In addition, the optical transceiver module and equipment system used to transmit data signals are very different from the traditional optical transceiver module and equipment system used to transmit continuous code streams. In the access network, the implemented systems include ATM-PON, EPON or GPON. In the core network, it is a well-known IP over Optical technology to realize the direct bearing of data signals such as IP in the optical layer (including in wavelength division multiplexing systems).
Because of the good characteristics of SDH system and a large number of existing resources, we can make full use of the original SDH system to transmit data signals. Only ATM was considered at first. Later, more and more types of data signals were carried through SDH networks, such as FR, ATM, IP, 10M-baseT, FE, GE, 10GE, DDN, FDDI, Fibre Channel, FICON, ESCON and so on.
Therefore, many methods have been proposed to send IP and other signals into the virtual container VC of SDH. Initially, IP or Ethernet was put into ATM and then mapped into SDH transmission, that is, IP/Ethernet over ATM and then over SDH. Later, the intermediate process was omitted and IP or Ethernet was sent directly to SDH, such as PPP, LAPS, SDL, GFP, etc. , that is, IP over SDH, POS or EOS.
Increase channel capacity
Optical communication system can be developed from PDH to SDH, from 155Mb/s to 10Gb/s, and 40GB/s has been commercialized recently. At the same time, systems with larger capacity are also being explored, such as 160Gb/s (single channel) system, which has been successfully developed in the laboratory and is being considered to formulate standards for it. In addition, by using channel multiplexing technology such as wavelength division multiplexing, the system capacity can be further improved. At present, the OTDM system of 32× 10Gb/s (i.e. 320Gb/s) has been widely used, and the system of 160× 10Gb/s (i.e. 1.6Tb/s) has been put into commercial use, and the system in the laboratory has exceeded. There is no doubt that these are very conducive to the transmission of backbone networks.
Ultra-long distance transmission of signals
From a macro point of view, the requirement for optical fiber transmission is, of course, as far as possible, and all institutions that study optical fiber communication technology have made great efforts in this regard. Especially after the appearance of optical fiber amplifier, the records in this field are endless. Not only is the length of each span increasing, for example, from the original 20km and 40km to 80km, to 120km and 160km. And the total non-regenerative relay distance is also increasing, for example, from about 600km to 3000km and 4000km.
From a technical point of view, the appearance of fiber amplifier in Raman fiber amplifier creates conditions for increasing the non-regenerative relay distance. Meanwhile, line codes, such as RZ or CS-RZ codes, are used for long-distance transmission. Use FEC, EFEC or SFEC to improve the receiving sensitivity; Using dispersion compensation and PMD compensation technology to solve the cost of optical channel, and choosing suitable optical fiber and optical device, the ultra-long distance transmission of ultra-STM-64 or DWDM system based on 10Gb/s and 4000km non-electric regenerative repeater can be realized.
Integration of optical transmission and switching technology
With the demand of optical communication gradually shifting from backbone network to metropolitan area network, optical transmission gradually approaches to service nodes. In application, people feel that optical communication, as a means of transmission, can no longer fully meet people's needs. As a service node, it is close to users, especially for users of data services. People hope that optical communication can provide the transmission function and access function of various services at the same time. This optical communication technology can actually be regarded as the fusion of transmission and switching. MSTP, a widely used multi-service transmission platform based on SDH, is a typical example.
MSTP based on SDH refers to the multi-service node equipment that realizes the access processing and transmission of TDM, ATM, Ethernet and other services on SDH platform and provides unified network management. In fact, some MSTP devices can provide FR, FDDI, Fibre Channel, FICON, ESCON and other services besides the above services.
Besides MSTP based on SDH, there can also be MSTP based on WDM. In fact, each channel of WDM is used as a channel for various services, which can be used transparently and can also support access processing of various services. For example, the Ethernet layer 2 or even layer 3 switching function is embedded in ports such as FE and GE, so that the WDM system not only has transmission capability, but also has service provision capability.
In addition, in the optical layer network, the concept of ASON is obtained by combining transmission and switching functions. In addition to the original optical transmission plane and management plane, ASON has also added a control plane. In addition to the fixed connection (hard connection) of the original optical transmission network, under the control of signaling, it can also realize exchange connection (soft connection) and hybrid connection. That is, in addition to the transmission function, there is also the exchange function.
Internet development demand and development trend of next generation all-optical network
In recent years, with the rapid development of the Internet, IP services have exploded. It is predicted that IP will carry a variety of services including voice, image and data, which will form the basis of future information networks. At the same time, the optical transport network with WDM as the core and intelligent optical network (ION) as the target further introduces control signaling into the optical layer to meet the needs of multi-granularity information exchange in the future network, and improve the resource utilization rate and flexibility of networking application. Therefore, how to build the next generation optical network that can effectively support IP services has become one of the hot spots of widespread concern.
For the optical network carrying services, the main problems to be faced in the next step are not only the obvious requirements of ultra-large capacity and broadband access, but also the need for the optical layer to provide higher intelligence and realize optical switching on optical nodes. Its purpose is to establish an economic, efficient and flexible QoS to expand and support services through the adaptation and integration of optical layer and IP layer, so as to meet the requirements of IP services for information transmission and exchange systems.
Intelligent optical network absorbs the intelligent characteristics of IP network and adds a control plane to the existing optical transmission network. The control plane is not only used to establish connections for users, provide services and control the underlying network, but also has outstanding characteristics such as high reliability, scalability and efficiency, supports different technical schemes and different business requirements, and represents the development direction of the next generation optical network construction.
The research shows that with the explosive growth of IP services, the telecommunications industry and IT industry are in the "shuffle" stage of integration and conflict, and new technologies are constantly emerging. Especially with the use of software control ("soft light" technology), today's optical network will gradually evolve into an intelligent optical network, which allows operators to automatically configure and manage traffic more effectively. At the same time, it will provide a good recovery mechanism to support services with different QoS requirements, so that operators can build and flexibly manage optical networks and develop some new applications, including bandwidth leasing, wavelength services, optical layer networking and optical virtual private network (OVPN).
To sum up, the optical wave technology based on high-speed optical transmission technology, broadband optical access technology, node optical switching technology and intelligent optical network technology applied to IP Internet has become the research focus of optical fiber communication. In the future, people will continue to study and build all kinds of advanced optical networks, and at the same time, they will conduct more comprehensive and in-depth research on the key technologies of the next generation optical transmission network while verifying the relevant new concepts and schemes.
From the technical development trend, WDM technology will develop towards more channels, higher channel rate and denser channel spacing. From the application point of view, optical network is developing towards IP Internet, which can integrate more services, allocate resources flexibly and have stronger survivability. Especially in order to meet the recent demand, optical communication technology will develop to intelligent transmission function on the basis of basically realizing ultra-high speed, long distance and large capacity transmission function.
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