Which component is described as mapping the binary sequence at the source/channel interface into a channel waveform?

The correct choice is channel encoder. This component's primary function is to transform the binary data produced by the source encoder into a signal that can be transmitted over a communication channel. The channel encoder works by creating a channel waveform, ensuring that the data is formatted optimally for the physical medium used in transmission. This encoding often includes the addition of redundancy to help detect and correct errors during transmission, thereby enhancing the reliability of data delivery over potentially noisy channels.

The source encoder, on the other hand, is responsible for compressing the original information into a binary format before it reaches the channel encoder. The decoder retrieves the original data from the encoded waveform at the receiver, while the channel decoder focuses on correcting any errors that may occur during transmission. Hence, the channel encoder's role is critical in ensuring that the binary sequence is appropriately mapped into a format suitable for sending across the channel, which is why it is the correct answer.