Functions of the physical layer From data link layer To data link layer DL-PDU DL - PDU Physical lyer101010101111 Physical 10101010111101 layer m今 Physical characteristics of interfaces and media - interface between the devices and the transmission medium(e.g network card). It also defines the type of transmission medium(e.g.wire Representation of bits -encoding the bit(0s and 1s)into electrical or optical signals. This layer also defines the type of encoding(e.g. ASK or FSK) Data rate- the transmission rate in term of number of bit sent each second (e.g. 56 Kb/s Synchronization of bits- the sender and the receiver clocks must be synchronized 哈工大计算机学院李全龙 Netork Application Development 1: Introduction 21
哈工大计算机学院 李全龙 Network Application Development 1: Introduction 21 Functions of the Physical Layer 10101010111101 DL - PDU From data link layer Physical layer 10101010111101 DL - PDU To data link layer Physical layer • Physical characteristics of interfaces and media - interface between the devices and the transmission medium (e.g. network card). It also defines the type of transmission medium (e.g. wire) • Representation of bits - encoding the bit (0s and 1s ) into electrical or optical signals. This layer also defines the type of encoding (e.g. ASK or FSK) • Data rate - the transmission rate in term of number of bit sent each second (e.g. 56 Kb/s) • Synchronization of bits - the sender and the receiver clocks must be synchronized
Functions of the physical layer Line confiquration the connection of devices to the medium (point-to-point or multipoint configuration) Physical topology the configuration for the devices to be connected to form a network(mesh topology, star topology, ring topology or bus topology) Transmission mode the physical layer also defines the direction of transmission between two devices: Simplex, half duplex, or full-duplex Example for the physical layer protocol RS-232 哈工大计算机学院李全龙 Netork Application Development 1: Introduction 22
哈工大计算机学院 李全龙 Network Application Development 1: Introduction 22 Functions of the Physical Layer • Line configuration - the connection of devices to the medium (point-to-point or multipoint configuration) • Physical topology - the configuration for the devices to be connected to form a network (mesh topology, star topology, ring topology or bus topology) • Transmission mode - The physical layer also defines the direction of transmission between two devices: Simplex, halfduplex, or full-duplex Example for the physical layer protocol: • RS-232
Functions of the data link layer rom network layer To network layer N-PDU N-PDU Data Data link DH Frame Frame DT link lay er layer 10101010111101 10101010111101 To physical layer From physical layer The data link layer is responsible for node-to-node delivery, it makes the physical layer appear error free to the upper layer (network layer). It also take care of the following functions: Framing The data link layer divides the stream of bits received from the network layer into manageable data units called frames Physical addressing- the data link layer adds a header to the frame to define the physical address of the sender(source address) and/or receiver(destination address)of the frame 哈工大计算机学院李全龙 Netork Application Development 1: Introduction 23
哈工大计算机学院 李全龙 Network Application Development 1: Introduction 23 Functions of the Data Link Layer 10101010111101 DT DH N - PDU Data link layer Frame To physical layer From network layer 10101010111101 DT DH N - PDU Data link layer Frame From physical layer To network layer The data link layer is responsible for node-to-node delivery, it makes the physical layer appear error free to the upper layer (network layer). It also take care of the following functions: • Framing - The data link layer divides the stream of bits received from the network layer into manageable data units called frames • Physical addressing - the data link layer adds a header to the frame to define the physical address of the sender (source address) and/or receiver (destination address) of the frame
Functions of the data link layer 20 25 62 DT Data 62 Trailer Source address destination address Flow control -If the rate at which the data are absorbed by the receiver is less than the rate produced in the sender, the data link layer will impose a flow control mechanism to prevent overwhelming the receiver Error control mechanism that can detect and retransmit damaged or lost frames and also prevent duplication of frames. Error control is normally achieved by the trailer at the end of the frame Access control- When one or more devices are connected to the same link, data link layer protocols are necessary to determine which device has control over the link at any given time 哈工大计算机学院李全龙 Netork Application Development 1: Introduction 24
哈工大计算机学院 李全龙 Network Application Development 1: Introduction 24 Functions of the Data Link Layer 20 25 32 48 62 DT Data 20 62 Trailer Source address destination address • Flow control - If the rate at which the data are absorbed by the receiver is less than the rate produced in the sender, the data link layer will impose a flow control mechanism to prevent overwhelming the receiver • Error control - mechanism that can detect and retransmit damaged or lost frames and also prevent duplication of frames. Error control is normally achieved by the trailer at the end of the frame • Access control - When one or more devices are connected to the same link, data link layer protocols are necessary to determine which device has control over the link at any given time
Functions of the Network Layer From transport layer To transport layer T-PDU T- PDU Network Network layer pacl packet NH layer N-PDU N-PDU To data link layer From data link layer The network layer is responsible for the source-to-destination delivery of a packet possibly across multiple networks, if two systems are connected to the same link, no need for a network layer The functions of a network layer are Logical addressing-the network layer adds a header to the incoming packet from the upper layer with a logical address of the sender. If a packet passes the network boundary, this universal (logical) address helps to distinguish whether the packet belong to the source or destination systems 哈工大计算机学院李全龙 Netork Application Development 1: Introduction 25
哈工大计算机学院 李全龙 Network Application Development 1: Introduction 25 Functions of the Network Layer N-PDU NH T- PDU Network layer packet To data link layer From transport layer N-PDU NH T- PDU Network layer packet From data link layer To transport layer • Logical addressing - the network layer adds a header to the incoming packet from the upper layer with a logical address of the sender. If a packet passes the network boundary, this universal (logical) address helps to distinguish whether the packet belong to the source or destination systems The network layer is responsible for the source-to-destination delivery of a packet possibly across multiple networks, if two systems are connected to the same link, no need for a network layer. The functions of a network layer are: