In my June column, I gave an overview of IPv4
(Internet Protocol, version 4), and described some common problems with
its implementation. This month, I’m going to give you the same kind of
information for TCP; the Transmission Control Protocol, which makes up
well over 95% of unencrypted traffic on the Internet.
In my June column, I gave an overview of IPv4 (Internet Protocol, version 4), and described some common problems with its implementation. This month, I’m going to give you the same kind of information for TCP; the Transmission Control Protocol, which makes up well over 95% of unencrypted traffic on the Internet.
IP’s mission in life is to get a packet from one point on the network to another. TCP’s mission is to use IP (hence the name TCP/IP, for TCP over IP) to provide a reliable stream of data between two points. While IP is an efficient protocol for transferring large quantities of information, its specification allows it to drop packets, deliver them out of order, or even deliver them with corrupt data. TCP is needed to ensure that all the required packets make it to their destination, uncorrupted, and in the correct sequence.
After the IP header in the packet, which is almost always 20 bytes long, we have the TCP header, which is at least 20 bytes long. You can see what it looks like in Figure 1.
Connections
Figure 1: An example of a transmission control protocol (TCP) header.
The most important thing TCP offers is a ‘connection:’ a stream of related packets. Each packet identifies the connection it is part of, and where in…
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