From the original 2G IS-95 standard to the 3G CDMA 2000 standard evolution, there are six primary steps involved.

• IS-95A: This is the standard 2G format heavily deployed providing 14.4 Kbps based on circuit switched connection.
• IS-95B: This standard has been deployed in Asia but not widely deployed in the United States. It incorporates several enhancements as well as packet switched data providing data rates up to 64 Kbps. It is also called 2.5G standard.
• 3G-1x: It is also known as radio transmission technology (RTT) with one carrier (1xRTT) (CDMA 2000-1xRTT), or the first phase: This is often called 1x. It is the first 3G phase of CDMA based on packet switched connection. This technology took a large leap from IS 95 B, The number of Walsh codes has been increased to 128 with increase in length. Stronger error coding, faster and more improved forward power control and transmit diversity are the main features of this technology. The addition of these features doubled the voice capacity as well as offered high-speed packet switched data services (up to 153 Kbps).

• 1xEV-DO (CDMA 2000 EV-DO): It is also known as Qualcomm high data rate (HDR) or EVolution for Data Only. This is a high-speed data only solution that can be integrated easily into existing CDMA networks. It can provide data rates up to 307.2 Kbps on both forward link as well as reverse link. There is a thought that 1xEV would be deployed in parallel with 1x, thus using 1x for voice services and 1xEV for data services.
• 1xEV-DV (CDMA 2000 EV-DV): An enhanced version of 1xEV-DO, i.e. Evolution for Data and Voice. It allows both data and voice services, has capability to deliver data at a rate of 307.2 Kbps on reverse link (1+Mbps in revision D) and 3.1 Mbps on forward link.
• 3G-3x (CDMA 2000- 3xRTT): The complete 3G version of CDMA. The 3x technology took another leap from 1x. The concept is basically to use three 1.2288 MHz channels together as illustrated in Figure 25 (3 carriers, hence, it uses what is called spreading rate 3). In 3x, the Walsh codes can be up to 256 chips long, allowing for much more voice capacity in addition to very high-speed data rates (in excess of 2 Mbps per user). Figure 24 gives the evolution path of CDMA 2000.