A modem architecture that supports the application of joint source channel decoding (JSCD). The modem architecture includes two channel decoders, one of which is modified to provide improved signal quality. The modem architecture further includes transparent network layers that enable the passage of data from one layer to another layer. For example, the modem architecture enables the passage soft bits, when available, from a physical layer to an application layer. The soft bits may be utilized for JSCD, packet loss concealment, or other applications. The modem architecture enables encryption and decryption of data to incorporate extrinsic information in operating JSCD.