An Investigation into Transport Protocols and Data Transport ...

4.2. Protocol Description 53
is dependent upon the Maximum Segment Size (MSS) of the TCP segment
and constrained by the MTU of the network path. The variable Padding field
at the end of the TCP Options is used to ensure that the TCP header ends at
a 32-bit boundary. Control Flags determine the type of TCP segment (e.g.
SYN, ACK, SYN-ACK, FIN, reset, or urgent) and denoted by either a true
or false bit for each type of segment (e.g. a SYN packet will have the SYN
bit marked, whilst a SYN-ACK will have both SYN and ACK fields marked).
The TOS field determines quality of service and enables packet level service
differentiation. The entire TCP segment is check-summed to facilitate the
detection of header and/or payload corruption.
4.2.1 Connection Initialisation
TCP connections are established between two hosts via a three-way handshake.
According to [Jac88], the sending and receiving of data after the
initialisation of the TCP connection is bounded by a packet conservation
principle; when this principle is obeyed, congestion collapse from excessive
data being put into the Internet will become the exception rather than the
rule.
The principle of packet conservation utilises the idea that data packets
cannot be placed into the network any faster than that at which acknowledgments
(ack’s) by the sender of the data are received. This is called ackclocking
and is an important property in maintaining a stable and even data
flow [VH97, Jac88, BPS99].
In the following we will give an overview of the features and implementations
that have made TCP such a success.