RU2719318C1 - Method of transmitting information over fiber-optic communication lines with distributed access nodes - Google Patents

Abstract

FIELD: fiber-optic communication lines.

SUBSTANCE: invention relates to systems for transmitting information over fiber-optic communication lines with distributed access nodes. Optical switches are connected to outputs of power supply units of access units and perform transmission of linear signals bypassing access units with switched off power supply or connection of linear signals of two communication directions to first and second ports of access nodes with switched on power supply.

EFFECT: technical result consists in reduction of energy budget losses FOCL, which provides considerable reduction of required number of optical fibers for communication of terminal stations of FOCL section with distributed access nodes and reduced volume of station equipment FOCL.

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Description

Application area

The invention relates to systems for transmitting information via fiber optic communication lines (FOCL) with access nodes distributed along the inter-station sections connecting the terminal stations.

State of the art

Fiber-optic communication lines (FOCL) with a large number of access nodes distributed at inter-station sites are used on technological communication networks of various departments (Russian Railways, PJSC Gazprom, Svyaztransneft, etc.). When the power is off, the access nodes are in a passive state, and communication from the subscriber terminals of these nodes with the terminal stations is not performed. When the power is on, the access nodes are in an active state, and communication is made from subscriber terminals with terminal stations of the site. The possibility of organizing communication from each active access node, in principle, should be provided in the directions to both stations installed at the start and end points of the FOCL section. The number of access nodes in the FOCL inter-station section is determined by the length of the section and the specified intervals between the access nodes.

The maximum length of the FOCL inter-station section with distributed access nodes is limited by the FOCL energy budget. Modern devices for transmitting / receiving optical signals provide an energy budget of the order of 35-37 dB. In practice, taking into account the necessary operational margin, the FOCL energy budget is usually taken into account ~ 30 dB. The energy budget of the fiber-optic communication line is spent on the compensation of losses introduced by the optical cable and the compensation of losses in devices connecting access nodes.

The loss of the energy budget introduced by the optical cable increases in proportion to the increase in the length of the inter-station section, and, therefore, the part of the energy budget that can be used to connect access nodes decreases. At the same time, the required number of access nodes increases with the length of the inter-station section of the fiber optic link. If it is impossible to organize a given number of access nodes connected to one optical fiber (due to restrictions on the energy budget), it is necessary to use additional optical fibers with dividing the total number of access nodes into groups connected to different optical fibers.

Thus, the technical problem is the need to reduce the loss of the energy budget of the fiber optic link with distributed access nodes. The solution to this technical problem provides:

- an increase in the number of access nodes connected to one optical fiber;

- increase the maximum length of the inter-station section of the fiber optic link;

- reducing the number of optical fibers for communication with a given number of access nodes;

- reduction in the volume of FOCL station equipment, which is proportionally related to the number of optical fibers involved.

Losses in the energy budget that occur in devices connecting access nodes depend on the method used to transmit information over fiber optic links with distributed access nodes.

There is a known method of transmitting information over fiber optic links with access nodes distributed along inter-station sections and having two ports — the first port for communication with the first terminal station of the section and the second port for communication with the second terminal station of the section, based on CWDM (Coarse Wavelength Division Multiplexing) technology in accordance with ITU-T Recommendation G.694.2 [1]. The attached drawing (Fig. 1) shows a communication organization diagram based on CWDM technology. Information is transmitted using 16 wavelengths located in the range 1310-1610 nm with an interval of 20 nm. Two wavelengths are allocated for each access node: one for receiving a signal from station 1 or 2, and the second for transmitting a signal from an access node to stations. Moreover, for the connection of access nodes 8, 9 with two stations of the FOCL section, two optical fibers 4 are required. The station equipment contains a packet switch 3 and an optical multiplexer-demultiplexer 18 of the CWDM spectrum.

