6.4.4 Outline the need for protocols in packet switching.
Teaching Notes:
Students do not need to know technical details of TCP, IP, OSI, but must understand that protocols include essential information that allows packets to be reassembled at their destination according to the requirements of the receiving computer.
JSR Notes:
With this assessment statement, the emphasis is not so much on the protocols themselves as the need to have them in the first place. So this is a **protocols** assessment statement more than it is a TCP/IP one.
Look through the text on 344 and 345 to remind yourself what TCP and IP are, and on which levels of the OSI (Open System Interconnection) model they are found. And also remember that the OSI model is just that, a model. To fully understand all of what makes TCP/IP work within the full context of networking would take a couple of advanced degrees. And neither TCP nor IP necessarily fit perfectly into one of the seven layers of that model. And that’s not the point. The point is the ‘P’ in each of these, the protocol; the idea that however this networking is going to work, the computers on either side of the connection had better agree on the ways to proceed.
And in terms, then, of what is to be agreed with TCP, think of the postal analogy; the way in which these packets are to be transported, both sent and received, must be agreed on from both ends. To take a simple, extreme case with the analogy, there would be no sense of sending a parcel air mail to a place with no airport. And oh yeah, don’t forget that it is “Transmission” Control Protocol. In other words what are the rules and regulations for the actual control of the transmission of the packets through the network.
And with the IP part of it, again think of the postal analogy. This is the “inter-network” set of rules for how the packets will be addressed; the format of the “where they are coming from” and the “where they are going to”. Does the postal code need to be included, and how many numbers and letters should it have. Actually IP is pretty easy compared to all of the non-standard postal address configurations out there; it is simply four 8 bit numbers separated by points, from 0.0.0.0 all the way up to 255.255.255.255. And remember the interesting fact that this makes for around 4 billion possible IP addresses (in IP version 4).
It wouldn’t hurt to also remind you that Domain Name Servers (DNS servers) keep a list of all the IP addresses out there with their corresponding short-cut domain name. johnrayworth.info, for example is actually the IP address 195.250.148.236.
But anyway, much of this is beyond the point of the assessment statement; in packet switching systems, such as the one used for the Internet, there are certain protocols that once chosen must be followed; certain ways to, among other things, transmit packets and address them. Without agreement on and adherence to these rules, these protocols, networking, in this case, would not work.