Question: In the context of Adaptive Multi-Rate (AMR) speech codec's Source Controlled Rate (SCR) operation, how does the Transmission (TX) part of the Access Network (AN) handle frames marked with `TX_TYPE = (NO_DATA)` in comparison to other frame types?
Option 1: They are prioritized for immediate transmission to maintain network throughput.
Option 2: They are processed but not transmitted, to conserve network resources.
Option 3: They are scheduled for transmission after all other frame types have been sent.
Option 4: No processing or transmission is carried out for these frames.
Explanation: According to the specified behavior for SCR operation in the TX part of the Access Network, when frames are marked with `TX_TYPE = (NO_DATA)`, no further action is taken. This means neither processing nor transmission occurs for such frames, distinguishing them from other types (SPEECH, POST0, POST1, PRE) which are all scheduled for transmission, with SPEECH frames taking precedence in exceptional cases. This approach optimizes resource utilization by not allocating bandwidth or processing power to empty or non-essential data transmissions.