{"id":"iso-on-tcp","model_id":"RFC 1006","name":"RFC 1006 ISO Transport Service on top of the TCP","summary":"RFC 1006 defines how ISO transport class 0 (TP0) is carried over TCP, so ISO session, presentation and application layers can run on a TCP/IP internetwork without change. Each transport protocol data unit (TPDU) is framed in a TPKT packet consisting of a 4-octet header (version, reserved, packet length) followed by the TPDU defined in ISO 8073. TCP port 102 is reserved for hosts implementing the standard, and TCP connection open/close events are mapped onto the ISO N-CONNECT, N-DATA and N-DISCONNECT primitives.","study_notes":["The protocol is ISO transport class 0 over TCP, which is stated to achieve functionality identical to transport class 4.","Version 3 obsoletes RFC 983; the changes are minor but incompatible.","Default TPDU size is 65531 octets instead of the 128 octets of ISO 8073; a smaller size is negotiated with the TPDU Size variable part.","Quality of Service parameters of ISO 8072 are not supported and are left for further study.","The TSAP ID field format is not specified by ISO; this memo mandates the GOSIP specification (GOSIP86, section 5.2 Upper Layers Addressing).","The ISO TSAP is symmetric: there is no underlying client/server model, and TS-users sit in the IDLE state until they generate a REQUEST or accept an INDICATION.","Expedited data transfer is negotiated during connection establishment via the Additional Option Selection variable part; the default is not to use it.","The non-standard ED TPDU for expedited data is sent on the same TCP connection as all other TPDUs; its only difference from the DT TPDU is the code value ED.","Documents referenced but not matching available entries: ISO 8072, ISO 8073, ISO 8327, RFC 791, RFC 793, RFC 983, X.214, X.224, X.225.","In most implementations a single server perpetually LISTENs on port 102 and hands off connections as they are made."],"safety_notes":["Packet length field is 16 bits, minimum 7 and maximum 65535 octets, including the packet header.","Maximum TPDU size is 65531 octets, giving a maximum TSDU size of 65524 octets.","The TP specification limits the expedited transport service data unit (XSDU) to 16 octets.","Only TPDUs formatted for transport class 0 are exchanged.","The reserved header field must be handled per the TPKT header definition; the vrsn field is always 3 for this version of the protocol."],"sources":[{"url":"https://datatracker.ietf.org/doc/html/rfc1006","title":"RFC 1006: ISO Transport Service on top of the TCP Version: 3","accessed":"2026-10-25"}],"verification":{"status":"source_checked","checked_at":"2026-10-25","values":15,"method":"llm_source_check"},"updated_at":"2026-10-25","type":"protocol","spec":{"transports":["tcp"],"architecture":"request_response","encoding":"binary","default_ports":[{"port":102,"transport":"tcp","secure":false,"purpose":"ISO transport service on top of TCP (TSAP connections)"}],"data_types":[{"name":"vrsn","size_bits":8,"description":"Version of the protocol; always 3 for the version described in this memo."},{"name":"packet length","size_bits":16,"description":"Length of the entire packet in octets including the packet header; min 7, max 65535."},{"name":"TPDU-NR and EOT","size_bits":8,"description":"Bit 7 (mask 1000 0000) indicates end of a TSDU; all other bits zero on output and ignored on input."}],"standard_ref":"RFC 1006","related":[]},"url":"https://machineschema.com/protocol/iso-on-tcp","license":"https://creativecommons.org/licenses/by/4.0/"}