Unit 4 – Individual Project 4

TCP packet fields consists of a header and a data field. The header length can vary between 20 and 60 bytes of data with a total packet size than can be as large as 65535 bytes. Most systems cannot handle packets as large as the protocol allows so the standard size of most packets are usually kept to 576 bytes.

UDP packets are sent by computers without establishing a connection to the recipient. UDP data packets are carried in a single IP packet which limits the size to a maximum of 65507 bytes for IPv4 and 65527 bytes for IPv6. To transmit a UDP packet the computer completes the appropriate fields in the UDP header and forwards them together with the IP header for transmission.

The three-way TCP/IP handshake in connection setup is as follows:

• This begins with a SYN (Synchronise) segment (as indicated by the code bit) containing a 32-bit Sequence number A called theInitial Send Sequence (ISS) being chosen by, and sent from, host 1. This 32-bit sequence number A is the starting sequence number of the data in that packet and increments by 1 for every byte of data sent within the segment, i.e. there is a sequence number for each octet sent. The SYN segment also puts the value A+1 in the first octet of the data. • Host 2 receives the SYN with the Sequence number A and sends a SYNsegment with its own totally independent ISS number B in the Sequence number field. In addition, it sends an increment on the Sequence number of the last received segment (i.e. A+xwhere x is the number of octets that make up the data in this segment) in its Acknowledgment field. This Acknowledgment number informs the recipient that its data was received at the other end and it expects the next segment of data bytes to be sent, to start at sequence number A+x. This stage is aften called theSYN-ACK. It is here that the MSS is agreed. • Host 1 receives this SYN-ACK segment and sends an ACK segment containing the next sequence number (B+ywhere y is the number of octets in this particular segment), this is calledForward Acknowledgement and is received by Host 2. The ACK segment is identified by the fact that the ACK field is set. Segments that are not acknowledged within a certain time span, are retransmitted
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The TCP/IP handshake in connection release is also uses the three way handshake but it uses FIN in place of the SYN for connectionrelease.

References

SET (n.d.) Software Engineer Training: Transmission Control Protocol. Retrieved from, http://www.software-engineer-training.com/higher-layer-network-protocols/transmission-control-protocol-tcp/.

Parker, D. (2005). Understanding the UDP Protocol. Retrieved from, http://www.windowsnetworking.com/articles_tutorials/understanding-udp-protocol.html.

InetDaemon (n.d.). TCP 3-Way Handshake (SYN, SYN-ACK, ACK). Retrieved from, http://www.inetdaemon.com/tutorials/internet/tcp/3-way_handshake.shtml.