CN1258969A - 4 optical fibre bidirectional circuit change ring network system in valve division multiplex system - Google Patents

Abstract

A 4-fiber BLSR (Bidirectional Line Switched Ring) network. Multiple nodes are connected by two pairs of working and protection lines used to transmit wavelength division multiplexed (WDM) optical signals. Each node has first and second add-drop (add-drop) multiplexers (ADM), and each ADM is connected to a pair of working and protection lines, so as to add-drop multiplexers to the working lines. Multiplexing, and relaying through optical amplification for protection lines.

Description

4-fiber two-way line switching ring network system in wavelength division multiplexing system

This application refers to an earlier application filed at the Korea Industrial Assets Office on December 30, 1998, and officially assigned thereto serial number No. 98-61037, entitled "4-Fiber Bidirectional Line-Switched Ring Network in a Wavelength Division Multiplexing System ", which is incorporated herein, and all benefits deriving from such application under 35 U.S.C. § 119 are claimed.

The present invention relates to BLSR (Bidirectional Line Switched Ring) networks, and more particularly to a 4-fiber BLSR network in which one node is connected to an adjacent node by two pairs of working and protection lines.

BLSR is a self-healing ring commonly used to protect Synchronous Digital Hierarchical (SHD) networks. Self-repairing rings are divided into BLSR and UPSR (unidirectional path switching ring). Although the latter has the advantage of a simple working algorithm, the former is more widely used because of its higher communication capacity per fiber. In BLSR, like in a typical linear network, transmission and reception are bidirectional, and there are two types of BLSR: 2-fiber BLSR and 4-fiber BLSR.

Meanwhile, wavelength division multiplexing (WDM) schemes are becoming more popular in optical transmission systems. WDM transmission is the propagation of optical signals of various wavelengths through a single optical fiber. On the other hand, wavelength division demultiplexing refers to the inverse operation of wavelength division multiplexing.

WDM transmission technology is the most convenient method to improve transmission capacity in optical communication network, and it is reflected in WDM transmission system. The WDM transmission system performs wavelength division multiplexing on the transmitted multi-channel data, performs wavelength division demultiplexing on the received data, and distributes the demultiplexed data to the lower-level low-rate transmission system. Here, wavelength division multiplexing is performed with an optical coupler or AWG (Arrayed Waveguide Grating), and wavelength division demultiplexing is performed with an AWG or FBG (Fiber Bragg Grating). EDFA (Erbium Doped Fiber Amplifier) was used as the optical amplifier.

In the development of WDM transmission systems, the following three issues are the most challenging: (1) The offset stability of each wavelength relative to the reference wavelength and the power flatness of the wavelength contained in the multiplexed signal ; (2) processes associated with optical couplers, AWGs or FBGs for wavelength division demultiplexing at each wavelength; and (3) for long-distance optical signal transmission without electrical-to-optical conversion or optical-to-electrical conversion EDFA process.

Efforts have been made to provide protection techniques for obtaining stable service from each of the above three requirements. However, due to the SNR (signal-to-noise ratio) of the optical switch and EDFA and the power non-uniformity of each wavelength, only 1+1 protection can be achieved with an add-drop multiplexer (ADM), Moreover, it is still impossible to achieve the goal with 4-fiber BLSR at the current technological level.

This is due to the fact that the optically multiplexed signal passing through the add-drop multiplexer (ADM) node and EDFA must pass through a wavelength division demultiplexer and a 3R channel converter. If it directly passes through the wavelength division multiplexer, long-distance transmission is impossible due to the difference in optical power of the wavelength. The 3R channel converter performs re-pumping, re-timing and reglitching. In operation, the 3R channel converter converts an optical signal into an electrical signal, performs retiming and reglitching on the electrical signal, converts the resulting electrical signal into an optical signal, and re-pumps the optical signal. This increases design complexity and increases equipment cost. As mentioned above, although the 4-fiber BLSR is urgently needed for WDM systems, the 4-fiber BLSR is difficult to achieve with the current technology, and exhibits the disadvantages of inefficiency in design and cost.

It is therefore an object of the present invention to provide a simple and efficient 4-fiber BLSR network in a wavelength division multiplexing system.

In order to achieve the above purpose, a 4-fiber BLSR network is provided. Multiple nodes are connected with two pairs of working and protection lines for transmitting wavelength division multiplexing (WDM) optical signals. Each node has first and second add-drop (add-drop) multiplexers (ADM), and each ADM is connected to a pair of working and protection lines, so as to add-drop multiplexers to the working line. Multiplexing, and relaying through optical amplification for protection lines.

