TCP/IP Stack (TcpIp)

In the Classic Ethernet stack, TcpIp provides IPv4 and IPv6 with ARP, NDP, ICMP, and DHCP as well as UDP and TCP, thereby serving socket owners such as SoAd [SWS_TCPIP_00052]. EthSM controls the states ONLINE, ONHOLD, and OFFLINE for each EthIf controller. A controller becomes ONLINE only after a local address has been assigned to it [SWS_TCPIP_00085]. Sockets are requested, bound, and in the case of TCP actively or passively connected; data flows via transmit services and callbacks. Most important boundary condition: TcpIp accepts new TCP connections only in the ONLINE state, and rejects new transmit requests in ONHOLD.

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In the Classic Ethernet stack, TcpIp is responsible for IP communication. It consists of submodules for IPv4 (with ARP, ICMP, DHCP, and Auto-IP), for IPv6 (with NDP, ICMPv6, and DHCPv6), and for UDP, TCP, and TLS ([SWS_TCPIP_00052], [SWS_TCPIP_00150]). Upwards, it serves socket owners, i.e., SoAd or CDDs, with dedicated TcpIp_<Up>GetSocket functions and callbacks ([SWS_TCPIP_00220], [SWS_TCPIP_00222]). Downwards, it exchanges frames with EthIf [SWS_TCPIP_00029].

Context diagram: TcpIp is situated between socket owners and EthIf, is controlled by EthSM, and reports to DET and IdsM. Sources: [SWS_TCPIP_00220], [SWS_TCPIP_00070], [SWS_TCPIP_00361], SWS TcpIp p. 17

TcpIp maintains the communication state separately for each EthIf controller [SWS_TCPIP_00083]. EthSM requests one of the states ONLINE, ONHOLD, or OFFLINE via TcpIp_RequestComMode [SWS_TCPIP_00070]. STARTUP and SHUTDOWN are transient states and cannot be requested [SWS_TCPIP_00089]. ONLINE initiates address assignment. ONHOLD retains sockets and addresses, but does not accept transmit requests. OFFLINE closes the sockets ([SWS_TCPIP_00075], [SWS_TCPIP_00074], [SWS_TCPIP_00072]).

State diagram: A controller becomes ONLINE only once an address has been assigned to it. It takes the path to OFFLINE via SHUTDOWN, in which resources are released. Sources: [SWS_TCPIP_00085], [SWS_TCPIP_00077], [SWS_TCPIP_00087], SWS TcpIp p. 60

The addresses originate from a configured table of local addresses. They are assigned statically, via DHCP, or as link-local, selected by priority, and optionally stored in NvM ([SWS_TCPIP_00099], [SWS_TCPIP_00065], [SWS_TCPIP_00127], [SWS_TCPIP_00219]). <Up_LocalIpAddrAssignmentChg> informs the upper layer about changes [SWS_TCPIP_00229]. Sockets are requested and bound with TcpIp_Bind. TCP connections are established via TcpIp_TcpConnect or TcpIp_TcpListen ([SWS_TCPIP_00111], [SWS_TCPIP_00112], [SWS_TCPIP_00113]).

Transmission is performed asynchronously via TcpIp_TcpTransmit or synchronously via TcpIp_UdpTransmit. For TCP, the upper layer passes the data directly or provides it via <Up_CopyTxData> ([SWS_TCPIP_00124], [SWS_TCPIP_00120]). TcpIp assigns received datagrams to a socket via local address and port [SWS_TCPIP_00170]. If the destination MAC address is missing, TcpIpArpPacketQueueEnabled determines whether the packet is queued or rejected [SWS_TCPIP_00192]. TcpIp reports runtime errors such as timeouts, unreachable hosts, or address conflicts to DET. In R20-11, codes 0x01 to 0x05 are defined for this [SWS_TCPIP_00255]. For security, TLS from version 1.2 and IPsec with IKEv2 are added ([SWS_TCPIP_00302], [SWS_TCPIP_00353]).

