Currently, three most popular IP transmission technologies are available: IP over ATM, IP over SDH, and IP over WDM. All three IP transfer technologies will play their own roles in different periods of telecommunication network development and different parts of the network. The three will coexist and complement each other. However, from a future-oriented perspective, IP over WDM will be the most vital technology, and its huge bandwidth potential matches the explosive growth of IP services, this best transfer technology for IP services will become the dominant Transmission Technology for networks, especially backbone networks in the future.
In recent years, the rapid development of the Internet has prompted the IP technology to achieve rapid development that has never been before in communication and information technology. In recent years, IP technology has made great progress in both network structure, transmission capability and business development. In 1970s, TCP/IP was proposed as an internetworking protocol between networks. In the past two decades, TCP/IP has not attracted the attention of the outside world except for its role in interworking with American LAN. ITU-T did not accept this standard for a long period of time. Until the beginning of 1990s, the emergence of Web fundamentally changed this state, and the IP network had achieved rapid development, and the corresponding IP technology had also achieved rapid development.
IP is a network layer protocol, and SDH and WDM are physical layer transmission technologies. A data link layer is required between the two layers. The data link layer is responsible for converting the signals provided by the physical layer into the signals required by the network layer, currently, three most popular IP transmission technologies are available: IP over ATM, IP over SDH, and IP over WDM.
The traditional method of expansion is TDM time division multiplexing (TDM), that is, time division and multiplexing of electrical signals. Whether it's PDH's 34 Mbit/s-140 Mbit/s-565 Mbit/s, or SDH's 155 Mbit/s-622 Mbit/S-2 488 Mbit/S-9 952 Mbit/s, they all follow this principle. According to statistics, when the system speed is lower than 2.5 Gbit/s and contains 2.5 Gbit/s, the transmission cost per bit is reduced by about 30% every time the system is upgraded. Therefore, in the past system upgrades, people first thought of and used TDM technology. The time-division multiplexing (TDM) method is an effective measure for digital communication to improve transmission efficiency and reduce transmission costs. However, with the dramatic increase in transmission capacity requirements of modern telecom networks, the use of TDM has become increasingly close to the limits of silicon and GA arsenic technology, such as for the current 10 Gbit/s, TDM does not have much potential to be tapped, and the price of transmission equipment is also high. The effects of optical fiber color dispersion and polarization mode dispersion are also increasing. More and more people are switching their interests from electroreuse to optical reuse, that is, they use various multiplexing methods in the optical field to improve transmission efficiency and reuse rate.
From 1996 onwards, the most representative is the emergence of wavelength division multiplexing (WDM) systems. The so-called WDM Technology is to make full use of the huge bandwidth resources brought about by Single-Mode Optical Fiber low-loss areas, using a wavelength division multiplexing ), the sender merges optical carriers of different wavelengths and sends them to a single optical fiber for transmission. At the receiving end, a wave of division multiplexing filters are used to separate optical carriers with different wavelengths carrying different signals. Because optical carrier signals of different wavelengths can be considered independent of each other without considering non-linearity of optical fibers, bidirectional transmission is easy to solve, you only need to arrange the signals in two directions for transmission at different wavelengths. Depending on the wavelength division, the number of wavelengths that can be reused varies from two to dozens, depending on the allowable optical carrier wavelength interval.
Wavelength Division Multiplexing Technology has the following features:
(1) Make full use of the huge bandwidth resources of the optical fiber, so that the transmission capacity of an optical fiber is several to dozens of times higher than that of a single wavelength. What people are using now is the low-loss optical fiber spectrum of 1 310 nm ~ 1 550 nm) very small part. Even if all the resources are amplified by the bait-doped fiber amplifier EDFA, the bandwidth is 1 530 nm ~ 1 565 nm), it only occupies about 1/6 of its bandwidth. WDM Technology can make full use of the huge bandwidth of single-mode optical fibers by about 25 THz ).
(2) Enable N wavelengths to be reused for transmission in a single-mode optical fiber, which can save a lot of Optical Fiber During large-capacity long-distance transmission.
(3) because the signal wavelengths transmitted in the same optical fiber are independent of each other, different signals can be transmitted to complete the synthesis and separation of various telecom business signals, including digital and analog signals, and the integration and separation of PDH and SDH signals.
(4) The wavelength division multiplexing channel is transparent to the data format, that is, it has nothing to do with the signal rate and electrical modulation method. In network expansion and development, it is an ideal means of expansion and a convenient means to introduce new broadband services.
Using WDM Technology to achieve network switching and recovery may achieve transparent and highly survivability optical networks in the future.
