![]() ![]() Since this is the first packet in the flow, acknowledgement number is set to zero. Relative sequence number is just for easy analyzing. For easy understanding, Wireshark starts ISN from zero which is called " relative sequence number" while in the screen shot above, we can clearly see the client has set its real sequence number to 332215980. ![]() Although the first packet (SYN) does not contain any data, it consumes one sequence number and as a result the actual data begins at ISN+1. This is the first packet (it is also called SYN packet) from the client to the server with source and destination port of 62834, 80 respectively.Īll data in a TCP connection are numbered, starting at a randomly chosen ISN (Initial Sequence Number). For visualization, see screen shot below. We will analyse the flow packet by packet, starting from the first packet. TCP sequence and acknowledgement numbers are counters used to keep track of every bytes sent and received during the connection.īreaking down to Packet by Packet Analysis Packet Number 1 In short, TCP provides this reliability mostly by Sequence Number and Acknowledgement Number. TCP ensures that all packets one end sends will be delivered to the other end, keeping track of which packets have been received successfully, resending any packets that have been lost, and specifying the order for reassembling the data on the other end. Reliability is one of TCPs strong feature. See below for a SYN packet which contains an initiator (a client) settings. The settings include Sequence Number, Maximum Segment Size, if SACK is permitted or not, Window Scale, Window Size etc. In another saying, they inform each other about what kind of settings they would like to use during the connection establishment. During 3-way handshaking both sides synchronize (SYN) and acknowledge (ACK) each other. The connection remains active until it gets terminated. Before data exchange between two parties, it requires to establish a connection, using TCP 3-way handshaking. TCP (Transmission Control Protocol) is a connection oriented and highly reliable protocol. Getting started with TCP Sequence and Acknowledgement Numbers Breaking down to Packet by Packet Analysis.Getting started with TCP Sequence and Acknowledgement Numbers. ![]()
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