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Role in the Ethernet stack: Intermediary between socket owners and EthIf

TcpIp bundles the IP-based communication of a Classic ECU in submodules [SWS_TCPIP_00052]. For IPv4, IP, ARP, ICMP, DHCPv4 (client and server), Auto-IP, UDP, and TCP are required ([SWS_TCPIP_00053], [SWS_TCPIP_00056], [SWS_TCPIP_00058], [SWS_TCPIP_00057], [SWS_TCPIP_00061]). For IPv6, IPv6, NDP, ICMPv6, and a DHCPv6 client are added ([SWS_TCPIP_00160], [SWS_TCPIP_00164], [SWS_TCPIP_00166]). Three scalability classes tailor the scope: IPv4 stack, IPv6 stack, and dual stack SWS TcpIp p. 18. For Class 3, the full scope is mandatory [SWS_TCPIP_00150].

Upwards, TcpIp serves socket owners. If TcpIpSocketOwnerUpperLayerType is set to SOAD, the callbacks are named SoAd_…. For CDD, the configured function names apply ([SWS_TCPIP_00220], [SWS_TCPIP_00221]). Each owner receives its own TcpIp_<Up>GetSocket function, and the sockets requested in this way belong exclusively to it [SWS_TCPIP_00222].

Downwards, TcpIp receives frames via TcpIp_RxIndication [SWS_TCPIP_00029]. It transmits via EthIf_Transmit, and always with TxConfirmation = FALSE [SWS_TCPIP_00131]. EthSM controls the state via TcpIp_RequestComMode SWS EthSM p. 27. Optionally, TcpIp uses CSM services [SWS_TCPIP_00028] and reports security events to IdsM [SWS_TCPIP_00361]. An overview of the embedding is given in SWS TcpIp p. 17.

Context diagram: TcpIp is situated between socket owners (SoAd or CDD) and EthIf. It is controlled by EthSM, reports errors to DET and events to IdsM, and optionally uses CSM. Sources: [SWS_TCPIP_00220], [SWS_TCPIP_00222], [SWS_TCPIP_00029], [SWS_TCPIP_00070], [SWS_TCPIP_00028], [SWS_TCPIP_00361], [SWS_TCPIP_00255], [SWS_TCPIP_00219], SWS TcpIp p. 17

Controller states: from TCPIP_STATE_OFFLINE to TCPIP_STATE_ONLINE

The module is initialized with TcpIp_Init and an implementation-specific TcpIp_ConfigType ([SWS_TCPIP_00002], [SWS_TCPIP_00067]). TcpIp_MainFunction is the entry point for the scheduler [SWS_TCPIP_00026]. Interpretation: Time-controlled operations such as timeouts likely take place there. Question Q-77b083e447651768 (open) The specification only states "Schedules the TCP/IP stack".

TcpIp maintains a dedicated state for each EthIf controller: OFFLINE, STARTUP, ONLINE, ONHOLD, or SHUTDOWN [SWS_TCPIP_00083]. If the stored request deviates from the active state, TcpIp initiates the necessary steps [SWS_TCPIP_00136].

• An ONLINE request from OFFLINE activates the configured address assignments [SWS_TCPIP_00075]. As soon as an address is assigned, the controller transitions to ONLINE [SWS_TCPIP_00085].
• ONHOLD reports TCPIP_IPADDR_STATE_ONHOLD for all addresses. Sockets and addresses are retained, but new transmit requests are not accepted ([SWS_TCPIP_00076], [SWS_TCPIP_00074]). Returning to ONLINE reports TCPIP_IPADDR_STATE_ASSIGNED [SWS_TCPIP_00086] again.
• An OFFLINE request or the release of all addresses reports TCPIP_IPADDR_STATE_UNASSIGNED and closes the sockets ([SWS_TCPIP_00077], [SWS_TCPIP_00072]). Once resources are released, OFFLINE follows [SWS_TCPIP_00087].

State diagram: Each EthIf controller has its own state machine. Only ONLINE, ONHOLD, and OFFLINE can be requested; STARTUP and SHUTDOWN are transient states. Sources: [SWS_TCPIP_00075], [SWS_TCPIP_00085], [SWS_TCPIP_00076], [SWS_TCPIP_00086], [SWS_TCPIP_00077], [SWS_TCPIP_00087], [SWS_TCPIP_00088], SWS TcpIp p. 60 (Diagram from R25-11, transitions covered by R20-11 requirements)

In STARTUP, an OFFLINE request aborts ongoing assignments [SWS_TCPIP_00088]. If someone requests STARTUP or SHUTDOWN, this is rejected with E_NOT_OK [SWS_TCPIP_00089].

