University:
York University
Course:
AP/ITEC 1610 | Introduction to Computer Programming
Academic year:

2023
Views:

58

Pages:

3
Author:

Nick T.

TRANSPORT LAYER Transport Layer: provide logical communication between application processes running on different hosts -> Sender: breaks application messages into segments, passes them to the network layer -> Receiver: Reassembles segments into messages, passes to application layer Multiplexing/Demultiplexing: Multiplexing at Sender: Handle data from multiple sockets, add transport header Demultiplexing: Host receives Network datagram (Source IP, dest IP) Each data gram carries one segment Uses IP+ port to direct segment to correct socket TCP demultiplexing: receiver uses src IP, src port, dest IP, dest port to direct segment to appropriate socket Reliable Data Transfer Sender side Interfaces: rdt-send(Data): sends data rdt-rcv(ack): indicates successful receipt of data by receiver. Updates sender state Go-Back-N Sender: sends up to N, consecutive transmitted but un ACKed packets [Diagram of packets with arrows indicating sent, not acked, not sent, and acked states] window size [N] Pointers: send-base nextsegnum: next packet to send While nextsegnum < send-base + N, sender sends next packet and increments nextsegnum. send-base incremented after receiving acks A single timer for the whole sending window measures the timeout for the packet at send-base. At timeout, sender restarts timer and retransmits all packets in the sending window from send-base Receiver Only tracks next sequence number it expects to receive: nextsegnum Out-of-order packets discarded Sends ack for last in-order packet May generate duplicate acks if something goes wrong