What's a protocol? Key elements of a protocol u Used for communications between entities in a system Data formats Must speak the same language a Entities Signal level otocols define format, order a Semantics e-mail facilitie f mmsgs sent and received Control information among network entities, and actions taken on msg Error handling transmmission, receipt Timing Terminal Speed matching Remote senso Sequencing Protocol Functions The OSI Mode Encapsulation ms Interconnection(osr)model is defined by Segmentation and reassembly ernational Standard Organization (ISO)in 1984 a To open communication between different systems without changing the underlying architecture (software and hardware) Ordered delivery O An international standard that referenced by most network Error control a Best tools for teaching people about sending and receiving data a network. Multiplexing a Transmission services particular network function, This separation networking functions is called layering. Data flow and Peer communication in sI ay 7 layers of OSI model Advantages of multi-layered Layer 6: Presentation a Reduce complexity-simplified o Standardize interface ion6 Laver 4 o Allow communication between different network hardware 15 Layer 3 Layer 2: Data lin D A layer provide service for the layer above it3 哈工大计算机学院 李全龙 Network Application Development 1: Introduction 13 What’s a protocol? „ Used for communications between entities in a system „ Must speak the same language „ Entities „ User applications „ e-mail facilities „ terminals „ Systems „ Computer „ Terminal „ Remote sensor protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt 哈工大计算机学院 李全龙 Network Application Development 1: Introduction 14 Key Elements of a Protocol „ Syntax „ Data formats „ Signal levels „ Semantics „ Control information „ Error handling „ Timing „ Speed matching „ Sequencing 哈工大计算机学院 李全龙 Network Application Development 1: Introduction 15 Protocol Functions „ Encapsulation „ Segmentation and reassembly „ Connection control „ Ordered delivery „ Flow control „ Error control „ Addressing „ Multiplexing „ Transmission services 哈工大计算机学院 李全龙 Network Application Development 1: Introduction 16 The OSI Model ˆ The Open Systems Interconnection (OSI) model is defined by International Standard Organization (ISO) in 1984. ˆ To open communication between different systems without changing the underlying architecture (software and hardware). ˆ An international standard that referenced by most network vendors for their products and services ˆ Best tools for teaching people about sending and receiving data on a network. ˆ Consist of seven layers: Physical (layer 1), data link (layer 2), Network (layer 3), Transport (layer 4), Session (layer 5), Presentation (layer 6) and Application (layer 7). Each of the layer illustrates a particular network function. This separation of networking functions is called layering. 哈工大计算机学院 李全龙 Network Application Development 1: Introduction 17 7 layers of OSI model Application Presentation Session Transport Network Data link Physical Layer 7: Layer 6: Layer 5: Layer 4: Layer 3: Layer 2: Layer 1: ˆ Advantages of multi-layered model ˆ Reduce complexity - simplified teaching and learning ˆ Standardize interface ˆ Allow communication between different network hardware and software ˆ Prevent the change of one layer from affecting the other layers ˆ Accelerate Evolution Some Characteristics for the 7-layer model ˆ Peer-to-peer process - layer N of one computer (device) can communicate with layer N on another computer (device) through protocols of that layer. ˆ A layer provide service for the layer above it 哈工大计算机学院 李全龙 Network Application Development 1: Introduction 18 Data flow and Peer communication in OSI layers Application Presentation Session Transport Network Data link Physical 7 6 5 4 3 2 1 Network Data link Data link Physical Physical Application Presentation Session Transport Network Data link Physical 7 6 5 4 3 2 1 PC 1 Intermediate PC 2 node link link For PC1 sends a message to PC2 Physical medium Physical medium Transport-layer protocol Session-layer protocol Presentation-layer protocol Application-layer protocol Data flow Peer communication within layer