The A - Z Guide of TCP/IP Stack of AUTOSAR Ethernet Communication Stack
Tags: autosar, tcpipstack, comstack, ethernet
Published: 2023-02-24 14:02:15

As a software engineer at Luxoft, I have had the opportunity to work extensively with the AUTOSAR Ethernet, CAN, and TCP/IP stack and have gained a deep understanding of its features and capabilities. In this article, I will provide an overview of the AUTOSAR TCP/IP stack, including its architecture. Whether you are an automotive software developer or simply interested in learning more about this important technology, this article will provide a valuable resource for understanding the AUTOSAR TCP/IP stack and its role in modern vehicle communication systems.

AUTOSAR TCP/IP is a networking stack based on the Transmission Control Protocol/Internet Protocol (TCP/IP) suite, which is widely used for communication over the Internet and other networks. The AUTOSAR TCP/IP stack is designed specifically for use in automotive systems and is compliant with the AUTOSAR standard.

#### The AUTOSAR TCP/IP stack includes the following main components:

- TCP/IP protocol suite: The TCP/IP protocol suite includes the TCP, UDP, IP, and ICMP protocols. These protocols are responsible for providing reliable communication over the network, including error detection, flow control, and congestion control.

- Socket interface: The socket interface provides a standardized way for applications to communicate with the TCP/IP stack. The socket interface includes functions for creating sockets, sending and receiving data, and managing connections.

- Network interface: The network interface is responsible for managing the physical connection to the network, including configuring the network interface settings and handling network events such as link-up and link-down.

- Ethernet driver: The Ethernet driver is a hardware-specific component that provides a low-level interface between the TCP/IP stack and the network interface hardware.

The AUTOSAR TCP/IP stack can be used for a wide range of networking applications in automotive systems, including diagnostics, software updates, and multimedia streaming. The stack is highly configurable and can be customized to meet specific system requirements, such as the use of different network protocols or the integration with other automotive software components.

![TCP/IP Stack of AUTOSAR Ethernet Communication Stack](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/5rgbeidgztuv67uwfbqn.png)

The AUTOSAR TCP/IP module's main functionality is sending and receiving internet protocol data. The TCP/IP stack is located between the Ethernet Interface (EthIf) modules and the Socket Adapter (SoAd).

TCP/IP stands for Transmission Control Protocol/Internet Protocol. It is a suite of communication protocols used for communication over the Internet and other networks. The TCP/IP protocol suite consists of several protocols that work together to provide reliable and efficient communication between devices.

Here are some of the main protocols that make up the TCP/IP suite:

## Internet Protocol (IP):

This protocol is responsible to send and receive data as packets across the networks through routers. Each packet has a source and destination address called an IP address. And those IP addresses (source and destination address) are set to a node of a network that uses IP protocol for communication over the network.

**There are two types of Internet Protocol (IP):**
#### IPv4: 
 It has 32-bit addresses. It supports manual DHCP configuration. It generates 4.29 x 10^9 addresses. Representation of address IPv4 is in decimal. The checksum is available in IPv4. It works with MAC addresses.

#### IPv6: 
 It has a 128-bit address. It supports auto and renumbering address configuration. In IPv6 address space is too large it can be produced 3.4 x 10^38 address space. The address representation of IPv6 is in hexadecimal. The checksum is not available in IPv6. It works with DUID.

## Transmission Control Protocol (TCP):
 TCP/IP requires an established connection to transmit the data. It will always be given us the guarantee of delivery of data to the destination router. In the case of data, packets are not sent or sent to fail or if any issue occurs during sending the data, then here retransmission of the lost packet is possible.
 It also gives error checking and acknowledgment of data. Here once data transmission is completed or the data is sent completely then the connection should be closed. It is unicast, it is a peer-to-peer connection, and this is the disadvantage of TCP/IP.
 As per the below figure, here once the connection is established then only the operation request will send, which means, the client will send a connection request to the server and the server gives acknowledgment to the client after receiving the acknowledgment, at that moment we called it the connection is established. And then only the data packet will be sent to the server or any operation request will be sent to the server and then the server will give a response to the client.

![TCP/IP Data Transmission Request and Response](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/rmmmqyoddectrnh6cavm.png)

## User Datagram Protocol: 
 UDP is a connection-less protocol with no requirement for opening, maintaining, or terminating a connection. It cannot guarantee the delivery of data to the destination like TCP/IP. No retransmission of loss packets. Basic error-checking mechanism using checksum. It is unicast, multicast, and broadcast. Here speed is very fast as compared to TCP/IP but here lots of chances of data loss are high and it is not much secure. 

![UDP Data Transmission Request and Response](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/r98qe883k4kn08q6r8vp.png)

## Address Resolution Protocol (ARP): 
 ARP stands for Address Resolution Protocol. It is a protocol used to map a network address (such as an IP address) to a physical address (such as a MAC address). ARP is used by devices on a network to communicate with each other.

**Here is how ARP works:**
When a device wants to send a packet to another device on the same network, it needs to know the MAC address of the destination device. The device knows the IP address of the destination device, but it needs the MAC address to send the packet.

The device sends an ARP request to the network asking "Who has this IP address?" The request is broadcast to all devices on the network. The device with the IP address in question responds with its MAC address. The device that sent the ARP request caches this information in its ARP table, which is used to speed up future communication with the same device.

Once the device has the MAC address of the destination device, it can send the packet directly to that device. If the destination device is not on the same network, the device sends the packet to the default gateway, which is responsible for forwarding the packet to the correct network.

