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Optical transport network

Optical transport network is a physics topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Optical transport network rather than just read about it. In short: An optical transport network (OTN) is a digital wrapper that encapsulates frames of data, to allow multiple data sources to be sent on the same channel. This creates an optical virtual private network for each client signal.

Optical transport network — main illustration
Optical transport network — illustration

Key takeaways

  • Optical transport network belongs to physics; place it in that map before memorising details.
  • Learn the definition first, then one example that makes the definition concrete.
  • Connect Optical transport network to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of Optical transport network from memory before moving on to harder problems.

Reference excerpt

An optical transport network (OTN) is a digital wrapper that encapsulates frames of data, to allow multiple data sources to be sent on the same channel. This creates an optical virtual private network for each client signal. ITU-T defines an optical transport network as a set of optical network elements (ONE) connected by optical fiber links, able to provide functionality of transport, multiplexing, switching, management, supervision and survivability of optical channels carrying client signals. An ONE may re-time, re-Amplify, re-shape (3R) but it does not have to be 3R – it can be purely photonic. Unless connected by optical fibre links, it shall not be OTN. Mere functionality of switching, management, supervision shall not make it OTN, unless the signals are carried through optical fibre. Unlike SONET/SDH, OTN provides a mechanism to manage multiplexed wavelengths in a DWDM system.

Comparing OTN and SONET/SDH

Standards

OTN was designed to provide higher throughput (currently 400G) than its predecessor SONET/SDH, which stops at 40 Gbit/s, per channel. ITU-T Recommendation G.709 is commonly called Optical Transport Network (OTN) (also called digital wrapper technology or optical channel wrapper). As of December 2009, OTN has standardized the following line rates.

The OTUk (k=1/2/2e/3/3e2/4) is an information structure into which another information structure called ODUk (k=1/2/2e/3/3e2/4) is mapped. The ODUk signal is the server layer signal for client signals. The following ODUk information structures are defined in ITU-T Recommendation G.709

Equipment At a very high level, the typical signals processed by OTN equipment at the Optical Channel layer are:

SONET/SDH Ethernet/FibreChannel Packets OTN A few of the key functions performed on these signals are:

Protocol processing of all the signals:- Mapping and de-mapping of non-OTN signals into and out of OTN signals Multiplexing and de-multiplexing of OTN signals Forward error correction (FEC) on OTN signals Packet processing in conjunction with mapping/de-mapping of packet into and out of OTN signals

Switch Fabric The OTN signals at all data-rates have the same frame structure but the frame period reduces as the data-rate increases. As a result, the Time-Slot Interchange (TSI) technique of implementing SONET/SDH switch fabrics is not directly applicable to OTN switch fabrics. OTN switch fabrics are typically implemented using Packet Switch Fabrics.

FEC Latency On a point-to-point OTN link there is latency due to forward error correction (FEC) processing. Hamming distance of the RS(255,239) code is 17

See also G.709

References

External links Anritsu Poster - Details of all OTN areas including breakdown of the full frame Anritsu Poster - Details of all OTN areas including breakdown of the full frame at the Wayback Machine (archived 2014-05-17) Optical Transport Network (OTN) Tutorial, ITU-T, only covers G.709 (2003/03) [1] Hot topics in Optical Transport Networks, Steve Trowbridge (Nokia), Chairman, ITU-T Study Group 15

Illustrations

Optical transport network: Function diagram 200 Gbit/s transponder/muxponder, aggregating 4x40 Gbit/s and 4x10 Gbit/s into a single 200 Gbit/s /OTU2C standard OTN trunk.
Function diagram 200 Gbit/s transponder/muxponder, aggregating 4x40 Gbit/s and 4x10 Gbit/s into a single 200 Gbit/s /OTU2C standard OTN trunk.
Optical transport network: OTN multiplexing and mapping structures. Show the relationship between ODU Clients, ODU, ODU-Groups and OTU
OTN multiplexing and mapping structures. Show the relationship between ODU Clients, ODU, ODU-Groups and OTU

Worked examples

Example 1 — a first encounter with Optical transport network

Start with the simplest possible case. Write down what Optical transport network claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Optical transport network before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Optical transport network ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Optical transport network

In research
Optical transport network appears in physics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry
Engineering practice reuses Optical transport network in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom
Optical transport network is common in secondary-school and first-year university syllabi. It links to neighbouring topics ITU-T recommendations, Optical Transport Network, so understanding it makes those chapters shorter.
In everyday life
Look for Optical transport network outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Optical transport network in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what Optical transport network means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain Optical transport network out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Optical transport network in simple terms?

An optical transport network (OTN) is a digital wrapper that encapsulates frames of data, to allow multiple data sources to be sent on the same channel. This creates an optical virtual private network for each client signal.

Why does Optical transport network matter?

Because it connects several physics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Optical transport network?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Optical transport network.

Tags

  • ITU-T recommendations
  • Optical Transport Network

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