Show understanding of bit streaming

2.1 Networks – Bit Streaming

What is Bit Streaming?

Bit streaming is the continuous transmission of a sequence of bits over a communication medium. Unlike packet‑switched transmission, where data is divided into discrete packets, streaming sends data as a steady flow, which is essential for real‑time applications such as audio, video and online gaming.

Why Use Streaming?

• Low latency – data is processed as soon as it arrives.
• Predictable bandwidth usage – the data rate is constant.
• Simplifies synchronization for time‑sensitive media.

Serial vs Parallel Transmission

In networking, bits are usually sent serially over a single channel, but the concept of parallel transmission is useful for understanding internal bus architectures.

Key Parameters of a Bit Stream

1. Bit Rate (R): Number of bits transmitted per second, measured in bits per second (bps). \$R = \frac{N}{T}\$ where \$N\$ is the number of bits and \$T\$ is the transmission time in seconds.
2. Bandwidth (B): The range of frequencies a channel can carry. For a binary signal, the Nyquist formula gives the maximum bit rate: \$R{\max}=2B\log2 M\$ where \$M\$ is the number of discrete signal levels.
3. Latency (L): Time taken for a bit to travel from source to destination, often expressed in milliseconds (ms).
4. Jitter: Variation in latency, which can affect the quality of streamed media.

Encoding Schemes for Streaming

Encoding converts digital data into signals suitable for the transmission medium. Common schemes include:

• NRZ (Non‑Return‑to‑Zero) – simple, but suffers from baseline wander.
• Manchester Encoding – each bit contains a transition, providing clock recovery.
• 8b/10b Encoding – maps 8 data bits to 10 transmitted bits, ensuring DC balance and enough transitions.

Error Detection and Correction in Streams

Because streaming is continuous, errors must be detected and, where possible, corrected without stopping the flow.

• Parity bits – simple detection, no correction.
• CRC (Cyclic Redundancy Check) – appended to each frame of the stream.
• Forward Error Correction (FEC) – e.g., Reed‑Solomon codes, allow reconstruction of lost bits.

Example: Calculating Required Bandwidth for \cdot ideo Streaming

Suppose a video stream has the following specifications:

• Resolution: 1920 × 1080 pixels (Full HD)
• Colour depth: 24 bits per pixel
• Frame rate: 30 frames per second

The raw data rate is:

\$R_{\text{raw}} = \text{Resolution} \times \text{Colour depth} \times \text{Frame rate}\$

\$R_{\text{raw}} = (1920 \times 1080) \times 24 \times 30 \approx 1.49 \times 10^9 \text{ bits/s} \; (1.49 \text{ Gbps})\$

After compression (e.g., using H.264) the effective bitrate might be reduced to 5 Mbps. The required channel bandwidth must therefore support at least this rate, plus overhead for error correction and protocol headers.

Practical Considerations for Real‑World Streaming

1. Choose an appropriate encoding scheme to balance complexity and robustness.
2. Implement buffering at the receiver to compensate for jitter and occasional packet loss.
3. Use adaptive bitrate streaming (ABR) to adjust the stream quality based on current network conditions.
4. Monitor latency and jitter to maintain quality of service (QoS) for interactive applications.

Summary

Bit streaming is the backbone of real‑time network services. Understanding the relationship between bit rate, bandwidth, latency, and encoding allows students to design and evaluate networks that can reliably deliver audio, video and interactive data. Mastery of these concepts is essential for the Cambridge A‑Level Computer Science examination.