IP architecture of a MOST150 based infotainment system
This article presents the definition of the functionality and the roles of the different devices, the specification of possible connections and access rights, as well as the definition of IP-related settings for the system’s IP architecture. The MOST Ethernet Channel introduced in MOST150 (see [1]) provides the necessary infrastructure to implement all necessary protocols and mechanisms (e.g., the Internet Protocol, IP, the Transmission Control Protocol, TCP, or the Hypertext Transfer Protocol, HTTP; for a definition of protocols used on the Internet see [2]) in a distributed infotainment system, while maintaining other essential communication features, e.g., the synchronous and isochronous channels for easy and efficient audio and video streaming.
In this article, we will discuss the elements of the IP architecture for the next generation of Daimler’s infotainment systems (for an overview of the system see [3]). We will describe the different basic features supported by the system’s IP architecture in the next section and the corresponding protocols, functionalities, and roles that are necessary for their implementation in Section 3. With the MOST Ethernet Channel, the underlying MOST150 network provides an efficient and easy to use solution for transmitting IP traffic. In Section 4 we will present the current status of the implementation and the results of performance tests with the respective protocol stacks, as well as open issues and optimizations. We will conclude the paper with an outlook on future work in Section 5.
2. Functionality Provided by the IP Architecture
In this section we will outline the basic functionality of the IP architecture.
First, different ways for realizing Internet access are supported: Internet access can be achieved via the user’s mobile phone connected to the HU, which acts as the central router, using Bluetooth or USB. As an alternative, a special country-specific or optional communication unit can be used. Such a communication unit can also be used to access certain vehicle-centric services like remote diagnostics functionality.
The Internet connection can be accessed from any application on the infotainment system, regardless of the device it is deployed and executed on anything from a navigation application on the HU to a Web browser on the rear-seat entertainment unit. Using WLAN, the HU can also act as a WLAN hotspot for the user’s mobile devices such as a tablet PC.
IP-based protocols are also used for communication between applications on the infotainment network. For example, they are used to transmit large amounts of data like a metadata database for the media player application or to access HTML-based information. By using such stable and well-proven mechanisms, new features can be introduced more easily.
For security reasons, the Internet traffic of applications on the infotainment system is routed via an encrypted connection through a backend system. The backend system can control, filter, and modify the traffic through firewall mechanisms or through a virus scanner, and protect the infotainment system from the rapidly evolving threats of the Internet. In order to reduce the load on the backend system, the Internet traffic of the user’s mobile devices and of some media streaming applications (e.g., IP radio) is not routed through the backend system. Further security mechanisms need to be deployed on the infotainment system to guarantee the security of these applications.
3. IP Mechanisms and Roles
To achieve the functionality described above, the devices on the system implement different IP-related mechanisms accordingly (see Fig. 1).
Figure 1: IP Architecture of a Vehicle Infotainment System
Usually, the HU is the central router for the system and has similar responsibilities to a DSL router at home. Currently, the system does not contain a MOST-based communication unit with an embedded UMTS or LTE module, which could alternatively adopt the roles of the router and the mobile device, which provides Internet access. However, the IP architecture is prepared for such an extension. Other devices on the MOST network can access the IP connection provided by the router. Mobile devices either provide Internet access (for example through Bluetooth with a Dialup Network (DUN) or Personal Area Network (PAN) profile) or they use the Internet connection provided by the router via Wireless LAN (WLAN).
Figure 2 shows the IP stack of a device with optional elements that are only required for a router. Basically, the IP stack provides access to the TCP or UDP protocols for applications running on the device. Usually, applications will implement further application-level protocols on top of TCP, for example, the Hypertext Transfer Protocol (HTTP) in the case of a Web browser. A device will transmit the IP data on a given network interface. Depending on the number of network interfaces of a device, the IP stack contains a complex routing table, which decides over which interface an IP packet is transmitted.
Figure 2: IP-related Protocols and Services
To support dynamic addressing in an IP system, e.g., for the user’s mobile devices, the router implements a server for the Dynamic Host Configuration Protocol (DHCP), which provides IP addresses and other IP-related settings to devices in the system. MOST devices, however, are assigned with static IP addresses to allow for a faster start-up of the system. Network Address Translation (NAT) converts the IP address received from a service provider into local addresses. For the resolution of textual addresses (Universal Resource Locator, URL) into IP addresses, the HU also implements a forwarding mechanism for the Domain Name System (DNS).
