Path Accommodation Design Engine for Simply and Reliably Designing Multi-layer Transport Networks

1. Introduction

To flexibly keep up with future increases in communication traffic, core and metro networks are evolving into multi-layers integrating optical and electrical paths on the 100-Gbit/s packet transport system (100G-PTS) [1]. Furthermore, to simplify networks while improving their quality, reliability, and interoperability, it is necessary not only to design networks in such a way that the closed paths in each layer of the optical-path or electrical-path layers are accommodated—which we refer to as accommodation design—but also to achieve a way to select routes that takes into consideration both path layers, the assignment of resources (i.e., wavelength and bandwidth used for paths), and the accommodation design of the optimal paths for each service on the basis of various conditions such as redundancy and reliability of routes.

2. Multi-layer transport path accommodation design engine

The multi-layer transport path accommodation design engine (hereinafter, design engine) was developed by NTT Network Innovation Laboratories and is positioned as part of a logical design function block, as shown in Fig. 1. An overview of the design engine is shown in Fig. 2. The assignment of wavelength or bandwidth and the route of optical or electrical paths are automatically designed in consideration of source and destination nodes as well as various design conditions, and the results are returned to the operator.

Fig. 1. Image of application of the multi-layer transport path accommodation design engine.

Fig. 2. Overview of multi-layer transport path accommodation design engine.

In developing the design engine, we assumed a usage scenario in which an operator handles the accommodation design of paths. The following suppositions were made regarding application scenarios involving automatic design: (i) routes and resources should be designed as a whole; (ii) routes should be designed by operators themselves, but resources should be designed automatically; (iii) routes and resources should be designed by operators themselves, but delay times and other elements should be calculated; and (iv) not only optimal design results (best matched to the design conditions) but also quasi-optimal design results (approximately matched to the design conditions) should be looked at and judged in an integrated manner. Moreover, we considered requirements such as providing designs applicable to specific design policies for each service, future expandability such as the addition of equipment and equipment vendors, and easy of embedding in network operation systems.

The design engine has the following features: (1) functional partitioning based on the usage scenario; (2) multiple candidate routes in accordance with the design policy; (3) flexibility and expandability thanks to a configuration file that sets various design conditions and software startup parameters when adding other network elements and network equipment vendors; and (4) easy implementation of embedded equipment in network operation systems. These four features are first described here in terms of the entire design engine, and the primary functions and key features of the design engine are then explained.

3. Path-route-design function block

The path-route-design function block provides integrated path designs in accordance with a variety of path-route-design conditions and the state of physical, optical, and electrical layers. To put that concretely, it makes it possible to select routes on the basis of design conditions such as the building that the system will be accommodated in, the number of nodes, links, and conduit lines for the physical layer, the delay time of paths in path layers, and the delay-time difference between paths of the currently used system and the backup system. The path-route-design function block has four primary functions, which are described below and shown in Fig. 3.

Fig. 3. Path-route-design function.

4. Resource-design function block

The resource-design function block provides wavelength and bandwidth for the routes calculated by the path-route-design function block or the routes set by the operator in advance. In the design of resources for assigning wavelengths to optical paths, a wavelength-continuity constraint is imposed on the links routed; that is, the same wavelength must be used between source and destination nodes. The concept of optical paths was advocated by NTT research & development laboratories in 1992; therefore, an algorithm for carrying out path accommodation design to allocate optical-path routes and wavelengths was proposed [3].

An algorithm called least fragmentation (LF) [4], which was devised by NTT Network Innovation Laboratories, is implemented in the resource-design function block. When multiple candidate wavelengths can be assigned to candidate routes, the LF algorithm selects a single wave number that minimizes fragmentation (i.e., a state in which wavelengths utilized for certain routes are fragmented) while considering the wavelength-utilization status of adjacent links on the candidate path routes. To put that more concretely, the wavelength-utilization status of links is expressed as two values: “0” (false) for unused and “1” (true) for used. The value of an exclusive OR (XOR) between adjacent links is taken as a linear measure, and the wave number that minimizes that XOR value is selected as the wavelength to be assigned. In this manner, the wavelength allocated to candidate routes is calculated in a short time—even in the case of a large-scale network—by a simple logic operation including the candidate path route and the wavelength-utilization status of adjacent links on that path.

