What is OTN(Optical Transport Network)?
Nowadays, the SONET/SDH network is an universal network that combines with WDM (wavelength division multiplexing) technique to transmit multiple optical signals over a single fiber. In future networking, high speed transmission is no doubt the migration trend. Inspired by the SONET/SDH network, ITU-T (ITU Telecommunication Standardization Sector) has defined the optical transport network (OTN) to achieve a more cost-effective high speed network with the help of WDM technology.
Generally speaking, OTN is a network interface protocol put forward in ITU G.709. OTN adds OAM (operations, administration and maintenance) functionality to optical carriers. It allows network operators to converge networks through seamless transport of the numerous types of legacy protocols, while providing the flexibility required to support future client protocols. Unlike the previous SONET/SDH, OTN is a fully transparent network that provides support for optical networking on a WDM basis. Since multiple data frames have been wrapped together into a single entity in OTN, it is also known as the “digital wrapper”.
What is OTN?
Also commonly called ‘digital wrapper,’ OTN—or Optical Transport Networking—is a next-generation, industry-standard protocol that provides an efficient and globally accepted way to multiplex different services onto optical light paths.
Telecommunications industry and service provider networks must quickly evolve to deal with an explosion of digital traffic driven by multimedia services, mobile applications, social media, VoIP, and cloud computing. Plus, there’s an ever-growing array of bandwidth-hungry applications.
Network traffic used to be all about voice calls carried over circuit-based networks in a predictable network connection between pairs of endpoints. Today, most network traffic is packet-based, generated by a multitude of services and applications in bursty, unpredictable traffic patterns, with widely varying and more stringent demands on bandwidth and data transmission performance.
OTN wraps each client payload transparently into a container for transport across optical networks, preserving the client’s native structure, timing information, and management information. The enhanced multiplexing capability of OTN allows different traffic types—including Ethernet, storage, and digital video, as well as SONET/SDH—to be carried over a single Optical Transport Unit frame.
Because OTN is a fully transparent protocol, adapting existing services is pretty straightforward.
OTN leaves current OSS/BSS solutions intact, utilizes all available tools and automation, and requires little to no retraining. OTN’s cost-effectiveness, ease of implementation, and simplicity offer companies a straightforward, painless solution to evolving network needs.
OTN-based backbones and metro cores offer significant advantages over traditional WDM transponder-based networks, including increased efficiency, reliability, and wavelength–based private services. The IP-over-OTN infrastructure also offers better management and monitoring, reduced hops, increased protection of services, and reduced costs for equipment acquisition. In addition to scaling the network to 100G and beyond, OTN plays a key role in making the network an open and programmable platform, enabling transport to become as important as computing and storage in intelligent data center networking.
OTN is a digital wrapper that provides an efficient and globallyaccepted way to multiplex different services onto optical light paths.
Working Principle of OTN
You may wonder how OTN works in practice. Actually, its working structure and format very resemble the SONET/SDH network. Six layers are included in the OTN network: OPU (optical payload unit), ODU (optical data unit), OTU (optical transport unit), OCh (optical channel), OMS (optical multiplex section) and OTS (optical transport section).
OPU, ODU and OTU are the three overhead areas of OTN frame. OPU is similar to the “path” layer of SONET/SDH, which provides information on the type of signal mapped into the payload and the mapping structure. ODU resembles the “line overhead” layer of SONET/SDH, which adds the optical path-level monitoring, alarm indication signals, automatic protection switching bytes and embedded data communications channels. OTU is like the “section overhead” in SONET/SDH, and it represents a physical optical port that adds performance monitoring and FEC (forward error correction). OCh is for the conversion of electrical signal to optical signal and modulates the DWDM wavelength carrier. OMS multiplexes several wavelengths in the section between OADMs (optical add drop multiplexer). OTS manages the fixed DWDM wavelengths between each of the in-line optical amplifier units.
Advantages of OTN
There are many advantages of OTN. Firstly, it separates the network against uncertain service by providing transparent native transport of signals encapsulating all client-management information. Secondly, it performs multiplexing for optimum capacity utilization which enhances network efficiency. Thirdly, it improves maintenance capability for signals transmitting through multi-operator networks by providing multi-layer performance monitoring.
Reduction in transport costs: With multiple clients transported on a single wavelength, OTN provides an economical mechanism to fill optical network wavelengths.
Efficient use of optical spectrum: OTN facilitates efficient use of DWDM capacity by ensuring consistent fill rates across a network using OTN switches at fiber junctions.
Determinism: OTN dedicates specific and configurable bandwidth to each service, group of services, or network partition, guaranteeing network capacity and managed performance for each client and no contention between concurrent services or users.
Virtualized network operations: New virtualization techniques such as Optical Virtual Private Networks (O-VPNs) provide a dedicated set of network resources to a client, independent of the rest of the network.
Flexibility: OTN networks enable operators to employ the technologies they need now while enabling the adoption of new technologies as business requirements dictate.
Secure by design: OTN networks ensure a high level of privacy and security through hard partitioning of traffic onto dedicated circuits.
Robust yet simple operations: OTN network management data is carried on a separate channel, completely isolated from user application data, so settings are much more difficult to access and modify through a client interface port.
Migration to High Speed OTN
With the fast evolution of networking, OTN standard is able to reach a higher speed service. Its multiplexing hierarchy allows any OTN switch and any WDM platform to electronically groom and switch lower-rate services within 10 Gbps, 40 Gbps, or even 100 Gbps wavelengths. This eliminates the need for external wavelength demultiplexing and manual interconnects. OTN network is definitely the best solution for future high speed networking over long distance. The picture below shows the OTN mapping diagram for high speed transmission.
Things You Should Be Aware of Before Deploying an OTN Network
If you are about to deploy an OTN network by yourself or get a customized OTN solution from solution suppliers, there are some details and requirements that you should know in advance.
How many spans do you have, and how far between each of the span?
The specific distance your network transports will determine the fundamental equipment needed in the OTN system. Specifically, the transmission distance between each span will indicate whether the Dispersion Compensation Module (DCM) would be needed to compensate in the fiber optical link.
What's your fiber type and the link loss (typical 0.25dB/KM)?
OTN solutions offered by solution suppliers can be tailored to both dual and single fiber type. And link loss is necessary for collocating the most appropriate optical transceivers and some active components such as EDFA amplifiers.
What's the data rate between each span?
And how many businesses do you plan to transmit?
To make clear the data rate and capacity for each span in your network is conducive to choosing the most practical types of MUX or OADM to for your current OTN infrastructure. And a good acquisition of the numbers of businesses you are to deploy can pave the way for future network expansion.
Over the years, OTN has never stopped improving itself. Driven by the needs for high speed transmission, OTN combined with WDM is obviously a better choice in networking. All in all, OTN technology represents both a technical leap forward in optical networking over SONET/SDH and a business opportunity for carriers and service providers alike. OTN networks can fully leverage the transport infrastructure in the era of data/transport convergence by offering carriers unprecedented architectural flexibility, client-protocol independence, and service differentiation. OTN network has come of age and will certainly continue to evolve as traffic demand grows.