DWDM and OTN are two technical systems developed by wavelength division transmission technology in recent years: DWDM can be regarded as the previous PDH (point-to-point transmission), and the online and offline services are completed on ODF through hard jumpers; OTN is like SDH (various types of Networking), with the function of cross-connection (whether it is the cross-connection of the electrical layer or the optical layer).
With the continuous acceleration of the process of ALL IP, at present, regardless of the national backbone, provincial backbone or local network WDM system, OTN is the mainstream when selecting equipment in the initial stage of network construction. OTN equipment has gradually replaced DWDM equipment with its unique advantages ( Similar to SDH equipment replacing PDH equipment). As a new technology and new product form, OTN has become the focus of the current industry. This article will analyze and compare DWDM, OTN equipment and technology.
1 Basic concepts of DWDM and OTN
With the change of service requirements and granularity, it is necessary to multiplex large-granularity services through optical fibers (single-fiber or dual-fiber) and then divide them into different wavelengths for long-distance transmission. The wavelength division multiplexing technology emerges as the times require.
DWDM is wavelength division multiplexing (Wavelength Division Multiplexing), which multiplexes optical signals of different wavelengths into the same fiber for transmission. WDM technology is a very mature traditional wavelength division technology for more than ten years. It can be divided into two specifications: sparse wavelength division multiplexing (CWDM), with a large wavelength interval (20nm); dense wavelength division multiplexing (DWDM), with a small wavelength interval ( less than or equal to 0.8nm). Due to the short transmission distance of CWDM, a large number of DWDM devices are deployed in the existing transmission networks of various operators.
The open DWDM system consists of the following parts: OTM completes service loading and unloading for the optical line terminal station, OA completes the pure optical relay amplification processing of the multiplexed signal for the optical line amplifying station, and the OTU completes the non-standard wavelength signal light to meet the G .694.1(2) wavelength conversion function of standard wavelength signal light, OMU/ODU: completes the multiplexing/demultiplexing of G.694.1(2) fixed wavelength signal light, OBA (power amplifier) improves the power of the combined optical signal by increasing , thereby increasing the output optical power of each wavelength, and OPA (pre-amplification) improves the receiving sensitivity of each wavelength by increasing the optical power of the input multiplexed signal.
OTN is an Optical Transport Network (Optical Transport Network), also known as OTH (Optical Transport Hierarchy) in ITU-T. It was developed on the basis of traditional wavelength division and combined the advantages of DWDM and SDH. It integrates the advantages of optical domain and electrical domain processing, provides huge transmission capacity, completely transparent end-to-end wavelength/sub-wavelength connection and carrier-level protection, and is an excellent technology for transmitting broadband large-particle services. In the past five years, operators have deployed OTN equipment on a large scale in various transmission networks.
2 Comparison of technical characteristics of DWDM and OTN
Although the DWDM system greatly improves the transmission efficiency of optical fibers and supports the transmission of large-granularity services, due to the limitation of wavelength division technology, wavelengths are configured in a point-to-point form and cannot be dynamically adjusted. The resource utilization rate is not high, and the flexibility of service adjustment is not enough. The flow of business has changed, and it is very complicated to adjust. The scheduling between DWDM services is mainly physical scheduling on the ODF. The network management only monitors the performance of the optical layer (the network management bytes are few and the network management information is simple), and there are few troubleshooting methods and high maintenance difficulty.
OTN inherits the large-capacity transmission function of DWDM and has flexible optoelectronic joint scheduling and protection capabilities. Through the introduction of ROADM technology, OTH technology, G.709 encapsulation and control plane, it solves the problem of traditional WDM networks without wavelength/sub-wavelength service scheduling capabilities. , Weak networking capability, weak protection capability and other issues. The electrical layer implements scheduling based on sub-wavelengths (such as GE, 2.5G, 10G, 40G, 100G particles), and the optical layer scheduling is mainly based on 10G, 40G or 100G wavelengths, with high bandwidth utilization; it has abundant overhead bytes, and its OAM The /P function is stronger than WDM.
In addition, OTN and DWDM can be used in common on the optical layer, the difference is that OTN has an electrical layer subframe. Therefore, some DWDM devices on the existing network are added with electronic cross-connect sub-frames and upgraded to OTN.
3 DWDM and OTN networking comparison
The mixed networking of OTN and DWDM will lose the advantages of OTN (the frame structure is different from the traditional WDM, and the connection will have an impact).
Since OTN optical cross-connect is mainly implemented by ROADM module (loaded with WSS switch), considering the high price of ROADM, OM/OD and OADM are used to form ring network and chain network in OTN networking.
For chained networks (such as long-distance trunk lines), the advantages of OTN are not necessarily fully manifested due to the relatively fixed intermediate services and protection methods, but there are still advantages in some aspects (high channel efficiency leads to lower costs than traditional WDM) , the current trunk network mostly uses DWDM and OTN for superimposed networking.
For the local network, since services need to be connected frequently, the network structure is frequently changed and scheduled, and the protection method needs to be changed flexibly, the traditional WDM must be unable to do so. The advantages of using OTN networking are self-evident.
OTN provides the ability to manage each wavelength on each fiber, and OTN can better adapt to future network development.
4 Comparison of DWDM and OTN Bearer Services
The demand for OTN electrical crossover comes from the emergence of a single-wave 10G rate. When a channel reaches 10G, its OTU can carry 4*2.5G or 8 to 9 GEs; DWDM adopts a point-to-point method. If the service demand is small , OTU investment appears to be wasteful. To this end, it is necessary to introduce a cross-connect function similar to SDH on DWDM, so as to evolve the electrical cross-connect function of OTN.
OTN has electrical crossover capability, that is, sub-rate crossover capability per channel (much like SDH). At the same time, optical cross-connection and electrical cross-connection are independent of each other. If there is optical cross-connection capability but no electrical cross-connection, or electrical cross-connection without optical cross-connection, it can be called OTN.
Due to the differences in network construction models (cost, service particle and flow direction), the electrical crossover method is mostly used in China, and the optical crossover method is mostly used abroad.
5 Conclusion
Through the above analysis and comparison, it can be seen that OTN and DWDM are significantly different in terms of technology and application. From the perspective of cross-connection capacity, service granularity and networking flexibility, OTN is very powerful and can better meet the needs of future network cross-connection.
Due to the transparency of OTN system service transmission, strong error correction capability, flexible optical/electrical layer scheduling capability, maintenance management capability and scalability of equipment capacity (80*100G equipment is now commercialized), various transmission networks The introduction of OTN equipment has become inevitable.
Post time: Oct-25-2022