The access nodes to the optical fiber are connected via optical OADM (Optical Add / Drop Multiplexer) 19 multiplexers that branch two spectral components of the linear signal with the wavelengths assigned to this access node and transit the rest of the spectrum of the linear signal. This spectral branching is performed continuously, regardless of the active or passive state of the access nodes.

The attenuation of the spectral components of a linear signal in OADM multiplexers usually does not exceed 0.7-0.8 dB both in the branch direction and in the transit passage direction, i.e. connecting eight access nodes introduces a 5-6 dB energy budget loss. However, it should be noted that with CWDM technology, the wavelength range (16 wavelengths) limits the number of access nodes connected to one optical fiber to eight. This prevents the full use of the fiber optic energy budget to increase the number of access nodes in the inter-station section, which in fact leads to losses of the unused portion of the fiber optic fiber energy budget.

With an FOCL energy budget of ~ 30 dB, a line cable attenuation of up to 0.5 dB / km and an interval between access nodes of 1 km, 6 optical fibers are required to connect 24 access nodes in a 25 km section. With a section length of 35 km, for connecting 34 access nodes with two stations of a section, it is required to use 8-10 optical fibers, and with a length of 50 km for connecting 49 access points with two stations in a section, 12-14 optical fibers are required.

The disadvantage of the method based on CWDM technology is the significant amount of energy budget losses due to its incomplete use in inter-station areas due to the limited wave range. As a result, there is a need for a significant number of optical fibers for communication with distributed access nodes. In addition, as part of the station equipment, implemented on the basis of CWDM technology, optical multiplexers-demultiplexers are required to combine the spectral components of a linear signal in transmission and separation in reception. The number of such devices is equal to the number of optical fibers used in the fiber optic section. As a result, the volume of station equipment CWDM significantly increases in long sections of fiber-optic communication lines.

Closest to the claimed method is a method of transmitting information over a fiber optic link with access nodes distributed along inter-station sections and having two ports - the first port for communication with the first terminal station of the section and the second port for communication with the second terminal station of the section, based on GPON technology ( Gigabit Passive Optical Network) in accordance with ITU-T Recs G.984.2 and G.984.3 [2], [3]. The attached drawing (Fig. 2) shows a communication organization diagram based on GPON technology. Information is transmitted from station 1 or 2 to access nodes 8, 9 at one wavelength (for example, 1310 nm), and information is transmitted from access nodes to the station at another wavelength (for example, 1490 nm). At the same time, two optical fibers are required to connect the access nodes with two stations of the FOCL section 4. A linear signal from the FOCL station equipment containing the server 16 and packet switch 3 is sent to all access nodes, but its reception, processing, and transmission of response messages are performed only when the active state of the node and when the address of the node matches the address of the received message.

Connecting the access nodes to the optical fiber is carried out through optical splitters (splitters) 17, which branch out part of the signal energy to the access node and the transit passage of the rest of the energy of the linear signal to other access nodes. This branching of the linear signal is performed continuously, regardless of the active or passive state of the access node, i.e. from the on or off state of the power source of the access node.

Losses in the energy budget due to the connection of access nodes depend on the branch coefficients of a portion of the energy of the linear signal in the access nodes. Optical splitters are mainly used with branch coefficients of 5%, 10%, etc. up to 50% having branch attenuation respectively 15.2 dB, 11.3 dB, etc. up to 3.6 dB, and the attenuation of the transit passage, respectively, 0.45 dB, 0.6 dB, etc. up to 3.6 dB. To minimize energy budget losses introduced by access nodes in one optical fiber, the access nodes closest to the station (having a high level of a linear signal) should be connected through splitters with a minimum branch coefficient, and as the access nodes move away from the station (and therefore when the level decreases) linear signal) it is required to use splitters with increasing branch coefficients.

