Ultra High-Speed SONET Fiber-Optic Transmission System

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1 Ultra High-Speed Fiber-Optic Transmission System Takashi Mori Hirokuni Tsuji Hiroyuki Nakano, D.E. Shigeo Shinada ABSTRACT: Recently, there have been numerous demands not only on voice but also data/image signals. To answer these demands, a transmission system with advanced management functions that can transfer high capacity is essential. The demands on the networks can be realized using SDH (Synchronous Digital Hierarchy) equipment, recommended by ITU-T (International Telecommunication Union- Telecommunication Standardization Sector) as the international standard. Hitachi has been developing a series of transmission systems that comply with (Synchronous Optical Network), the SDH standard used in North America. is one such system which satisfies the demands of high capacity transmission and advanced management functions. It features a long transmission span, an equipment lineup for various network configurations, an advanced management function with high flexibility in connecting management networks, and expandability through DWDM (dense wavelength division multiplex). INTRODUCTION IN North America, communication systems with high transmission capacity have been developed to realize newly emerging services such as image signals (video). An advanced network management function, that can work flexibly under various network configurations is deemed necessary. The (Synchronous Optical Network) has been developed as a standard for SDH (Synchronous Digital Hierarchy) transmission in North America. Recently, Hitachi, Ltd. has been developing a series of transmission systems which conform with. Hitachi has succeeded in developing a 10-Gbit/s optical transmission system ( OC- 192, shown in Fig. 1) that accommodates over 120 thousands lines. The main features of the OC- 192 are; To realize an equipment lineup for various network configurations that use a MUX/ (multiplexer/ add-drop multiplexer). The easy upgrade of network configurations by modifying existing equipment. To realize long span transmission using EA (electroabsorption) modulation and an optical dispersion compensation technique. Fig. 1. An advanced network management function and operational interface that comply with TMN (Telecommunications Management Network). Expandability, by combining WDM (wavelength division multiplex) technology. This report discusses the highlights and the visions of for the future. Hitachi Review Vol. 47 (1998), No. 2 79

2 Operations center OS : 10-Gbit/s line OS: operations system EMS: Element Management System : Line Terminating Equipment EMS EMS Fig. 2 High-Speed Communication Network (). Working Protection Linear network 2.4G/ 600M bit/s 2.4G/600M bit/s Ring network (1 + 1) Working (1 + 1) Protection (1:3) (1:3) Working 1 Working 2 Working 3 Fig. 3 Linear Network System. Extra traffic channel Protection Extra traffic channel NETWORK CONFIGURATION Fig. 2 shows a high-speed communication network configuration which features the system. There are two types of network available: a linear network, which connects nodes via point-topoint, and a network, which connects nodes in a circular configuration. The offers two types of nodes, the MUX and the, the combination of which allows various network configurations to be created. In linear networks, the equipment is installed along transmission lines to realize high-capacity transmission via a point-to-point configuration. Traffic on the transmission line is protected when the line fails, since the network becomes redundant. The two switching methods available for use on this line, are the configuration, where each working line has a corresponding protection line, and a 1:N configuration, which has one protection line for N number of working lines. It is possible to extend the span by inserting (line regenerator equipment) between the nodes (Fig. 3). In the network, the equipment is installed in a configuration. This allows the network configuration to be designed flexibly, depending on the traffic since it is possible to add/drop paths in an (synchronous transport signal) unit. The network can adopt a configuration with either 2 or 4 fibers, and can support BLSR (bi- 80 Hitachi Review Vol. 47 (1998), No. 2

