3310 -- Computer Networks

   To be frank, before attending the course Computer Networks in this term, though I have been as one of the beneficiaries of the Internet since even seven or eight, I know little about how actually the whole huge and exquisite world of Internet works. Maybe the only concept that I am well aware is that the information asked by clients served in the form of some kinds of signals through some certain pipes. I even do not know what a protocol is, not to mention the concepts of TCP/UDP, IP, CSMA/CD or the seven layer architecture and so on. I feel like that I am stepping one of my foot into a new field.

   For a beginner, a detailed reference textbook as well as wiki are both indispensable.

Figure 1-Wikipedia

Figure 2-Textbook

   The first task is to establish the basis of this course, which means that I need to go through all the basic concepts. For example, from both the textbook and the wiki, we can know that :

   TCP stands for transmission control protocol – a kind of transport protocol and it is on the transmission layer in the OSI architecture.

 

Figure 3-Basic Concepts Collection

   Fortunately, my roommate is a senior in IE department and I will of course put all of my questions to him. In face, we have just discussed about the question that why TCP is connection-oriented while IP is connectionless a few minutes ago.

   After collecting all these concepts, I am now ready to explore the operation mode of the network.

    The course is on every Tuesday and Thursday. After each class, I would overview the whole PPT of the lecture to make sure that I clearly get the information and knowledge from the professor. To make the review effectively, I print all of the course contents and take notes on the paper  to set up a clear structure about what I have learnt.

Figure 4-The Lecture and the Notes

Topic：The OSI Reference Model

Figure 5- OSI Seven-Layer Model

The origin of the model:

http://zh.wikipedia.org/wiki/OSI%E6%A8%A1%E5%9E%8B

                                                         – The introduction of wikipedia

   The early architectures developed by various computer vendors were not compatible with each other, which hindered the communication between different users with different network architecture. Therefore, the unified model --OSI (Open System Interconnection Reference Model) come along.

The Architecture of the Seven Layer Model

OSI partitioned the communication process into seven layers which are :

1.  application layer

        -- provide services that involve communication

2.  presentation layer

        -- provide the application layer with the representation of data

3.  Session layer

        -- control the manner that data are exchanged

4.  Transport layer

        -- be responsible for the end-to-end transfer.

5.  Network layer

        -- provide for the transfer of data in the form of packet

6.  Data link layer

        -- provides for the transfer of frames, which are the block of information

7.  Physical layer

        -- deal with the transfer of bits over a communication channel

   From my point of view, as a beginner, I cannot imagine a better model to describe the whole work of communication since it has taken almost every part into consideration such as flow controlling and data capsulation as well as error detection in each layer.

   However, in practical application, the TCP/IP model which has only four layer, is used much more frequently. I think the reason should be that in most instances, neither the presentation nor the session layer would be useless. What’s more, maybe executing flow controlling ,data capsulation as well as error detection in each layer would be expensive, and as we know, there is always trading between cost and theoretical efficiency.

    In the further study, I want to know more about the tasks for each layer and how do they finish these tasks. What’s more, I would explore the cooperation of the whole architecture to see clearly that how the whole communication network would be done.