Question

Suppose a shared medium \(\mathrm{M}\) offers to hosts \(\mathrm{A}_{1}, \mathrm{~A}_{2}, \ldots, \mathrm{A}_{N}\) in round-robin fashion an opportunity to transmit one packet; hosts that have nothing to send immediately relinquish M. How does this differ from STDM? How does network utilization of this scheme compare with STDM?

Short answer

Round-robin reallocates turns by bypassing idle hosts, increasing efficiency, unlike STDM that assigns fixed slots regardless of data presence.

Step-by-step solution

- Understand the Round-Robin Scheme

The round-robin scheme gives each host an opportunity to transmit a packet in a cyclic order. If a host has no packet to send, it forfeits its turn.

- Define STDM

Synchronous Time-Division Multiplexing (STDM) divides the time into fixed intervals where each host gets a dedicated time slot to transmit a packet, regardless of whether it has data to send or not.

- Compare Round-Robin and STDM

In STDM, time slots are allotted whether a host has data to send or not, which can lead to wasted bandwidth. In the round-robin scheme, if a host has no data to transmit, the opportunity is passed to the next host, reducing idle periods.

- Analyze Network Utilization

Round-robin method is more efficient in terms of bandwidth utilization because it does not allocate resources to idle hosts. STDM can result in poor utilization if many hosts don't have data to send during their time slots.

Key concepts

Round-Robin Scheme

The Round-Robin Scheme ensures that each host connected to the shared medium gets a fair chance to transmit data. In this system, the hosts take turns in a cyclic order. If one host doesn't have any data to send, it simply skips its turn and the next host is given the opportunity. This process continues until all hosts have had their chance. Since a host's unused slot can be immediately taken by another, there is a reduction in idle time. This scheme is dynamic and adaptable to current network traffic, making it efficient and reducing delays. By forfeiting the turn when no data is available to send, the system maintains high responsiveness and low latency.

Synchronous Time-Division Multiplexing (STDM)

Synchronous Time-Division Multiplexing (STDM) divides available bandwidth into fixed time slots, each allocated to a specific host. Regardless of whether the host has data to send, these slots remain reserved. One advantage of STDM is its predictability and simplicity in implementation. Each host knows its exact time to transmit, which can simplify timing and synchronization. However, the major downside is inefficiency in bandwidth utilization. If a host doesn’t have data to send during its allocated slot, that time slice goes wasted. This can lead to potential underutilization of the network capacity, particularly in environments where not all hosts are constantly transmitting data.

Network Utilization

Network utilization refers to how effectively the total available network resources are used. In the context of the Round-Robin Scheme versus STDM, Round-Robin typically results in higher network utilization. This is because it dynamically reallocates the transmission opportunity to hosts ready to send data. On the contrary, STDM might lead to wasted bandwidth if some hosts don't utilize their fixed time slots. Dynamic systems like Round-Robin are better at adapting to varying traffic loads, thereby maintaining higher overall efficiency and minimizing unused resources.

Bandwidth Allocation

Bandwidth allocation is the method of distributing available network capacity among various users or applications. In the Round-Robin Scheme, bandwidth is allocated on an as-needed basis. Each host transmits in its turn if it has data, passing the opportunity if not. Synchronous Time-Division Multiplexing (STDM), on the other hand, allocates fixed time slots to each host in a repetitive cycle. This static allocation can lead to inefficient use of bandwidth, as slots are reserved regardless of the actual need. Adaptive systems like Round-Robin are generally more flexible, ensuring that bandwidth is allocated where it’s needed most at any given time.

Transmission Efficiency

Transmission efficiency measures how effectively data is transmitted across the network with minimal waste. The Round-Robin Scheme enhances efficiency by ensuring that only those hosts with data to send are transmitting, thus minimizing idle times. STDM can suffer from lower efficiency because time slots are allocated regardless of whether hosts have data to transmit. If many slots go unused, it results in wasted transmission opportunities, degrading efficiency. Thus, from a transmission efficiency perspective, the adaptability of the Round-Robin Scheme generally outperforms the rigid structure of STDM.