Internet protocol stack Transport layer Application Transport Network

Internet protocol stack Transport layer Application Transport Network Transport Layer: Deliver services for Application layer Transport layer protocols: TCP and UDP: User Datagram Protocol is an connectionless unreliable protocol which offers no guarantied delivery Link Physical TCP: Transmission Control Protocol is an connection oriented protocol • Connection setup (3 way handshake), • Flow control • Congestion control

Internet protocol stack Transport layer To identify sender and reciever process, it is necessary to combine IP address and the applications port no. Port no. is a part of the TCP and UDP headers www. iana. org mangage the fixed part of port numbers Application Transport P 5 5002 Socket (port) Application P 3 80 Transport Network Link Physical

Internet protocol stack TCP header typically 20 bytes 32 bits Source port # Destination port # Sequence number Acknowledgement number FIN SYN RST PSH ACK Unused URG Heade r length Internet checksum Receive window Urgent data pointer Options Data

Internet protocol stack TCP header fields Source port: This field identifies the sending port. Destination port: This field identifies the receiving port. Sequence number: The byte number of the first byte in the Acknowledgement number: The value of this field is the sequence number the sender expects next. Data offset: This 4 -bit field specifies the size of the TCP header Reserved: 6 -bit reserved field for future use and should be set to zero. URG: Urgent pointer field is significant ACK: Acknowledgement field is significant PSH: Push function RST: Reset the connection SYN: Synchronize sequence numbers FIN: No more data from sender Window: The number of bytes the sender is willing to receive Checksum: The 16 -bit checksum field is used for error-checking of the header and data

Internet protocol stack Client Http and TCP working together Server SYN RTT Round Trip Time SYN, ACK Get TCP 3 way handshake ission m s n a r File t File Transfer time Time

Internet protocol stack Client Acknowledge and loss of packets Server ata bytes d 8 , 2 9 Seq= Ack 100 X Loss Timeout bytes data Seq=92, 8 Ack 100 bytes data 2 3 , 0 0 1 Seq= Time

Internet protocol stack Ping command RTT Exercise: Open a DOS prompt and try to ping som URL’s and figure out the Round Trip Time by sending a ping command bytes data Seq=92, 8