Efficiency of CSMA/CD

CSMA/CD (Carrier Sense Multiple Access/ Collision Detection) is a networking protocol more precisely it is an Access protocol its standard is IEEE802.3 and used to broadcast links, widely used in Ethernet network systems. It is very effective and easy the implement. But the efficiency of CSMA/CD is an important factor that decides its usage for different types of network topologies and environments. In this article, we will explore the efficiency of CSMA/CD in terms of its capability to handle network congestion and minimize the number of collisions.

Working(Basics) of CSMA/CD

CSMA/CD works by detecting whether the broadcast channel is idle or not, if any stations sense that the channel is transmitting data. He will not transmit. If two stations try to transmit simultaneously then a collision occurs, and the data gone corrupted. In this case, both the stations stop transmitting and they wait for a random amount of time. Before they try again. The waiting time is called backoff time and is calculated using the backoff algorithm, this algorithm ensures that the station waits for different amounts of time so that collision is avoided.

The efficiency of CSMA/CD

The Efficiency of CSMA/CD is affected by so many factors, including the topology of the network, the number of stations connected to the broadcast channel, and the transmission speed. In small-size networks with fewer transmitting stations, CSMA/CD can be quite efficient because the chances of occurring collision are less, and the waiting time between stations is short. However, in a bigger size network with so many transmitting stations.

Another factor that can affect the efficiency of CSMA/CD is the transmission rate. In a high-rate bandwidth network, collisions can occur more frequently due to a shorter time for unit-size packet transfer. This can lead to more waiting times and reduce network efficiency. To resolve this issue, Ethernet networks use a technique called carrier extension, which extends the transmission time to give stations more time to detect and respond to collisions.

The Basic formula for efficiency is −


and the simplified formula after complex derivation comes is −


where $\mathrm{a\:=\:T_{P} /T_{t}}$,

Tt is transmission delay and Tp is Propagation delay

Key points to remember

  • CSMA/CD can handle network traffic effectively

  • High network traffic can be reduced by increasing the waiting time between transmissions

  • This reduces overall network traffic and improves efficiency

  • Large packets are not preferable as they take longer to transmit and increase collision chances

  • Smaller packets are favorable for high-speed bandwidth and network efficiency

As we discussed above transmission delay and propagation delay are also responsible for the good efficiency of the CSMA/CD network as the formula suggests if the Tt (Transmission delay) increases denominator increases and efficiency decreases similarity we can relate with the propagation delay if the Tp is increased denominator decreases and overall efficiency increases.

Despite its effectiveness, CSMA/CD has some limitations that can affect its efficiency. For example, CSMA/CD is not suitable for high bandwidth requirements or where low latency is the problem. In such scenarios other protocols such as CSMA/CA Carrier sensing Multiple Access/ Collison Avoidance is helpful.

If we expand the formula of Tt which is L/B where L is the data packer size and B is the Bandwidth and for Tp =d/v, where d represents the distance between two stations and v represents transmitting speed it is generally 70% of the speed of the light but it will be given in the problem statement.

If we consider Tp and Tt if the length of the packet increases the efficiency increases because the chances of collision are decreased. If the distance between the two transmitting stations increases the efficiency decreases.

Overall we can conclude that CSMA/CD is better for LANs and not for WANs. CSMA/CD is used in wired LANs. The problem with CSMA/CD is it doesn’t take any steps to prevent the collision unless the collision has taken place.


The efficiency(η) of CSMA/CD depends on so many factors, which include the network topology type, the number of transmitting stations, and as we discussed the length of the data packet and the transmission speed. While CSMA/CD is a widely used protocol due to its effectiveness and easiness of implementation, its efficiency can be affected by network traffic and the number of connected stations to the broadcast link, it is not suitable for local area networks (LANs) and not for wide area networks (WANs). This technique is used in Ethernet protocol.

Updated on: 03-May-2023


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