29-05-2012, 12:48 PM
The Reference model of data communication
[attachment=23320]
Introduction
Today, the main reference for most present day protocol specification is the ISO/OSI “reference
model” of data communication devised by the International Standardization Organization (ISO)
to support the development and implementation of open communication protocols.
According to OSI model, data communication systems are described as a hierarchical model
consisting of seven layers of different functionality. A communication layer instance provides its
service to layer instance immediately above it and uses the services of the instance immediately
below it, without the need for knowledge of the any other lower layers. The functionalities of all
lower layers are hidden and completely transparent for higher layers.
1. Peer entities communicate with each other by following a set of agreed rules, known as
peer to peer protocols.
2. Each layer passes data to the layer below in the form of a so called “SDU” (service
data unit).
3. The lower layer adds its own “PROTOCOL CONTROL INFORMATION”(PCI) to the
received SDU
4. The new SDU is passed to the next lower layer, and so on down to the physical layer.
5. The physical layer then has a physically transmittable PDU. This data is called “frame”
which is transmitted.
6. The remote end where the data is received is remote system(s).
7. The received frame is passed up through the layered structure of the receiving system.
8. Each PCI header is stripped off at its respective layers. The information contained in the
various PCI header determines how an individual layer responds to the SDU’s which it
receives from or passes to the next higher layer.
Each layer is aware of its immediate adjacent layer above and below, and generally passes on
SDU’s without modification or understanding it.
Node –Oriented Protocol:
With this type of protocol, the exchange of data between two or more nodes is based on node
addressing.
1. The data frames transmitted over the communication medium contain the target and
sometimes the source address of the nodes involved as well.
2. Thus, a frame is sent to a specific node or a group of nodes.
3. Special addresses are reserved for transmission of frames which are addressed to a group
of nodes or to all nodes (broadcasting).
4. Node oriented frame transmission not only requires specification of the receiving node
but also the specification of the content to be transmitted frame within the frame.
5. Node oriented communication is the basis of connection oriented, confirmed data
communication. Almost all the conventional data communication systems are based on
this principle.
Message –Oriented Protocol:
With this class of protocol, exchange of data is based on the frame or message identifier.
1. A message transmitted by a node identified itself with a specific unique identifier
(message identifier).
2. The target address of a message is not defined.
3. All the nodes in the network receive the data, and the nodes decide whether to accept the
data or to discard it.
4. Thus a message can be accepted by one or more nodes or none of the nodes in the
network.
5. The transmitter or the node that generated the data, does not know who the receiver of its
message is, Confirmed message exchange is not possible.
6. Message oriented protocol implements a principle of “ERROR SIGNALING” instead of
“ACKNOWLEDGEMENT PRINCIPLE”.
7. All the data communication systems in the cars, except those for transfer of high volume
data are based on message oriented protocol.
Introduction
What is the Controller Area Network (CAN)?
• Two-wire multi-transmitter serial data bus
• Designed by Bosch as automobile network
• Configurable data rate (5 kBit/s ... 1MBit/s)
• Bus length 0.2m to 10.000m (with linear data rate reduction)
• Real time capabilities (guaranteed transmission times)
• Message oriented transmission (2031 message identifiers)
• Network wide data consistency through broadcasting principle
• > 200 bus masters
[attachment=23320]
Introduction
Today, the main reference for most present day protocol specification is the ISO/OSI “reference
model” of data communication devised by the International Standardization Organization (ISO)
to support the development and implementation of open communication protocols.
According to OSI model, data communication systems are described as a hierarchical model
consisting of seven layers of different functionality. A communication layer instance provides its
service to layer instance immediately above it and uses the services of the instance immediately
below it, without the need for knowledge of the any other lower layers. The functionalities of all
lower layers are hidden and completely transparent for higher layers.
1. Peer entities communicate with each other by following a set of agreed rules, known as
peer to peer protocols.
2. Each layer passes data to the layer below in the form of a so called “SDU” (service
data unit).
3. The lower layer adds its own “PROTOCOL CONTROL INFORMATION”(PCI) to the
received SDU
4. The new SDU is passed to the next lower layer, and so on down to the physical layer.
5. The physical layer then has a physically transmittable PDU. This data is called “frame”
which is transmitted.
6. The remote end where the data is received is remote system(s).
7. The received frame is passed up through the layered structure of the receiving system.
8. Each PCI header is stripped off at its respective layers. The information contained in the
various PCI header determines how an individual layer responds to the SDU’s which it
receives from or passes to the next higher layer.
Each layer is aware of its immediate adjacent layer above and below, and generally passes on
SDU’s without modification or understanding it.
Node –Oriented Protocol:
With this type of protocol, the exchange of data between two or more nodes is based on node
addressing.
1. The data frames transmitted over the communication medium contain the target and
sometimes the source address of the nodes involved as well.
2. Thus, a frame is sent to a specific node or a group of nodes.
3. Special addresses are reserved for transmission of frames which are addressed to a group
of nodes or to all nodes (broadcasting).
4. Node oriented frame transmission not only requires specification of the receiving node
but also the specification of the content to be transmitted frame within the frame.
5. Node oriented communication is the basis of connection oriented, confirmed data
communication. Almost all the conventional data communication systems are based on
this principle.
Message –Oriented Protocol:
With this class of protocol, exchange of data is based on the frame or message identifier.
1. A message transmitted by a node identified itself with a specific unique identifier
(message identifier).
2. The target address of a message is not defined.
3. All the nodes in the network receive the data, and the nodes decide whether to accept the
data or to discard it.
4. Thus a message can be accepted by one or more nodes or none of the nodes in the
network.
5. The transmitter or the node that generated the data, does not know who the receiver of its
message is, Confirmed message exchange is not possible.
6. Message oriented protocol implements a principle of “ERROR SIGNALING” instead of
“ACKNOWLEDGEMENT PRINCIPLE”.
7. All the data communication systems in the cars, except those for transfer of high volume
data are based on message oriented protocol.
Introduction
What is the Controller Area Network (CAN)?
• Two-wire multi-transmitter serial data bus
• Designed by Bosch as automobile network
• Configurable data rate (5 kBit/s ... 1MBit/s)
• Bus length 0.2m to 10.000m (with linear data rate reduction)
• Real time capabilities (guaranteed transmission times)
• Message oriented transmission (2031 message identifiers)
• Network wide data consistency through broadcasting principle
• > 200 bus masters