wavelengths of subscribers and optical receivers, as well as ONU, devices for separation of propagation directions were introduced, and in OLT the optical ports of the transmitters are connected to by the first divided ports of the separation direction separation devices, the optical ports of the receivers are connected to the second divided ports of the separation devices, the combined ports of these devices are connected to the corresponding component signal ports of the first optical demultiplexer multiplexer, and the combined port of this multiplexer-demultiplexer is connected via an optical trunk (AML) to the same port of the second multiplexer-demultiplexer, which performs the function of a passive optical evils, and the ports of component streams of the second multiplexer-demultiplexer connected by subscriber lines to subscriber units in which the ports are attached to the combined separating device to the first split ports of the devices attached optical receiver port and to the second split ports connected subscriber node transmitter ports.