<P> Rowland provides a proof of concept as well as practical encoding and decoding techniques for exploitation of covert channels using the TCP / IP protocol suite . These techniques are analyzed considering security mechanisms like firewall network address translation . </P> <P> However, the non-detectability of these covert communication techniques is questionable . For instance, a case where sequence number field of TCP header is manipulated, the encoding scheme is adopted such that every time the same alphabet is covertly communicated, it is encoded with the same sequence number . </P> <P> Moreover, the usages of sequence number field as well as the acknowledgment field cannot be made specific to the ASCII coding of English language alphabet as proposed, since both fields take into account the receipt of data bytes pertaining to specific network packet (s). </P> <P> After Rowland, several authors in academia published more work on covert channels in the TCP / IP protocol suite, including a plethora of countermeasures ranging from statistical approaches to machine learning . The research on network covert channels overlaps with the domain of network steganography, which emerged later . </P>

Describe countermeasures that could be employed to detect or prevent the use of this covert channel