Evolution trend of modern optical network

At present, the evolution of Optical Network presents two trends, the first trend is that optical network from the original can only provide fixed transmission channel point-to-point network to be able to provide dynamic transmission channel according to the needs of the intelligent network development, the essence of this change from the original channel manual control to the development of automation, The original network management platform developed into a network control platform; the second trend is that the original network is opaque, the network contains a number of wavelength point-to-point connection, each wavelength of the channel in the Terminal photoelectric transformation, processing in the electrical field, with the rapid development of optical devices, This kind of opaque network is developing to all optical network, and the end-to-end communication of all optical networks is mainly in the optical domain. The development trends listed above are specific in the following aspects.

One, from static to dynamic trend

The first generation optical network uses the static point-to-point Wavelength division multiplexing (WDM) system to increase the bandwidth, this optical network is widely used in long-distance backbone network transmission, can provide dozens of wavelength OC-48 (2.5gbit/s) or OC-192 (10GBIT/S) signal channel. The optical network uses static channel allocation technology to provide a fixed transmission channel between two points.

The next Generation Optical network is an intelligent Optical network (ION), which provides a dynamic point-to-point connection using optical switching, ION can quickly provide end-to-end link connections between two points, which can range from STM-1 to STM-64, greatly altering the characteristics of previous communication services, Stimulate the development of bandwidth utilization. At the same time, this method can effectively reduce the operating costs, the establishment and demolition of communication links can be completed in seconds or minutes, shortening the communication link establishment time.

Ii. Trends from the electrical field to the optical field

The key of Intelligent Optical Network (ION) is that it can provide the service layer with powerful, easy to maintain and manage low cost optical network. The optical network layer includes efficient and stable line system, functional modules, such as optical switching arrays and tunable devices, combine to form a network of optical layers that provide flexible links, in which efficient and stable line systems provide a mega-premium all-optical data channel between two cities, which are thousands of kilometers apart, Compared with the traditional line system, the line system has little electric relay, so the circuit system has the advantages of easy operation and low cost.

The development direction of the optical switching array is also all-optical, which completes the switching of a single optical signal or a set of optical signals or even a whole fiber signal. Tunable light source, optical filter and optical receiver can provide flexible selectivity, effectively simplify system structure and reduce operating cost, these tunable devices assign wavelength resources through fixed regenerator, while minimizing the probability of wavelength blocking. At present, 2.5gbit/s and 10gbit/s transmission rates, suitable for long-distance transmission of tunable light source and optical receiver can be commercially available.

Iii. trends in switching from electricity to light exchange

Operators require that light Exchange components have the characteristics of convenient testability, low price and convenient maintainability. Therefore, the present characteristics of the optical switch include: can support a variety of speed and the operation of a single wavelength signal, but also can be exchanged with a lot of wavelength signal composite signal.

From the technical point of view, with the development of all optical network technology and optical switching devices, the optical transmission system with no electric relay distance up to 3000km has been commercially available, and optical switching technology has matured, which can provide highly reliable and maintainable optical switching devices in the market. In addition, considerable progress has been made in the construction of a control layer agreement on how to provide fast link building and dismantling characteristics. All of this has laid a solid foundation for the development of optical exchange.

Four, from the management platform to the control platform trend

The management and control network element is another important part of the intelligent network, and the control platform can automatically complete the End-to-end link's establishment, maintenance and removal in a few seconds. With this control platform, operators can quickly provide routing and services based on business needs, and often, in algorithms, a protocol similar to this application is used, such as the use of related routing protocols applied to the Internet. The control platform includes the following techniques.

1. Manage and maintain channel

The management and maintenance channel has two kinds of systems, such as Out-of-band and in-band. In practical applications, it is best to use the Out-of-band approach, the advantage of this approach is that it can easily control such as Sdh/sonet, IP, ATM, Gigabit Ethernet and other types of equipment, but also compatible with optical switching array and non-transparent photoelectric switching network. In addition, the Out-of-band approach can also be based on the needs of the different use of appropriate bandwidth. For example, if 10mbit/s Ethernet does not meet the requirements, we can use 100mbit/s Ethernet or even Gigabit Ethernet (Gigabit Ethernet) to form a management maintenance channel.

