Wire image and ossification The wire data of TCP provides significant information-gathering and modification opportunities to on-path observers, as the protocol metadata is transmitted in cleartext. While this transparency is useful to network operators and researchers, information gathered from protocol metadata may reduce the end-user's privacy. This visibility and malleability of metadata has led to TCP being difficult to extend—a case of protocol ossification—as any intermediate node (a 'middlebox') can make decisions based on that metadata or even modify it, breaking the end-to-end principle. One measurement found that a third of paths across the Internet encounter at least one intermediary that modifies TCP metadata, and 6.5% of paths encounter harmful ossifying effects from intermediaries. Avoiding extensibility hazards from intermediaries placed significant constraints on the design of MPTCP, and difficulties caused by intermediaries have hindered the deployment of TCP Fast Open in web browsers. Another source of ossification is the difficulty of modification of TCP functions at the endpoints, typically in the operating system kernel or in hardware with a TCP offload engine.
Wire image and ossification The wire data of TCP provides significant information-gathering and modification opportunities to on-path observers, as the protocol metadata is transmitted in cleartext. While this transparency is useful to network operators and researchers, information gathered from protocol metadata may reduce the end-user's privacy. This visibility and malleability of metadata has led to TCP being difficult to extend—a case of protocol ossification—as any intermediate node (a 'middlebox') can make decisions based on that metadata or even modify it, breaking the end-to-end principle. One measurement found that a third of paths across the Internet encounter at least one intermediary that modifies TCP metadata, and 6.5% of paths encounter harmful ossifying effects from intermediaries. Avoiding extensibility hazards from intermediaries placed significant constraints on the design of MPTCP and difficulties caused by intermediaries have hindered the deployment of TCP Fast Open in web browsers. Another source of ossification is the difficulty of modification of TCP functions at the endpoints, typically in the operating system kernel or in hardware with a TCP offload engine.