The number of access nodes having a minimum branch coefficient is limited by reducing the level of the linear signal to a value less than the branch attenuation introduced by the splitter with a coefficient of 5%. In this case, a splitter with a branch coefficient of 10% should be used in the next access node. The number of access nodes with a coefficient of 10%, etc., is likewise limited. The maximum allowable number of access nodes in one optical fiber depends on the FOCL energy budget (~ 30 dB), the kilometer attenuation of the line cable (usually no more than 0.5 dB / km), and the interval between the access nodes.

Typically, on technological communication lines, the interval between access nodes is about 1 km. With an interval between access nodes of 1 km, with an optimal choice of branch coefficients of a linear signal in the range from 5% to 50% and with a uniform distribution of access nodes in the FOCL section, up to 24 access nodes can be connected to one optical fiber. This number consists of the limit number of access nodes with a branch coefficient of 5% (namely, 16, because at the connection point of the next node, the linear signal level is 14.3 dB less than the branch attenuation of 15.2 dB), three access nodes with a coefficient of 10% and etc. The length of the FOCL section is 25 km. With a section length of 35 km, energy budget losses limit the number of access nodes connected to one optical fiber to 16. Therefore, to connect 34 access nodes with two station stations, 4-6 optical fibers are required. With a section length of 50 km, the number of access nodes connected to one optical fiber is reduced to four, and for connecting 49 access nodes with two station stations, 24-26 optical fibers are required.

As an example, we can cite the following data on the development of optical systems of distillation communications for Russian Railways networks carried out by the Giprotransssignalsvyaz Institute (GTSS), St. Petersburg [4]. The GTSS project implemented on the basis of GPON technology provides the following data: - 6 optical fibers are provided for connecting 26 access nodes (distributed with an interval of 1 km) on an inter-station section of 26.0 km in length (between Glubokoe-Novoye and Siya stations); - on a 39.4 km long section (between Lodma and Lukovetsky stations) for connecting 39 access nodes, the number of optical fibers is 16; - on a 45.5 km long section (between Siya and Karpogory stations) for connecting 46 access nodes, the number of optical fibers is 26. The disadvantage of this method, based on GPON technology, is a significant amount of energy budget loss when branching a linear signal at the access point connection points . As a result, there is a need for a significant amount of optical fibers, which limits the use of this method based on GPON technology. At the same time, over long sections of fiber optic links (more than 25 km), the volume of station equipment also increases substantially in proportion to the number of optical fibers involved. In addition, the complexity of the GPON station equipment is associated with the need for a special server to control the sequence of access nodes depending on the time delays of the signal in the optical linear path.

Short description

The objective of the invention is to develop a method for transmitting information over fiber optic links with distributed access nodes.

The technical result when using the proposed method of transmitting information over fiber-optic communication lines with distributed access nodes is to significantly reduce the loss of fiber energy budget (compared to GPON technology), which provides a significant reduction in the required number of optical fibers for connecting terminal stations of the fiber-optic communication line with distributed access nodes and reducing the volume of FOCL station equipment.

The technical result is achieved in the invention due to the fact that:

- a linear signal is transmitted bypassing the access nodes when the power is off, without branching part of the energy of the linear signal to these access nodes;

- a linear signal of two directions of communication is connected to access nodes when the power is on;

- the linear signal is relayed with input / output of information in the access nodes when the power is on, which ensures the restoration of the level of the linear signal to the initial value, i.e. full compensation of energy budget losses caused by attenuation of a linear signal when passing through a fiber optic link to the connection point of this access node.

The communication organization scheme based on the proposed method is presented in figure 3. In figures 1 and 2, the communication organization schemes are presented, respectively, based on CWDM and GPON technologies. All schemes use the following position designations:

Position 1 - station A (the first terminal station of the fiber optic link);

Position 2 - station B (the second terminal station of the fiber optic link);

Position 3 - station packet switch with optical ports;

Position 4 - optical fiber in the fiber optic section;

Position 5 - subscriber terminal of the access node;

Position 6 - power supply in the off state;

Position 7 - power source in the on state;

Position 8 - access node in a passive state;

Position 9 - access node in the active state;

