A Deeper Touch – OSI Seven-Layer Model and Protocols

        After a brief and conceptual introduction of computer network, the teacher gave us more detailed knowledge of it in recent weeks.

        There are many things that I newly learn, but OSI Seven-Layer Model and Protocols impressed me most, not only because they are significant basis in computer network but also for they confused me a lot when I was firstly exposed to them.

 

        In order to make the communication process through network clearer, the layer models are brought out. There are 7 layers in the layer models – Application, Presentation, Session, Transport, Network, Data Link and Physical. Each of them has particular function during the communication, and it is shown as below,

        I easily confuse them with each other. For example, I sometimes might mistake Data Link layer as Network layer at the beginning for they have some similar function (such as both adding a header to the transmitted data). However, after several lessons, I have almost understood them and can distinguish them by now.

 

        Protocols are rules that govern the communications. There are many protocols, such as, HTTP, TCP, UDP, IP, etc. I was suddenly enlightened after that lesson when the teacher talked about the protocols.

        In the past, I was puzzled why each address of the webpage has “http:” in the front of it. But I haven known now that it represents the Hyper Text Transport Protocol (HTTP). I also got some knowledge of other protocols. For instance, TCP is connection oriented and error free while UDP is connectionless and only tries its best while transmitting data (which means not error free).

 

        Computer network is complicated and abstract, but if I go deeper into it, I can find more interesting things. In fact, I am still feeling confused about many of the protocols, and I hope I could make them completely clear after the following few weeks!

The First Touch of Computer Network

       I’m using the Internet everyday, however, I never knew about how the Internet works until I entered the course – IERG3310 Computer Networks.

Fig.1 Computer Networks



        After the first lesson of this course, in fact, many of my past ideas of computer networks have been overthrown.

        In the past, I thought that when we are surfing on the Internet, our computers are sending some orders to the Internet and then the Internet will send back the information that we need.

        But the teacher told us that there will be many other procedures before we can get the information. For example, “Three-Way Handshake” is needed before our computer could connect to Yahoo when we want to get some information from Yahoo.

Fig.2 Three-Way Handshake

        There is a series of numbers representing the IP address of our computer, which confused me a lot every time I saw it in the past. I didn’t know what each group of numbers represents and how important they are. They were just massy code for me.

        But after the class, I learned something about the IP address. Although I still don’t know what each group of numbers represents, I have known that without IP addresses, we could not communicate with others on the Internet.

        As there are so many Internet clients in the world nowadays, we can’t assign everyone an IP address. Thus, when we use the Internet, our computer will be assigned an IP address, which are usually different every time but will never be the same as the one of the other computer at the same moment.

Fig.3 Different IP Addresses

        This is the first time that I am exposed to Computer Net work and I have just got some simple concept of it and thus, I am still confuse by many things. But the course is interesting, and I have already been attracted by it, and I hope that I could solve the problems soon!