# The 6G Ecosystem as Support for IoE and Private Networks: Vision, Requirements, and Challenges
## 2 From 1G to 5G
### The Third Generation (3g)  
In 2000, the 3 rd Generation Partnership Project (3 GPP) introduced the 3G mobile communication system, recognized as universal mobile telecommunications systems (UMTS) in Europe. The ITU-T refers to this standard as International Mobile Telecommunications-2000 (IMT2000), while, in the United States, it is called CDMA2000 [35].  
The third generation of mobile transmission systems represents a significant leap forward, offering impressive speeds, to date, of up to 144 kbps up to 2 Mpps and beyond, ideal for high-speed mobile access and data transfer with internet protocol services. Certainly, 3G encompasses enhancements over its predecessors, focusing on features like \"high-speed transmission, multimedia access, and global roaming capabilities\" [21], improved QoS, and better voice call quality [35].  
One of the primary applications of 3G is its widespread use in mobile phones and handheld devices, serving as a reliable means to connect these devices to internet protocol suite networks. This enables users to make voice and video calls, transfer data, and browse the web easily. The multimedia potential of 3G is evident, supporting full video streaming, video conferencing, and seamless internet access [36].  
Data transmission in 3G networks is facilitated through a technology known as packet switching, which efficiently handles data packets, allowing for efficient data transfer. On the other hand, voice calls are handled using circuit switching for clarity and reliability. This modern communication process has evolved significantly over the past era, revolutionizing how we connect and communicate, and unlocking a world of possibilities for multimedia applications and seamless connectivity [21]. Exemplified by WCDMA, C2K, time-division synchronous CDMA (TD-SCDMA), and worldwide interoperability for microwave access (WiMAX), 3G has facilitated an array of data services encompassing video calls, internet access, and mobile television. Concurrently, there was a transformation in the network core toward the IP multimedia subsystem (IMS), introducing a perspective of data-switched communications using the session initiation protocol (SIP). This shift strengthened the connection between cellular network cores and the broader internet, enabling portable mobility across various radio interfaces.  
The emergence of technologies like WCDMA, high-speed uplink/downlink packet access (HSUPA/HSDPA), and evolution-data only (EV-DO) led to the introduction of an intermediate wireless communication generation known as 3.5G, offering data rates ranging from 5 to 30 Mbps [34].  
The transition in user engagement perception within 3G networks has altered the landscape of service evaluation in network management. Initially, network management and performance were contingent on quality of service (QoS) metrics, considering factors like delay, instability, and call drop rate. However, with 3G facilitating the integration of voice and multimedia content, the assessment of both the system and services now incorporates metrics rooted in quality of experience (QoE) [33].