The combination of IP and ATM is a unified connection-oriented ATM and non-connected IP address. It is also an optimized combination of routing and switching. However, its network structure is complex and its overhead loss is more than 25%. The combination of IP and SDH is to map IP groups directly to SDH frames through the Point-to-Point Protocol, saving the intermediate ATM layer, thus retaining the connectionless features of the Internet, the network structure is simplified and the transmission efficiency is improved, but there is no priority for service quality. The advantage of IP over WDM lies in its huge bandwidth potential, which can meet the huge bandwidth requirements of IP services and solve the asymmetry problem of IP services. The business transparency of the WDM system can be compatible with services of different protocols to achieve business convergence. According to * WDM's high bandwidth and simple priority scheme, it can also basically solve the quality of service QoS that people are concerned about. More and more people are realizing that IP over WDM and IP over SDH will become the main technologies of large IP High-Speed Backbone Networks to ease high-speed data streams. The difference between IP over SDH and IP over WDM lies in the capacity of carrying traffic and the flexibility to adapt to asymmetric services. The particle size transmitted by IP over SDH is "small", which is more suitable for our current needs. It is technically mature and highly standardized. The combination of IP over WDM and "Optical Network" applies to the interconnection of IP addresses in "Transparent" man or the core convergence of large-scale IP backbone networks in the future. From the perspective of development, IP over WDM undoubtedly represents the development direction of the network. It integrates the development of "Optical Network" and IP, it can make full use of the advantages of "transparent transmission" in "Optical Network" and the huge bandwidth of optical fiber, but its particles are "too large" and there is no interface below 2.5 Gbit/s, however, with the emergence of low-speed WDM interfaces, it will be applied to more and more man applications.
The idea of IP over WDM is: it not only saves the ATM layer, but also saves the intermediate SDH layer, and directly places the IP address on the optical path for transmission. Obviously, this is the simplest and most direct architecture. It saves the intermediate ATM and SDH layers, simplifies the layers, reduces the overlapping of network devices and functions, and reduces the complexity of network management, in particular, the complexity of network configuration; the lowest additional overhead and the highest transmission rate; through the business volume engineering design, it can match the asymmetric business volume characteristics of IP addresses, the optical fiber loop can also be used to protect the optical fiber absorption of burst services, so as to avoid caching and reduce latency. The cost of expensive ATM switches and a large number of common SDH multiplexing devices is reduced, which simplifies network management, wavelength Division Multiplexing is adopted, and its cost is one to two orders of magnitude lower than that of the traditional circuit switching network!
How to map IP addresses directly to the optical network layer is a new scheme under research-wavelength grouping scheme. This scheme maps the group to the WDM optical link directly, and combines the group and the physical layer. Using a new structure called high-speed synchronous frame (HSSF,
HSSF uses the SDH125-μs frame structure to provide link status identification for Link faults and performance pipelines. HSSF simplifies the implementation of forward correction (FEC. FEC improves the performance Noise Ratio in WDM Systems. In short, HSSF implements the frame structure of IP over SDH, but removes unnecessary SDH functions and overhead, such as the Net Load pointer technology ). The biggest advantage of IP over WDM is its huge bandwidth potential. Currently, the capacity of the commercial WDM system has reached 400 Gb/s. obviously, only such a high speed rate can match the huge IP traffic in the future, and no other technology can be compared with it.
Another important feature of WDM is that there are up to hundreds of available channels, and each channel signal can be isolated from each other. Therefore, it is easy to be compatible with businesses of different nature and protocols and serve as a gathering of businesses. Network managers no longer need to try to mix various services on the same circuit, so they may no longer need to use complex ATM to collect services, simplifying the architecture. As for the quality of service, the solution of IP over WDM is * high bandwidth and simple priority solution of WDM. Based on queuing theory, QoS is required only when the network utilization rate exceeds 75%. When the network utilization rate is lower than 70%, the queue is very short or does not have a queue at all. Generally, you only need a simple priority scheme. Therefore, you can put high-quality real-time services in front of the queue to ensure QoS. Actual service prediction shows that there will be a few real-time businesses with high quality in the future. Therefore, it is reasonable to use a simple priority scheme and high-bandwidth WDM to deal with QoS problems.
To sum up, there are various network solutions. All three IP transfer technologies will play their roles in different periods of telecommunication network development and different parts of the network. The three will coexist and complement each other. However, from a future-oriented perspective, IP over WDM will be the most vital technology. Its huge bandwidth potential matches the explosive growth of IP services. This best transfer technology for IP services will become the dominant Transmission Technology for networks, especially backbone networks, in the future.
- The key to seamless combination of GMPLS--IP and WDM