Question

Multiplexing STS-1 multiple data streams, called tributaries, plays an important role in SONET. A \(3: 1\) multiplexer multiplexes three input STS-1 tributaries onto one output STS-3 stream. This multiplexing is done byte for byte. That is, the first three output bytes are the first bytes of tributaries 1,2, and 3 , respectively. The next three output bytes are the second bytes of tributaries 1,2 , and 3 , respectively, and so on. Write a program that simulates this \(3: 1\) multiplexer. Your program should consist of five processes. The main process creates four processes, one each for the three STS-1 tributaries and one for the multiplexer. Each tributary process reads in an STS-1 frame from an input file as a sequence of 810 bytes. They send their frames (byte by byte) to the multiplexer process. The multiplexer process receives these bytes and outputs an STS-3 frame (byte by byte) by writing it to standard output. Use pipes for communication among processes.

Short answer

Create four processes; three read STS-1 streams and send data via pipes to the fourth, which multiplexes them into an STS-3 stream.

Step-by-step solution

Define the Problem

You need to simulate a 3:1 multiplexer that combines three STS-1 streams into one STS-3 stream. Each STS-1 stream consists of 810 bytes, and each byte from the three streams is combined in sequence to form the STS-3 stream.

Design the Process Structure

Plan to have four processes: three for reading the three STS-1 streams and one for the multiplexing. The main process will create these four processes, assign the required tasks, and manage communication between them using pipes.

Reading STS-1 Frames

Each of the three STS-1 processes will read a stream of 810 bytes from an input source (file) and send these bytes one by one over a pipe to the multiplexer process.

Multiplexer Setup

The multiplexer process listens for input from the three pipes connected to the tributary processes. It sequentially reads one byte from each pipe, forming and outputting the STS-3 stream byte by byte.

Use Pipes for Communication

Implement pipes using language-specific functions or libraries to facilitate inter-process communication. Each tributary process has a pipe to send data to the multiplexer.

Write the Code

Implement the logic in a suitable programming language. Create processes, set up pipes, and simulate the data flow from tributaries to the multiplexer. Ensure the correct order of byte handling to perform multiplexing accurately.

Key concepts

STS-1 Tributaries

STS-1 tributaries are fundamental components in the process of multiplexing within the Synchronous Optical Networking (SONET) framework. Essentially, an STS-1 (Synchronous Transport Signal level 1) frame carries a payload of 810 bytes. These frames serve as the basic building blocks for creating higher-level streams in SONET systems.
In the exercise detailed above, three STS-1 tributaries are combined to form an STS-3 stream. This process happens byte by byte, where each byte from the three tributaries is collected in sequence to generate the output stream.

• STS-1 can be understood as a digital signal.
• Each STS-1 frame is like a box carrying exactly 810 bytes of data.
• When multiplexing, bytes are interleaved from each tributary to form a larger data stream.

This process ensures that data transmission is organized, manageable, and maximally efficient, essential for handling high volumes of data across networks.

SONET

SONET, which stands for Synchronous Optical Network, is a standardized protocol used for transmitting multiple digital data streams over optical fiber. The purpose of SONET is to ensure efficient and synchronized data transfer, which is crucial for large-scale network operations.
A big part of SONET's structure is its ability to combine smaller data streams, like the STS-1 tributaries, into larger and more complex streams, like STS-3, STS-12, and beyond. This method of combination employs time-division multiplexing which allows simultaneous data streams to be transmitted over a single optical fiber.

• SONET supports network synchronization, which prevents data loss and improves efficiency.
• It's highly versatile, enabling the integration of different digital signals.
• The structure of SONET allows for easy management of bandwidth and network resources.

By using SONET, telecommunications providers can ensure that vast quantities of data can be transferred with minimal delay or error.

Inter-Process Communication

Interprocess communication (IPC) is crucial for the multiplexing program detailed in the exercise. IPC enables different processes (or programs) to exchange data in a controlled and efficient manner. In this context, IPC allows the tributary processes to send data to the multiplexer process.
To simulate the STS-1 and STS-3 multiplexing, the program uses a mechanism called pipes. Pipes create a unidirectional communication channel between processes, facilitating the transfer of bytes from each tributary process to the multiplexer.

• Pipes act like a single-lane road for data between processes.
• They ensure ordered and structured data transmission.
• By using pipes, programs can efficiently manage data exchange, synchronizing the flow to match process needs.

Each tributary process transfers its byte stream through its respective pipe, aligning the data correctly so the multiplexer can assemble the STS-3 frame seamlessly.

Programming for Data Streams

Programming for data streams involves writing code that can handle the continuous flow of data from one system part to another. In this particular exercise, it involves managing byte streams from multiple STS-1 tributaries and assembling them into an STS-3 stream.
When programming for such situations, several techniques and structures are important:

• Each tributary process should be designed to read data sequentially and efficiently.
• The multiplexer must accurately collect and interleave the bytes from each tributary.
• Error handling ensures that incomplete or corrupt data is managed appropriately.

The central objective here is to create a seamless flow of data while ensuring the synchronization and order of bytes. Utilizing effective programming constructs and logic will result in a robust and efficient data streaming application that achieves these goals.