Why is the actual mobile phone (UE) data rate far lower than what carriers advertise? (Continued)

Mobile communication carriers advertise very high data rates for 4G (LTE) and 5G (LTE) networks (4G can reach 300 Mbps, and 5G can reach 20 Gbps); however, the actual speeds experienced on mobile phones and in real-world tests differ significantly. Besides transmission loss and time delay, network congestion and transmission protocols are also major reasons.

I. Network Congestion: This is caused by excessive network traffic, outdated or slow hardware, inefficient network design, and bottlenecks caused by errors or congestion leading to retransmissions. Raw speed isn't everything; in some data center applications, higher overhead protocols are often chosen to gain advantages such as higher reliability, better error detection and correction, and congestion control, rather than prioritizing raw data transmission speed.

II. Protocol Overhead: Mobile data uses high-overhead protocols such as TCP (Transmission Control Protocol) to provide a high level of data integrity and reliability. Its main features are as follows:

• TCP ensures that data is transmitted correctly and in the right order by breaking data into packets, assigning sequence numbers, detecting errors, and retransmitting lost or corrupted packets.
• TCP uses checksums to detect whether data has been corrupted during transmission. If an error is detected, the receiver requests a retransmission.
• In TCP, the receiver sends acknowledgment messages to confirm successful receipt of data packets. If the sender does not receive an acknowledgment, it retransmits the packet.
• TCP manages data flow, preventing the sender from sending too much data and overwhelming the receiver, thus avoiding network congestion. Some routing algorithms in data centers can quickly route retransmitted packets around network failures, minimizing downtime and latency.

Standard protocols, although potentially high-overhead, ensure that various devices from different manufacturers can seamlessly interface and exchange data. This significantly simplifies network management in complex networks. High-overhead protocols may also require additional data and processing power to ensure security; protocols like SSL and TLS use encryption and authentication mechanisms to prevent unauthorized data access and ensure secure transmission. Data center operators, especially those handling critical data (such as financial transactions), often need to make trade-offs between raw speed and other critical requirements such as stability, security, and data accuracy and delivery guarantees.

III. Bandwidth and Data Rate: Wireless cell bandwidth represents the theoretical maximum transmission speed, while the data rate is the actual limit based on network "imperfections." These imperfections stem from inherent physical and software performance limitations, as well as the need for additional features such as higher security and better data reliability. Therefore, regardless of the reason, the data rate is always lower than the theoretical maximum bandwidth.