Some of the overall features of TCP include:

• Point-to-point
  • Single sender + single receiver
• Reliable, in-order byte stream
  • No message “boundaries”
  • Bytes are simlply written on socket - no max size
• Full duplex data
  • Bi-direction data flow in the same connection
  • Maintain maximum segment size (MSS)
• Cummulative ACKs (similar to go-back N)
  • TCP is optimized for receivers who will buffer out-of-order packets
• Pipelining
  • Sender can send N bytes in a window - this is controlled via flow control + congestion control
    • e.g. with separate threads for flow control/congestion control, take min from threads
  • Ensures that sender does not send too many bytes to overwhelm receiver
• Connection-oriented
  • Handshake (exchange oc control message) initializes sender/receiver state before data exchange
• Flow control
  • Sender will not overwhelm receiver

TCP Segment Structure

• Sequence number
  • Designates order number of first byte in payload
• ACK number
  • Can be sent in separate control packet or piggybacked on current packet
  • TCP performs cummulative ACK
• Header length
  • Can be 20B or more (options available)
• Follow header
  • Contains control messages, etc.
• RST, SYN, FIN
  • Connection management flags (e.g. finish connection)
• Checksum
  • Error detection code

TCP Sequence Numbers/ACK

Sequence number is byte stream “number” of first byte in segment data.