ARP is a crucial protocol for communication on a network, as it allows devices to communicate with each other even if they do not know each other's MAC addresses. Without ARP, devices would need to know the MAC addresses of all other devices on the network, which would be impractical and inefficient.

## Dynamic Host Configuration Protocol (DHCP):
 DHCP (Dynamic Host Configuration Protocol) is a network protocol that is used to automatically assign IP addresses and other network configuration parameters to devices on a network. The DHCP server is responsible for managing the allocation of IP addresses to clients.
 In DHCP (Dynamic Host Configuration Protocol) the server section is shall be pre-compile time configurable On/Off by the configuration parameter TcpIpDhcpServerEnabled.
 The server part of DHCP should respond to client requests by assigning available IP addresses according to the DHCP server configuration for the related TcpIpCtrl.
 If the configuration/parameter contains TcpIpDhcpAddressAssignments that means to specific ports of an Ethernet switch, the DHCP server shall identify the port the request was received, by calling EthIf_GetPortMacAddr() with the MAC address of the DHCP client and select an available IP address of the TcpIpDhcpAddressAssignment related to the same port.

**Steps to get an IP address in DHCP (Dynamic Host Configuration Protocol):**
•	DHCPDISCOVER -> looks for a DHCP Server
•	DHCPOFFER -> DHCP server offers an IP address
•	DHCPREQUST -> The host request to use the IP address
•	DHCPPACK -> DHCP Server sends the IP address to the host request
      IP address assignment type as:
•	Dynamic IP address assignment
•	Static IP address assignment
•	Auto IP address assignment

#### DHCPv4:
 The TcpIp shall implement the client and the server port of the Dynamic Host Configuration Protocol (DHCPv4) for the dynamic configuration of IPv4 addresses as per IETF RFC 2131 (DHCP). The TcpIp shall support the Fully Qualified Domain name (FQDN) Option for Dynamic Host Configuration Protocol (DHCP) for IPv4 clients as defined in IETF RFC 4702 (DHCPv4). No DNS (Domain Name System) shall be supported.

#### DHCPv6:
DHCPv6 (Dynamic Host Configuration Protocol version 6) is the IPv6 equivalent of DHCP. It is a network protocol that is used to automatically assign IPv6 addresses and other network configuration parameters to devices on a network.

 It only has the client functionality shall be supported; the following sections shall not be supported:
   o	Relay agent behavior
   o	Server behavior
   o	Management of temporary addresses
   o	Authentication of DHCP messages
   o	Identify association for temporary addresses option
   o	Authentication option
   o	Rapid commit option
   o	The TcpIp shall support the FQDN (Fully Qualified Domain Name) option for DHCP for IPv6 as per client requirements.

## Internet Control Message Protocol (ICMP):
 It is a protocol that devices within a network used to communicate problems with data transmission. It is a network layer protocol that works in the data link layer of the OSI model, and it is used in network devices to diagnose network communication issues.
 The main functionality of an Internet Control Message Protocol (ICMP) is to check whether data is reaching its intended destination promptly. Mainly it is used in network devices, like routers. Internet Control Message Protocol (ICMP) is important for reporting and testing, but it also can be used in DDoS attacks by many attackers.

#### ICMPv4:

 The TcpIp shall be supported the reception and transmission of ICMPv4 messages as defined in IETF RFC 792 (ICMP in v4).
 The TcpIp shall only reply to ICMPv4 echo request messages if they are valid and TcpIpIcmpEchoReplyEnabled is set to TRUE.
 If a TcpIpIcmpMsgHandler is configured, the TcpIp shall call the respective <UP>_IcmpMsghandler() if an ICMPv4 message is received and not handled by the TcpIp directly.
 Example: if the TcpIp replies to an ICMP echo request <UP>_IcmpMsgHandler() is not called for this message.

#### Icmpv6:

 The TcpIp shall support the ICMPv6 as defined in IETF RFC 443 (ICMPv6).
 TcpIp shall only reply to ICMPv6 Echo request messages if they are valid and TcpIpIcmpv6EchoReplyEnabled is set to TRUE. 
 If a TcpIpIcmpv6MsgHandler is configured, the TcpIp shall call the respective <UP>_IcmpMsgHandler() if an ICMPv6 message is received and not handled by the TcpIp directly.
 Example: if the TcpIp replies to an ICMPv6 echo request <UP>_IcmpMsgHandler() is not called for this message.

## Neighbor Discovery Protocol:

 NDP stands for Neighbor Discovery Protocol, which works with IPv6 protocol responsible for tasks such as stateless autoconfiguration, address resolution, Neighbor Unreachability Detection (NUD), and Duplicate Address Detection (DAD).
 It worked at layer two of the OSI model, the data link layer and it was developed to improve data transmission efficiency and consistency across multiple networks and processes.
 In IPv4, we are using ARP (Address Resolution Protocol) and nowadays we are no longer using Address Resolution Protocol (ARP) in IPv6. In IPv6 Neighbor, Discovery Protocol (NDP) replaces this function. 

## Conclusion
In conclusion, the AUTOSAR TCP/IP stack is a powerful and flexible networking protocol that can be used in a variety of automotive applications. Its modular design allows for easy customization and integration with other AUTOSAR components, making it an ideal choice for vehicle manufacturers and suppliers.

The AUTOSAR TCP/IP stack provides a high degree of interoperability and compatibility, which allows for seamless communication between different electronic control units (ECUs) and other devices within the vehicle network. Its robust and reliable design ensures that it can handle the demanding requirements of automotive applications, including real-time communication and high-speed data transfer.

Overall, the AUTOSAR TCP/IP stack is an essential component of modern automotive systems, and its continued development and improvement will help drive the advancement of connected and autonomous vehicle technology.