Quantum repeaters are essential for long-distance quantum communication, as photon loss in optical fibers limits direct transmission. Quantum repeaters use entanglement swapping to create long-distance entanglement from shorter-distance entanglement. The DLCZ protocol is a key approach, using atomic ensembles as quantum memories and linear optics with photon counting. This protocol enables heralded entanglement creation, storage, and swapping. The paper reviews the theoretical and experimental status of this approach, comparing different methods to outperform direct transmission. The DLCZ protocol involves creating entanglement between two remote atomic ensembles via single-photon detection, which erases which-way information. This process uses spontaneous Raman emission to generate a spin excitation in the ensemble, which is then converted back into a photon. The protocol allows for entanglement swapping between neighboring links, enabling the extension of entanglement over longer distances. The performance of the protocol depends on factors such as storage time, phase stability, and detection efficiency. Improvements to the DLCZ protocol include using two-photon detections for entanglement swapping and generation, which enhances robustness against phase fluctuations. Multiplexing techniques, such as using temporal and spatially multiplexed memories, reduce the requirements on memory time. Single-photon sources and protocols based on local generation of entangled pairs also improve performance. These improvements aim to increase the entanglement generation rate and reduce errors caused by multi-photon emissions. The paper compares the performance of different protocols, focusing on entanglement distribution time, robustness, and complexity. It highlights the challenges of implementing quantum repeaters, including the need for long memory times and high detection efficiencies. The DLCZ protocol's limitations, such as quadratic growth of multi-photon errors with the number of links, are addressed through various improvements. The paper concludes that while the DLCZ protocol is promising, further advancements are needed to achieve practical quantum repeaters that can outperform direct transmission over long distances.Quantum repeaters are essential for long-distance quantum communication, as photon loss in optical fibers limits direct transmission. Quantum repeaters use entanglement swapping to create long-distance entanglement from shorter-distance entanglement. The DLCZ protocol is a key approach, using atomic ensembles as quantum memories and linear optics with photon counting. This protocol enables heralded entanglement creation, storage, and swapping. The paper reviews the theoretical and experimental status of this approach, comparing different methods to outperform direct transmission. The DLCZ protocol involves creating entanglement between two remote atomic ensembles via single-photon detection, which erases which-way information. This process uses spontaneous Raman emission to generate a spin excitation in the ensemble, which is then converted back into a photon. The protocol allows for entanglement swapping between neighboring links, enabling the extension of entanglement over longer distances. The performance of the protocol depends on factors such as storage time, phase stability, and detection efficiency. Improvements to the DLCZ protocol include using two-photon detections for entanglement swapping and generation, which enhances robustness against phase fluctuations. Multiplexing techniques, such as using temporal and spatially multiplexed memories, reduce the requirements on memory time. Single-photon sources and protocols based on local generation of entangled pairs also improve performance. These improvements aim to increase the entanglement generation rate and reduce errors caused by multi-photon emissions. The paper compares the performance of different protocols, focusing on entanglement distribution time, robustness, and complexity. It highlights the challenges of implementing quantum repeaters, including the need for long memory times and high detection efficiencies. The DLCZ protocol's limitations, such as quadratic growth of multi-photon errors with the number of links, are addressed through various improvements. The paper concludes that while the DLCZ protocol is promising, further advancements are needed to achieve practical quantum repeaters that can outperform direct transmission over long distances.