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Optoelectronics & Communications

Merging telecommunication backbone networks with IP optical technologies

By deploying a new network architecture and enhancing international standard technologies, internet protocol and optical interworking can be brought together to support several telecommunication services.
27 April 2006, SPIE Newsroom. DOI: 10.1117/2.1200603.0175

The rapid growth in broadband Internet-related services is expected to reach roughly half of all households in Japan by 2010. The maximum speed has rapidly grown from a few kbits/s to hundreds of Mbits/s. In parallel, we have been seeing various new services emerging, including voice over IP (VoIP), multimedia file downloads, and videoconferencing. All of these new services are based on IP, and, since optical technology offers exceptional capacity, we see this as the most promising infrastructure with which to support them. What is needed is a way to integrate and migrate IP and optical technologies into the single backbone network architecture.

The Internet Engineering Task Force (IETF) has standardized IP, VoIP, and Multiprotocol Label Switching (MPLS) technologies, all of which have been widely deployed. However, smooth and efficient operation was still an issue because different technologies (such as IP and MPLS) have different principles and control mechanisms.

Generalized MPLS (GMPLS)1 is a controlling technology that enables route determination, setup, and tear down for paths on any layer: this is regardless of the technologies used, whether IP, MPLS, optical, or other technologies. Since current standards and implementations assume a pure GMPLS control technology over end-to-end connections, we needed to establish a network architecture that would enable this migration and could actually enhance GMPLS capability.

We proposed an architecture called the multi-layer service network (MLS-NW)2,3 that has four components: a shared optical core network (CN), legacy and new service-specific service networks (SN), a border router between the SN and CN, and a path computation element (PCE) on top of the other components. Our analysis showed that this architecture enables the introduction of large-capacity optical technology and GMPLS-based dynamic control at the core, while still supporting various existing legacy services. An MLS router can capture multi-layer information for advanced multi-layer coordination, and the PCE makes it easier for the operator's policies to be reflected in the network.

Our activities in the fields of standardization and interoperability have directed us towards establishing and supporting internationally interoperable technologies to realize MLS-NW. The generalized concept is now a part of an International Telecommunication Union--Telecommunication Standardization Sector (ITU-T) recommendation for next generation networks.4 The expanded concept of and modifications to GMPLS are in official working documents within IETF.5 We have demonstrated the MLS-NW concepts using self-developed software and existing node systems in an international conference6 and have published many papers on the subject.2,3,7,8

MLS-NW offers a multi-layer traffic engineering (TE) capability that decides path routes according to various conditions. It also offers easy accommodation of multiple services and migration in the same way an overlay model does (seeTable 1).

Table 1. Comparing the available network models reveals the benefits of a multi-layer service network (MLS-NW) as compared to peer and overlay models.

Figure 1 shows the MLS-NW architecture and key enabling technologies. The network accommodates the technologies of different layers over different domains, so it can be called a multi layer and region architecture. When SNs use IP/MPLS, the signaling and routing are different: interworking is needed between the SN and CN. The PCE is the controlling entity with which the carrier's policy can determine the multi-layer traffic engineering.

Figure 1. Using a multi-layer service network (MLS-NW) allows Internet Protocol (IP) and optical technologies to be integrated into a single backbone network architecture.

The technical components and their supporting technology enable a layer-1 virtual private network (L1VPN)8 where a large-capacity layer-1 path can be dynamically controlled by the customer. IETF has a dedicated working group addressing L1VPN.9 In order to be successful, GMPLS need to be fully interoperable with the systems of different layers and manufacturers.

The IP optical technologies that we have developed can be used in the development of a backbone network that can support emerging IP-related services efficiently, and enable the smooth migration of today's services. Compared to today's operation-in-isolation alternatives, various services can now be accommodated far more efficiently and smoothly. The core technologies for MLS-NW are already well established in international standards, and implementation issues are currently being examined in international forums.

In future research, we will continue developing detailed protocol specifications so that the widest possible variety of implementations are achieved that offer full interoperability, and we will work to promote standards in close cooperation with industry.

Shigeo Urushidani
Network Service Systems Laboratories, NTT
Dr. Urushidani is a senior manager and research group leader at NTT Network Service Systems Laboratories and a visiting professor at National Institute of Informatics (NII).
Ichiro Inoue
Network Service Systems Laboratories, NTT
Mr. Inoue is a senior research engineer and supervisor at NTT Network Service System Laboratories.