3 directional line switching ). Moreover, the incorporation of span- and -switching reduces the effects on traffic when failure occurs in the network (Fig. 4). The network also supports interconnection, which allows paths to be set between nodes placed in different s. Furthermore, it is also possible to have advanced path settings (Fig. 5). Two common applications are supported by both linear and networks. The first application is called the Transparent Transport function. This allows overhead signals, such as the DCC (data communication channel), OW (order-wire) and APS (automatic protection switch), as well as low-speed interfacing, to be transferred to the other end transparently. With this function, both and OC-48 networks can be accommodated into 10-Gbit/ s transmission lines as independent networks. This function simplifies the networks while keeping managed networks independent (Fig. 6). The second application is called the sub-tending. This function is a part of the low-speed interface which is incorporated into a section of another. With the sub-tending, it is possible to offer 10 Gbit/s in large s and 600 Mbit/s or 2.4 Gbit/s in small s without losing cost efficiency (Fig. 7). HARDWARE CONFIGURATION Table 1 shows the main specifications of the OC- 192 system. The function block diagram is shown in Fig. 8. High-Speed Interface The high-speed interface converts optical signals into electrical signals and performs signal processing. Long span (140 km) and high-capacity transmission have been achieved without the use of s, even in conventional fibers which can handle a large dispersion by combining wavelength compensation technology. A 0.3-µm GaAs-Si bipolar process has been used for high-speed analog receiver/transmitter ICs. In the system, the signal processing circuit was made path Fault path (a) Usual state (b) Ring switch state Fig. 4 Ring Network System. path path Fig. 5 Ring Inter-Connection Scheme. Ultra High-Speed Fiber-Optic Transmission System 81

4 10 Gbit/s 10 Gbit/s 600 Mbit/s 600 Mbit/s Fig. 6 Transparent Transport Scheme. Fig. 7 Sub-Tending Ring Scheme. using a large-scale IC (0.35-µm CMOS, complementary metal oxide semiconductor) process. Since FEC (forwarded error correction) is incorporated in high-speed interfacing, the bit-error rate on the transmission line can be improved. Low-Speed Interface The and OC-48 systems are two types of low-speed interface which can be used. It is possible to select upto four s and OC-48 interfaces arbitrarily. Three switching configurations, 1 + 1, 1:4 and 1:8 are available for low-speed switching, where the selection is flexible depending on the switching type of the node at the other end. The interface automatically recognizes the connected interface, i.e. /SDH, and switches the interface accordingly. With this function, it is possible to expand the network easily. MUX/DEMUX The MUX is used to convert the data transmitted between low- and high-speed interfaces. It is possible to change the configuration by inserting a selector card, to make the unit a terminal multiplexer, or by inserting a switch card to make it an. It is even possible to change the configuration while the system is running. Fig. 9 shows an outline of the upgradability. It is possible to fully utilize the transmission line bandwidth by incorporating a TSI (time slot interchange) function into the. TABLE 1. Main Specifications of the System CMISE/ANSI: Common Management Information Service Element/American National Standards Institute Item Basic function Application High-speed interface Multiplexing method Low-speed interface Operations interface Specification Terminal (1 + 1, 1:N) (2-fiber BLSR, 4-fiber BLSR) Repeater Ring interconnection Transparent transport Sub-tending Optical hubbing ( Mbit/s) Transmission distance: 140 km FEC (forwarded error correction) Selector TSI (time slot interchange) OC-48 ( Mbit/s) ( Mbit/s) OC-3 ( Mbit/s) /SDH automatic recognition TL-1/X.25, TL-1/LCN, CMISE/ANSI 82 Hitachi Review Vol. 47 (1998), No. 2

