Packet Data Transmission - Essay Example

Packet Data Transmission and Packet Data Transmission The communication between a browser, from a remote location (for example, home) and a server at x-stream.leedsmet.ac.uk involves a series of complex processes that is made possible by the TCP/IP protocol. Cerf and Kahn (1974, p.1) assert that the packet communication network constitutes a transportation mechanism for transmitting data between two hosts or between computers and terminals. The transmission of the packets, to request a web page from the server, goes through various network layers before arriving at the server side before a feedback is transmitted back to the browser. This report will cover in technical details the processes that occur in transmission of packet data. The report will first provide a brief summary of the TCP/IP networking protocol during data transmission. Technical details will follow after highlighting the overview process. The diagram above represents the OSI and TCP/IP architecture (Torres, 2007, p.4). The transmission of packets occurs via a stack of layers. The TCP/IP consists of four layers: application, transport, internet, network interface (Bonaventure, 2011, p.20). The application layer directly communicates with the browser (application) where data requested is by entering data into the host computer and sending a request via the internet. The application layer then communicates with the transport layer (Transmission control protocol). The transport layer establishes a session management between the two hosts. Data received from the application layer is segmented into packets. Each packet is given a unique label before being transmitted. The packets contain the necessary information that is sent to the host computer to fetch a web page; these packets are transmitted to the internet layer. The internet layer constitutes the Internet Protocol (Parziale, 2006). Data is packaged into Internet Protocol datagrams, which hold the address details of the client and server. The addresses of the client and server side are referred to as IP addresses (Osterloh, 2001). The packets are then transmitted to network interface layer. The network interface layer is responsible for determining how data is transmitted over the network (Rufi, 2008). The transmission of data is dependent on the network medium used, for example Ethernet and the optical fiber. TCP/IP protocol stack In order for communication to be effective, the internet protocol is based on the TCP/IP model. The TCP/IP constitutes protocols, mainly the Transmission Control Protocol (TCP) and the Internet Protocol (IP), hence the name but there exists other protocols as well. The TCP/IP is a hierarchical model composed of interactive modules where each module is assigned a specific task (Bonaventure, 2011, p.75). The layers in the model are composed of protocols that can relate to each other depending on the system type. In terms of hierarchy, a number of layers below the higher layer protocols support it. The TCP/IP protocol suite specifies how the IP packets are put into the frames and how to retrieve them back to the host computer. TCP/IP is considered to be a peer protocol stack, which implies that every implementation of TCP/IP is considered to have equal capabilities. However, all protocol stacks differ in terms of their functionality (Bonaventure, 2011, p.86). The TCP/IP is implemented according to a client-server model. In our case, the client is the host computer on the remote location, say home whereas the server is the computer being accessed at x-stream.leedsmet.ac.uk. Each of the TCP/IP’s layers perform a distinct function from the rest but the layers can be combined to perform effectively. 1. Application Layer The application layer initiates the data transfer. This layer consists of application programs that use the network; in our case we are using a browser as the application program. It contains all the host-host transport protocols to deliver data. Protocols such as http, ftp, telnet, and SMTP handle the URL command depending on the format of the command. The command is disintegrated into various packets. The Hypertext Transfer Protocol (HTTP) is a connectionless text based protocol where the communication between the client (browser) and the server. The HTTP client sends a request to the server in the form of a request method, URL (x-stream.leedsmet.ac.uk), client information, and possible body content. The HTTP request uses a generic message format of RFC 822 to transfer the required data (Tutorialspoint, 2014). The generic message contains a start-line, zero or more header fields followed by CRLF. It also comprises an empty line to signify the end of the header field, and an optional message body (Cerf and Kahn, 1974). The HTTP header field presents the information about the request. The message request-line begins with a method type, the request URL follows and the protocol version, and a CRLF in the end. The request method designs what method to be applied on the resource identified by the given Request-URI (Uniform resource identifier). X-stream.leedsmet.ac.uk implies the Request-URI is a get method thus it is used to retrieve information from the given server using x-stream.leedsmet.ac.uk. The URI determines the source in which to reply to the given request. The Transfer-encoding general header indicates the information type that is contained in the message body so that it can transfer it to the server. A cookie request-header can also be transferred if the server uses cookies to store information for future easy accessibility. The HTTP URL is sent to the server via the internet using the ASCII character-set through a method called encoding (Tutorialspoint, 2014). 