Transmission Control Protocol
Enable an AI agent to recognise TCP behaviour, assess a connection's transport state and delivery limits, and choose justified diagnostic or control actions.
Research draft, second pass
A second pass drafted this model: the structure a model of this thing needs, and what is known about it in the world. The line under this one says how the second half was obtained - researched against sources, or recalled without web access, in which case nothing here was read anywhere and every claim is a lead to verify. Unreviewed either way.
recalled by Codex without web access - no source was read
Researched by: Codex
Purpose and description
Enable an AI agent to recognise TCP behaviour, assess a connection's transport state and delivery limits, and choose justified diagnostic or control actions.
Transmission Control Protocol (TCP) is a connection-oriented transport protocol in the Internet protocol suite that provides applications with a reliable, ordered, bidirectional byte stream using sequence numbers, acknowledgements, retransmission, flow control and congestion control.
It can be Classify a flow as TCP and associate its observed segments with a connection instance.; Reconstruct supported endpoint-state transitions and identify missing evidence.; Assess byte-stream progress, gaps, duplicate acknowledgements and retransmission behaviour.; Distinguish receiver-window limits, congestion-control limits and application inactivity using available evidence.; Evaluate compatibility of TCP options and diagnose suspected path interference.; Recommend or perform authorised connection shutdown, targeted measurements or transport configuration changes with explicit expected effects..
Distinguishing features
Presents an ordered byte stream: application write boundaries are not preserved as message boundaries.
Maintains connection state at endpoints and normally establishes a connection through a SYN, SYN-ACK and ACK exchange.
Uses byte sequence numbers, acknowledgements and retransmission to recover from loss while suppressing duplicate delivery.
Separately constrains sending through receiver-advertised flow control and sender congestion control.
An acknowledgement indicates transport-level receipt, not application processing; TCP itself supplies neither encryption nor authenticated peer identity.
Scope
+ Reliable, ordered, bidirectional byte-stream semantics and their limits
+ Connection establishment, endpoint identity, lifecycle and termination
+ Segment interpretation, sequencing, acknowledgements and loss recovery
+ Receiver flow control, sender congestion control and transport performance
+ TCP options, implementation variation and evidence-based diagnosis
- IP addressing allocation, routing and network-layer forwarding
- Application message framing, transaction completion and business semantics
- TLS encryption, certificate validation and application authentication
- UDP, QUIC and other transport protocols except as boundary comparisons
- Physical links, network equipment and operating-system internals beyond their observable effects on TCP
Characteristics
- Protocol profile
- Base specification, applicable extensions and implementation-specific behaviour Establishes which requirements and capabilities apply before judging observed behaviour.
- Connection identity
- Local and remote IP addresses and TCP ports, with observation time and network context Associates evidence with an endpoint pair while accounting for address translation and tuple reuse.
- Endpoint connection state
- CLOSED, LISTEN, SYN-SENT, SYN-RECEIVED, ESTABLISHED, FIN-WAIT-1, FIN-WAIT-2, CLOSE-WAIT, CLOSING, LAST-ACK or TIME-WAIT Determines which transitions and operations are valid at each endpoint.
- Sequence and acknowledgement position
- 32-bit sequence-space values interpreted modulo 2^32 Supports reasoning about received data, missing ranges and progress; SYN and FIN also consume sequence space.
- Effective receive window
- Bytes, interpreted with the applicable negotiated window scale Shows how much additional sequence space the receiver permits the sender to use.
- Congestion-control state
- Algorithm, congestion window in bytes, recovery phase and pacing state where observable Explains sender limits imposed by congestion control and separates them from receiver limits.
- Timing estimates
- Round-trip time, round-trip variation and retransmission timeout in milliseconds Supports assessment of delay, retransmission decisions and stalled progress.
- Directional option status
- Offered, negotiated, active, absent or unknown for each relevant capability Prevents assuming that observed options or host capabilities apply equally in both directions.
- Observation coverage
- Endpoint telemetry, bidirectional capture, one-sided capture or partial capture; capture location and time interval Bounds what can be concluded about loss, state, timing and peer behaviour.
Where this came from
wikidata · CC0 1.0
Drafted structure
Bundle to layer to finding to question, as the second pass will find it: 6 bundles · 11 layers · 18 findings · 28 questions.
Byte-stream contract The service TCP provides and the boundaries of its delivery claims.
An agent must distinguish transport progress from application success and avoid treating segments as application messages.
Stream semantics
Ordering, duplication and message-boundary interpretation.
Ordered bytes without message boundaries
Record the two directional byte streams and the application's framing expectations without inferring message boundaries from TCP segments.
- Does the consumer require an ordered byte stream, and how does it identify application messages within that stream? definition
- Which apparent message boundaries come from application framing, and which are merely segment or capture boundaries? boundary
Delivery evidence
What transport acknowledgements and connection outcomes establish.