Position 10 - the first port of the access node (for communication with station A);

Position 11 - packet switch access node;

Position 12 - the second port of the access node (for communication with station B);

Position 13 is an optical switch in the position of transmitting a linear signal bypassing the access node;

Position 14 is an optical switch in the position of the lead of the linear signal to the ports of the access node;

Position 15 - control input of the optical switch;

A, B - communication direction from the subscriber terminal of the access node to station A or station B of the FOCL section (respectively);

λ1 is the wavelength of the optical linear signal received by the access node from station A and transmitted to station B;

λ2 is the wavelength of the optical linear signal received by the access node from station B and transmitted to station A;

Position 16 - server;

Position 17 - optical splitter (splitter);

Position 18 - optical spectrum multiplexer-demultiplexer CWDM;

Position 19 - optical input / output multiplexer;

λN is the wavelength of the spectrum of CWDM (N≤16).

DETAILED DESCRIPTION OF THE INVENTION

The proposed method of transmitting information over FOCL with distributed access nodes is free from the disadvantages indicated in the analogues.

The attached drawing (Fig. 3) shows a communication organization scheme based on the proposed method for transmitting information on fiber-optic communication lines with access nodes distributed along inter-station sections and having two ports — the first port for communication with the first terminal station of the section and the second port for communication with the second terminal station of the site. At the fiber optic link between stations 1 and 2, the access nodes are connected to the optical fiber 4 and the access nodes are bypassed using the optical switches 13, 14. When the power supply 6 is off, the access node 8 is in the passive state, and the optical switch 13 is in the position providing a bypass of the linear signal without branching to the access node 8. When the power source 7 is turned on, the access node 9 is in the active state, and the optical switch 14 is in the connection position of the linear signal of both directions of communication to the access node. In the access node 9, the packet switch 11 retransmits the linear signal received by the first port 10 of the access node in the direction of transmission of the second port 12, the relay of the linear signal received by the second port 12 of the access node in the direction of transmission of the first port 10, as well as input and output information related to the subscriber terminal of this access node.

A linear signal is transmitted from station A of the FOCL section towards station B at one wavelength λ1 (for example, 1310 nm), and information is transmitted in the opposite direction at another wavelength λ2 (for example, 1490 nm). To maintain the wavelength of the linear signal when switching from the bypass mode of the access node to the relay mode, the access nodes use optical transceivers with an appropriate wavelength distribution, in which the first linear port 10 receives an optical linear signal at a wavelength of λ1 and transmission at a length of wave λ2, and the second linear port 12 receives an optical linear signal at a wavelength of λ2 and transmission at a wavelength of λ1.

The specified method essentially differs in that:

- optical switches are introduced into the fiber-optic communication line, connected to the outputs of the power sources of the access nodes and transmitting linear signals bypassing the access nodes when the power is off or connecting linear signals of two directions of communication to the first and second ports of the access nodes when the power is on;

- a packet switch is introduced into each access node, providing relay of the linear signal received by the first port of the access node in the direction of transmission of the second port, relay of the linear signal received by the second port of the access node in the direction of transmission of the first port, as well as input and output of information, related to the subscriber terminal of the access node;

- in access nodes, when the power is on, the first port receives an optical linear signal at a wavelength of λ1 and transmits at a wavelength of λ2, and the second port receives an optical linear signal at a wavelength of λ2 and transmits at a wavelength of λ1.

Thus, a linear signal is transmitted bypassing access nodes that are in a passive state, a linear signal of both directions of communication is connected to access nodes when they transition to an active state, and a linear signal is relayed with input / output of information in access nodes that are in an active state.

Bypassing access nodes that are in a passive state, a significant reduction in the losses of the FOCL energy budget at the connection points of access nodes is achieved. The connection of the linear signal of both directions of communication to the access nodes upon their transition to the active state and relaying of the linear signal in these nodes ensures the restoration of the level of the linear signal to the initial value, i.e. full compensation of energy budget losses caused by attenuation of a linear signal when passing through a fiber optic link to the connection point of this access node.