2. Transport Layer Data is received in form of stream bytes that contains the request to fetch xstream.leedsmet.ac.uk. The process of data encapsulation occurs at this layer where details of a packet are hidden from the user. The transport layer incorporates two protocols, which are entirely responsible for the transfer of the packets. In this layer, there exists the TCP (Transmission Data Protocol) and the UDP (User Datagram Protocol). The packets in this network protocol range between 64-1500 bytes. TCP partitions the data into segments, and labels a header to each fragment (oracle, 2010). The two protocols differ in terms of their usage depending on the format of the request. TCP is a connection-oriented layer to imply that is supports conversations from the higher layers. The TCP transmits data in a continuous byte stream form. The TCP is mainly comprised of the source port, sequence number field, acknowledgement number field, data offset field, reserved field, flags field, window field, checksum field, urgent pointer field, options field, and data field. Each of the fields has a particular function. Each of the destination Port field contains 16 bits, which recognize the end points of the connection (Mullins, 2010). The sequence number field specifies the number assigned to the initial byte in the current message. The acknowledgement number field also has 32 bits in each field. The field comprises the value of the sequence unit that follows that the sender of the segment expects. However, the ACK control bit must be set for the sequence to be achieved. Rufi (2008) asserts that the header length field defines the number of 32-bit words that the TCP header contains. The reserved field is usually zero. The flag field which contains 6 bits, comprises of a number of flags that perform different functions. The URG flag shows that data, which is urgent has been received. The ACK flag is used to specify that the acknowledgement number is applicable. The PSH flag designates that the packet is of emergent need in the application. The SYN flag synchronizes the sequence numbers to ascertain a connection. The last flag called the FIN signifies that the host has completed transmitting the packets. The window field contains 16 bits in each field; it is responsible for determining the size of the sender’s receive window. The checksum field is used to show that the header has been damaged during transmission. The urgent pointer field indicates the most urgent byte in the packet whereas the data field comprises of information pertaining to the application layers (oracle, 2010). The transmission of information between the receiving and the sending TCP apply a process called the three-way handshake. The segments that have been divided by the TCP are used by the protocol to determine whether the recipient is in a position to accept the data from the protocol. A SYN segment is sent to the TCP protocol on the recipient side for the connection to be established. The recipient host returns an ACK to confirm the arrival of the SYN segment. Before sending the required data, an additional ACK segment is sent over to the receiving TCP. TCP packets implement sophisticated mechanisms to ensure that there exists a flow of control and a stable connection in the transmission of the data packets. The mechanisms involve streaming where the data is in form of stream bytes. TCP also retransmits data in case the data gets lost. TCP automatically detects the network behaviours, and restructures itself to optimize its operations during delays. The exchange of data packets is closely monitored by the protocol, and data is resent in case of delays in confirmation of the segment’s arrival. The UDP packets comprise of the source port, destination port fields, length fields, and the checksum field. The source port and destination port fields are used to determine the connection’s end points. The length field indicates the header’s length; it also indicates the data’s size. The checksum field permits the verification of the packets integrity (Oracle, 2010). Information from the application layer is packaged in the UDP packets. The protocol attaches a header to the respective packets. Contrary to the TCP, the UDP protocol does not depend on connection for the transmission of data. The protocol is also unordered since there is no confirmation of whether the data has been received. However, it overrides the performance of the TCP where reliability is not mandatory. Its headers comprise of lesser bytes than the TCP due to its simplicity. 