Hello friends, hope that you are all well by the grace of almighty. Lets see what we will have in todays post.
Today we’ll learn about the client server network working system and if you gain knowledge about the client server network, you also can able to monitor network through your knowledge. Here in this post we will discuss data sending and receiving using a OSI model. I think that you have knowledge about the OSI model. If not, then don’t worry. You can check the previous post of this website. Also we can summary the OSI model like this. OSI model has seven layer. They are:
2. Data Link
So as we are considering a LAN network, we can have a Client and a server. We can consider that the client is connected to a router and remotely the server is also connected with a router. So we can have a look at the network like this:
1. A webpage is stored in the server and a user of the LAN network wants to access the web page. The user opens a browser of his/her computer and type the URL of the webpage.
2. Now with the help of the layer 7 Application layer these data are identified as the application data and the data type.
3. Now these data come to the transport layer. The transport layer identifies the data as World Wide Web (WWW) data service. So for this reason the transport layer then associates the service with TCP protocol. This process is done, because there is needed to assign a port number. It uses a randomly selected port which is associated with the established session.
4. Now the TCP also sends acknowledgement number for informing that the WWW server service is active to receive the service. The sequence number is placed in the series of related segments. Sometimes in this case flags are also used.
5. Now data comes to the network layers. Here in this layer, the IP packet is contrasted to identify the destination and hosts. For the destination address, the client host uses the IP address associated with the WWW server host name which is in the host table. It then uses its own IPv4 address as the source address. The another important of network layer is to identify the upper layer protocol encapsulated in the packet as a TCP segment.
6. After that the data comes to the data link layer. This data link layer protocol identifies the MAC address which is associated with the interface of client end router with the help of Address Resolution Protocol (ARP). This is done for exploring the default gateway. It then uses this address to build an Ethernet II frame to transport the IPv4 packet across the local media. The MAC address of the client is used as the source MAC address. And the MAC address of the client end router interface is considered as the destination MAC address, which is stayed in the frame.
7. The frame also indicates the upper layer protocol of IPv4 with a value of 0800 in the type field. The frame begins with a preamble and start of force indicator and end with a cyclic redundancy check. It is done at the end of the frame for the error detection.
8. Now the data comes to the physical layer. The physical layer begins encoding the frame onto the media bit by bit. The bits are also encoded using Manchester Differential encoding. The client end router buffers the bits as it receives.
9. The client end router examines the bits in the preamble. It also looks for the two consecutive 1 bits that indicate the beginning of the frame. It then buffers the bits as the part of reconstructed frame. When the entire frame is received, the client end router generates a CRC of the frame. It then compares it with the FCS at the end of the frame, tp determine that the frame is received intact. When the frame is confirmed as a good frame, the destination MAC address in the frame is compared to the MAC address of the client ended router interface MAC address. Here for this scenario the MAC address of RouterB fa0/0 is taken.
10. At the network layer the destination IPv4 address of the packet is compared against the riutes in the routing table. A match is found that is associated with a next hope out of interface S0/0/0. The packet inside routerB is then passed to the circuitry for the S0/0/0 interface.
11. After that routerB creates a PPP frame to transport the packet through the WAN. In the header of PPP a binary bit is added to indicate the start of the frame. It is done because the PPP is point-to-point and used as direct link between the two nodes, actually this field has no real meaning.
12. Also includes a protocol field with a hexadecimal value to indicate that the IPv4 packet is encapsulated. The frame trailer then ends, but it ends with a CRC (Cyclic Redundancy Check) in the FCS (Frame Check Sequence) for the error detection. Finally, a binary flag value indicates the end of a PPP frame.
13. The physical layer associated with this work start to encode the frame onto the WAN media bit by bit. These bits are received by the RouterA.
14. After the receiving of the bit the RouterA examine the bits to identify the beginning of the bit. RouterA then buffers the bits as a part of reconstructed frame When the entire bit is received, the routerB reconstruct the bit as per the flag. RouterB also take helps from FCS to indicate that the whole frame is received. When the frame is confirmed as good frame, the headers are removed and the packet is pushed up to the network layer of RouterA.
15. At the network layer the destination IPv4 packet address is compared against the route in the routing table. For this scenario, a match is found that it is directly connected to the interface fa0/0. The packet then passed the circuitry for the Fa0/0 interface.
16. The Data Link layer refers to the ARP cache of RouterA to determine the MAC address that is associated with the interface of Web Server. It then uses this MAC address to build an Ethernet II frame to transport the IPv4 packet across the local media to the server. The MAC address of the fa0/0 interface of RouterA is used as the source MAC address, and the MAC address of the server is used as the destination MAC address in the frame. The frame also indicates the upper layer protocol of IPv4 with a value of 0800 in the Type field. The frame begins with a Preamble and Start of Frame (SOF) indicator and ends with a cyclic redundancy check in the Frame Check Sequence at the end of the frame for the error detection. It then uses CSMA/CD to control the placing of the frame onto the media.
17. In the Physical layer it begins to encode frame to the media bit by bit. After that the server buffers the bits as it receives.
18. The web server receives the bits and after that it examines the bits with the help of SOF to search for the beginning of the frame. The server then reconstructs the frame by buffering. The server generates a CRC when it receives the entire frame. With the help of FCS, it determines the entire frame is received or not.
19. When the frame is confirmed as a good frame, then server compares the destination MAC address in the frame with the MAC address of the server. It is done because, through this it matches, the headers are removed and the packet is prepared for the Network layer.
20. So the packet is come to the network layer. The destination IPv4 address of the packet is examined to identify the destination host. The network layer identifies the upper layer protocol as TCP and it then refers to the TCP service in the transport layer.
21. At the transport layer of the server, the TCP segment is examined to determine the session to which the data contained in the segment belongs. This is done by examining the source and destination port. After that the data is sent to Application layer.
22. At the application layer the web server service is requested to provide the HTTP request.
The information I’ve provided here is taken from cisco.
If you want, you an also look this video, hope that you will like it.
So in this way the system works. Hope that you’ve enjoyed this session. If you have any kinds of opinion or request, please feel free to comment. Have a good day. Thank you. 🙂
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