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Protocol ossification
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<p>Protocol ossification is the loss of flexibility, <a href="/facts/Extensibility/AEPWNwxp">extensibility</a> and evolvability of <a href="/facts/Network_protocols/5uady7cB">network protocols</a>. This is largely due to <a href="/facts/Middlebox/NQTBjrDr">middleboxes</a> that are sensitive to the <a href="/facts/Wire_image_(networking)/jkWl9TzV">wire image</a> of the protocol, and which can interrupt or interfere with messages that are valid but which the middlebox does not correctly recognise. This is a violation of the <a href="/facts/End-to-end_principle/6RkKmdUm">end-to-end principle</a>. Secondary causes include inflexibility in endpoint implementations of protocols. </p><p>Ossification is a major issue in <a href="/facts/Internet/Xw1rVvJU">Internet</a> protocol design and deployment, as it can prevent new protocols or extensions from being deployed on the Internet, or place strictures on the design of new protocols; new protocols may have to be <a href="/facts/Encapsulation_(networking)/xttAQnu0">encapsulated</a> in an already-deployed protocol or mimic the wire image of another protocol. Because of ossification, the <a href="/facts/Transmission_Control_Protocol/WW4sPrt9">Transmission Control Protocol</a> (TCP) and <a href="/facts/User_Datagram_Protocol/dxLU0D6q">User Datagram Protocol</a> (UDP) are the only practical choices for <a href="/facts/Transport_protocol/UmIGUCeK">transport protocols</a> on the Internet, and TCP itself has significantly ossified, making extension or modification of the protocol difficult. </p><p>Recommended methods of preventing ossification include <a href="/facts/Encrypting/16q29Fdv">encrypting</a> protocol metadata, and ensuring that extension points are exercised and wire image variability is exhibited as fully as possible; remedying existing ossification requires coordination across protocol participants. <a href="/facts/QUIC/nQt0oLRW">QUIC</a> is the first <a href="/facts/IETF/tIcCsFhX">IETF</a> transport protocol to have been designed with deliberate anti-ossification properties. </p>