This class implements the Telnet protocol (as described in RFC 854) and its most common extensions. Although not all possible options are checked by the low level proxy, it is possible to filter any option and suboption negotiation sequences using policy callbacks. AbstractTelnetProxy serves as a starting point for customized proxy classes, but is itself not directly usable. Service definitions should refer to a customized class derived from AbstractTelnetProxy, or one of the predefined TelnetProxy proxy classes. AbstractTelnetProxy denies all options by default.