The metropolitan area network (MAN), as the foundation of urban informatization, will meet various data and image service demands beyond voice, such as high-speed Internet access, virtual private networks, video on demand, and remote services. To satisfy these service requirements, the MAN needs to support multiple customer layer signals and provide the bandwidth necessary for these signals.
Currently, a new wave of MAN construction will focus on adopting solutions capable of carrying multiple services, primarily utilizing next-generation SDH/SONET transmission technology and optical technologies centered around DWDM and Optical Cross-Connects (OXC).
With characteristics such as high capacity, flexibility, ease of management, and reliability, SDH/SONET transmission technology is widely adopted by operators. In the United States alone, there are at least 100,000 SONET rings in operation, and nearly all voice and data services are transmitted based on the SDH/SONET architecture. Although some inherent characteristics of the SDH/SONET architecture are not suitable for IP service transmission, many operators have invested significant effort and funds into building SDH/SONET networks. This is especially true for those operators and private network customers whose primary revenue comes from voice services, as they are unlikely to completely abandon SDH/SONET technology for economic reasons. Therefore, it is necessary to adopt new technologies that can meet the demands of data service transmission while fully leveraging the existing characteristics of SDH/SONET technology.
Currently, there are three main methods for frame mapping between IP data and SDH/SONET:
(1) Traditional IP/PPP/HDLC/SDH
(2) LAPS - ITU-T X.86 Link Access Procedure
(3) GFP - ANSI T1X1.5 Generic Framing Procedure
With the development of new technologies, next-generation SDH/SONET transmission technology is increasingly gaining attention for its ability to adapt to multi-service platforms from metropolitan access networks to metropolitan backbone networks.
DWDM-based optical technology has been widely used by operators and private network customers in long-haul trunk networks, providing high-capacity backbone channels. As optical cross-connect technology matures, the commercialization of intelligent OADM and OXC becomes possible, enabling functionalities such as wavelength routing, wavelength reuse, wavelength division multiplexing, and cross-connection. With the advancement of new technologies, DWDM, as a high-capacity transmission platform that supports multiple customer layer signals, offers flexible networking and various protection methods, will increasingly be applied in the construction of metropolitan networks.
The network closely related to us is actually a complex composite of new and old technologies, services, and design philosophies. Fujitsu believes that this complexity will continue to challenge operators, private network customers, and suppliers for a considerable period. To enable operators and private network customers to develop newer networks, the networks being built now should be as rationally connected to previously constructed networks as possible. Each operator and private network customer has unique requirements for the network, and Fujitsu believes that the demand for comprehensive solutions far exceeds the demand for specific products. Leveraging years of experience in providing optical transmission solutions to operators and private network customers, along with feedback and requirements collected from them, Fujitsu is confident in its ability to tailor optical transmission network solutions for each operator and private network customer. For the construction of metropolitan transmission networks, Fujitsu offers the next-generation high-capacity SDH/SONET multi-service transmission platform - FLASHWAVE 4000 series and the metropolitan DWDM multi-service transmission platform - FLASHWAVE 7000 series to meet the overall solution needs from metropolitan access networks to metropolitan backbone networks.
Multi-Service Transmission Based on SDH/SONET
10G Bandwidth Sharing - SDH Channel and IP Channel
Operators and private network customers who have chosen SDH/SONET technology often need to consider two aspects:
(1) Provide services that are affordable for the customer.
(2) Recovery of investments used for building SDH/SONET networks
Fujitsu's new generation of high-capacity SDH/SONET multi-service transport platform - FLASHWAVE 4000 series, effectively utilizes the bandwidth of SDH/SONET rings to transmit multiple services, achieving rapid configuration of line connections and differentiated service control. This not only ensures the transmission quality of traditional voice services but also, by distinguishing between different services, achieves the goal of bandwidth service enhancement, thereby overall reducing the maintenance and investment costs for operators. Figure 1 illustrates how SDH and IP channels can share 10G bandwidth based on the SDH transport network.
Fujitsu's next-generation high-capacity SDH/SONET multi-service platform - FLASHWAVE 4000 series provides Gigabit Ethernet interfaces (1000Base-SX/LX) and Fast Ethernet interfaces (100Base-T), supporting Ethernet service transparent transmission and Layer 2 switching (L2SW) functionalities, respectively. This allows the SDH/SONET system to connect directly to local area networks or routers via Ethernet branch interfaces. The Ethernet service transparent transmission feature offered by Fujitsu directly encapsulates and rate adapts data frames from the Ethernet branch interface, mapping them into SDH virtual containers (VC) or SONET virtual tributaries (VT), and then transmits them point-to-point through the SDH/SONET system lines. The Layer 2 switching function operates at the second layer of the OSI seven-layer reference model, facilitating packet exchange between the Ethernet branch interface of the SDH/SONET system and the SDH virtual containers (VC) or SONET virtual tributaries (VT).
