THE FLOW OF DATA BASED ON SCENARIO

THE FLOW OF DATA BASED ON SCENARIO

Based on the scenario given, the data transmission between UTeM Lecture who using the internet (Public IP) and UTeM IT Centre where the network using Class C Private to communicate on their LAN Network. There is some technical method involved during this data transmission between public and private IP addresses. Most of the public IP are created by a unique IP Address which will provide by the ISP to communicate on Internet. On this scenario, UTeM Lecture and the main router in UTeM Network contains a unique Public IP address to communicate on internet, whereas the private IP address which assigned on the UTeM Departments and their hosts will communicate Internet using the main router which able to access Internet by requesting transmission from the router.  The reason why Private IP can’t access internet because those Private IP Address are not unique on the Internet, there are some high probability host which having the same IP Address. Based on that issues, the problem may occur is, if a user make request on www.google.com directly to the internet using private IP, then the problem will occur while receive the request from the Internet, where the host which as same IP Address globally will receive the request will made. So, there will be happen some data collision. That is the main why we don’t use Private directly to access Internet. Now going to explain this scenario using OSI Layer Model.

This OSI Layer Model explanation will start from UTeM Lecture which using Home Network (Public IP Address) to Ulearn System Server on their private network (Private IP Address). Assume that the UTeM Lecture is trying to upload a word.docx file on UTeM Ulearn platform. Let’s start from the Application Layer, on here the file which UTeM Lecture willing to upload into Ulearn platform will be providing a service for the data travel such as SMTP, POP3, and etc... Is this case a file transfer protocol (FTP) is be assigned to make the data to travel. Next, on the Presentation Layer, the word.docx will be translate into binary form, then the file compression begun for the purpose of reduces the size of the file. Example is a 5mb file will be compress into 2mb, this technique able to send the file even faster. Lastly, it’s will encrypt the file from the sender for the purpose of data security using SSL or other security protocol. After that, the data will pass to session layer to managing communicate session without any distortion between communicating system. The packet data unit for this three process are Data, on the next the data will be breakdown those data into segments. On this transport layer where the segmentation start. Each the segments contain port number which are source and destination number, and the sequence number. The aim port number is to make the data reach on the correct path and sequence number also the rearrange the segments which misplace. Besides that, error control is one major part on this layer to make whether the segment reach or not, if the segments didn’t reach, then it’s will re-send the segments again. There are two protocol involved on this process which is TCP and UDP. In our case TCP will be used to transfer the word.docx file because TCP will make sure every data packet gets delivered and receive message whether the data has been reach or not. Why we didn’t implement UDP because most of UDP are used video streaming and it’s also won’t reply the message whether the data has been reach or not. Next is on the network layer, this the interesting parts in our data travel based on the scenario due to the communicate between public IP address and private IP address. This layer is responsible for the delivery of packets (PDU) from the original source(Sender) to the final destination (Receiver). The process involved in this layer are logical addressing where every segments will be assign with the destination of IPv4 and routing is where managing the packet to be deliver based on the IP address and subnet mask. On this case, the routing will different due to the public to private IP address where the sender (Public IP address) will be transmit the UTeM main router (Public IP address), then another routing happens inside the UTeM Private IP Address to transmit the data to the host which requested.

Figure 1 : Routing

Next is data link layer, on this layer the MAC address of the hardware is added on the packet and form the frame. The purpose of MAC is for monitoring data packets from one Network Interface Card (NIC) to another across a shared channel (Hop-to-Hop Delivery). Finally, physical layer is responsible for transmitting individual bits form one to the next. Physical layer is also convert the binary into a signal to transmit on a media. In this case, the media used are the wireless and wired media.

            Now the hop-hop delivery process occur from the UTeM Lecturer home modem until the UTeM main router. This process only occurs from layer 1 until layer 3, if the destination source is valid, then it’s will proceed layer 4 until layer 7.

Figure 2 : Hop - to Hop Delivery

Let’s start from physical to application layer to decrypt the word.docx file which the UTeM Lecturer uploaded. Firstly, on the physical layer where the data receive from the wired media, then will proceed to next layer. Secondly on data link layer, where MAC address of the source and destination are removed which is frame becoming a packet. On the network layer, the logical address will be removed if it’s found the valid destination (packet to segments). If destination invalid, then hop-to-hop delivery to next node. On the transport layer, data (segment) will check on the sequence addressing whether data misplace during transmission and port addressing is to identify the whether the is reached or not using error control technique. On the session layer, the session is closed at this layer and no more dialog is allowed between both sides, of further dialog is needed there must be another request done to open a new dialog session. On the presentation layer, the data will translate on original form and decrypt the data using the same encryption method done at the sending side. Finally, on the application layer will the permission to read, write and view the word.docx which send by the UTeM Lecturer from the public network.

Figure 3 : Overall Process in OSI Model Layer Diagram

Network Components

The possible network components involve throughout the communicate are the router, modem, access point and switch. Router will be on this network to public network and also same networks around UTeM Department. Modem is used by the lecturer which using the Ulearn system from their home. Switch is to makes all the hosts to accessible into the UTeM Network. Access Point for guest or student who want to use UTeM Network.