As a security mechanism, an Internet Protocol Security (IPSec) client is used to establish an encrypted connection with a Daimler backend system. All traffic to and from applications on the infotainment system is routed through this backend, where suitable security mechanisms can be implemented and managed in one place. Firewall mechanisms prevent any other traffic to and from these applications. Only defined exceptions are allowed to bypass the secure tunnel to the backend and directly access services on the Internet, e.g., for multimedia streaming.
The settings of the IP architecture define the (static) IP addresses and IP-related settings of the devices, their routing tables, as well as the rules for the firewall in the system. Through the routing tables, it is possible to divide the IP traffic into certain subnetworks. For example, the IP traffic of a mobile device using the Internet connection of the HU can be routed directly to the Internet, while bypassing the IPSec connection. Firewall rules prevent any IP traffic for the mobile device from being forwarded to other applications and devices on the infotainment network.
4. MOST150 Ethernet Channel
For the transmission of IP traffic between devices connected to MOST, the MOST150 Ethernet Packet (MEP) channel is used. We have already presented our investigations on the throughput with the maximum bandwidth allocated for the packet channel. In these experiments (see [3]) a net bandwidth of over 107 MBit/s was achieved, showing that the maximum bandwidth of 142.8 Mbit/s can be utilized to a large extent (i.e., 75%).
We are currently investigating the performance of the MEP channel in an actual system with development samples of their devices. For our experiments, the boundary was set to 65, leaving a maximum bandwidth of 43.75 Mbit/s for the packet channel. Due to the characteristics of MOST, this bandwidth is not influenced by parallel synchronous or isochronous channels used for the transmission of audio or video streams. However, it is influenced by parallel traffic on the MOST Data Packet (MDP) channel. We did our measurements without (yet) generating parallel traffic on the MDP channel.
The throughput was measured for TCP and UDP with iperf executed on the HU and the rear-seat entertainment unit. For unidirectional traffic, we achieved for TCP a bandwidth of 36 Mbit/s, which is about 82% of the maximum available bandwidth. Because of the protocol overhead of TCP, this is a good rate in comparison with other network technologies such as Ethernet. For UDP, the numbers are slightly lower. For bidirectional traffic, we achieved a similar combined bandwidth for the traffic from the HU to the rear-seat entertainment unit and vice versa. While for UDP the bandwidth in both directions is almost similar, we observed some variations in the bandwidth for TCP, which we are currently investigating.
5. Conclusion and Future Work
In this paper, we described the IP architecture of the next generation of Daimler’s vehicle infotainment systems. The IP architecture provides the basic mechanisms for applications on the infotainment system to access information and services on the Internet. Based on the Ethernet channel of MOST150, all devices in a MOST network are provided with access to the Internet. The mechanisms of the IP architecture provide the flexibility to configure the connections according to the requirements of the IP access or security considerations.
As next steps, the IP architecture of the infotainment system will be integrated more tightly with the IP mechanisms of the user’s mobile devices. To this end, the appropriate standards also on the higher layers need to be supported (see, e.g., [4], [5]). In particular, the use case of of seamlessly integrated mobile consumer devices over WLAN is currently becoming more and more relevant and will have to be supported by vehicle infotainment systems.
Publications
[1] MOST Cooperation: MOST Specification, Rev. 3.0E2, 07/2010,
URL: https://www.mostcooperation.com.
[2] Internet Engineering Task Force (IETF): Request for Comments (RFC) Pages, Web-Site,
URL: https://www.ietf.org/rfc.html.
[3] A. Leonhardi, S. Wachter, M. Bösinger, T. Pech: MOST150’s New Features in a Series Project in Elektronik Automotive, Special issue MOST, pp. 54-56, April 2011.
[4] A. Leonhardi, T. Gschwandtner, R. Hauke, M. Stümpfle: Using UPnP in a MOST Environment, in Elektronik Automotive, Special issue MOST, pp. 38-40, March 2010.
[5] Universal Plug and Play Forum: UPnP Homepage, Web-Site, URL: https://www.upnp.org.
About the authors:
Dr. Alexander Leonhardi is responsible for the system architecture of infotainment systems in the series development Electrical/Electronic Telematics at Daimler AG. He represents Daimler AG in the MOST Cooperation Technical Coordination Committee. He can be reached under Alexander.leonhardi@daimler.com.
Dr. Uwe Walter works in the development Electrical/Electronics unit at Daimler AG on the IP architecture of infotainment systems. uwe.walter@daimler.com.
Rico Hauke is responsible for networking architecture of infotainment systems for the C-Class and E-Class vehicles at Daimler AG. He represents the Daimler AG in the MOST Device Architecture working group. rico.hauke@daimler.com
Marco Maniscalco marco.maniscalco@daimler.com
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