======= Review 1 ======= *** Submission Policy: Does the paper list the same author(s), title and abstract (minor wording differences in the abstract are ok) in its PDF file and EDAS registration? YES *** Strong aspects: Comments to the author: what are the strong aspects of the paper The paper discusses the dynamic and dense nature of the vanet environment and its influence on the IEEE 802.11p standard, particularly in the event of safety applications using the cooperative awareness messages, or CAM. The authors present the well known problems related to broadcast messages in 802.11 and propose a modification of the backoff mechanism to deal with expired beacons, to eventually reduce the number of collisions. Such mechanism can essentially prioritize the event driven messages. *** Weak aspects: Comments to the author: what are the weak aspects of the paper? - though the paper reviews the technical limitations of the 802.11p standard thoroughly w.r.t the broadcast beacons, the actual problem from the application perspective is not completely addressed and the novelty is questionable. The adjustment in backoff mechanism is acceptable, but the balance achieved with the expired beacons is only a minor improvement as one can observe. Perhaps, a delineated analysis in the saturated and non-saturated cases may improve the model, but these are not clearly stated in the paper. - the simulation analysis provided are quite limited to better understand the performance of the mechanism, it would have been beneficial to include the influence of the beacon generation rates on the proposed mechanism. The beacons lost during the process will have direct effects on the generation rate. moreover, the beacon transmission delays and the measure of successful beacon reception statistics is important to understand the effectiveness of the mechanism which are completely ignored. *** Recommended changes: Recommended changes. Please indicate any changes that should be made to the paper if accepted. The exact contribution of the paper is not clearly stated in the introduction and the reader need to arrive at the final phases of section III to understand in depth the exact logic behind the proposed backoff mechanism. To avoid this confusion, the authors need to introduce a concise but intuitive view of the proposed backoff mechanism in the introduction also clearly stating the motivation behind the balance between collision and expired beacons. *** Relevance and timeliness: Rate the importance and timeliness of the topic addressed in the paper within its area of research. Good (4) *** Technical content and scientific rigour: Rate the technical content of the paper (e.g.: completeness of the analysis or simulation study, thoroughness of the treatise, accuracy of the models, etc.), its soundness and scientific rigour. Marginal work and simple contribution. Some flaws. (2) *** Novelty and originality: Rate the novelty and originality of the ideas or results presented in the paper. Minor variations on a well investigated subject. (2) *** Quality of presentation: Rate the paper organization, the clearness of text and figures, the completeness and accuracy of references. Well written. (4) ======= Review 2 ======= *** Submission Policy: Does the paper list the same author(s), title and abstract (minor wording differences in the abstract are ok) in its PDF file and EDAS registration? Yes, the paper matches the EDAS registration. *** Strong aspects: Comments to the author: what are the strong aspects of the paper The paper presents a modification to the IEEE 802.11p protocol for VANETs that enhances support for broadcast messages in VANETs. The strong aspects of the paper are as follows: 1. The authors explain in great detail about the particular issues that arises in broadcast messages in VANETS. This discussion is valuable to the community in highlighting a possible inefficiencies in the 802.11p protocol 2. Although the proposed modification is simple, the authors have shown through their simulation that is improves the performance of the 802.11 protocol 3. Additionally since the proposed modification is simple, it could be added to the standard after a detailed evaluation. 4. The paper is well written *** Weak aspects: Comments to the author: what are the weak aspects of the paper? There were no weak aspects. *** Recommended changes: Recommended changes. Please indicate any changes that should be made to the paper if accepted. No changes recommended. *** Relevance and timeliness: Rate the importance and timeliness of the topic addressed in the paper within its area of research. Excellent (5) *** Technical content and scientific rigour: Rate the technical content of the paper (e.g.: completeness of the analysis or simulation study, thoroughness of the treatise, accuracy of the models, etc.), its soundness and scientific rigour. Solid work of notable importance. (4) *** Novelty and originality: Rate the novelty and originality of the ideas or results presented in the paper. Some interesting ideas and results on a subject well investigated. (3) *** Quality of presentation: Rate the paper organization, the clearness of text and figures, the completeness and accuracy of references. Excellent. (5) ======= TPC review 3 ======= *** Relevance and timeliness: Rate the importance and timeliness of the topic addressed in the paper within its area of research. Good (4) *** Technical content and scientific rigour: Rate the technical content of the paper (e.g.: completeness of the analysis or simulation study, thoroughness of the treatise, accuracy of the models, etc.), its soundness and scientific rigour. Solid work of notable importance. (4) *** Novelty and originality: Rate the novelty and originality of the ideas or results presented in the paper. Significant original work and novel results. (4) *** Quality of presentation: Rate the paper organization, the clearness of text and figures, the completeness and accuracy of references. Well written. (4) *** Submission Policy: Does the paper list the same author(s), title and abstract in its PDF file and EDAS registration? Yes. *** Strong aspects: Comments to the author: what are the strong aspects of the paper? The paper proposes a modification of the IEEE 802.11p MAC layer back off mechanism. It focuses on an adaptive contention window to find an equilibrium between the collisions and expired beacons. The scalability problem of IEEE 802.11p and different measures to solve this problem with their limitations have been also discussed. This provides a good background and motivation of the proposed method. The proposed back-off mechanism has been mathematically modeled and simulations results have also been presented in favor of the proposal. *** Weak aspects: Comments to the author: what are the weak aspects of the paper? No major weakness has been found, however some minor modifications would improve the quality of presentation. *** Recommended changes: Recommended changes. Please indicate any changes that should be made to the paper if accepted. 1- The last paragraph in Introduction: it has some inconsistency, either add section numbers (III and IV) or remove II and V. 2- Some acronyms (e.g. DCF) have been presented without any abbreviation. 3- In the texts, ``figure 1" should be ``Figure 1", same for other figures also. 4- Figures 2 and 3 are not understandable (the dotted lines are not differentiable) in the printout. Figure 1 could be presented in single-column, which would provide enough space to make Figures 1 and 2 bigger. ======= TPC review 4 ======= *** Relevance and timeliness: Rate the importance and timeliness of the topic addressed in the paper within its area of research. Good (4) *** Technical content and scientific rigour: Rate the technical content of the paper (e.g.: completeness of the analysis or simulation study, thoroughness of the treatise, accuracy of the models, etc.), its soundness and scientific rigour. Solid work of notable importance. (4) *** Novelty and originality: Rate the novelty and originality of the ideas or results presented in the paper. Significant original work and novel results. (4) *** Quality of presentation: Rate the paper organization, the clearness of text and figures, the completeness and accuracy of references. Well written. (4) *** Submission Policy: Does the paper list the same author(s), title and abstract in its PDF file and EDAS registration? yes *** Strong aspects: Comments to the author: what are the strong aspects of the paper? In this paper, the authors propose adaptive approach on back-off mechanism and contention window in seeking equilibrium between collisions and expired beacons. These approaches seem promising in solve the scalability issues of 802.11p protocol for Vehicular network. *** Weak aspects: Comments to the author: what are the weak aspects of the paper? Can you please clearly point out the difference of this work from the work below? Although you mentioned "However, this solution would require to buffer an important number of messages and, as we shall discuss further on, it does not solve all the problems of the MAC layer." R. Stanica, E. Chaput, A.-L. Beylot Broadcast Communication in Vehicular Ad-Hoc Network Safety Applications Proceedings of the IEEE Consumer Communications and Networking Conference, pp. 1-5, Las Vegas, January 2011 *** Recommended changes: Recommended changes. Please indicate any changes that should be made to the paper if accepted. refer to above section