The achieved reduction in losses of the fiber-optic fiber budget allows increasing the number of access nodes connected to one optical fiber. As a result, the number of optical fibers for communication with the required number of access nodes in the inter-station section is reduced, and the volume of FOCL station equipment associated with the number of optical fibers involved is also reduced.

It should be noted that when using the proposed method for connecting access nodes with two stations of the FOCL section, one optical fiber is required, and not two fibers, as in the indicated analogues. In the FOCL station equipment, in this case, only packet switch 3 is required, but no server is needed to control access nodes, as in the GPON variant, and optical multiplexers, as in the CWDM variant, are not required.

The signal attenuation in commercially available optical switches usually does not exceed 0.5-0.6 dB both in the position of connecting the linear signal to the access node and in the position of transmitting the linear signal bypassing the access node. With an FOCL energy budget of ~ 30 dB, a line cable attenuation of up to 0.5 dB / km and an interval between access nodes of 1 km, to connect 24 access nodes on a 25 km section, in the case of the proposed method, only one optical fiber is required, and not 2 -6 fibers, as in the specified analogues. With a section length of 35 km, it is sufficient to use two optical fibers rather than 4-6 fibers (as with the GPON method) or 8-10 fibers (as with the CWDM method) for connecting access nodes with two station stations. With a section length of 50 km, it is sufficient to use 7 optical fibers rather than 24-26 fibers (as with the GPON method) or 12-14 fibers (as with the CWDM method) for connecting access nodes with two station stations.

Thus, when using the proposed method of transmitting information over fiber optic links with distributed access nodes, a significant reduction in the loss of the fiber budget energy budget is achieved. As a result, the required number of optical fibers is reduced in comparison with the indicated known analogues: twice in sections up to 25 km long and up to four times in sections up to 50 km long. The volume of station equipment is significantly reduced due to the fact that the number of optical fibers involved is reduced, and a server is not required to control the sequence of work of distributed access nodes, as in the GPON version, and station optical multiplexers, as in the CWDM version, are not required.

Bibliography

1. ITU-T Recommendation G.984.2 Spectral grids for the application of WDM technologies: CWDM technology wavelength grid. International Telecommunication Union, 12/2003.

2. ITU-T Recommendation G.984.2 Passive fiber optic networks with support for gigabyte bit rates (GPON): Specification of a physical medium dependent (PMD) layer. International Telecommunication Union, 03/2003.

3. Recommendation ITU-T G.983.3 Gigabit-capable passive optical networks (G-PON): Transmission Convergencelayer Speeification. International Telecommunication Union, 01/2014.

4. "Modernization of the communication line on the section of Arkhangelsk-Karpogory of the Northern Railway" (project number 311607-04) - Giprotransssignalsvyaz, St. Petersburg, 2016

Claims (3)

1. The method of transmitting information on fiber-optic communication lines with access nodes distributed along the inter-station sections and having two ports - the first port for communication with the first terminal station of the section and the second port for communication with the second terminal station of the section, characterized in that fiber-optic communication line introduced optical switches connected to the outputs of the power sources of the access nodes and transmitting linear signals bypassing the access nodes when the power is turned off or s linear signals of two directions of communication to the first and second ports of the access node when the power supply. 2. The method of transmitting information according to claim 1, characterized in that a packet switch is introduced into each access node, providing relaying of the linear signal received by the first port of the access node in the direction of transmission of the second port, relaying the linear signal received by the second port of the access node to direction of transmission of the first port, as well as input and output of information related to the subscriber terminal of this access node. 3. The method of transmitting information according to claim 1, characterized in that in the access nodes, when the power is turned on, the first port receives an optical linear signal at a wavelength of λ1 and transmits at a wavelength of λ2, and the second port receives an optical linear signal at a length λ2 waves and transmission at a wavelength of λ1.

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