As a conventional wavelength-assignment algorithm, the first fit (FF) algorithm (Fig. 4) for assigning wavelength in ascending order of wave number does not account for the wavelength-utilization status of adjacent links on the candidate route. Accordingly, to accommodate a new path request in the network (i.e., source node PTS-A and destination node PTS-C in Fig. 4), it is necessary to add links between nodes, for example, between nodes PTS-A and PTS-B in Fig. 4. In contrast, with the LF algorithm, the wavelength is selected so that the same wavelength can be assigned to maintain continuity for as many links as possible; consequently, new requests for paths can be accommodated in the network without having to add links in response to those requests, as shown in the example in Fig. 4.

Fig. 4. Improved accommodation efficiency by LF algorithm.

In addition to the LF and FF algorithms, a random algorithm (which randomly selects allocable wavelengths) can be used. The results of a comparative evaluation of the three algorithms—on the basis of the number of paths that can be accommodated in relation to network configuration (i.e., scale)—are shown in Fig. 5. Over the entire network scale range, the number of paths that can be accommodated is largest when the LF algorithm is used. It can thus be concluded that the LF algorithm can effectively utilize network resources to the maximize extent possible.

Fig. 5. Quantitative evaluation of LF algorithm.

5. Conclusion

We developed a multi-layer transport path accommodation design engine that achieves optimal path design and satisfies the required conditions for various services. From here on, we will continue to research and develop technologies for optical-path accommodation design while aiming to create core and metro networks for economically providing a multitude of broadband services.

References

	Akihiro Kadohata Research Engineer, The First Promotion Project, NTT Network Innovation Laboratories. He received a B.S. in applied physics from Tokyo University of Science in 2005, an M.S. in earth and planetary science from the University of Tokyo in 2007, and a Ph.D. in electrical engineering and computer science from Nagoya University, Aichi, in 2016. In 2007, he joined NTT Network Innovation Laboratories, where he has been researching photonic network architecture and design. He is a member of the Institute of Electronics, Information, and Communication Engineers (IEICE). He received the Young Engineers Award from IEICE in 2013.
	Fumikazu Inuzuka Senior Research Engineer, The First Promotion Project, NTT Network Innovation Laboratories. He received a B.E. and M.E. in applied physics from the Tokyo University of Agriculture and Technology in 2002 and 2004. In 2004, he joined NTT Network Innovation Laboratories, where he is engaged in research on photonic transport and processing systems and photonic networking systems. He is a member of IEICE.
	Wataru Kawakami Senior Research Engineer, Supervisor, The First Promotion Project, NTT Network Innovation Laboratories. He received his B.E., M.E., and Ph.D. in electrical engineering from Kyoto University in 1986, 1988, and 1997. He joined NTT Telecommunication Networks Laboratory in 1988 and studied optical signal processing. He was with NTT EAST from 1999 to 2008, where he developed IP (Internet protocol) network services (including the FLET’S service). He also worked on the development of NGN (Next Generation Network) at NTT during 2008–2010.
	Atsushi Watanabe Senior Research Engineer, Supervisor, The First Promotion Project, NTT Network Innovation Laboratories. He received a B.S. and M.S. in information science from Ibaraki University in 1989 and 1991. In 1991, he joined NTT Transmission Systems Laboratories, where he engaged in research on traffic control in asynchronous transfer mode networks. Since 1993, he has been involved in research and development of optical path-based photonic networks. He is currently the Engineering Assistant Manager of the Electronics Device & System Business Unit, Broadband System & Device Business Group, NTT Electronics Corporation. He received the Young Engineer Award in 1997 from IEICE, of which he is a member.
	Mitsuhiro Teshima Director, Senior Research Engineer, Supervisor, The First Promotion Project, NTT Network Innovation Laboratories. He received a B.E. and M.E. from Tokyo Institute of Technology in 1989 and 1991. He joined NTT Transmission System Laboratories in 1991, where he has been researching frequency control of semiconductor lasers, optical cross-connects, and metropolitan and access area network technologies. From 2003 to 2007, he developed a digital television transport network system at NTT Communications. Since 2007, he has been engaged in research on high speed access control and transport technologies at NTT Network Innovation Laboratories. He is currently the Manager of the Electronics Device & System Business Unit, Broadband System & Device Business Group, NTT Electronics Corporation. He received the Young Engineers Award from IEICE in 1998 and the APCC-IEEE ComSoc APB Joint Award from the Asia-Pacific Conference on Communications and IEEE (Institute of Electrical and Electronics Engineers) Asia-Pacific Board in 2001.