Calculating Ethernet Delays: Transmission and Propagation

In network communication, understanding delays is crucial. Two primary types of delays are transmission delay and propagation delay. Let's calculate these for the given Standard Ethernet scenario.

Understanding Transmission Delay and Propagation Delay

• Transmission Delay: This is the time required for a transmitter to push all of the packet's bits onto the link. It depends on the packet's length and the transmission rate of the link.
• Propagation Delay: This is the time it takes for a bit to travel from one end of the link to the other. It depends on the length of the link and the propagation speed of the signal in the medium.

Calculating Transmission Delay

Transmission delay is calculated using the formula:

\( \text{Transmission Delay} = \frac{\text{Frame Size (bits)}}{\text{Transmission Rate (bits/s)}} \)

Given:

• Transmission Rate = 10 Mbps = \( 10 \times 10^6 \) bits/s
• Frame size = 512 bytes. However, the options provided suggest a transmission delay corresponding to a smaller frame size or perhaps the minimum frame size in bits. Standard Ethernet has a minimum frame size of 64 bytes, which is 512 bits. Let's use 512 bits for the calculation to match the options.
• Frame Size (using minimum bit size) = 512 bits

Calculation:

\( \text{Transmission Delay} = \frac{512 \text{ bits}}{10 \times 10^6 \text{ bits/s}} \)

\( \text{Transmission Delay} = \frac{512}{10^7} \text{ s} \)

\( \text{Transmission Delay} = 51.2 \times 10^{-6} \text{ s} \)

\( \text{Transmission Delay} = 51.2 \ \mu s \)

Calculating Propagation Delay

Propagation delay is calculated using the formula:

\( \text{Propagation Delay} = \frac{\text{Length of Medium}}{\text{Propagation Speed}} \)

Given:

• Length of Medium = 2500 m
• Propagation Speed = \( 2 \times 10^8 \) m/s

Calculation:

\( \text{Propagation Delay} = \frac{2500 \text{ m}}{2 \times 10^8 \text{ m/s}} \)

\( \text{Propagation Delay} = \frac{2500}{200,000,000} \text{ s} \)

\( \text{Propagation Delay} = \frac{25}{2,000,000} \text{ s} \)

\( \text{Propagation Delay} = \frac{12.5}{1,000,000} \text{ s} \)

\( \text{Propagation Delay} = 12.5 \times 10^{-6} \text{ s} \)

\( \text{Propagation Delay} = 12.5 \ \mu s \)

Comparing Calculated Delays with Options

Our calculations resulted in:

• Transmission Delay: 51.2 \( \mu s \)
• Propagation Delay: 12.5 \( \mu s \)

Let's check the given options:

• Option 1: 25.25 \( \mu s \) and 51.2 \( \mu s \) (Transmission and Propagation) - Does not match.
• Option 2: 51.2 \( \mu s \) and 12.5 \( \mu s \) (Transmission and Propagation) - Matches our calculated values.
• Option 3: 10.24 \( \mu s \) and 50.12 \( \mu s \) (Transmission and Propagation) - Does not match.
• Option 4: 12.5 \( \mu s \) and 51.2 \( \mu s \) (Transmission and Propagation) - Does not match the order (Transmission delay is listed first in the options).

The transmission delay is 51.2 \( \mu s \) and the propagation delay is 12.5 \( \mu s \).

Revision Table: Comparing Transmission vs. Propagation Delay

Additional Information on Ethernet Standards and Delays

Standard Ethernet, also known as 10BASE-T, operates at a data rate of 10 Mbps. It uses CSMA/CD (Carrier Sense Multiple Access with Collision Detection) as the access method. For CSMA/CD to work effectively, there are constraints on the minimum frame size and the maximum cable length.

• The minimum Ethernet frame size (including header and FCS) is 64 bytes (512 bits). This minimum size is important for ensuring that a station can detect a collision before it finishes transmitting the frame, even on the longest allowed network segment.
• The maximum length of a single segment in 10BASE-T is typically 100 meters when using twisted-pair cable (although repeaters can extend the network). The 2500 m distance mentioned in the question likely refers to the total length of a collision domain involving repeaters or other connecting devices in an older Ethernet setup.
• Propagation speed in copper cable is typically around 60-80% of the speed of light in a vacuum (\( 3 \times 10^8 \) m/s). The value \( 2 \times 10^8 \) m/s used in the question falls within this realistic range.
• Delays are critical factors in network performance, affecting throughput and real-time application quality. In systems like Ethernet using CSMA/CD, round-trip propagation delay is particularly important for collision detection timing.