Question

A bit string, 0111101111101111110 , needs to be transmitted at the data link layer. What is the string actually transmitted after bit stuffing?

Short answer

The transmitted string with bit stuffing is 011110011111011111010.

Step-by-step solution

Identifying Patterns for Bit Stuffing

Bit stuffing is used to prevent the accidental formation of special bit patterns used to mark the start or end of a frame in the transmission. The rule is that after five consecutive '1's in data, an extra '0' is stuffed. In the given bit string, 0111101111101111110, we first identify the positions where there are sequences of five consecutive '1's.

Determine Positions for Stuffing

In the given string, the pattern '11111' appears twice: starting at index 5 and again at index 11. These are the positions after which we need to stuff a '0'.

Insert '0's After Five Consecutive '1's

After identifying the positions, we will insert a '0' after each sequence of five consecutive '1's. Thus, after the first sequence (at index 5), and after the second sequence (at index 11), we add '0'.

Compose the Stuffed String

Inserting '0's at the identified positions, the bit sequence becomes: 011110011111011111010. The first five '1's are followed by a '0', and similarly, the second five '1's are followed by another '0'.

Key concepts

Data Link Layer

The Data Link Layer is a critical component of network communication, nestled between the Physical Layer and the Network Layer in the OSI model. Its primary role is to facilitate reliable data transfer over a physical medium by ensuring that the message reaches the next network device free from errors. The Data Link Layer is responsible for framing, error detection, and error correction.

One of the primary tasks of the Data Link Layer is to divide the raw bit stream received from the Physical Layer into manageable data units, called frames. These frames are then sequenced and transmitted over the network. To ensure accuracy, this layer uses various error-checking mechanisms to detect and sometimes correct errors without needing retransmission.

• **Framing**: Helps isolate user data from control data.
• **Error Control**: Ensures reliable delivery, often using techniques like checksums and automatic repeat requests (ARQ).
• **Flow Control**: Manages data buffer overflow or network congestion.

The Data Link Layer also implements protocols that help coordinate the sharing of the data link among multiple devices, making it indispensable for effective and efficient communication.

Bit Strings

A bit string is simply a sequence of bits, which are binary digits often represented as either 0s or 1s. In the digital world, these bits form the basis of data representation and processing.

In networking and data communication, bit strings convey information, settings, or commands between devices. They play a crucial role in encoding information in a format that's universally understood by digital devices.

• **Length**: Refers to the number of bits in the string.
• **Pattern Recognition**: Bit strings can contain specific patterns that may require special handling.
• **Transformation**: Techniques like bit stuffing ensure that message frames maintain structural integrity.

Understanding bit strings and their transformations is foundational in networking, ensuring that devices can clearly and effectively communicate complex instructions using simple binary sequences.

Frame Transmission

Frame transmission is an essential process in network communication where data frames are sent from one device to another through a communication channel. The integrity and order of frames are crucial for the correct reconstruction of original data at the destination.

When transmitting frames, it's vital to avoid any special sequences within the data that might be misinterpreted as control information. This is where techniques like bit stuffing come into play. Bit stuffing involves inserting non-informative bits into data streams to prevent accidental formation of special sequences that could muck up frame synchronization.

• **Synchronization**: Ensuring the sender and receiver are aligned, detecting start and end of frames accurately.
• **Error Handling**: Using techniques like checksums to verify data integrity.
• **Bit Stuffing**: Inserting a '0' after any occurrence of five consecutive '1's in a stream, preventing misinterpretation of data as control sequences.

By effectively managing these aspects, frame transmission can be reliable and efficient, which is fundamental for maintaining the fluid exchange of data in networks.