In the operation of CSMA/CD on a shared Ethernet segment, after the backoff algorithm has completed following a collision, which host or hosts have priority to attempt transmission?

Introduction / Context:
CSMA/CD (Carrier Sense Multiple Access with Collision Detection) was designed to manage access to a shared Ethernet medium and handle collisions. When a collision occurs, all transmitting hosts stop, send a jam signal and then wait for a random backoff time before attempting to retransmit. Understanding who gets priority after the backoff process is essential for grasping how CSMA/CD ensures fairness.

Given Data / Assumptions:

We are dealing with a traditional half duplex Ethernet network that uses CSMA/CD, such as a hub based or coaxial bus network.
A collision has occurred, and all transmitting hosts have detected it and invoked the backoff algorithm.
The question asks which host or hosts have priority to transmit after the backoff period expires.

Concept / Approach:
CSMA/CD is a decentralized access method. After a collision, each host involved chooses a random backoff interval based on the binary exponential backoff algorithm. No host is granted special priority; instead, each host independently waits its random backoff time, then senses the carrier again and transmits if the medium is idle. Because of the randomization, statistically, one host will likely win the next opportunity to transmit, but all hosts are treated equally by the algorithm.

Step-by-Step Solution:
When a collision is detected, all transmitting hosts send a jam signal to ensure that every host on the segment is aware of the collision. Each host then computes a random backoff time, often measured in slot times, according to the binary exponential backoff rules. During backoff, each host waits and continues to sense the medium. After its individual backoff timer expires, any host that finds the medium idle may attempt to transmit again. Because backoff times are random and independently chosen, no inherent priority is given; all hosts have equal opportunity.

Verification / Alternative check:
Descriptions of CSMA/CD in networking textbooks and IEEE 802.3 specifications emphasize its probabilistic nature and fairness. There is no mention of special treatment for the host that sent the jam signal or for hosts with particular MAC addresses. Over many transmissions, each host sees a fair share of the medium, assuming similar traffic patterns, which aligns with the idea of equal priority.

Why Other Options Are Wrong:
Option b wrongly suggests that only the two hosts involved in the collision have priority; in reality, any host on the segment can attempt transmission after its backoff expires.
Option c gives special priority to the host that sent the jam signal, but all transmitting hosts send jam signals and no priority is defined for them.
Option d and option e propose priority based on MAC address ordering, which is not a mechanism defined in CSMA/CD or the Ethernet standard.

Common Pitfalls:
A common misconception is to think of CSMA/CD as assigning turns or priorities, but in fact it relies on random backoff and carrier sensing to reduce the probability of repeated collisions. Another pitfall is to assume that CSMA/CD still applies on modern switched full duplex networks; in those environments, there is no shared medium and collisions are essentially eliminated, so CSMA/CD is not used.

Final Answer:
After the backoff algorithm, all hosts have equal priority and may attempt to transmit once their individual backoff timers expire and the medium is idle.