At present, although WDM system has been massively used in trunk backbone network, there remains great space for the improvement of bandwidth availability over the backbone network. With the application of various new access technologies, the capacity of access network will be dramatically improved. Under the influence of long-hall network and access network, MAN is undergoing rapid changes. Besides the factors such as technologies and users, the development and changes in bearer services of MAN become another main drive. The expansion of capacity of long-hall network plus the increase in IP services place MAN at the intersection.
The existing TDM-based infrastructure could not meet the requirements of network efficiency and flexibility and is also constrained in its capacity expansion; accordingly, it fails to generate quick and effective response to outburst traffic. Meanwhile the number of service providers is increasing further, the difference between access network and MAN became blurry, bringing a series of problems to the traditional voice-based network infrastructure.
In the market with fierce competition, the competitive edges lie in capacity allocation according to needs, personalized services and costs, and the service providers need corresponding solutions accordingly. DWDM-based structure is the most cost-effective solution for metropolitan area optical network to realize capacity scalability, multiple service provision and flexibility.
There are mainly two forms of OADM system: fixed wavelength and dynamic configurable OADM. If certain or some fixed wavelength channels are chosen to conduct add/drop multiplexing, it is called fixed wavelength OADM; if the add/drop multiplexed wavelength channel is configurable, it is called configurable OADM. Dynamic configurable OADM can add/drop wavelength signals selectively, or add/drop the whole wavelength services.
OADM only freely and selectively adds/drops services through transmission equipment regardless of its specific contents, and can process signals in any format and at any rate. Thus it can increase the network flexibility. The operators can choose a more effective way to manage the traffic allocation through routers, ensuring the survivability of network. Since OADM equipment can flexibly add/drop the wavelength providing the operators with convenience to utilize the optical network, the operators can not only sell wavelength according to market demands but also control and manage each wavelength to ensure QoS.
The metropolitan area DWDM system with OADM technology has the following features:
1. Flexible upgrading ability of waves at the node wavelength of 1 to 32 and can fully satisfy the requirements of service expansion and service deployment, and providing the add/drop multiplexing of any number of wavelengths over any network node to meet the flexible deployment services.
2. Offering overall integrated services transport capability. The system provides open protocol and rich client layer interfaces, and can accommodate all kinds of services that a typical MAN should have, including supporting STM-N (N=1,4,16,64), GE, FE, Fiber Channel, ESCON, Digital Video, FICON and other services. The system brings network providers with new business opportunities and new profitable opportunities, allowing them to provide optical wave channels independent from protocols and bit rates. Through ordering such service, the users can flexibly adopt any protocols suitable for their own network, and they even can add coding algorithms to reduce hidden dangers of data security.
3. High efficient and flexible sub-rate convergence. The system provides several kinds of sub-rate multiplexers, that is, modularly configure the client wave channels (sub-wave channels) of some rates, then converge (multiplex) them to an individual wave channel with larger capacity wavelength so as to specifically realize multiple service hybrid multiplexing functions respectively, including 4x155 Mbit/s, 4x622 Mbit/s, 2xGE, 4x2.5 Gbit/s, multiple channel FE convergence, etc. Such “multiple protocols/wavelengths” mode is more cost-effective. The sub-rate multiplexing enables the MAN service providers to deploy network according to market demands and to make the most of bandwidth resources, thus significantly reducing the costs. The reduction in costs allows the service providers to offer services to users at lower prices, thereby increasing its own competitiveness.
4. Providing diversified optical layer protection mechanism. Ring structure is the better mode to ensure the survivability of network. The ring structure itself can provide two paths between any two points over the ring. The failure of any one path can be remedied by re-selection of other paths for services. OADM ring network system can support UPSR (unidirectional optical path protection switching), BPSR (bi-directional optical channel shared protection switching), BLSR (bi-directional optical line shared protection switching) and other protection modes.
The emergence of OADM ring network system not only solved the bearing problems of large capacity services, but also took into account the compatibility with client signals of different grains. In addition, it provides reliable protection measures, which are a kind of excellent solution for MAN backbone layer. Under the guidance of Ministry of Information Industry (MII), China has drafted the technical specifications for metropolitan area OADM, founding a theoretical basis for planning and construction of transport network of metropolitan area. Meanwhile, all the leading operators are planning their solutions to transmission layer for its MANs, and expressly put forward their assumptions and ideas of constructing the backbone layer of MAN with OADM technology.
The market requires cost-effective MAN solutions, so ZTE Corporation launched OADM- based ZXMP 800 metropolitan equipment to meet such requirement. ZXMP 800 can realize seamless interoperation with ZTE series ZXMP MAN optical transmission platform products to jointly construct a future-oriented MAN system, providing the ideal solutions for metropolitan area telecom operators.
(By Yin Shengqi)