A typical startup proceeds as follows: EthSM requests ONLINE at the request of ComM SWS EthSM p. 42. TcpIp subsequently reports the assigned address. Thereupon, SoAd requests sockets and binds them ([SWS_TCPIP_00229], SWS SoAd p. 20). The diagram from R25-11 also shows a feedback via EthSM_TcpIpModeIndication SWS TcpIp p. 60. This is likely also true for R20-11. Question Q-a5e26ad792c23d58 (open)

Sequence diagram: Only asynchronous address assignment makes the controller ONLINE. Afterwards, SoAd can request and bind sockets. Sources: [SWS_TCPIP_00070], [SWS_TCPIP_00075], [SWS_TCPIP_00085], [SWS_TCPIP_00229], [SWS_TCPIP_00018], [SWS_TCPIP_00015], SWS EthSM p. 42. Feedback to EthSM is presumably also present in R20-11.

Local addresses and their assignment

The basis is a table of local addresses from TcpIpLocalAddr, which are assigned to EthIf controllers at runtime ([SWS_TCPIP_00099], SWS TcpIp p. 220). An entry is addressed via TcpIp_LocalAddrIdType [SWS_TCPIP_00030]. Multiple methods are possible per entry, such as static, DHCP, or link-local ([SWS_TCPIP_00065], SWS TcpIp p. 224). If an address with higher priority becomes available, it replaces the previous one [SWS_TCPIP_00127].

How assignment and release are triggered depends on the configured trigger:

• For TCPIP_MANUAL, TcpIp_RequestIpAddrAssignment and TcpIp_ReleaseIpAddrAssignment control availability ([SWS_TCPIP_00195], [SWS_TCPIP_00196]).
• With TCPIP_AUTOMATIC, both calls are rejected with E_NOT_OK ([SWS_TCPIP_00198], [SWS_TCPIP_00199]).
• With TCPIP_STORE, TcpIp adopts a valid address from the NvM block [SWS_TCPIP_00219]. TcpIp_ResetIpAssignment invalidates these stored addresses [SWS_TCPIP_00216].

Each change of an assignment is reported by <Up_LocalIpAddrAssignmentChg> with a value of type TcpIp_IpAddrStateType ([SWS_TCPIP_00229], [SWS_TCPIP_00082]). TcpIp announces new IPv4 addresses via Gratuitous ARP [SWS_TCPIP_00093]. It checks IPv6 addresses via Duplicate Address Detection [SWS_TCPIP_00159]. TcpIp_GetIpAddr, TcpIp_GetPhysAddr, and TcpIp_GetCtrlIdx serve for querying ([SWS_TCPIP_00032], [SWS_TCPIP_00033], [SWS_TCPIP_00141]). If a DHCP option is queried that is not set, the read service returns length 0 [SWS_TCPIP_00237].

Sockets: Requesting, Binding, Connecting, Closing

A socket is requested with address family and protocol ([SWS_TCPIP_00018], [SWS_TCPIP_00009], [SWS_TCPIP_00010]). TcpIp_Bind binds it to a local address and a port [SWS_TCPIP_00111]. This fails if port, protocol, and address are already in use or the address is not assigned ([SWS_TCPIP_00146], [SWS_TCPIP_00254]). With TCPIP_PORT_ANY, the stack itself selects a port between 49152 and 65535 SWS TcpIp p. 85.

For TCP, there are two ways to connect:

• As a client, TcpIp_TcpConnect establishes the connection asynchronously. Once established, TcpIp calls <Up_TcpConnected> ([SWS_TCPIP_00112], [SWS_TCPIP_00227]).
• As a server, TcpIp_TcpListen sets the socket to the listen state [SWS_TCPIP_00113]. For each incoming connection, TcpIp derives a dedicated socket and reports it with <Up_TcpAccepted> [SWS_TCPIP_00226]. If the upper layer returns E_NOT_OK, TcpIp closes the connection SWS SoAd p. 81.

TcpIp accepts new TCP connections only in the ONLINE state [SWS_TCPIP_00094].

