BASIC PRINCIPLES OF NETWORKING
NETWORK TOPOLOGY
• A network is understood to be a system
in which a group of elements can exchange information via
a transportation medium.
• In motor vehicles, complex control units such as those for
the engine management system (electronic diesel control,
EDC), the electronic stability program (ESP), the
transmission control system or the door modules can be
network subscribers
• However, a sensor with a conditioning circuit that merely
prepares and digitizes a measured value can also act as a
network subscriber and make the measured signals
available to other network subscribers
• The transport medium via which the communication takes
place is referred to as a bus or a data bus.
Network Topology
BUS TOPOLOGY STAR TOPOLOGY
Network Topology
RING TOPOLOGY MESH TOPOLOGY
Network Organization- Addressing
• In order to make it possible to transmit messages via a network and
evaluate the contents thereof, the useful data (payload) that is
transmitted is also accompanied by data transfer information.
• Subscriber-oriented method
• The data is exchanged on the basis of node addresses.
• The message sent by the transmitter contains the data to be transmitted
and also the destination node address
• All receivers compare the transmitter receiver address to their own
address, and only the receiver with the
• Message Oriented Method
• In this method it is not the receiver node that is addressed, but the
message itself
• Depending on the content of the message, it is identified by a message
identifier that has been predefined for
this message type.
Network Organization- Addressing
• In this method, the transmitter does not need to know anything
about the destination of the message, since each individual
receiver node decides whether or not to process the message.
• Of course, the message can be received and evaluated by
several nodes.
Network Organization- Bus Access
• A node must access the bus in order to transmit a
message
Time division multiple access (TDMA)
• TDMA is a deterministic (predictive) access method. In this case
each node is as- signed a time window in which it is allowed to
transmit (a priori). A fixed schedule is therefore required for the
network
Master-slave
• In the master-slave system, one node
on the network operates as the master. This node determines
the communication frequency by interrogating its subordinate
nodes (slaves). A slave only replies if it is spoken to by the
master.
• Ex: LIN
Multimaster
• In a Multimaster network, several nodes can access the
transport medium independently without the assistance of
another node.
• Bus access is uncontrolled. Every node can access the bus and
transmit a message if the bus appears to be free.
• This means that each node is its own master, and that any node
can start a message transfer with equal status.
• However, this also means that collision detection and handling
methods have to be in place.
• EX: CAN , Ethernet
Control Mechanisms
Event Control- In an event-driven bus system, messages are
transmitted as soon as an event that triggers the transmission of
a message has occurred
• Pressing a button on the air conditioning system control panel
• Operating the hazard warning flasher switch
• Incoming message that requires a reaction (e.g. information from rpm
sensor to speedometer needle motor)
• Expiration of a fixed time period (time frame, e.g. 100 ms), after which
messages are transmitted cyclically
• Since the stations are not synchronized with each other,
situations where several stations wish to access the bus
simultaneously are unavoidable. In order to allow a message to
be transmitted without falsification, only one station at a time
can transmit data on the bus.
• Collision avoidance mechanisms are available for preventing
or solving bus conflicts.
Event Triggered
• If a node wishes to transmit a
message whilst the bus is
occupied, the transmission is
delayed
Event Triggered
Advantages
• High level of flexibility and capability of retrofitting new nodes in
the network. Good response time to asynchronous external
events.
• Bus usage depending on event frequency in line with
requirements
• No network loading by unused events, since only events that
have actually occurred trigger a transmission
Disadvantages
• Static bus occupancy, non-deterministic (i.e. not possible to
prove that a message was transmitted at the right time)
Timer Control
• dynamic driving systems such as brakes and steering, an
increasing number of mechanical and hydraulic
components are being replaced with electronic systems
• steering column are becoming superfluous, and the
functionality thereof is being taken over by sensors and
actuators
• The reliability, safety and failure tolerance requirements of
these systems are extremely high.
• Messages must be received on time
• The latency time of critical messages must be extremely small
• The system must have a redundant design
• The failure of a node must affect the rest of the system as little
as possible
Timer Control
• All transmissions are processed sequentially in accordance
with the network planning (without collisions).
• Once each node has transmitted its message, the cycle re-
starts with the first transmitter.
• This makes it possible to determine how chronologically
up-to-date the data is at any time.
• Since missing messages are detected immediately, time-
triggered concepts are more reliable than event-driven
systems.
Timer Control
Advantages
• Deterministic system
• Punctual data transmission
• Reliable detection and isolation
of defective network nodes
Disadvantages
• Overall system must be planned
for distributed developments
• Capacity for expanding the
communication system must be
planned in
Bus Systems in Vehicles
Bus Systems in Vehicles
AUTOMOTIVE NETWORKING
Automotive Networking
AUTOMOTIVE NETWORKING
• Cross-system functions
Choice of a bus- Parameters
Parameters that decide the choice of a bus
• Data transfer rate
• Interference immunity
• Real-time capability - The antilock brake system (ABS) must
react to the incipient locking of a wheel within a few milliseconds
(wheel speed reduction), whereas response times of 100 ms are
adequate for actuating the power-window motor. Human beings
cannot perceive delay periods of less than 100 ms.
• Number of network nodes : Mercedes S class has more than
60 ECUs connected on CAN
Classification of bus systems
Classification of Bus Systems
Vehicle Clusters
• Power Train
• Chassis
• Body (Comfort)
• Telematics/Wireless
• Passive safety
• Active Safety
Coupling of Networks
Network with Central gateway Network with distributed
gateways
Networked Vehicles- Topology (Compact Class)
Networked Vehicles- Topology (Luxury Class)
Networked Vehicles
• Topology
• Signal Transmission
• Signal Types
• Resolution
• Output
• Multimedia data
• Different Applications need different speeds
Bus systems/Protocols
• CAN Bus
• LIN Bus
• Bluetooth
• MOST Bus
• TTP
• FlexRay
• Diagnostic Interfaces
