Network and Protocol Processes - Essay Example

 Network and Protocol Processes that occur in the Network When you Access X-Stream from a Remote Location The interaction between my laptop and the server at X-Stream takes client server architecture through TCP/IP protocols suite. The diagram below illustrates the interaction which is intensively explained thereafter. 1. Making an HTTP Request to the webserver at X-Stream (The Application Layer) To make an HTTP request to X-Stream, I open the browser in my laptop which is connected to the internet through wireless network from an internet service provider. This is done by typing the address: http://x-stream.leedsmet.ac.uk. By doing this, my laptop sends a request to my DNS server to translate the address: x-stream.leedsmet.ac.uk into an IP address. The DNS server is part of network configuration of my host. The DNS server returns the IP address 212.183.133.187 (Byrnes, 2000). Now my laptop has enough information needed i.e. IP address 212.183.133.187and the HTTP webserver port 80; it can establish a TCP connection to the X-Stream webserver. 2. Requesting a TCP connection by X-Stream webserver to port 80 at IP address 212.183.133.187 (Transport Layer) The data received from the HTTP request (From Application Layer) is divided into several packets. These data packets include: a) My laptop’s IP address which has been deliver by my DNS server and determined as 212.183.133.187 b) Port number: the default port number of the HTTP request is 80 and can be 443 if I make secure connection https://x-stream.leedsmet.ac.uk or if the X-Stream network requires a secure connection at the time I am making a request. c) Acknowledgement number: This specifies the next sequence of figures that are expected by my laptop which sends the segment. TCP shows that this field is active by setting the acknowledgement number bit that is usually set after the establishment of the connection. d) Reserved bits: This are reserved for future use and are therefore sent to zero e) Data offset: These are four bits that specify the number of the 32 bit word which defines the TCP header. f) Checksum (16 bits): Checksum is used for error control that covers the data fields and header. It also covers a pseudo-header; and includes destination and source addresses, the segment length and the protocol. This information is then forwarded together with the segment in order to IP to protect TCP from faulty routing of segments. The segment length’s value includes the TCP header and data (Comer, 1999). g) Control bits. My laptop (TCP Client) requests the Internet protocol to deliver an IP datagram with connection request to destination 212.183.133.187. 3. Routing the Connection Request (Network Layer). The IP process at my laptop defines the connection request datagram. This is done by defining the destination address of x-stream.leedsmet.ac.uk whose IP address is determined as 160.9.34.49. The process further defines the characteristics of the datagram: header address, fragment offset, time-to-live, protocol, header checksum, options, header address, source address, destination address, identification, total length and its flag since it is fragmented. This is done by adding header to the packet it receives (Gouda, 1998). The IP process at my laptop the compares the source and destination IP addresses and finds out that they are not in the same network. Since the IP process at my laptop cannot deliver the IP datagram directly, it makes the decision to send the IP datagram to my default gateway which has the address 212.183.133.1. 4. Forwarding the IP Datagram to the Default Gateway Using Wireless Network (Network Interface Layer/ Network Layer) In order to pass the IP datagram to the default gateway 212.183.133.1, my laptop passes the IP datagram to the Ethernet network device driver of its network interface card which allows my laptop to connect to the internet. The device driver inserts the IP datagram into Ethernet network frame and transmits the frame on the Ethernet network. The network layer process determines the media access control (MAC) address of my laptop since Ethernet network frames do not use IP addresses. For this reason, Address Resolution Protocol (ARP) is used in the translation between IP addresses and MAC addresses. The ARP query to the local subnet at my laptop resolves the IP address 212.183.133.187 to the MAC address 00:a0:e4:55:74:60. In order to send the frame it has to be assembled (McCabe, 2007). This ARP message is then sent in an Ethernet frame which is broadcasted to all Ethernet devices on this network. This enables proper routing of the message. When my network router, which has IP address 212.183.133.187, gets this ARP message, it replies with an ARP message which states that the “IP address 212.183.133.187 belongs to the MAC address 00:a0:e4:55:74:60”. Finally, when my laptop gets this ARP message, it forwards the MAC address of my default gateway 212.183.133.1 together with the IP datagram to the Wireless LAN driver and transmits the frame. The Ethernet network by this time has three Ethernet frames that are being transmitted. My laptop keeps a list of known MAC addresses in a local table such that subsequent transmissions of IP datagrams from it to my router do not require ARP messages. When my router receives the Ethernet frame from my laptop, it starts by the extraction of the IP datagram which is then forwarded to the IP module. Upon receiving the IP datagram from my laptop, the router makes a similar decision as my laptop. This decision involves determining whether the IP datagram can be forwarded directly to X-Stream network webserver or by selecting a router from my local routing table and pass the packet to another router. My router has multiple network interfaces. Therefore, it checks whether the intended destination of the IP datagram is directly via any of its interfaces. To check whether a node can be reached locally, the router tries matching the first three bytes of the IP address of X-Stream, that are included in the IP datagram, to the IP addresses in its own interfaces: 212.183.133.1 and 212.183.133.187. Since a match occurs for 212.183.133.1, the router will then try forwarding this IP datagram directly to X-Stream. 