Large capacity, multi-service and intelligent construction of metropolitan Optical Network

Generally, we define a metropolitan optical network as a light transmission network spanning dozens of km to hundreds of kilometres, generally serving large, business-focused urban areas. Metropolitan Optical Network bridging between long-distance network and access network, the access network in the enterprise network of various services connected to the backbone of the operator network. In recent years, with the large-scale construction of long-distance transmission backbone network, with the popularization of the broadband technology of the user access and the resident network, the bottleneck of the network has shifted to the metropolitan area Network, and the metropolitan Area Transmission network with the main voice has been unable to adapt to the rapid growth of metropolitan data Service, and the metropolitan Area Network environment has changed a lot.

Metropolitan DWDM is the direction of development

Because the Metropolitan DWDM system has the characteristics of large capacity, light level protection, multi service and back compatibility, the metropolitan DWDM becomes one of the important development directions of the future metropolitan Area Optical Network. But the most controversial point of using the Metropolitan Wavelength Division multiplexing system is its investment cost, and we can draw further conclusions by comparing the investment schemes of virtual fiber with physical optical fiber to Metro DWDM.

To facilitate comparison, it is assumed that a metropolitan area network is composed of 4 nodes, the total length of the ring is 40km, and the first scheme is to use 32-wave DWDM system, which is equivalent to providing 32 pairs of virtual fiber, and the second is to lay 32 pairs of physical fibers.

In addition to increasing the utilization of optical fiber (equivalent to providing virtual fiber), the other important feature of the Metropolitan DWDM Network is that it can provide a protected wavelength channel for transmitting data service, which has better QoS guarantee than the previous data service through optical fiber direct connection. By comparison, the cost of a protected wavelength channel provided by the Metro DWDM network is less than the protection channel provided by the SDH system for traffic signals such as GBE, which transmit large particles.

From the above two aspects is not difficult to see, when the network of operators in the optical fiber resources are relatively tight, and the network has a large number of data service transmission requirements, the use of Metro DWDM system to build core optical network is a very ideal solution.

It is noteworthy that in the transport interface layer, the transport access layer, the main business particles include: 10m/100m Ethernet signal, 2M, 34m/45m, 155M, 622M and a small number of GBE interfaces. Relative to the core layer, business is more decentralized (a small number of transactions per node), small business particles, the general need for business integration and reuse, so the city of DWDM is not suitable for the interface layer and access layer to use, (but in some cases, passive coarse wavelength division system (passive CWDM) may be applicable in the bridging layer and the access layer.

Construction of 10G backbone transport platform in metropolitan area

With the rapid growth of traffic in metropolitan Area Network and the maturity of 10G SDH technology, most metropolitan optical networks have started to use tdm10g system to build their backbone transmission network. At present, many manufacturers have been able to provide tdm10g SDH system, however, the performance and characteristics of the tdm10g equipment are not the same, especially the network function is not exactly the same, users in the selection of equipment and network in the process must be oriented to the business flow model, select the appropriate network topology and network structure scheme, Finally, select the device system that can support the networking scheme. Following this approach (analysis of the Business flow model, select the network topology, select the appropriate equipment) specific analysis of the current urban backbone network construction methods.

The comparison between the two schemes is as follows: In the network of the convergence of the business, it is a good networking scheme to build multiple SDH self-healing loops by using the dual-return method, which is the perfect support to the IP or Ethernet business, It makes the new SDH system occupy more and more important position in the optical network of the metropolitan area. Especially in the Metropolitan Access Layer network, the new MSTP can support voice and data access at the same time, which is one of the important networking technologies in the metropolitan Access layer.

The advantage of using SDH Multi-service platform in metropolitan Access network is: integrating SDH equipment with two-tier equipment in physics, merging multiple node devices into one; improving bandwidth utilization of TDM channels and reducing port number of local devices to optimize the existing SDH infrastructure through statistical multiplexing and oversubscribed services It also reduces footprint, reduces power consumption, simplifies business scheduling, improves system scalability, saves operating costs, and adds support for multiple voice and data services.

In the network planning and construction of metropolitan area networks, it is necessary to consider the network real business model, select appropriate network topology and layered structure, combine network scalability, economy, network equipment utilization, circuit scheduling flexibility and so on, select the equipment that can support the network topology and network layered structure. From the previous analysis and description is not difficult to draw the conclusion: the construction of large capacity, multiple services, intelligent metropolitan Area Optical Network is undoubtedly the future development direction of the metropolitan Area network.

The construction of metropolitan area network should be divided into three steps.

The current metropolitan area Optical Network should meet the following requirements: The network has large capacity and good scalability, the network must support multiprotocol and multiple services to adapt to the environment of metropolitan Area Network, the network has a variety of survivability, the circuit scheduling and business management are flexible, and the network should be economical, reliable and modular.

Therefore, the construction of metropolitan Optical Network must consider the following three issues:

1. According to the actual business model of the network, the suitable network topology (including tree type, ring net type, double return type, mesh network type, etc.) is adopted.

2. According to the size of the business particle and its distribution, the use of appropriate network layered structure (including two-layer structure, three-tier structure, etc.);

3. Consider the network topology and layered structure, choose the right technology and products.

At present, various manufacturers have launched a Metropolitan optical Network solution based on different technologies, such as: New and multi-service SDH equipment MSTP, Metropolitan dense wavelength division multiplexing technology Metro DWDM, Gigabit Ethernet GigE (IEEE 802.3ae), resilient packet ring resilient Packet Ring (IEEE 802.17), ATM PON or Epon (IEEE 802.3ah) + FTTB/FTTC/FTTH, after several years of technical development and practice, support for multiple business SDH MSTP and Metro DWDM has become one of the most popular technologies in the industry.

For now, most metropolitan optical networks can be easily divided into two levels: the backbone of the metropolitan area and the metropolitan Access layer. In the larger metropolitan area network, the city backbone layer can be subdivided into the city core layer and the Metropolitan convergence layer, with the further evolution of the network, the role of the metropolitan convergence layer will gradually disappear, and the network will become a real two-layer network, even a level-free network.