Question

What differences in traffic patterns account for the fact that STDM is a costeffective form of multiplexing for a voice telephone network and FDM is a costeffective form of multiplexing for television and radio networks, yet we reject both as not being cost-effective for a general-purpose computer network?

Short answer

STDM suits predictable voice traffic; FDM fits stable TV/radio broadcasts. Both inefficacious for diverse, variable computer network traffic.

Step-by-step solution

- Understand the Terminologies

First, differentiate between Statistical Time Division Multiplexing (STDM), Frequency Division Multiplexing (FDM), and their applications. STDM is used for voice telephone networks, while FDM is utilized for television and radio networks.

- Analyze the Nature of Traffic in Voice Telephone Networks

Voice telephone networks have consistent traffic patterns with predictable, small, and continuous data flows. STDM is efficient here because it dynamically allocates time slots based on demand, optimizing bandwidth usage.

- Analyze the Nature of Traffic in Television and Radio Networks

Television and radio networks broadcast over large areas and require dedicated bandwidth to ensure continuous and uninterrupted transmission. FDM is cost-effective here as it divides the available bandwidth into fixed frequency bands allocated to different channels or stations.

- Examine the Traffic Patterns in General-Purpose Computer Networks

General-purpose computer networks handle a wide variety of traffic patterns, including bursty and unpredictable data flows, large data transfers, and real-time communications. This variability makes it challenging for STDM and FDM to efficiently allocate resources.

- Conclusion

STDM is well-suited for consistent, predictable voice traffic, while FDM is effective for steady, frequency-specific television and radio transmissions. However, due to the unpredictable and diverse nature of data in general-purpose computer networks, neither STDM nor FDM provides a cost-effective solution.

Key concepts

Statistical Time Division Multiplexing (STDM)

In networking, multiplexing is a method to combine multiple signals into one medium. Statistical Time Division Multiplexing (STDM) is one such method, specifically optimized for voice telephone networks.
With STDM, time slots are dynamically allotted based on the actual demand rather than a fixed schedule. This flexibility reduces wastage of time slots when no data is present, making it an efficient strategy for voice networks where data flow is small and consistent.
Imagine a highway where lanes are opened or closed based on traffic. Cars (data) flow uninterrupted according to demand. That's STDM!
Its efficiency in handling voice calls stems from the predictable traffic pattern in such networks. However, this same flexibility doesn't translate well to general-purpose computer networks, where data flow can be bursty and unpredictable.

• Voice networks have consistent, small data flows.
• STDM adapts to demand, optimally utilizing bandwidth.
• Not suited for unpredictably bursty data, common in computer networks.

STDM is therefore perfect for voice telephone networks due to its adaptive nature and efficient bandwidth usage, but not for more variable data types.

Frequency Division Multiplexing (FDM)

Frequency Division Multiplexing (FDM) is another multiplexing technique used mainly in television and radio networks. Instead of time slots, FDM divides bandwidth into different frequency bands, each of which carries a separate signal.
Think of FDM as different ongoing conversations in various rooms (frequency bands) in a building (the communication medium). Each room is isolated, allowing multiple channels to exist simultaneously without interference.
This method is particularly effective for television and radio, where broadcasts are continuous and need dedicated frequencies to ensure uninterrupted transmission.
The isolation of frequency bands assures clarity and quality, making FDM the go-to for such networks.

• Television and radio have continuous, steady data streams.
• FDM uses dedicated frequencies, avoiding interference.
• Not cost-effective for diverse data in computer networks.

While FDM is perfect for steady flow applications like broadcasting, its rigid allocation of frequencies isn't practical for the varying needs of a general-purpose computer network.

Traffic Patterns in Networks

Understanding traffic patterns in different networks is crucial for picking the right multiplexing technique.
In voice telephone networks, the traffic is consistent, predictable, and involves small, continuous data packets. These attributes are why STDM excels here, as it dynamically allocates resources based on demand, ensuring efficient bandwidth use.
On the other hand, television and radio networks require a continuous, uninterrupted stream of data. FDM shines in this environment, offering dedicated frequencies for each broadcast, ensuring no signal interference and a smooth transmission.
However, general-purpose computer networks present a challenge for both STDM and FDM. The traffic here is diverse, ranging from large file transfers to real-time communications, with data transfer patterns that are often unpredictable and bursty.

• Voice networks: Predictable and consistent data flow; suitable for STDM.
• TV and radio: Continuous, steady streams of data; ideal for FDM.
• Computer networks: Unpredictable and bursty; not suitable for STDM or FDM.

Due to these complexities, neither STDM nor FDM can efficiently manage the wide range of traffic in general-purpose computer networks, highlighting the importance of matching traffic patterns to multiplexing techniques.