5 10 Gbit/s 10 Gbit/s OS interface High-speed interface unit OAM unit Office alarm Housekeeping Multiplexer unit Clock unit BITS DCC Low-speed interface unit Overhead unit Order-wire OAM: operation, administration, maintenance BITS: building integrated timing supply Fig. 8 Function Block Diagram. Clock Unit The clock unit provides the standard clock signal for the system, where the reference clock can be either an external clock or the time signal extracted from the transmission line. The signal generated in the clock unit complies with the standard clock used in the system. Overhead The overhead enables data to be communicated through the use of DCC and OW, and enables talking among nodes. The information must remain intact for the switching action in linear and networks. Therefore, when a transmission failure occurs, communication is protected automatically. Interoperability with other vendors is guaranteed since standard protocol is used in DCC communication. Structure The structure of the equipment used for the transmission system complies with the NEBS (network element building system). It is also possible to incorporate a MUX with configuration in one 2.1-m (7-feet) bay. OAM The OAM consists of an EM (element manager) and an OAM function block installed in the nodes. This system is based on the internationally recognized standard TMN, and is designed to have standardized, advanced-network nodemanagement functions. The OAM offers access from simple craft (with GUI, graphical user interface functions) and is interfaced with a remote OS. Provisioning, surveillance Fig. 9 Outline of Upgradability ( to ). Ultra High-Speed Fiber-Optic Transmission System 83

6 Optical Hubbing DCC 10 Gbit/s DWDM system is applicable to both bidirectional and unidirectional transmission and, depending on the number of wavelengths, (4, 8, 16 or 32), network expandability and cost efficiency are guaranteed. The combination of the DWDM and systems offers flexible applicability to various network configurations, such as point-to-point and short/long haul configurations. 600 Mbit/s 2.4 Gbit/s OC-48 Fig. 10 Optical Hubbing Scheme. and user-initiated testing functions are supported by OAM. It is also possible to expand the network using DCC as a remote-control method. With OAM, it is possible to access data from the DCC at high-speed (10 Gbit/s) and from the tributary side at 2.4G/600M bit/s. An Optical Hubbing function is also available (Fig. 10). TL-1/X.25, TL-1/LCN and CMISE/ANSI are supported as interfaces with OS to realize the easy connection to various operational systems. TEST RESULTS FROM THE SITE MCI Telecommunications Corp. and Hitachi conducted a joint test using conventional optical fibers between Chicago and St. Louis (about 440 km). The long term real traffic test was successful with no bit error. This was the first 10-Gbit/s 4- wavelength multiplex test (40 Gbit/s) ever performed. The test configuration is shown in Fig. 11. DENSE WAVELENGTH DIVISION MULTIPLEXING SYSTEM (DWDM) By integrating a DWDM system with the system, it is possible to design a network configuration more economically than before. The Chicago Lincoln St. Louis 40 Gbit/s 40 Gbit/s 440 km Fig. 11 Test Configuration in the Site. : Bi-directional line amplifier CONCLUSIONS This paper discusses the North American transmission system, which features a high transmission capacity and an advanced network management function. The system will be applied to various networks as a communication infrastructure in the multimedia age. REFERENCE (1) Y. Nakano, Signal Processing for SDH Digital Cross-Connect System, IEEE International Conference on Communication ICC 93 (23 26 May 1993). ABOUT THE AUTHORS Takashi Mori Joined Hitachi, Ltd. in Belongs to the Long Haul Transmission Department at the Telecommunications Division. Currently engaged in development of transmission systems. takashi_mori@cm.tcd.hitachi.co.jp Hirokuni Tsuji Joined Hitachi, Ltd. in Belongs to the Long Haul Transmission Department at the Telecommunications Division. Currently engaged in development of transmission systems. Member of the Institute of Electronics, Information and Communication Engineers (IEICE) of Japan. hirokuni_tsuji@cm.tcd.hitachi.co.jp Hiroyuki Nakano, D.E. Joined Hitachi, Ltd. in Belongs to the Long Haul Transmission Department at the Telecommunications Division. Currently engaged in development of optical transmission systems. Member of IEICE of Japan and IEEE of USA. hiroyuki_nakano@cm.tcd.hitachi.co.jp Shigeo Shinada Joined Hitachi, Ltd. in Belongs to the Software Department at the Telecommunications Division. Currently engaged in development of transmission network systems. Member of IEICE of Japan. shinada@cm.tcd.hitachi.co.jp 84 Hitachi Review Vol. 47 (1998), No. 2