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What is the difference between OTN and DWDM?

Global communication is advancing rapidly, the role of communication network is becoming more and more important, and the construction of communication network needs to be expanded continuously. DWDM (Dense Wavelength Division Multiplexing) and OTN (Optical Transport Network) technologies have been widely used in network communication construction. DWDM technology has greatly improved the transmission capacity of fiber optic networks, but it is insufficient in optical domain signal processing and service scheduling, and cannot meet the high standard requirements of broadband data services. As an evolving product of DWDM technology, OTN has a variety of customer signal packaging and transparent transmission, large particle bandwidth reuse, flexible cross configuration and scheduling, strong overhead and maintenance management capabilities, and enhanced networking and protection capabilities. The unique advantages of OTN equipment have gradually replaced DWDM equipment. Next, let’s compare the differences between DWDM and OTN.

Introduction of DWDM and OTN

WDM technology is a very mature traditional WDM technology for more than 10 years, which can be divided into two specifications: coarse wavelength division multiplexing (CWDM) with large wavelength interval (20nm) and dense wavelength division multiplexing (DWDM) with small wavelength interval (≤0.8nm). What is DWDM technology? DWDM (Dense Wavelength Division Multiplexing) is a laser technology for increasing bandwidth in fiber optic backbone networks. More specifically, it is the multiplexing of closely spaced spectra of individual fiber carriers in a given fiber in order to take advantage of the achievable transmission performance (e.g., to achieve minimal dispersion or attenuation). In this way, the total number of fibers required can be reduced for a given information transmission capacity.

OTN

OTN (Optical Transport Network) is based on WDM (Wavelength Division Multiplexing) technology and adds the powerful operation, maintenance, management and assignment capabilities of SDH (Synchronous Digital Hierarchy) to its large transmission capacity, while compensating for the lack of functionality of SDH in the transport-oriented layer. OTN combines the advantages of optical and electrical domain processing to provide huge transmission capacity, fully transparent end-to-end wavelength/sub-wavelength connectivity, and carrier-grade protection, making it an excellent technology for delivering broadband, large granular services. OTN switching modules are added to this technology, thus enabling the system to flexibly schedule communication services, allowing client information to be expanded, facilitated, and increased, and improving the service capability of network communication, thus solving the problems of weak networking capability and weak protection capability of traditional WDM networks.

The differences between DWDM and OTN

·Different signal formats

DWDM technology does not have a corresponding frame structure, in operation, the wavelength of a single signal through the converter, transformed into the corresponding wavelength in the network communication, through optical technology, multiplexing the transmission wavelength.

OTN has a complete frame structure. It schedules the wavelength through electrical crossing technology, which can realize the electrical crossing function similar to SDH, so that the signals of small particles can be combined and transmitted in large channels. OTN technology can also regulate the network communication electric regeneration part of the work performance, failure and other issues, in the process of performance fault detection, OTN technology is more superior.

· Differences in networking and protection mechanisms

DWDM technology networking mode is mainly point-to-point, chain, star and ring type networking, and only grassroots protection is provided in the protection mode. The protection mode is mainly optical multiplexing section protection, and 1+1 and 1:1 protection is used on the optical path. Because there is no protection for terminal equipment, this protection method requires two independently routed optical cables, and DWDM’s self-healing protection for services is carried out in the SDH ring network. 

OTN networking is usually ring networking, mesh networking and other networking methods. OTN provides the ability to manage each wavelength on each optical fiber. OTN can better adapt to the development of network in the future. In 5G application scenarios with OTN networking, 25G and 100G optical modules, such as 100G QSFP28 ER4 optical modules, are often used.

The hybrid networking of OTN and DWDM will lose the advantages of OTN (the frame structure is different from the traditional wavelength division, and the docking will be affected). Therefore, independent networking is the best choice.

·Differences in business scheduling capabilities

Although DWDM system greatly improves the optical fiber transmission efficiency and supports the transmission of large particle services. However, due to the limitation of wavelength division technology, the wavelength is configured in the form of point-to-point, which can not be dynamically adjusted. The resource utilization is not high, and the flexibility of business adjustment is not enough. Therefore, once the flow direction of business changes, the adjustment will be very complex.

OTN inherits the high-capacity transmission function of DWDM and has flexible optical and optical joint scheduling and protection capability. In OTN, data configuration can be used for cross-connection (similar to SDH service configuration), and multiple types of services can be accessed simultaneously, enabling intelligent scheduling of services.

  1. Optical layer scheduling capability: OTN optical layer provides OADM wavelength scheduling mode, which can pre-plan input/output fixed wavelengths or use AWG input/output all wavelengths, and connect wavelengths that need up/down services to service boards, and use pigtail hopping to schedule wavelengths that do not need up/down services.
  2. Electrical layer scheduling capability: provide distributed electrical crossover of ODU0/ODU1/ODU2/ODU2e/ODU3/ODU4 particles, and the crossover capacity of adjacent slots reaches 100/200Gbps.

·Application scenarios of DWDM and OTN

DWDM is mainly used in inter provincial trunk network and intra provincial backbone network, mainly in point-to-point networking mode, and 10G DWDM Tunable optical module may be required. If the line protection mode is adopted, more lines need to be laid, and the cost is high. OTN network is mainly deployed in the inter provincial backbone network, intra provincial backbone network and metropolitan core layer of telecom operation enterprises, which improves an ideal solution for large broadband granular services. The inter provincial backbone network carries PSTN/2G/3G/4G/ Internet and other long-distance services. OTN network can realize various forms of protection, with strong protection ability. The OTN of the intra-provincial backbone network carries services such as NGW/3G/4G/IPTV large customer dedicated lines between backbone routers, and the OTN of the metro core network carries large granular services between the core routers of the local network to the convergence routers.

Conclusion

Today, with the continuous growth of information level and service bandwidth, OTN equipment, as a derivative of DWDM, inherits and combines the advantages of SDH and WDM, and expands the networking function corresponding to the service transmission requirements. The network application, scheduling capability, service access capability and network management monitoring capability have been significantly improved, which can meet the requirements of new service quality. OTN system has the transparency of service transmission, strong error correction ability and flexible scheduling ability. With the advent of 5G era, the application of OTN technology will be more and more popular in the market, which is the inevitable trend of network development in the future.

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