3. Internet Layer The TCP and UDP protocols in the transport layer transmit the segments and packets to this layer. The main protocol in this layer that handles the packets is called the Internet Protocol (IP). The Address Resolution Protocol (ARP) is also found at this layer. IP maintains communication between the client and server. It also applies a connectionless system in the delivery of the packets. It is an unreliable protocol since there is no handshaking, therefore, the delivery of packets is not guaranteed. IP specifies a unique 32-bit number called the Internet Protocol Address (also known as the IP address) for every computer connected via the internet. Every packet that is sent across the internet contains the IP address of the packet’s source (remote location) and the IP address of its destination (x-stream.leedsmet.ac.uk). Packets from the transport layer are formatted into units called IP datagrams. The IP then determines the Internet addresses of the datagrams in order to be transmitted efficiently to the recipient computer. A header is attached to the datagram by the IP to relate the datagram to its respective IP address of the source and host destination. The attached header contains the datagram length and its sequence order. The IP’s main function is to transfer and route the packets to other computers. When the IP receives packets from the TCP or UDP, a routing table is searched for the route that has the closest similarity to the destination of the IP address. The entries in the routing contain the required information for every computer concerning the interaction with the remote networks. If a matching route is unavailable, IP disposes off the datagram. The IP packets may be divided into smaller packets to allow a large packet to be transmitted across a network that only allows small packets. Each IP packet has a Time To live (TTL) field, which is decremented. An outstanding advantage of the IP is that it permits a packet’s sender to set conditions on the path that the packet takes through the source route. The Address Resolution Protocol converts virtual addresses to physical ones (Hassell and Campbell, 2007). ARP applies the message exchange strategy where it defines a request and a response. A request message is placed in a hardware frame and broadcast to all computers on the network. The computer with a matching IP address responds to the request. 4. Network Interface Layer IP datagrams from the internet layer are transmitted to the network interface layer. The process of encapsulation occurs yet again where network interface protocols such as Point-to-Point (PPP) and the Serial Line internet Protocol (SLIP) format the IP datagram into a frame. The protocols attach a header and a footer to the datagram; this process is known as framing. The layer places the frames on the network medium for transfer to the server computer. Processes performed at this layer include encapsulating the IP datagrams into frames that are transmitted by the network. The network interface layer connects the internet layer to the physical layer in the OSI model. The IP datagrams cannot be transferred over a link without this layer. The IP addresses are mapped to the physical addresses that are used by the network. Data that is to be transmitted to the server computer originates from the internetwork layer. The Serial Line Internet Protocol is responsible for the framing of the IP datagrams. In most cases, the SLIP protocol has a simplistic feature. The PPP protocol is more advanced in terms of features and performance. The PPP has extra features such as authentication and compression; it detects errors during transmission. SLIP protocol applies a simple method of data linking. The protocol breaks an IP datagram into bytes before transferring each byte over the link in a sequence. After transmission of the final byte, a SLIP END character is sent to the recipient computer to indicate that the transmission of datagrams is over. The PPP encapsulates datagrams for the ease transfer over the physical layer. The PPP contains a Link Control Protocol (LCP) whose responsibility is to maintain and terminate links between the server and client computers. Physical Layer Although the physical layer is not part of the TCP/IP model, it plays a vital role in connecting the network interface layer to the physical components of the network system. The physical layer establishes the interface specifications, while also providing the medium requests. It provides the electrical and mechanical requirements that are needed in the transmission of packets in the connecting computers. The physical layer usually imposes an upper limit on the on the size of the frame that can be transmitted (Stevens, 1996, p.148). The physical layer consists of the networking cables, for example Ethernet and adapters. The adapters are responsible for linking the media to physical interfaces. Frames containing the web page request are transmitted via the cable to the server computer. On reaching the server computer, the frames are reassembled back to the initial page which requests the server to send the x-stream.leedsmet.ac.uk page back to the remote computer. The entire process of transmitting data packets through the TCP/IP model occurs, using the down- up stack. References Bonaventure, O., 2011. Computer Networking: Principles, Protocols, and Practice (Release 0.25).CS402: Local Area Networks.  Cerf, V. and Kahn, R., 1974. A protocol for packet network intercommunication. 1st ed. [New York: Institute of Electrical and Electronics Engineers.  Hassell, J. and Campbell, T., 2007. Understanding TCP/IP. Windows Vista: Beyond the Manual, pp.187--197. Mullins, M., 2010. Exploring the Anatomy of a Data Packet. 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