The above objects and advantages of the present invention will become more apparent by describing in detail preferred embodiments of the present invention with reference to the accompanying drawings. In the attached picture:

Figure 1 is a schematic diagram of a 4-fiber BLSR network according to one embodiment of the present invention; and

FIG. 2 is a simplified diagram of the 4-fiber BLSR network, with the fiber optic cable between node A 100 and node B 102 shown in FIG. 1 being severed.

FIG. 1 illustrates a normal conversation of 3 nodes A100, B102 and C104 in a 4-fiber BLSR network according to one embodiment of the present invention. Adjacent nodes are connected by a pair of working lines 106 and 110 and a pair of protection lines 108 and 112 for transmitting WDM optical signals. Nodes A100, B102 and C104 have the same configuration, and the internal structure of the first two nodes is shown in the figure. It should be noted here that the same components are given different reference numbers in the two nodes. The node A100 will now be described as an example.

Node A 100 includes first and second ADMs 114 and 116 that are identical in structure. The first ADM 114 is connected to the working line 106 and the protection line 108 , while the second ADM 116 is connected to the working line 110 and the protection line 112 . Like components in the first and second ADMs 114 and 116 are labeled with different reference numerals. Hereinafter, only the first ADM 114 representative of the second ADM 116 will be described.

The first ADM 114 includes a working preamplifier 200, a first loop switch 202, a wavelength division demultiplexer 204, a channel modulator 206, a wavelength division multiplexer 208, a second loop switch 210, and a working boost along the working line 106. amplifier 212 and jumper switch 214 . The first ADM 114 also includes a second loop switch 210 , a guard boost amplifier 216 and the first loop switch 202 along the guard line 108 . Both the first and second ring switches 202 and 210 are connected to both the working line 106 and the protection line 108 for parallel connection of the working line 106 to the protection line 108 during protection switching.

The working preamplifier 200 is an EDFA for amplifying the optical signal received from the node C104 through the working line 106 . The first ring switch 202 is an optical switch connected to the output line of the working preamplifier 200 and the guard line 108 . The first ring switch 202 switches the output line of the working preamplifier 200 to the wavelength division demultiplexer 204 or to the protection line 108 during protection switching. The wavelength division demultiplexer 204 performs wavelength division demultiplexing of the optical signal received from the first ring switch 202 through the working line 106 into a plurality of optical signals of different wavelengths. The demultiplexed signal is dropped to a lower layer system (not shown) or passed through to channel modulator 206 . In FIG. 1, one of the outputs of wavelength division demultiplexer 204 is dropped. The channel modulator 206 modulates the through signal and the add signal received from the wavelength division demultiplexer 204 and fed to the Node B 102 into different wavelengths. Here, FIG. 1 shows an added signal. The wavelength division multiplexer 208 performs wavelength division multiplexing on the signal received from the channel modulator 206 on one optical fiber. The second ring switch 210 is an optical switch which is connected to the output line of the wavelength division multiplexer 208 and the protection line 108 to the node B 102 through a working boost amplifier 216 and a jumper switch 214 . This second ring switch 210 switches the output of the wavelength division multiplexer 208 to the working boost amplifier 212 or to the protection line 108 connected to the protection boost amplifier 216 during protection switching. The working boost amplifier 214 is an EDFA for amplifying the optical signal received from the second ring switch 210 through the working line 106 and feeding the amplified signal to the node B 102 through the working line 106 . The jumper switch 214 is connected to the output side of the working boost amplifier 212 and the protection line 112 of the second ADM 116 for performing the general jumper protection function of the 4-fiber BLSR. That is, the jumper switch 214 connects the output working line of the working boost amplifier 212 to the protection line 112 of the second ADM 116 during protection switching. In FIG. 1 , reference character L denotes a crossover switching path of the crossover switch 214, and the crossover protection function is also applied to other nodes.

The protection boost amplifier 216 is an EDFA, used to amplify the optical signal received from the second ring switch 210 through the protection line 108 , and feed the amplified signal to the first ring switch 202 through the protection line 108 .

As shown in the first ADM 114 , the 4-fiber BLSR network of FIG. 1 operates differently for the working line 106 and the protection line 108 . That is, typical add-drop multiplexing is performed along the working line 106, while along the protection line 108 only the relay function is performed by means of optical amplification using the protection boost amplifier 216 as an EDFA.

