## 2 Related Works
### A Design of an In-Vehicle Gateway Module (In-VGM)  
The data types collected from the in-vehicle sensors are diverse. The existing CAN protocol has limits on transmission capacity and speed. However, even if the FlexRay and MOST protocol ensuring high communication speed, the exact transmission time is used instead of the CAN, as they might also have another problems such as cost and compatibility. Therefore, this paper proposes the dedicated In-VGM which integrates the CAN, FlexRay, and MOST protocol to solve compatibility and distributed data transmission and ensures reliable and real time communication by transforming various types of messages into a message type of a destination protocol. The existing in-vehicle gateway protocols like CAN, FlexRay, and MOST have the following problems. * First, they do not use a multi-directional network. * Second, they are inefficient and lack the overhead to transform messages in various protocols. * Third, they have a transmission delay because they have no priority protocol in place to hierarchize individual messages in transferring multiple messages. * Fourth, they do not ensure compatibility because an autonomous vehicle collects unstructured data like image, radar, and video. However, the In-VGM proposed in this paper has the following functions to solve the above problems. * First, it allocates ID to a CAN bus interface which collects and transfers the general sensing data of vehicles and to a FlexRay-CAN bus interface that collects and transfers the emergent sensing data of vehicles and to the MOST bus interface, which collects and transfers media data. It has a bus architecture connecting the interfaces. * Second, it supports a multi-directional network because the mapping table with message transformation information is used for it. * Third, it provides a priority based transmission mode to increases the transmission efficiency of messages based on an event and to reduce the transmission delay of important messages. * Fourth, it uses an inner scheduler to reduce the transmission delay. The In-VGM works as follows. * First, the in-vehicle data is classified into general sensing data, emergent sensing data, control system and sensor data, media data, and OBD data. The CAN, FlexRay, and MOST protocols are used according to the importance and classification of data. The Bus architecture of the In-VGM is shown in Figure 4.
* Second, the data collected and transferred in the sensor and control system is transferred to the In-VGM through the CAN, FlexRay, and MOST protocols. At this time, the In-VGM allocates ID according to a sending and receiving CAN, FlexRay, and MOST protocol. The kinds of IDs are shown in Table 1.
* Third, the source and destination protocol ID of the transmission data are recorded in a mapping table and transmission paths are set on the basis of the ID. If the transmission paths are set, the transmission message type is transformed into a message type of a destination protocol by using the mapping table. * Fourth, because the size of data collected and transferred by the FlexRay and MOST is very big, compared to that of the CAN, the header information like Start Message Delimiter, Length of message, and Identifier is to be added to every CAN Fragment so that the FlexRay and MOST data can be transferred to the CAN protocol. The Header information has a maximum of 35 bits. In a multi-directional network environment, because the number of the headers gets larger in proportion to the number of the CAN fragments, the CAN has overhead. If the CAN message type is transformed into a message type of the FlexRay or the MOST protocol, the problem is that all the messages are not transferred because of the overhead of the headers. To solve the problem, the ID of the proposed CAN Fragment Header, instead of the Priority and Service type of the existing CAN fragment Header, is proposed and the Sequential Number of the proposed CAN Fragment Header instead of the Request, Destination ID, Service, and Source ID of the existing CAN Fragment Header is proposed.