# Congestion Analysis of Transport Layer in a Multicell 5G DL Communication System
## 5 Conclusions  
In this paper, we analyzed how the 5G network behaves when dealing with congestion. It was underlined that adopting the TCP slow-start method in either a single-cell or a multicell scenario can have a significant impact and, additionally, offer many benefits (e.g., throughput up to 1.2 Gbps for a single-cell scenario vs. 800 Mbps for a multicell scenario, keeping the maximum delay under 50 ms, etc.). The parameters that were investigated were PRB utilization, data volume, delay, cell throughput, and average cell user throughput.  
We adopted FTP model two for all simulations performed. To obtain sufficient PRB utilization and divergent loading in the DL, the TCP slow-start algorithm was activated using 10 extended files of 5 Mbytes each, a length of 5 s, and geometric distribution. The slow-start algorithm was activated to ensure its influence on the congestion and delays in the 5G network. A single packet with a size of 1500 bytes was loaded into the buffer, however, the sizes of several smaller packets were incrementally raised until a value that was considered effective was obtained. The average user throughput was calculated by averaging the packet size over the transmission duration, including buffer waiting time. In the DL scenarios, these performance parameters were shown as a function of PRB utilization and the number of users.  
Given a greater number of UE devices in the cell, the cell edge user throughput decreased when the PRB utilization rate increased. Average throughput of 20 Mbps at the cell edge could be maintained up to around 38% PRB utilization in the cell for the multicell case, which was a similar value as that obtained for the single-cell scenario. Up to about 40% of the cell's PRBs could be used without negatively impacting the average throughput of 20 Mbps at the cell edge for the single-cell scenario. The cell throughput was more linear since more UE devices with larger files were simulated, generating more samples. The delays in the downlink direction for the multicell scenario were maintained at a low level (10 ms) up to approximately 45% PRB use; for the single-cell scenario, they were maintained at this level up to approximately 50% PRB utilization.  
Networks' focus shifts with each generation of communication technology. The next generation is the sixth generation (6G), intended to boost every network connectivity upgrade that 5G can currently provide to users. Smart cities, farms, industries, and robotics will improve with 6G. For several technological and use-case aspects, 6G will build on 5G, driving its adoption at scale through optimization and cost-cutting. Simultaneously, 6G will enable new applications.  
Conceptualization, C.M.A., G.B. and F.A.; methodology, G.B. and C.M.A.; software, C.M.A.; validation, F.A. and C.B.; investigation, C.M.A. and G.B.; resources, C.M.A., G.B. and F.A.; writing--original draft preparation, C.M.A. and G.B.; writing--review and editing, C.M.A., G.B. and F.A.; visualization, C.B.; supervision, G.B. and F.A.; project administration, F.A.; funding acquisition, F.A. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Data Availability Statement: Data sharing not applicable.  
This paper was financially supported by the project \"Network of excellence in applied research and innovation for doctoral and postdoctoral programs\"/InoHubDoc co-funded by the European Social Fund financing agreement no. POCU/993/6/13/153437.  
The authors declare no conflict of interest.