TCP Connection Setup and Data Transfer

TCP Connection

process 1

host A sends a TCP segment with the SYN bit set and the sequence number set to a randomly chosen initial number

process 2

host B replies with SYN and ACK bits set, sets the ack number to the next expected sequence number and includes its own randomly chosen initial number

process 3

host A replies with ACK bit set and its ack number set to the next expected sequence number

why do we randomly select initial sequence numbers?

protects against reused ports

connection teardown

the exact same process as connection, but with the FIN bit set instead of the SYN bit

acknowledgement number

indicates the next byte that the sender of the acknowledgement expects to receive

what do out of order packets do

trigger duplicate acknowledgements

how is loss indicated?

three duplicates arriving in sequence - four TCP segments with the same ack number

head of line blocking

periods where out-of-order data is buffered but can’t be delivered to the application