IP is the network layer service implemented by the TCP/IP protocol suite. IP was designed as a protocol with low overhead. It provides only the functions that are necessary to deliver a packet from a source to a destination over an interconnected system of networks. The protocol was not designed to track and manage the flow of packets. These functions, if required, are performed by other protocols in other layers. The basic characteristics of IP are:
 Show The role of the network layer is to transport packets between hosts while placing as little burden on the network as possible. The network layer is not concerned with, or even aware of, the type of communication contained inside of a packet. IP is connectionless, meaning that no dedicated end-to-end connection is created before data is sent. Connectionless communication is conceptually similar to sending a letter to someone without notifying the recipient in advance. As shown in Figure 1, the postal service uses the information on a letter to deliver the letter to a recipient. The address on the envelope does not provide information as to whether the receiver is present, whether the letter arrives, or whether the receiver can read the letter. In fact, the postal service is unaware of the information contained within the contents of the packet that it is delivering and, therefore cannot provide any error correction mechanisms. Connectionless data communications work on the same principle. IP is connectionless and, therefore, requires no initial exchange of control information to establish an end-to-end connection before packets are forwarded. IP also does not require additional fields in the protocol data unit (PDU) header to maintain an established connection. This process greatly reduces the overhead of IP. However, with no pre-established end-to-end connection, senders are unaware whether destination devices are present and functional when sending packets, nor are they aware if the destination receives the packet, or if they are able to access and read the packet. Figure 2 shows an example of connectionless communication.
IP is often referred to as an unreliable or best-effort delivery protocol. This does not mean that IP works properly sometimes and does not function well at other times, nor does it mean that it is a poor data communications protocol. Unreliable simply means that IP does not have the capability to manage and recover from undelivered or corrupt packets. This is because while IP packets are sent with information about the location of delivery, it contains no information that can be processed to inform the sender whether delivery was successful. There is no synchronization data included in the packet header for tracking the order of packet delivery. There are also no acknowledgments of packet delivery with IP, and there is no error control data to track whether packets were delivered without corruption. Packets may arrive at the destination corrupted, out of sequence, or not at all. Based on the information provided in the IP header, there is no capability for packet retransmissions if errors such as these occur. If out-of-order or missing packets create problems for the application using the data, then upper layer services, such as TCP, must resolve these issues. This allows IP to function very efficiently. If reliability overhead were included in IP, then communications that do not require connections or reliability would be burdened with the bandwidth consumption and delay produced by this overhead. In the TCP/IP suite, the transport layer can use either TCP or UDP based on the need for reliability in communication. Leaving the reliability decision to the transport layer makes IP more adaptable and accommodating for different types of communication. The figure shows an example of IP communications. Connection-oriented protocols, such as TCP, require that control data be exchanged to establish the connection. To maintain information about the connection, TCP also requires additional fields in the PDU header.
The network layer is also not burdened with the characteristics of the media on which packets are transported. IP operates independently of the media that carry the data at lower layers of the protocol stack. As shown in the figure, any individual IP packet can be communicated electrically over cable, as optical signals over fiber, or wirelessly as radio signals. It is the responsibility of the OSI data link layer to take an IP packet and prepare it for transmission over the communications medium. This means that the transport of IP packets is not limited to any particular medium. There is, however, one major characteristic of the media that the network layer considers: the maximum size of the PDU that each medium can transport. This characteristic is referred to as the maximum transmission unit (MTU). Part of the control communication between the data link layer and the network layer is the establishment of a maximum size for the packet. The data link layer passes the MTU value up to the network layer. The network layer then determines how large packets should be. In some cases, an intermediate device, usually a router, must split up a packet when forwarding it from one medium to a medium with a smaller MTU. This process is called fragmenting the packet or fragmentation.
IP encapsulates, or packages, the transport layer segment by adding an IP header. This header is used to deliver the packet to the destination host. The IP header remains in place from the time the packet leaves the network layer of the source host until it arrives at the network layer of the destination host. Figure 1 shows the process for creating the transport layer PDU. Figure 2 shows the subsequent process for creating the network layer PDU. The process of encapsulating data layer by layer enables the services at the different layers to develop and scale without affecting other layers. This means that transport layer segments can be readily packaged by IPv4 or IPv6 or by any new protocol that might be developed in the future. Routers can implement these different network layer protocols to operate concurrently over a network to and from the same or different hosts. The routing performed by these intermediate device only considers the contents of the packet header that encapsulates the segment. In all cases, the data portion of the packet, that is, the encapsulated transport layer PDU, remains unchanged during the network layer processes.
IP is the network layer service implemented by the TCP/IP protocol suite. IP was designed as a protocol with low overhead. It provides only the functions that are necessary to deliver a packet from a source to a destination over an interconnected system of networks. The protocol was not designed to track and manage the flow of packets. These functions, if required, are performed by other protocols in other layers. The basic characteristics of IP are:
TCP is a connection oriented protocol and offers end-to-end packet delivery. It acts as back bone for connection.It exhibits the following key features:
TCP ServicesTCP offers following services to the processes at the application layer:
Stream Deliver ServiceTCP protocol is stream oriented because it allows the sending process to send data as stream of bytes and the receiving process to obtain data as stream of bytes. Sending and Receiving BuffersIt may not be possible for sending and receiving process to produce and obtain data at same speed, therefore, TCP needs buffers for storage at sending and receiving ends. Bytes and SegmentsThe Transmission Control Protocol (TCP), at transport layer groups the bytes into a packet. This packet is called segment. Before transmission of these packets, these segments are encapsulated into an IP datagram. Full Duplex ServiceTransmitting the data in duplex mode means flow of data in both the directions at the same time. Connection Oriented ServiceTCP offers connection oriented service in the following manner:
Reliable ServiceFor sake of reliability, TCP uses acknowledgement mechanism. Internet Protocol (IP)Internet Protocol is connectionless and unreliable protocol. It ensures no guarantee of successfully transmission of data. In order to make it reliable, it must be paired with reliable protocol such as TCP at the transport layer. Internet protocol transmits the data in form of a datagram as shown in the following diagram: Points to remember:
User Datagram Protocol (UDP)Like IP, UDP is connectionless and unreliable protocol. It doesn’t require making a connection with the host to exchange data. Since UDP is unreliable protocol, there is no mechanism for ensuring that data sent is received. UDP transmits the data in form of a datagram. The UDP datagram consists of five parts as shown in the following diagram: Points to remember:
File Transfer Protocol (FTP)FTP is used to copy files from one host to another. FTP offers the mechanism for the same in following manner:
Trivial File Transfer Protocol (TFTP)Trivial File Transfer Protocol is also used to transfer the files but it transfers the files without authentication. Unlike FTP, TFTP does not separate control and data information. Since there is no authentication exists, TFTP lacks in security features therefore it is not recommended to use TFTP. Key points
Difference between FTP and TFTP
TelnetTelnet is a protocol used to log in to remote computer on the internet. There are a number of Telnet clients having user friendly user interface. The following diagram shows a person is logged in to computer A, and from there, he remote logged into computer B. Hyper Text Transfer Protocol (HTTP)HTTP is a communication protocol. It defines mechanism for communication between browser and the web server. It is also called request and response protocol because the communication between browser and server takes place in request and response pairs. HTTP RequestHTTP request comprises of lines which contains:
Key Points
HTTP ResponseLike HTTP request, HTTP response also has certain structure. HTTP response contains:
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What are the features of Internet Protocol?
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