Question

A token bucket scheme is used for traffic shaping. A new token is put into the bucket every \(5 \mu \mathrm{sec}\). Each token is good for one short packet, which contains 48 bytes of data. What is the maximum sustainable data rate?

Short answer

The maximum sustainable data rate is 9.6 MBps.

Step-by-step solution

Understanding the Token Mechanism

In a token bucket scheme, a token is added to the bucket at regular intervals. Each token allows one packet or a certain amount of data to be sent, controlling the flow rate.

Token Interval Identification

Each token is added to the bucket every \(5 \mu \mathrm{sec}\). This means that every \(5\) microseconds, traffic equivalent to one packet can be released.

Determining Packet Size

Every token allows the transmission of a short packet containing 48 bytes of data. Thus, every \(5 \mu \mathrm{sec}\), 48 bytes can be sent.

Conversion of Microseconds to Seconds

Convert the interval from microseconds to seconds to find how many intervals fit into one second: \(1 \text{ second} = 1,000,000 \mu \mathrm{sec}\).

Calculating Number of Packets Per Second

Determine how many packets can be sent per second by dividing \(1,000,000 \mu \mathrm{sec}\) by \(5 \mu \mathrm{sec}\) (interval time): \[ \frac{1,000,000}{5} = 200,000 \text{ packets per second} \]

Computing the Max Sustainable Data Rate

Multiply the number of packets that can be sent per second by the size of each packet (48 bytes): \[ 200,000 \times 48 = 9,600,000 \text{ bytes per second} \]. This converts to \(9.6 \text{ MBps}\) (MegaBytes per second).

Key concepts

Understanding the Token Bucket Scheme

The token bucket scheme is a mechanism used in traffic shaping to control the flow of data packets in a network. This mechanism is designed to balance the data burstiness and ensure that the transmission rate remains manageable. Here's how it works:

• Tokens are placed into the bucket at a fixed rate. Each token allows a fixed amount of data, often a packet, to be transmitted.
• When data is ready to be sent, it checks for available tokens. If there's a token available, the packet is sent, and one token is removed from the bucket.
• If there aren’t enough tokens, the packet waits until enough tokens accumulate.

This system ensures that data can burst at short intervals but maintains an average flow over time, preserving network stability and efficiency.

Calculating the Sustainable Data Rate

The sustainable data rate is the maximum rate at which data can be transmitted over a network without overwhelming it. In a token bucket system, this is determined by the rate of token generation and the size of each packet.
The exercise described places a token in the bucket every 5 microseconds, each allowing sending of a packet with 48 bytes. This means that:

• You can release a total of 200,000 packets every second, because \( \frac{1,000,000}{5} = 200,000 \).
• This results in a maximum sustainable data rate of 9,600,000 bytes per second, or 9.6 MBps.

By sustaining this level of data transmission, the network can efficiently handle bursts of data without congestion, allowing for smooth traffic flow.

Exploring Packet Transmission

Packet transmission refers to the method of sending a small, manageable chunk of data across a network. Each packet contains a portion of the overall data load and can be independently routed and delivered. In the token bucket scheme scenario:

• Each packet corresponds to a single token and in this specific system holds 48 bytes of data.
• The packet size is a key factor; it determines how frequently data is released and affects the overall flow of data through the network.
• Packets allow networks to handle data more efficiently and adjust to the changing conditions, such as varying levels of network congestion.

Understanding how packet transmission works helps in designing systems that optimize for speed while minimizing potential delays and errors—ultimately ensuring stable and reliable data communication.