Functions of the network layer Routing- Router (or gateways)connect independent networks together, network layer routes the packet to their final destination by router gateway) 02 37 DT Data sD2979 D IDT Data SD2309 Router DT Data SDo2 46 入 23 X 9 Router Ring U 61 The above figure shows the case for a computer s communicating with a remote computer D". S and D are the logical addresses of the source and destination computers respectively, where 02 and 79 are the local physical addresses of the source and destination computers respectively 哈工大计算机学院李全龙 Netork Application Development 1: Introduction 26
哈工大计算机学院 李全龙 Network Application Development 1: Introduction 26 Functions of the Network Layer • Routing - Router (or gateways) connect independent networks together, network layer routes the packet to their final destination by router (gateway). F R K L 15 D 78 79 DT Data S D 02 46 DT Data S D 23 09 DT Data S D 29 79 The above figure shows the case for a computer "S" communicating with a remote computer "D". S and D are the logical addresses of the source and destination computers respectively, where 02 and 79 are the local physical addresses of the source and destination computers respectively. T Ring Router Router U X 46 23 61 09 29 S A 02 37 C
Functions of the Transport Layer From session layer To session layer S- PDU S- PDU Transport layer segments segments Transport layer T-PDU T-PDU T-PDU T-PDU T-PDU T-PDU To Network layer From Network layer responsible for source-to-destination(end-to-end delivery of the entire message segmentation occurs and this layer also ensures the whole message arrives intact and in order a logical path can be set up(fixed pathway) between the source and destination for all packets in a message for additional security. This layer has more control over sequencing flow and error detection and correction 哈工大计算机学院李全龙 Netork Application Development 1: Introduction 27
哈工大计算机学院 李全龙 Network Application Development 1: Introduction 27 Functions of the Transport Layer T-PDU S- PDU Transport layer To Network layer From session layer TH TH TH T-PDU T-PDU T-PDU S- PDU Transport layer From Network layer To session layer TH TH TH T-PDU T-PDU segments segments • responsible for source-to-destination (end-to-end) delivery of the entire message • segmentation occurs and this layer also ensures the whole message arrives intact and in order • a logical path can be set up (fixed pathway) between the source and destination for all packets in a message for additional security. • This layer has more control over sequencing, flow and error detection and correction
Functions of the Transport Layer D Transport layer Transport layer Data Data-1 Network Network Data-1 Ixsd Data-2xVS lyer[Data2xy|s回 DT Data-1xyIsIDIDH Data link Data link DT Data-1xy SD DH DT Data-2 x y s DDH layer layer DT Data-2 x y S D DH Internet Segmentation and re-assembly -a message is divided into transmittable segments (can be handled by network layer)each contains a sequence number (for correct re-assembling at the destination) Service-point addressing the transport layer is responsible for the delivery of the entire message to the correct process on the computer that may be running several programs) by including a service-point address(port address)in its header 哈工大计算机学院李全龙 Netork Application Development 1: Introduction 28
哈工大计算机学院 李全龙 Network Application Development 1: Introduction 28 Functions of the Transport Layer Data x y DT Data-1 x y S D DH DT Data-2 x y S D DH Data-1 x y S D Data-2 x y S D Transport layer Network layer Data link layer S Data x y DT Data-1 x y S D DH DT Data-2 x y S D DH Data-1 x y S D Data-2 x y S D Transport layer Network layer Data link layer D Internet • Segmentation and re-assembly - A message is divided into transmittable segments (can be handled by network layer) each contains a sequence number (for correct re-assembling at the destination). • Service-point addressing - the transport layer is responsible for the delivery of the entire message to the correct process on the computer ( that may be running several programs) by including a service-point address (port address) in its header
Functions of the Transport Layer Connection control The transport layer can be either connectionless or connection-oriented. a connectionless transport layer deliver each segments as an independent packet to the destination a connection oriented transport layer firstly makes a connection with the transport layer at the destination, then deliver the packets and after all data are transferred without error the connection is terminated Flow control -Transport layer perform end to end flow control which differs from the data link layer which is responsible for flow control in single link Error control The transport layer performs end to end error control which make sure the entire message arrives at the receiving transport layer without error(damage, loss or duplication). Error correction is done by re-transmission 哈工大计算机学院李全龙 Netork Application Development 1: Introduction 29
哈工大计算机学院 李全龙 Network Application Development 1: Introduction 29 Functions of the Transport Layer • Connection control - The transport layer can be either connectionless or connection-oriented. A connectionless transport layer deliver each segments as an independent packet to the destination. A connectionoriented transport layer firstly makes a connection with the transport layer at the destination, then deliver the packets and after all data are transferred without error, the connection is terminated. • Flow control - Transport layer perform end to end flow control which differs from the data link layer which is responsible for flow control in single link. • Error control - The transport layer performs end to end error control which make sure the entire message arrives at the receiving transport layer without error (damage, loss or duplication). Error correction is done by re-transmission
Functions of the Session Layer From Presentation layer To Presentation layer - PDU P- PDU ession Session layer laver SH syn syn S-PDU S-PDU To transport layer From transport layer The session layer is the network dialog controlling. It establishes, maintains, and synchronizes the interaction between communication systems. Dialog control -The session layer allows two systems to enter into a dialog. The communication between two processes can be controlled in either half-duplex (one way at a time or full-duplex(two ways at a time) Synchronization -The session layer allows a process to add checkpoints(synchronization points) into a stream of data, when data loss during transmission occurred, more efficient re-transmission can be performed 哈工大计算机学院李全龙 Netork Application Development 1: Introduction 30
哈工大计算机学院 李全龙 Network Application Development 1: Introduction 30 Functions of the Session Layer S-PDU P- PDU To transport layer From Presentation layer SH Session layer syn syn syn S-PDU P- PDU From transport layer To Presentation layer SH Session layer syn syn syn • Dialog control - The session layer allows two systems to enter into a dialog. The communication between two processes can be controlled in either half-duplex (one way at a time) or full-duplex (two ways at a time). The session layer is the network dialog controlling. It establishes, maintains, and synchronizes the interaction between communication systems. • Synchronization - The session layer allows a process to add checkpoints (synchronization points) into a stream of data, when data loss during transmission occurred, more efficient re-transmission can be performed