Transport layer (4)
16-bit source & destination ports
Transmission Control Protocol User Datagram Protocol
PDU: segment PDU: datagram
IP protocol field: 6 IP protocol field: 17
reliable unreliable
guaranteed delivery not guaranteed delivery
connection-oriented connectionless
high overhead. heavyweight value-added to IP low overhead. lightweight port wrapper on top of IP
20 byte header 8 byte header
bidirectional connection Establishment (3-way handshake) & teardown unidirectional
Acknowledgments: sequence & ack numbers. timeouts & retransmission
flow & congestion control: sliding window
checksum optional (unused?) checksum
"file transfer" stuff streaming & short request/response stuff
accuracy speed
web, email, remote login, ftp DNS query, SNMP, DHCP. Real-time audio & video