Sequence diagram: The client receives a confirmation via <Up_TcpConnected>. The server gets a derived socket per connection, which the upper layer can accept or reject. Sources: [SWS_TCPIP_00022], [SWS_TCPIP_00023], [SWS_TCPIP_00226], [SWS_TCPIP_00227], SWS TcpIp p. 129 (the later diagram additionally contains LSduR, which is omitted here), SWS TcpIp p. 107

TcpIp_Close terminates a TCP connection regularly. With Abort = TRUE, it aborts it immediately via RST. For UDP, the resources are released immediately ([SWS_TCPIP_00109], [SWS_TCPIP_00110]). Events such as reset, FIN, or closing are reported by <Up_TcpIpEvent> [SWS_TCPIP_00144]. With TcpIp_ChangeParameter, socket parameters can be modified, such as receive window, frame priority, Nagle, TCP option filter, or UDP checksum ([SWS_TCPIP_00126], [SWS_TCPIP_00266], [SWS_TCPIP_00279]).

Data Paths: Transmission, Reception, Address Resolution

TcpIp_TcpTransmit operates asynchronously. If DataPtr is set, it takes the data from this linear buffer. If DataPtr is a NULL_PTR, it retrieves the data via <Up_CopyTxData>. With ForceRetrieve = TRUE, this is exactly AvailableLength bytes, with FALSE possibly less ([SWS_TCPIP_00124], [SWS_TCPIP_00125], [SWS_TCPIP_00228]). For TCP, TcpIp does not call <Up_TxConfirmation> until the remote peer has acknowledged ([SWS_TCPIP_00225], SWS SoAd p. 86). In contrast, TcpIp_UdpTransmit transmits synchronously and immediately ([SWS_TCPIP_00025], [SWS_TCPIP_00120]).

Sequence diagram: Data is passed directly or fetched via copy callback. Transmission to EthIf runs in the context of the MainFunction; the confirmation comes only after the ACK from the remote peer. Sources: [SWS_TCPIP_00050], [SWS_TCPIP_00123], [SWS_TCPIP_00124], [SWS_TCPIP_00131], SWS TcpIp p. 109

Upon reception, the IP layer assigns each datagram to an entry in the local address table [SWS_TCPIP_00169]. UDP and TCP then select the socket via destination port and local address ([SWS_TCPIP_00170], [SWS_TCPIP_00172]). For existing TCP connections, source address and source port must additionally match [SWS_TCPIP_00173]. UDP broadcasts go to all matching sockets; TCP segments to broadcast addresses are discarded ([SWS_TCPIP_00171], [SWS_TCPIP_00174]). TcpIp reassembles fragmented datagrams and may decouple reception for this purpose ([SWS_TCPIP_00054], SWS TcpIp p. 131). The data reaches the upper layer via <Up_RxIndication>. Once it has processed TCP data, TcpIp_TcpReceived reopens the receive window ([SWS_TCPIP_00223], [SWS_TCPIP_00115]).

Sequence diagram: A received frame is mapped to a socket via the local address and port. For TCP, the upper-layer acknowledgment releases the receive window. Sources: [SWS_TCPIP_00029], [SWS_TCPIP_00169], [SWS_TCPIP_00170], [SWS_TCPIP_00223], [SWS_TCPIP_00115], SWS TcpIp p. 108

To transmit, TcpIp needs the MAC address of the destination and maintains it in an ARP table:

• The table is limited to TcpIpArpTableSizeMax entries [SWS_TCPIP_00090]. Unused entries expire after TcpIpArpTableEntryTimeout [SWS_TCPIP_00091].
• TcpIp suppresses repeated requests to the same destination for the duration of TcpIpArpRequestTimeout [SWS_TCPIP_00350].
• In R20-11, each received IP packet updates the table [SWS_TCPIP_00092]. Later releases tie this to TcpIpArpDefensiveProcessing = FALSE SWS TcpIp p. 29.
• If an entry is missing, TcpIpArpPacketQueueEnabled decides whether the packet is queued or rejected ([SWS_TCPIP_00191], [SWS_TCPIP_00192]). The same applies to NDP [SWS_TCPIP_00193].

TcpIp reports any change in the ARP table via <Up_PhysAddrTableChg> [SWS_TCPIP_00142]. If the neighbor cache is full, the oldest entry is evicted [SWS_TCPIP_00264]. Queries are permitted by TcpIp_GetRemotePhysAddr and the cache read services ([SWS_TCPIP_00138], [SWS_TCPIP_91002], [SWS_TCPIP_91001]).

