Establishing Connection Three-Way handshake Each side notifies other of starting sequence number SYN: Seqc it will use for sending ° Why not simply chose0? Must avoid overlap with earlier ACK: Seqc+1 incarnation SYN: Seqs Security issues Each side acknowledges ACK: Seqs+1 other's sequence number SYN-ACK: Acknowledge sequence number 1 Can combine second sYn Client Server with first acK Lecture 18: TCP Details5 Lecture 18: TCP Details Establishing Connection: Three-Way handshake • Each side notifies other of starting sequence number it will use for sending • Why not simply chose 0? • Must avoid overlap with earlier incarnation • Security issues • Each side acknowledges other’s sequence number • SYN-ACK: Acknowledge sequence number + 1 • Can combine second SYN with first ACK SYN: SeqC ACK: SeqC+1 SYN: SeqS ACK: SeqS+1 Client Server