Since 2010, with the gradual maturity of technology and industry chain, and the deep penetration of the Internet into the economy and society, network bandwidth and transmission pipelines have been under tremendous planning pressure. 100G trunk transmission has been widely recognized and rapidly deployed on scale, advanced operators. Competing to upgrade the core and trunk networks from 10G/40G to 100G. There are already hundreds of 100G commercial transmission network deployments worldwide (ZTE deploys more than 150 100G networks worldwide) and is still undergoing continuous upgrades.
In view of the fact that the bandwidth of the trunk network still consumes the trunk bandwidth at a compound growth rate of not less than 30%, advanced operators, standards organizations, research institutes and equipment suppliers are focusing on the technologies and standards of next-generation optical transmission networks. At work, this is the super 100G optical transmission network such as 200G/400G/1T.
Technology adopted by Super 100G
The research on the new generation transmission network comes from the market demand for bandwidth. In fact, it is also the unremitting appeal of improving the spectrum transmission efficiency and reducing the transmission cost per bit, in order to cope with the continuous decline of broadband investment income of operators. The coherent-received single-carrier polarization multiplexing and QPSK modulation techniques used in the mainstream commercial 100G transmission mainstream systems have a spectrum transmission efficiency of 4 bits/s/Hz, supplemented by hard decisions or soft decisions to improve OSNR tolerance.
In order to achieve higher transmission bandwidth, the following main techniques can be employed.
First, a high-order modulation scheme is employed to boost the bits per symbol. In terms of single-carrier modulation, higher order can achieve higher transmission efficiency over a certain spectrum bandwidth. Compared to QPSK, the number of bits per symbol of 16QAM modulation is doubled, thereby improving transmission efficiency and capacity. In the field of super 100G transmission, the application of high-order modulation format is an important means commonly used in the industry. At the same time, the adoption of high-order modulation mode also has higher requirements on the receiving side OSNR, which limits the transmission distance. ZTE has continuously practiced on QPSK, 8QAM, 16QAM, 64QAM and other modulation formats, and accumulated a lot of experience and achievements. Its QPSK-based 400G transmission system has a transmission distance of more than 3,000 kilometers and is suitable for long-distance transmission. In the 16QAM modulation mode, the 400G system has a transmission distance of more than 1200 kilometers, which is more suitable for the metro transmission system.
Second, use a higher signal baud rate. Another important research direction of the Super 100G is to increase the signal baud rate. The overall transmission rate is improved by increasing the baud rate of a single signal. We can achieve 400G transmission by means of four-way subcarriers through 100G transmission per carrier. By boosting 28/32GBaud to 56/64GBaud, dual carriers can achieve 400G transmission. The single carrier baud rate is increased to 100 GBaud, which means that a 400G transmission system can be realized.
In June 2015, ZTE and OFS jointly released the latest 400G ultra long-distance high-speed transmission results. ZTE successfully transmitted the 128.8-GBaud 400Gb/s wavelength division multiplexing (WDM) QPSK signal over 10130 kilometers, refreshing the industry. Record, this result once again set a new benchmark for the global optical network industry. This test is based on TeraWave fiber, which is characterized by optimal effective area and low loss; thus, the adoption of new fiber is also an effective means to improve the super 100G transmission system.
Third, multi-carrier technology is adopted. In the super 100G system, a new concept super channel is introduced, which realizes a system with higher transmission capacity through carrier aggregation. The current mainstream 400G transmission system mainly has three implementation modes: 100G for four carriers, 200G for dual carriers (per carrier), and 400G for single carrier. Among them, the four-carrier 100G PDM-QPSK method is mature, low in cost and long in span, but there is no obvious substantial improvement compared to the 100G transmission system. The dual carrier (PDM-16AQM) mode can improve the spectrum transmission efficiency by more than 165%, and the technology is mature and the transmission distance is long. The single-carrier 400G mode has the highest spectral efficiency, and its technical implementation is difficult, the transmission distance is limited, and the cost is high, which is the direction that the research of the super 100G system continues to strive.
Fourth, the use of more advanced digital signal processing and chip technology. Through coherent reception, higher signal reception sensitivity can be achieved and a longer transmission distance can be achieved. Coherent reception is a key technology for implementing a 100G transmission system.
In the super 100G optical transmission system, there are a series of device constraints and linear and nonlinear signal impairment limitations of the link. Advanced digital signal processing is a necessary means to solve the above problems. For example, digital signal processing is used to equalize and compensate signal impairments, including key algorithms such as dispersion compensation, clock recovery, channel equalization, carrier frequency estimation and phase recovery.
Fifth, use a flexible grid. For the purpose of improving spectrum utilization, the new generation of wavelength division system generally supports the spectrum spacing adjustment range of 37.5GHz-400GHz, and the adjustment step is 12.5GHz, which satisfies the requirement of 400G multi-carrier spectrum interval and avoids excessive spectrum fragmentation. , wasting spectrum resources.