Activity diagram: If an ARP entry is missing during transmission, the packet is queued or rejected depending on the configuration. New requests to the same destination are throttled. Sources: [SWS_TCPIP_00191], [SWS_TCPIP_00192], [SWS_TCPIP_00350], [SWS_TCPIP_00142], SWS TcpIp p. 176. Interpretation: The queued packet is transmitted after successful resolution.

Security and Filtering: TLS, IPsec, IdsM

For TCP connections, TcpIp supports TLS according to IETF RFC 5246. Versions below 1.2 are rejected ([SWS_TCPIP_00300], [SWS_TCPIP_00302]). Configurable callouts provide PSK identities and the current time ([SWS_TCPIP_91014], [SWS_TCPIP_91012]). Cryptography runs via CSM ([SWS_TCPIP_00028], SWS TcpIp p. 251).

IPsec is supported with IKEv2, not IKEv1 ([SWS_TCPIP_00352], [SWS_TCPIP_00353]). Each datagram is assigned to a policy and, depending on the policy, protected, bypassed, or discarded ([SWS_TCPIP_00359], [SWS_TCPIP_00360]). Impermissible IPv6 extension headers result in silent discard [SWS_TCPIP_00260]. If TcpIpEnableSecurityEventReporting is set, TcpIp reports security events to the IdsM [SWS_TCPIP_00361].

Behavior in the event of an error

Development errors, including TCPIP_E_UNINIT, TCPIP_E_PARAM_POINTER, TCPIP_E_INV_ARG, and TCPIP_E_ADDRINUSE, are defined in [SWS_TCPIP_00042]. Checks include:

• an invalid address family when requesting a socket [SWS_TCPIP_00128],
• an invalid LocalAddrId for TcpIp_Bind [SWS_TCPIP_00147],
• conflicting address families for TcpIp_GetIpAddr [SWS_TCPIP_00206],
• invalid parameters of the DHCP option services [SWS_TCPIP_00243],
• a NULL_PTR as destination address in TcpIp_TcpConnect SWS TcpIp p. 86.

TcpIp returns some rejections as E_NOT_OK regardless of error detection, for example a port that is already in use or a mismatched address family ([SWS_TCPIP_00146], [SWS_TCPIP_00205]).

TcpIp reports runtime errors via Det_ReportRuntimeError:

• TCPIP_E_TIMEDOUT when no response is received to a SYN, keep-alive monitoring expires, or retries are exhausted [SWS_TCPIP_00256],
• TCPIP_E_CONNREFUSED, TCPIP_E_HOSTUNREACH, and TCPIP_E_PACKETTOBIG after the corresponding ICMP messages ([SWS_TCPIP_00257], [SWS_TCPIP_00258], [SWS_TCPIP_00259]),
• TCPIP_E_DADCONFLICT in case of a duplicate assigned address [SWS_TCPIP_00282].

R20-11 defines only codes 0x01 to 0x05 [SWS_TCPIP_00255]. The codes TCPIP_E_TX_QUEUE_OVERRUN and TCPIP_E_TX_INTERNAL_PROCESSING_FAILED added in later releases do not apply here SWS TcpIp p. 65.

Many error cases remain silent because mismatched packets are simply discarded. TcpIp_GetAndResetMeasurementData counts such discarded packets and resets the counters ([SWS_TCPIP_91006], [SWS_TCPIP_00296]). If a MAC address cannot be resolved, TcpIp reports TCPIP_E_PHYS_ADDR_MISS [SWS_TCPIP_00066]. For destinations outside the local subnet, TcpIp_GetRemotePhysAddr immediately returns TCPIP_E_NOT_OK [SWS_TCPIP_00139].

Further detailed evidence

• [SWS_TCPIP_00083], [SWS_TCPIP_00077]: State machine per controller, see also SWS TcpIp p. 60.
• [SWS_TCPIP_00065], [SWS_TCPIP_00219]: Assignment methods and stored addresses.
• [SWS_TCPIP_00222]: Socket owner, configuration in SWS TcpIp p. 232.
• [SWS_TCPIP_00125]: How much data TCP fetches during transmission.
• [SWS_TCPIP_00172]: Mapping of received TCP segments to sockets.
• [SWS_TCPIP_00359]: Processing according to IPsec policy.
• [SWS_TCPIP_00255]: Runtime error codes for R20-11.