The working call flow of working lines 106 and 110 indicated by thick solid lines in FIG. 1 will now be described. Pass-through or added traffic, for example, SDH 2.5Gbps (gigabits per second) traffic is modulated by channel modulator 206 to different wavelengths. The wavelength division multiplexer 208 multiplexes optical signals of different wavelengths on one optical fiber. The multiplexed optical signal is passed to the working boost amplifier 212 or switched onto the protection line 108 by the second ring switch 210 . In the normal state shown in FIG. 1 , the multiplexed signal is amplified by the working boost amplifier 212 and fed to the node B 102 . The working preamplifier 400 of node B 102 amplifies the optical signal received from node A 100 . The amplified signal passes through the first ring switch 402 and is demultiplexed by the wavelength division demultiplexer 404 into signals of different wavelengths. The demultiplexed signal is dropped or passed through.

FIG. 2 illustrates a 4-fiber BLSR network, with the fiber cut between node A 100 and node B 102 shown in FIG. 1 . In FIG. 2, switching is performed between nodes adjacent to the severed cable. The signal multiplexed by the wavelength division multiplexer 208 is added to both the working boost amplifier 212 and the protection boost amplifier 216 through the branching operation of the second ring switch 210 . The protection boost amplifier 216 optically amplifies the received optical signal, and feeds the amplified optical signal to the node C104. The node C104 transmits or amplifies the received optical signal along the protection line without being switched by the ring switch, and feeds the output signal to the node B102. On the other hand, the node B 102 switches the optical signal received through the protection line to the working line by switching in the first ring switch 402 . The wavelength division demultiplexer 404 demultiplexes the signal received through the working line into optical signals of different wavelengths. The demultiplexed signal is dropped to a lower layer system, or transmitted to a channel modulator 406 . In Figure 2, all demultiplexed signals are dropped. The subsequent light path is the same as in the normal state.

According to the present invention, since the typical 4-fiber BLSR add-drop multiplexing is implemented along the working line, and only a single optical amplifier is used to complete the relay function by means of optical amplification along the protection line, it is not necessary to perform optical-electrical conversion Or electrical-optical conversion can realize reliable protection switching, which simplifies the design and reduces the cost. The cost required for performing optical-to-electrical conversion or electrical-to-optical conversion can be reduced by approximately 30 to 40% using a 3R channel converter.

Although the invention has been described in detail with reference to specific embodiments, these are exemplary applications only. Although a maximum of 8 nodes with a distance of 80 km between nodes can be accommodated in the present invention, because the number of nodes depends on the number of EDFAs without optical-to-electrical conversion or electrical-to-optical conversion, however, along the protection line every 7 A node can realize multi-node ring structure in the existing SDH network by using 3R repeater. It is therefore evident that many changes can be made by any one skilled in the art within the spirit and scope of the invention.

Claims (3)

1. A 4-fiber BLSR (bidirectional line switched ring) network comprising: Multiple nodes connected by two pairs of working and protection lines used to transmit wavelength division multiplexed (WDM) optical signals, It is characterized in that each node has first and second add-drop (add-drop) multiplexers (ADM), and each ADM is connected to a pair of working and protection lines, so that the working lines Add-drop multiplexing, and relaying by optical amplification for protection lines. 2. The 4-fiber BLSR network of claim 1, wherein each ADM comprises: a working preamplifier connected to the working line of the first adjacent node for amplifying the optical signal received from said neighboring node through said working line; A first ring switch, which is connected to the output line of the working preamplifier and the protection line of the first adjacent node, is used for shunting the output line of the working preamplifier to the said protective circuit; a wavelength division demultiplexer, used to demultiplex the optical signal received from the first ring switch through the working line into optical signals of different wavelengths; a channel modulator for modulating the through signal and the added signal received from the wavelength division demultiplexer and fed to the second adjacent node into different wavelengths; a wavelength division multiplexer configured to perform wavelength division multiplexing on signals received from the channel modulator; A second ring switch, which is connected to the output working line of the wavelength division multiplexer and the protection line of the second adjacent node, is used to switch the output line of the wavelength division multiplexer shunting to said protection line; a working boost amplifier for amplifying the optical signal received from the second ring switch through the working line, and transmitting the amplified optical signal to the working line connected to the second adjacent node; and A protection boost amplifier, configured to amplify the optical signal received from the second ring switch through the protection line, and transmit the amplified optical signal to the protection line connected to the first ring switch. 3. The 4-fiber BLSR network of claim 2, further comprising a jumper switch in each node connected to said output side of said working boost amplifier and said protection side of said other ADM line.

Images