Currently, the SDH/SONET system primarily has two methods for transmitting IP data services: point-to-point and bandwidth-sharing based on Layer 2 switching functionality. From a long-term perspective, the Layer 2 switching functionality introduces intelligence into the SDH/SONET transmission system in the data network domain, offering certain advantages. Figure 2 illustrates the application of the bandwidth-sharing method based on Layer 2 switching functionality.
Bandwidth Sharing Applications of SDH Rings
Fujitsu's two-layer switching functionality supports various frame structures such as VLAN and MPLS, with a maximum MTU size of 1530 bytes and a maximum support for 4096 VLANs. The FLASHWAVE 4000 series can transparently transmit the original VLAN tags in the received data frames, ensuring transparent delivery of Ethernet services. The FLASHWAVE series implements data frame switching control through store-and-forward Ethernet data frames and can achieve packet-level error checking. For maintaining the MAC address list, the FLASHWAVE 4000 series utilizes a self-learning method. The FLASHWAVE 4000 series implements QoS functionality for data frames through flow-in limitation and flow control. Flow limitation can be configured via the network management system, while flow control is set to open. Once the received data traffic exceeds the threshold set by the flow limitation, a pause frame will be sent to each Ethernet branch port of the SDH/SONET system.
The bandwidth required for the Ethernet tributary interface of the SDH/SONET multi-service transport platform will vary with changes in services. The FLASHWAVE 4000 series will allocate different capacities of a single virtual container - VC3/VC4 or use cascading to allocate multiple virtual containers - VC4-4c/VC4-8v flexibly.
As a metropolitan area network transport platform for multi-services, the FLASHWAVE 4000 series can adapt to various levels of service transport from access rings to backbone rings, making efficient use of fiber resources. It is an optimal choice for many operators and private network customers transitioning from SDH/SONET network architecture to IP network architecture.
DWDM-based Multi-Service Transport
Wavelength division multiplexing technology, specifically Dense Wavelength Division Multiplexing (DWDM), has been widely applied in long-haul trunk networks, providing high-capacity, multi-service transport channels. However, it is primarily used in back-to-back terminal modes, which are not suitable for metropolitan area network applications. With the rapid development of urban information technology, operators and private network customers will face increasing demands for service bandwidth. Additionally, some services, such as ESCON, FICON, and Fiber Channel, are not suitable for SDH/SONET transport. As optical cross-connect technology matures and intelligent OADMs become commercially available, DWDM technology, with its transparent data format and signal rate capabilities, support for multi-services, high capacity, flexible networking, dynamic bandwidth allocation, and comprehensive wavelength protection methods, can effectively address the bandwidth and service challenges faced by operators and private network customers in metropolitan area networks.
Fujitsu's metropolitan DWDM multi-service transport platform - the FLASHWAVE 7000 series will meet the needs of operators and private network customers for building metropolitan access networks and metropolitan backbone networks.
Among them, the FLASHWAVE 7500, as a next-generation metropolitan DWDM backbone transport platform, features several technical characteristics:
(1) Supports 40 wavelength channels, providing a transport capacity of 400 Gb/s, which can be upgraded to 80 wavelength channels, providing a transport capacity of 800 Gb/s.
(2) Supports various services - SDH/SONET, GbE and 10GbE, ESCON, FICON, Fiber Channel, HDTV.
(3) Comprehensive optical layer protection methods - two-fiber unidirectional path switched ring (2F-OUPSR) and two-fiber shared protection ring (2F-OSPPR).
(4) Configurable OADM.
(5) Intelligent Optical Power Adjustment
(6) Circumference exceeds 100 km
(7) Various types of wavelength conversion units and wavelength-tunable wavelength conversion units.
The adoption of DWDM technology is a long-term goal.
It is expected that in the next 10 years, telecom business volume will grow by 40 to 50 times, and system capacity will increase by about 100 times. According to statistics, metropolitan area networks account for 80% of circuit business traffic. If TDM technology is fully adopted, network nodes will become larger and more complex, inevitably increasing the cost of building the network.
With the development of new technologies, transmission networks will feature an optical channel layer, where DWDM technology, OADM, and OXC will be applied to the optical channel layer, enabling the transmission of signals with different protocols and formats at varying rates. This trend will gradually evolve from long-haul trunk networks to metropolitan area networks, with SDH/SONET transmission platforms progressively moving towards the network edge, while optical transmission platforms primarily based on DWDM technology will become the backbone of metropolitan networks.