The flexibility of the MOST network has already been proven: differing topologies such as star, chain and tree are equally possible, as are diverse physical layers: polymer optical fiber (POF), coax based electric physical layers as well as shielded or unshielded, twisted copper cables (STP/UTP). The MOST150 Specification Rev. 1.0 for the electric physical layer for MOST150 via coax cable has recently been released. This standard extends the existing optical physical layer for MOST150 in the infotainment domain and opens up new possibilities into vehicle domains like driver assistance, as it allows bi-directional communication and power supply across a single cable. Both physical layers are fully compatible.
MOST is designed as a synchronous network system solution with high bandwidth at nearly no overhead for administrative communication.
The management of synchronous and isochronous streaming connections allows for an appropriate allocation of resources and thus provides access to quality of service (QoS) communication. Concerning the isochronous channel, QoS IP communication is provided as well.
The bandwidth requirements will still be increasing. In addition to USB 3.0 and display link application in driver assistance there will be a need for uncompressed video transmission and sensor fusion.
MOST is committed to a clear definition of a roadmap. MOST Technology is open for future extensions, e.g. considering high bandwidth. The next generation of MOST will enhance the bandwidth into the Gigabit range. This seems to be promising for both optical link and coax links, which are both used today in telecom standards, whereas today´s UTP approach seems to stay in a niche.
Depending on the grade of safety relevance, in driver assistance systems safety aspects need to be considered. For those applications, potential communication failures such as:
- Failure of communication peer
- Unintended message reception
- Message loss
- Message corruption
- Message delay need to be detected safely [4
To this purpose, an adequate safety software layer concept can be introduced. The safety layer is added to one or the other application (Figure 3
). The counter measures are, for example:
- CRC (cyclic redundancy check)
- Sequence counter
- Message length
- Timeout detection
Figure 3: Safety layer concept example
The feasibility of this concept has already been proven by corresponding studies in cooperation with the German TÜV [3
]. MOST150 supports the safety layer concept to enable fail-safe application up to SIL level 3 according to IEC 61508 and ASIL C according to ISO 26262 [4
The latest generation MOST150 already fulfils the requirements to the greatest possible extent. And, as in an infotainment system, the functional system model can be used for internal device communication, so for the application it does not matter whether the communication partner is sitting in the same control unit or connected across the network. Moreover, the network can be mixed with “normal” network nodes without a safety layer.