Receipt versus processing
Separate bytes acknowledged by TCP from bytes read, processed or durably committed by the receiving application.
- Which byte ranges have been cumulatively acknowledged, and what independent evidence shows application consumption? measurement
- After a timeout or reset, what application-level evidence is needed before retrying an operation that might already have taken effect? action
Connection lifecycle Connection identity and the endpoint state machines that govern opening and closing.
TCP actions depend on endpoint-local state; an open socket, an established connection and a completed exchange are different conditions.
Identity and establishment
Endpoint association and evidence of connection opening.
Handshake and instance identity
Record the endpoint tuple, handshake evidence and temporal context needed to distinguish a connection from earlier uses of the same tuple.
- Which addresses and ports identify this connection at the observation point, and does translation change that identity elsewhere? boundary
- What SYN and acknowledgement evidence supports the inferred establishment state at each endpoint? measurement
Shutdown and residual state
Directional closure, aborts and state retained after exchange completion.
FIN, reset and TIME-WAIT
Distinguish an orderly end to one sending direction from an aborted connection and from post-closure TIME-WAIT state.
- Which direction has sent or acknowledged FIN, has a reset occurred, and what state is supported for each endpoint? measurement
- Given pending data and application intent, should the agent wait, half-close, close normally or request an authorised abort? action
Sequencing and recovery How TCP represents byte progress and recovers from suspected loss.
A stalled or repeated segment cannot be interpreted correctly without sequence-space, acknowledgement and timer context.
Sequence-space accounting
Byte ranges, cumulative acknowledgements and selective acknowledgement evidence.
Received and missing ranges
Track acknowledged progress and selectively reported ranges while accounting for wraparound, SYN and FIN.
- Which sequence ranges are cumulatively acknowledged, selectively reported as received or still unresolved? measurement
- Could an apparent gap or duplicate arise from capture loss, reordering or an incorrect connection association? boundary
Loss detection and timers
Evidence behind retransmissions and recovery decisions.
Retransmission cause and confidence
Record the available evidence for timeout-based or other loss-recovery triggers without treating every retransmission as proof of network loss.
- Which acknowledgement pattern, timer event or endpoint diagnostic supports the inferred retransmission trigger? provenance
- What additional measurement would distinguish actual loss from reordering, delayed feedback or a spurious retransmission? action
Flow, congestion and performance Receiver capacity, network feedback and the constraints that determine sending progress.
Receiver protection and network congestion control impose different limits and require different interventions.
Receiver flow control
Advertised windows, scaling and zero-window behaviour.
Receive-window limits
Record the effective advertised window in each direction and evidence that receiver capacity is limiting progress.
- What effective receive window is advertised after applying the scale established for that direction? measurement
- If the window remains zero or small, what receiver-side evidence would justify changing application consumption or buffer configuration? action
Sender congestion and throughput
Congestion algorithms, feedback and useful data-transfer rate.
Active throughput constraint
Relate useful acknowledged-byte progress to congestion state, receive-window limits, path timing and application supply.
- Which congestion-control algorithm and sender metrics are directly known, and which would be guesses from packet traces? provenance
- Over the measured interval, does evidence identify congestion control, the receive window, path capacity or application supply as the active constraint? measurement
Protocol profile and observability Applicable requirements, optional capabilities and limits of observation or trust.
Judging TCP behaviour requires the right protocol profile and evidence that distinguishes endpoint behaviour from path and capture effects.
Requirements and capabilities
Standards applicability, TCP options and implementation-specific choices.
Applicable TCP profile
Associate observed behaviour with researched specifications and record option availability separately from successful use.
- Which authoritative specifications and implementation documentation establish the requirements applicable to this connection? provenance
- Which capabilities, such as selective acknowledgements, timestamps, window scaling or explicit congestion notification, were offered and successfully enabled? measurement
Observation and trust boundaries
Capture limitations, path transformations and security properties outside TCP's base service.
Evidence limits and peer trust
Record observation location, offload effects and possible intermediaries while keeping transport endpoint association separate from authenticated identity.
- Could checksum or segment-size anomalies reflect host offloading, capture position or intermediary behaviour rather than malformed traffic on the wire? boundary
- What separate mechanism, if any, establishes peer authentication and protects the stream's confidentiality and integrity? boundary
Evidence and external alignment What the world already says about this thing, gathered so the model can be checked against it.
A model that cannot be lined up against existing standards, identifiers and practice cannot be adopted by anyone who already uses them.
Reported evidence
Findings from the breadth pass, kept separate from the structural claims.
Check these first
Recalled without web access and unsourced; every item is a lead to verify.
- The sense described is the Internet transport protocol, conventionally abbreviated TCP.
- The listed kinds are congestion-control implementation choices and a protocol extension, not a mutually exclusive taxonomy.
