This paper presents a joint protocol-channel decoding techniques to improve the estimation quality of the type of a packet corrupted by transmission errors. It exploits the redundancy present in the protocol stack to determine the packet type which is the most probable a posteriori. An optimal and a suboptimal estimation algorithm are presented. The latter is illustrated on the type estimation of packets compressed with the Robust Header Compression algorithm in unidirectional mode. Compared to a classical packet type estimation technique, improvements of more than 3.9 dB are observed in terms of channel SNR at header error rates of 10-2.1