Super 100G standard progress
Major organizations involved in the development of the Super 100G standard include ITU-T SG15, IEEE802.3 and OIF. Q6 and Q11 of ITU-T SG15 are responsible for the standardization of the over 100G physical layer and optical transport network (OTN) logic layer respectively. The standardization work for the specific physical transmission parameters of the super 100G has not been carried out, but mainly the new physics of the super 100G application. The transmission technology is included in the G.sup39 file; for the standardization work of the super 100G OTN, most of the content of the B100G OTN technology has formed a working hypothesis. The content of the B100G OTN common part (ie, 400GE unrelated part) has been relatively stable, including B100G OTN frame structure, B100G OTN electrical layer and optical layer overhead, multiplexing hierarchy and bit rate, slot granularity, customer signal mapping, fault handling, and Maintenance signals, etc., will be followed by the B100G OTN customer signal mapping and physical interface related parts according to the progress of the IEEE 400GE standard. The relevant standards are expected to be released in mid-2016.
The IEEE 802.3 working group mainly undertakes the standardization work of 400GE. The standard was formally established in March 2014. Up to now, many consensuses have been reached on system architecture, logic interface, electrical interface and optical interface, and D1 was formed in July 2015. Version .0 is expected to be released in 2017.
OIF is mainly responsible for the standardization of physical chain (PLL) optoelectronic modules and high-speed interfaces, focusing on CEI-56G and 400G WDM. The CEI-56G's ultra-short-range, short-range and mid-range projects basically entered the voting stage, with a focus on long-distance projects. The 400G WDM white paper has been released, and projects such as the 400G WDM system framework will be established to further standardize the 400G WDM system and optical modules.
In addition, China's CCSA TC6 WG1 and WG4 standardization research work on super 100G is basically synchronized with the international. According to the overall research progress of the current standardization organization, it is expected that in 2016, the key schemes and technical parameters of the super 100G standard with 400G as the typical rate will tend to be stable.
The future application prospects of the Super 100G are promising, but its future development is also subject to various factors. First, the target rate fuzzification will significantly affect the development progress of the super 100G technology. Unlike 100G and below high-speed transmission, Super 100G is a general term for a variety of possible rates, which may be 400G, 1Tb/s or n×100G.
In view of the current research, development and trial commercial network deployment, the dual-carrier DPM-16QAM 400G system reuses the 100G phase technology to the greatest extent, and its industrial chain is more mature, the cost is lower, the transmission distance is moderate, trial commercial or There are more commercial cases, and the future application prospects are more optimistic, especially in the metro transmission system that does not require high transmission distance. According to the industry's optimistic forecast, under the premise of reasonable cost, the 2017 400G system will enter a new course of scale deployment. The single-carrier 400G/1T signal transmission is limited by the performance of the device, and it is difficult to be commercialized in a short period of time. Looking back at the extraordinary process of continuous innovation of the optical transmission network, the single-carrier 400G/1T system is still worthy of optimistic expectations. The higher-level rate will also appear in people's field of vision. Whether the spectrum efficiency of the new system is effectively improved, the effective transmission distance, and the comparative cost advantage that can be commercialized will be the key indicators for identifying its advanced nature.
Super 100G combined with SDN
The core idea of the network defined by SDN software is to separate the control plane and data plane of the network device, and to open the programming interface (API) of the data plane, and to flexibly control the operation of the network through centralized control. SDN originated from a new network innovation architecture proposed by the clean slate research group at Stanford University in the United States, and conducted early experiments on the campus network. Based on the SDN concept, Google successfully implemented its B4 network, which greatly improved the network flexibility, efficiency and flexibility of the leased optical cable and data center network distributed around the world. SDN immediately attracted the attention of the industry, the industry's leading operator and the Internet. Service providers, equipment providers and research institutes jointly established the Open Network Foundation (ONF) to promote the standardization of SDN. ZTE is an early founder and staunch supporter of ONF. Dr. Dick from the American Institute is acting on behalf of ZTE. Director of ONF.
Optical transmission has separated the transmission plane, control plane and management plane in the ASON era. ASON has fast service deployment capability and rich service protection level, but its openness is not enough to open its programming capability to third parties. The application of SDN in the transport network is to open up its programming capabilities to users, which may be operators, Internet providers or third-party vendors in the application field, in order to carry out new services more efficiently and agile, and at the same time the potential of the carrier network. It can also be shared to the greatest extent possible.
In the ultra-100G era, optical transmission introduces a richer modulation scheme (QPSK, 8QAM, 16QAM, 64QAM), which directly affects the transmission distance of optical signals; in order to improve transmission distance and OSNR, HD/SD FEC technology is also used to enhance The ability to transmit systems, but with more redundancy overhead. Flex Grid, multi-subcarrier and super channel technology, combined with the ROADM features of traditional WDM systems, the flexible and configurable nature of optical transmission systems combined with the open concept of SDN helps customers build flexibility and high availability. And the automated SDON (Software defined optical network) network, frees customers from the tedious physical layer device configuration work, and puts more effort into the pipeline operation of the transmission network.