5. The Preparing and Executing the Response from X-Stream At this moment, the webserver at X-Stream has all the information it requires to respond to the HTTP request from my laptop. X-Stream responds with an ARP response to the router. It starts by forwarding the IP datagram it has received to its default gateway 160.9.34.1. The X-Stream webserver passes the IP datagram to its Ethernet network device driver of its NIC. The device driver inserts the IP datagram into Ethernet network frame and transmits the frame on the Ethernet network. The network layer process in the X-Stream webserver will determine the MAC address of the X-Stream webserver. An ARP query is sent to the local subnet of the X-Stream network to resolve the IP address 160.9.34.49 to the MAC address 00:a0:c4:23:14:11.The message from ARP is then sent in an Ethernet frame that is broadcasted to all Ethernet devices on this network that the X-Stream belongs to. The X-Stream webserver router receives this message. It then makes a response with an ARP message which indicates that “IP address 160.9.34.49 belongs to MAC address 00:a0:c4:23:14:11”. The X-Stream webserver receives this message, it passes the MAC address of its default gateway 00:a0:c4:23:14:11 together with the IP datagram to the Ethernet driver and transmits the frame. This is followed by the transmission of Ethernet frames on the X-Stream Ethernet network. The X-Stream network webserver will store a list of all known MAC addresses locally in a table to make subsequent transmissions of IP datagrams to its router easier. This will make the retrieval of ARP messages quicker and efficient. 6. Routing the Response from the X-Stream webserver (Network Layer) The X-Stream network router receives the Ethernet frame from the X-Stream webserver. It starts the routing process by first extracting the IP datagram and then passes the datagram to the IP module. The router makes a similar decision as the X-Stream webserver after receiving the IP datagram from the webserver. This involves determining whether the datagram can be forwarded directly to X-Stream or by selecting one router from the local routing table and passing the packet to another router. The X-Stream network router has multiple interfaces of its network, and, hence checks whether the intended destination of this IP datagram is directly via any of its network interfaces. For the purposes of determining whether a node can be reached locally, the router tries matching the first three bytes of the IP address of my laptop. These bytes are included in the IP datagram and the IP addresses of its own network interfaces: 160.9.34.1 and 160.9.34.49. The router will then try forwarding the IP datagram directly to my laptop because a match occurs to the IP address 160.9.34.49. 7. The X-Stream Webserver Determines the IP Address of My Laptop First, the X-Stream network router acquires the Ethernet address of my laptop. This is done by sending an ARP request which is on the Ethernet interface that is directly associated with the IP address 212.183.133.187. X-Stream webserver sends its MAC address, 00:a0:c4:23:14:11, in a response in form of ARP message. When the router gets the MAC address of X-Stream, it sends an Ethernet frame that contains the IP datagram to my laptop. Before sending the response, the X-Stream network webserver has to determine whether the computer that made the request exists or not. This is done contacting it network’s DNS server. It sends a message “Who is the owner the MAC address 00:a0:e4:55:74:60”. The DNS server is part of the X-Stream network configuration to its host (Jones, 2001). The DNS server returns the IP address 212.183.133.187. By this time, the X-Stream network webserver has enough information needed i.e. IP address 212.183.133.187and the HTTP webserver port 80; it can establish a TCP connection to my laptop. The IP process at the X-Stream webserver defines the connection request datagram. This is done by defining the destination address of my laptop whose IP address has been determined as 212.183.133.187. The process further defines the characteristics of the datagram: header address, fragment offset, time-to-live, protocol, header checksum, options, header address, source address, destination address, identification, total length and its flag since it is fragmented. This is done by adding header to the packet it receives. The IP process at X-Stream webserver the compares the source and destination IP addresses and finds out that they are not in the same network (Kurose & Ross, 2005). Since the IP process at X-Stream webserver cannot deliver the IP datagram directly, it makes a decision to send this IP datagram to its default gateway 160.9.34.1. 8. The X-Stream Network Webserver Finalizes the HTTP Connection Now, the HTTP webserver at X-Stream network has the information that is needed for the establishment of a TCP connection, and requests a TCP connection to port 80 at IP address 212.183.133.187. Just like HTTP, TCP is a client server protocol it initiates the connection is called the TCP client. The X-Stream network is waiting for a connection by my laptop. When the X-Stream network webserver is started, the HTTP server sets up the TCP server that is waiting on the well - known port 80 for requests for TCP connections by my laptop. At this moment, the establishment of a TCP connection to complete the HTTP request involves three steps: a. My laptop (TCP client) sends a TCP connection request to the X-Stream webserver (TCP server) which has gone through all the procedures explained above. b. The X-Stream webserver responds to the request by making DNS requests to its DNS server to get the IP address of my laptop and respond to my laptop’s request HTTP request. c. My laptop acknowledges this response from the X-Stream webserver and now views the home page at https://x-stream.leedsmet.ac.uk. This procedure does not include any sending of data from my laptop to the X-Stream network webserver. The HTTP request is made to browse the website. Reference List Byrnes, P. (2000) Protocol management in computer networking. 1st ed. Boston, Artech House. Chappell, L. (2010) Wireshark network analysis. 1st ed. San Jose, CA, Protocol Analysis Institute, Chappell University. Comer, D. (1999) Computer networks and internets. 1st ed. Upper Saddle River, N.J., Prentice Hall. Gouda, M. (1998) Elements of network protocol design. 1st ed. New York, John Wiley. Jones, P. (2001) Computer networks. 1st ed. Exeter, Learning Matters. Kranakis, E., Haroutunian, E. & Shahbazian, E. (2008) Aspects of network and information security. 1st ed. Amsterdam, IOS Press. Kurose, J. & Ross, K. (2005) Computer networking. 1st ed. Boston, Pearson/Addison Wesley. McCabe, J. (2007) Network analysis, architecture, and design. 1st ed. [San Francisco Calif.], Morgan Kaufmann. Odom, W. (2004) Computer networking first-step. 1st ed. Indianapolis, Ind., Cisco Press. Terplan, K. (1999) Web-based systems & network management. 1st ed. Boca Raton, FL, CRC Press. Read More