The ISO OSI Reference Model CHAPTER1 The ISO OSI Reference Model Host A Host B Application Data Link Presentation Network Physical Session Transport Physical Medium Sami S.Al-Wakeel Sami S.Al-Wakeel

The ISO OSI Reference Model CHAPTER1 The ISO OSI Reference Model Application Data Link Presentation Network Physical Session Transport Physical Medium Host A Host B Interface Sami S.Al-Wakeel Sami S.Al-Wakeel

The ISO OSI Reference Model CHAPTER1 The ISO OSI Reference Model Application Data Link Presentation Network Physical Session Transport Physical Medium Host A Host B Protocol Layer 7 Protocol Layer 6 Protocol Layer 5 Protocol Layer 4 Protocol Layer 3 Protocol Layer 2 Protocol Layer 1 Protocol Sami S.Al-Wakeel Sami S.Al-Wakeel

The ISO OSI Reference Model CHAPTER1 The ISO OSI Reference Model Application Data Link Presentation Network Physical Session Transport Physical Medium Layer 7 Protocol Layer 1 Protocol Layer 2 Protocol Layer 3 Protocol Layer 4 Protocol Layer 5 Protocol Layer 6 Protocol Layer 6/7 Interface Layer 5/6 Interface Layer 4/5 Interface Layer 3/4 Interface Layer 2/3 Interface Layer 1/2 Interface Host A Host B Sami S.Al-Wakeel Sami S.Al-Wakeel

The ISO OSI Reference Model CHAPTER1 The ISO OSI Reference Model Interface: It defines which primitive operations and services the lower layer offers to the upper layer. Peer: The similar layer on a different machine. Protocol: It is a set of rules and conventions used by the layer to communicate with similar peer layer in another (remote) system. The peer processes communicate with each other using a protocol. A set of layers and protocols is called a network architecture. Sami S.Al-Wakeel Sami S.Al-Wakeel

The ISO OSI Reference Model Sami S.Al-Wakeel

The ISO OSI Reference Model CHAPTER1 The ISO OSI Reference Model In reality, no data are directly transferred from layer i on one machine to layer i on another machine. Instead, each layer passes data and control information to the layer immediately below it, until the lowest layer is reached. Below layer 1 is the physical medium through which actual communication occurs. Send-To-Other-side ( ) Get-From-Other-side ( ) Protocol (Virtual Communication) Host A Host B Layer i Sami S.Al-Wakeel Sami S.Al-Wakeel

The ISO OSI Reference Model CHAPTER1 The ISO OSI Reference Model Sami S.Al-Wakeel Sami S.Al-Wakeel

The ISO OSI Reference Model CHAPTER1 The ISO OSI Reference Model Host A Host B Layer 7 Protocol Application Application Data Link Presentation Network Physical Session Transport Layer 6 Protocol Presentation Layer 5 Protocol Session Layer 4 Protocol Transport Network Network Network Data Link Data Link Data Link Physical Physical Physical Sami S.Al-Wakeel Sami S.Al-Wakeel

The ISO OSI Reference Model CHAPTER1 The ISO OSI Reference Model Information Flow: Source machine Destination machine m Layer 7 Protocol m M M Layer 6 Protocol M M Layer 5 Protocol M2 H4 M2 H4 Layer 4 Protocol M2 H4 H3 M2 H4 H3 Layer 3 Protocol M2 H4 H3 H2 T2 M2 H4 H3 H2 T2 Layer 2 Protocol Sami S.Al-Wakeel Sami S.Al-Wakeel

The ISO OSI Reference Model CHAPTER1 The ISO OSI Reference Model 1. The Physical Layer: It concerns with transmitting raw bits over a communication channel. Voltage Levels for 0 and 1. Connectors: Number of bins and purpose of each bin. Transmission Media. Attenuation and Distortion. Analog PSTN Circuits and Digital Leased Circuits. Sami S.Al-Wakeel Sami S.Al-Wakeel

The ISO OSI Reference Model CHAPTER1 The ISO OSI Reference Model 2. The Data Link Layer: The main task of the data link layer is to take a raw transmission facility and transform it into a line that appears free of transmission errors to the network layer. Point-to-point error control: If a frame is destroyed, the data link layer retransmits the frame. If an acknowledgement frames is lost, a duplicate frame is produced. Destination Source Frame Acknowledgement Sami S.Al-Wakeel Sami S.Al-Wakeel

The ISO OSI Reference Model CHAPTER1 The ISO OSI Reference Model 2. The Data Link Layer: Point-to-point flow control: Some regulation mechanism must be employed to let the transmitter know how much buffer space the receiver has at the moment. This is to prevent a fast transmitter from drowning a slow receiver in data. Framing: It creates and recognizes frame boundaries. STX Message ETX Sami S.Al-Wakeel Sami S.Al-Wakeel

The ISO OSI Reference Model CHAPTER1 The ISO OSI Reference Model 3. The Network Layer: Routing: It determines how packets are routed from source to destination. Congestion Control: Many packets in the subnet trying to use the same route. Internetworking: It allows heterogeneous networks to be interconnected. Accounting Function. Sami S.Al-Wakeel Sami S.Al-Wakeel

The ISO OSI Reference Model CHAPTER1 The ISO OSI Reference Model 4. The Transport Layer: It acts as interface between the higher application oriented layers and the network dependent protocol layers. Disassembling and Reassembling: It accepts data from a session layer, split it up to smaller units if needed, pass these to the network layer, and ensure that the pieces all arrive correctly at the other end. End-to-end error control. End-to-end flow control. Sami S.Al-Wakeel Sami S.Al-Wakeel

The ISO OSI Reference Model CHAPTER1 The ISO OSI Reference Model 4. The Transport Layer: It defines Quality of Service (QOS). There are five classes of service ranging from 0, which provides only basic functions needed for connection establishment and data transfer, to class 4, which provides full error and flow control procedures. It is an end-to-end layer. Lower layers communicate with intermediate nodes. Sami S.Al-Wakeel Sami S.Al-Wakeel

The ISO OSI Reference Model CHAPTER1 The ISO OSI Reference Model 5. The Session Layer: It allows users on different machines to establish sessions between them. Interaction Management: The data exchange associated with a dialog may be: Duplex: Two-way simultaneous. Half-Duplex: Two-way alternate. Simplex: One-way. Synchronization: For lengthy transaction, the user may choose to establish synchronization points associated with the transfer. If a fault develops during a transaction, the dialog may be restarted at an agreed synchronization point. Sami S.Al-Wakeel Sami S.Al-Wakeel

The ISO OSI Reference Model CHAPTER1 The ISO OSI Reference Model 6. The Presentation Layer: It converts from a code used by a computer to a standard network code. Different computers have different codes for representing characters (e.g., ASCII and EBCDIC), integers (e.g., one’s complement and two’s complements), and so on. Data Compression. Data Encryption. Sami S.Al-Wakeel Sami S.Al-Wakeel

The ISO OSI Reference Model CHAPTER1 The ISO OSI Reference Model 7. The Application Layer: The application layer contains a variety of protocols that are commonly needed. It handles the incompatibilities on the different machines. Sami S.Al-Wakeel Sami S.Al-Wakeel

Data transmission in OSI Reference Model CHAPTER1 Data transmission in OSI Reference Model Application Data Link Presentation Network Physical Session Transport Receiving Process Sending Process Data Data AH Data PH Data SH Data TH Data NH Data DH DT Bits Sami S.Al-Wakeel Sami S.Al-Wakeel