- Standard identifiers are recalled without source inspection; researchers should check updates and implementation support, especially for congestion-control variants.
- Which of these check these first hold for the sense of Transmission Control Protocol this model covers, and on what evidence? provenance
Kinds and varieties
Recalled without web access and unsourced; every item is a lead to verify.
- TCP implementations using Reno congestion control
- TCP implementations using CUBIC congestion control
- TCP implementations using BBR congestion control
- Multipath TCP, an extension supporting multiple subflows within one connection
- Which of these kinds and varieties hold for the sense of Transmission Control Protocol this model covers, and on what evidence? provenance
Identifiers and schemes
Recalled without web access and unsourced; every item is a lead to verify.
- IANA IP Protocol Numbers - 6 - Identifies TCP in the IPv4 Protocol field and IPv6 Next Header field.
- IANA Service Name and Transport Protocol Port Number Registry - TCP port number: 0-65535 - Source and destination ports identify transport endpoints; port 0 is reserved.
- TCP connection four-tuple - (source IP address, source port, destination IP address, destination port) - Distinguishes connections within a network context; this is not a globally persistent identifier.
- Which of these identifiers and schemes hold for the sense of Transmission Control Protocol this model covers, and on what evidence? provenance
Standards and regulation
Recalled without web access and unsourced; every item is a lead to verify.
- IETF RFC 9293, Transmission Control Protocol: core TCP specification.
- IETF RFC 5681, TCP Congestion Control.
- IETF RFC 6298, Computing TCP's Retransmission Timer.
- IETF RFC 7323, TCP Extensions for High Performance.
- IETF RFC 8684, TCP Extensions for Multipath Operation with Multiple Addresses.
- Which of these standards and regulation hold for the sense of Transmission Control Protocol this model covers, and on what evidence? provenance
Real-world use
Recalled without web access and unsourced; every item is a lead to verify.
- Transport for HTTP/1.1 and HTTP/2 web connections.
- Transport for email protocols including SMTP, IMAP and POP3.
- Transport for SSH remote access and associated file transfers.
- Transport for many database client-server connections.
- Transport for DNS exchanges, including zone transfers and responses requiring TCP.
- Which of these real-world use hold for the sense of Transmission Control Protocol this model covers, and on what evidence? provenance
Typical measurements
Recalled without web access and unsourced; every item is a lead to verify.
- Application goodput - No universal range; depends on path capacity, round-trip time, loss and endpoint limits. - bit/s
- Round-trip time - No universal range; depends on path propagation, processing and queueing. - ms
- Advertised receive window - Representable range is 0-65535 bytes without window scaling; negotiated scaling permits larger windows. - byte
- TCP header length - 20-60, depending on included options. - byte
- Which of these typical measurements hold for the sense of Transmission Control Protocol this model covers, and on what evidence? provenance
Failure modes and hazards
Recalled without web access and unsourced; every item is a lead to verify.
- Lost data delays delivery of subsequent bytes to the application until the gap is repaired, causing head-of-line blocking.
- Congestion, loss or excessive buffering can reduce throughput and increase latency.
- SYN flooding can exhaust connection-establishment resources.
- TCP alone provides neither encryption nor cryptographic peer authentication; its checksum does not prevent deliberate tampering.
- Path failures, endpoint crashes and middlebox timeouts can interrupt connections; a TCP acknowledgement does not prove that an application processed or durably stored the data.
- Which of these failure modes and hazards hold for the sense of Transmission Control Protocol this model covers, and on what evidence? provenance
Neighbouring kinds and how to tell them apart
Recalled without web access and unsourced; every item is a lead to verify.
- Internet Protocol - IP carries addressed datagrams between hosts; TCP runs over IP and supplies reliable byte-stream transport between endpoints.
- User Datagram Protocol - UDP preserves datagram boundaries and does not itself provide TCP's connection establishment, ordered delivery or retransmission.
- QUIC - QUIC runs over UDP and integrates cryptographic security and multiple streams, whereas TCP exposes a byte stream per connection without built-in encryption.
- Transport Layer Security - TLS provides cryptographic protection for application communication; TCP provides transport reliability and ordering.
- Stream Control Transmission Protocol - SCTP is message-oriented and supports multiple streams within an association; TCP is byte-stream-oriented.
- Which of these neighbouring kinds and how to tell them apart hold for the sense of Transmission Control Protocol this model covers, and on what evidence? provenance
What the second pass must settle
- Which base specification, updates and optional extensions should define the publication's researched TCP profile?
- How much connection state and congestion-control information must an agent obtain from endpoint telemetry when packet observations alone are inconclusive?
- Which operating-system behaviours for keepalive, retransmission limits, user timeouts and aborts require explicit implementation profiles?
- How should the model represent connection identity across NAT, TCP proxies and tuple reuse without merging separate transport connections?
- What evidence thresholds should justify active probing, configuration changes or connection termination in each deployment context?