1 Chap. 2 Protocol

2 Communication model Simplified communication model  source node  gather data from sensor or switch using ADC (analog-to-digital converter) or external interrupt  generate digital binary data  generate frame by adding source/destination address and error detection code

3  transmitter  covert into electro-magnetic signal to transmit frame via transmission medium  transmission system  transmission medium  point-to-point link vs. network link or multi-point link  receiver  covert into binary data  destination node  check error  transmit acknowledgement

4 Communication function Segmentation and reassembly Message formatting Signal generation and encoding Transmission medium Interface Topology Addressing Flow control Error detection and error control Medium access control

5 Protocol and standard Need for protocol  Rules for communications between communication nodes  Communication nodes  computer  controller, sensor, actuator  robot, NC machine  Must speak the same language for successful communications successful transmissionunsuccessful transmission

6 Standard  Required to allow for interoperability between communication nodes  de facto standard vs. de jure standard  de facto standard or voluntary standard ( 임의 표준 ) : TCP/IP  de jure standard or regulatory standard ( 규제적 표준 ) : IEEE  unique standard vs. multiple standard

7  International Standards Organization  ISO (International Organization for Standards)  ISO8802  IEEE (Institute of Electrical and Electronics Engineers)  IEEE 802.3, IEEE  EIA (Electronics Industries Association)  EIA-232, EIA-485

8 Layer architecture Why?  Communications is a complex task, too complex for single unit  Better if task broken into subtasks  implemented separately in layers in stack  Structured design breaks down problem into smaller units; modules  each layer provides functions needed to perform communication for layers above  using functions provided by layers below

9 Advantage of layer architecture  If each layer’s functions are well defined  each layer’s standardization is performed separately and rapidly  If boundary between layers is well defined  one layer does not affect the other layers  development of new protocol for specific layer is possible without change of the other layers  If service between services  vendor can develop software for specific layer without consideration of the other layers  interface between upper and lower layers is not problem

10 Logical connection between layers  connection  physical connected between lowest layer (layer 1)  logical connected between upper layer (layer N)  PDU (protocol data unit)  segmentation  overhead : header, trailer  frame

11 Consideration of the number of layer  advantage of layer architecture  many !  disadvantage of layer architecture  overhead per each layer  waste of transmission capacity  the number of layer  to simplify protocol  to minimize overhead of frame

12 OSI RM (Open System Interconnection, Reference Model Developed by the International Organization for Standardization (ISO) Seven layer Architecture Each layer performs a subset of the required communication functions

13 Physical  Transmission of electromagnetic signal via transmission medium  transmission medium, connector  encoding  interface : mechanical, electrical, functional, procedural specification Data Link  Activating, maintaining, and deactivating a reliable data transmission between point-to-point link  message formatting, addressing, flow control, error control, medium access control

14 Network  If two node are connected to different network, network & transport layer are necessary  Transmission of frame from source to destination  connection control, routing Transport  Exchange of data for error free transmission between end systems  flow control, error control between end systems

15 Session  Control of dialogues between applications  dialog control, synchronization Presentation  Information such as encryption, compression Application  Means for applications to access network services  Service  read service, write service, notification service

16 3 layer architecture for embedded network system