2. A signaling protocol that enables the rapid establishment and dismantling of end to end links

This can be accomplished with existing RSVP or CR-LDP protocols applied to the Internet, as well as the SS7 protocols that apply to telephony networks.

3. A distributed database topology structure

This can be achieved by using the Internet to achieve the shortest path priority algorithm topology.

4. A recovery mechanism capable of providing rapid recovery for signalling and routing

With the increasing demand of new business, the connection of various optical fiber signals is more frequent, which requires that the control platform can manage many kinds of circuits at the same time, it can not only manage the opaque photoelectric switching network, but also manage all optical switching network, both one-way transmission and bidirectional transmission are supported. The control platform is required to be able to measure the optical path, and it can be flexibly and easily upgraded.

Control platform should also have the role of management, management functions, including network element management and network management of two parts, its role is: to participate in the provision of optical routing, network performance monitoring to understand the quality of service, to provide fault location for maintenance, to help operators configure network resources module. In the future, the control platform should also complement the management platform with distributed signaling and routing protocols to enable the application of optical path connections such as event-driven and calendar-driven customer-driven approaches.

Five, the connection platform's light exchange

Because of the different size of the information bandwidth of the core network, the management of the bandwidth should be carried out at several levels, providing the corresponding bandwidth for the various information bandwidth particles. Within the core network, the management of communications is usually done on the light road. For a node, a large number of signals simply pass through the node rather than terminate it, and for those signals, the network will prioritize and let them pass through. With the increase of transmission nodes in the network, the demand for wavelength management of a set of wavelength and even the whole fiber is becoming more and more urgent. The part that completes this function is called the Optical crossover Connector (OXC), and its function is to exchange signals on a large scale at different levels. The OXC consists of the following two types.

Pure Light Oxc: This kind of oxc is not limited by the bit rate of the fiber signal and the type of service, can exchange the signal of single wavelength signal, compound wavelength signal or whole fiber, it is usually called photon Exchange (PXC), it is not suitable for the signal that the exchange rate is less than the transmission rate.

The other is the OXC, which is constructed using an electric switch, which is used to exchange low speed signals. It transforms the received light signal into a high speed electric data stream through photoelectric conversion, and then uses the high-speed electric data stream to solve many low-speed channels. These low-speed channels are connected to the corresponding route via electrical oxc, and then the Low-speed channel multiplexing becomes a high-speed data stream, and is modulated to a light wavelength.

Vi. the development of IP over DWDM

As we all know, the next generation of communication network will have more IP business, so, the industry on IP over DWDM voice is increasingly high, the relevant standards and programs are increasingly perfect. One way to achieve this is to connect IP routers directly to WDM devices, in which case, IP routers not only assume the source and terminal signal routing algorithms, but also all the direct signal processing. However, at least for large capacity backbone networks, it is not suitable for such a scenario, for four reasons.

The IP router's capacity is much smaller than the PXC capacity. A high-end router can access the 16-channel OC-192 signal, while a PXC can handle up to 1000-way OC-192 direct signal, obviously, as the technology progresses, PXC can handle more OC-192 signals, if the use of IP routers directly into the WDM device scheme, A large number of routers must be used to process the pass-through signal. Therefore, the average cost per port used to process passthrough signals with IP routers will be much greater than the average cost per port used to process direct signals using PXC.

The IP router is much larger than the PXC volume. A routing device with access to 16-channel OC-192 (160GBIT/S) occupies 1 rack locations, while a 1000-port PXC occupies only 3 rack locations.

Because a large number of buffers are used in IP routers, it is difficult to ensure the real-time requirement of signal transmission by introducing a large random delay at the intermediate point.

Using IP routers to process pass-through signals will waste a greater power consumption than using PXC.

Based on the above reasons, the router is best used only to deal with the source and terminal signals, and the direct signal to the PXC device to deal with.

It should be noted that the use of PXC to deal with the direct signal of the scheme has a problem, that the current routers provide a OC-192 interface, according to the above scenario, these OC-192 interfaces only to deal with the source and terminal signals, Because there is no two routers between any of the OC-192 so large bandwidth of the source and terminal signal demand, so will cause a great waste of bandwidth. A better solution is to transform the existing router products, using the channel interface on the router, the function is to classify the signals, pass the direct signals to the PXC to process, and only handle the source and terminal signals.