SONET protocol for data transmission over fiber optics

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Discussion Overview

The discussion centers around the SONET protocol, a physical layer protocol for data transmission over fiber optics, specifically focusing on its structure, multiplexing methods, and comparison with its European counterpart, SDH. Participants explore the organization of SONET frames, the concept of time division multiplexing (TDM), and the interleaving of data from multiple users.

Discussion Character

  • Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • Some participants describe SONET as a TDM method where time is divided into slots for different users, suggesting that the SONET frame consists of 810 bytes that may include headers and other information.
  • There is a question about whether the 810 bytes in a SONET frame contain data from multiple sources or a single source, with a participant proposing the idea of different laser sources using wavelength division multiplexing (WDM) to carry SONET frames.
  • One participant notes the complexity of the SONET frame structure, indicating that the protocol is heavily multiplexed and that the header is interleaved with the data, making reconstruction of the underlying payloads challenging.
  • Another participant contrasts SONET with Ethernet, highlighting that SONET/SDH allows for easier extraction of individual user data from a payload and provides better fault location capabilities.
  • There is a request for clarification on the term "word" in the context of SONET and SDH, with some participants suggesting that it may refer to byte interleaving or octets.

Areas of Agreement / Disagreement

Participants express varying levels of understanding regarding the structure and terminology of SONET, with some agreeing on the complexity of the protocol while others seek clarification on specific terms. The discussion remains unresolved regarding the precise definitions and implications of the terms used.

Contextual Notes

Limitations include potential misunderstandings of the terminology used in telecommunications, such as the distinction between words, bytes, and octets, as well as the specific formatting of payloads within SONET frames.

fog37
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hello forum,
I have read about SONET which seems to be a physical layer protocol to transport data over fiber optics.
SONET is a TDM (time division multiplexing method). TDM means that that time divided into slots and shared between different users. For example, given three users A, B and C, the transmission would be ABCABCABC...

That said, I would think SONET works the same way. The SONET frame is 810 bytes. I am sure those bytes contain extra information (header, etc.) besides the actual data. Do those 810 bytes contain data from multiple different sources or from the same source? For instance, I imagine different laser sources (each with its own wavelength) being WDM together but each individual wavelength carries SONET frames which carry each TDM type traffic...

It is said that the frame is composed of 9 rows of 90 columns of 8-bit bytes. I am not sure how to interpret ths row/columns structure. It is easier to see the 810 bytes arranged sequentially. I think that is how they are physically transmitted...
thanks,
fog37
 
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The bytes are pretty disordered. "The protocol is a heavily multiplexed structure, with the header interleaved between the data in a complex way."

You will have to look for a standard to see, for example, how a DS3 payload is formatted into an STS-1 payload.

three STS-1 frames can be interleaved to form an STS-3 frame.

Receiving SONET frames and reconstructing the underlying payloads is always confusing.
 
May I mention that in SONET and the European equivalent, which is SDH (Synchronous Digital Hierarchy), the underlying concept is that different users data are interleaved in words, not in bits. This means that it is easy to extract (or drop off) one user from a large pay load, without the need for a multiplexer mountain.
Another feature of the system, which is in contrast to Ethernet, is that it talks to every repeater and node, so that a physical fault on the network can be geographically located. In the case of Ethernet, physical locations are not reported and an automatic re-routing might be occurring as a result of a fault which is not apparent to the network operator. For this reason, large Ethernet payloads are often carried on Sonnet/SDH bearers.
 
Thanks tech99.

what is a word? I am familiar with packet, frame, datagram...
 
fog37 said:
Thanks tech99.

what is a word? I am familiar with packet, frame, datagram...
My apologies, I should have said byte interleaved for SDH and Sonet.
 
tech99 said:
My apologies, I should have said byte interleaved for SDH and Sonet.
Actually, in telecom speak, it is called octets.
 

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