Monday, 3 October 2016

Q . Draw and Explain TCP/IP protocol suite in detail.


TCP/IP Protocol Suite

The Internet Protocol suite (commonly TCP/IP) is the set of communications protocols used for the Internet and other similar networks. It is named from two of the most important protocols in it: the Transmission Control Protocol (TCP) and the Internet Protocol (IP), which were the first two networking protocols defined in this standard. Today's IP networking represents a synthesis of several developments that began to evolve in the 1960s and 1970s, namely the Internet and LANs (Local Area Networks), which, together with the invention of the World Wide Web by Sir Tim Berners-Lee in 1989, have revolutionized computing.
The Internet Protocol suite like many protocol suites can be viewed as a set of layers. Each layer solves a set of problems involving the transmission of data, and provides a well-defined service to the upper layer protocols based on using services from some lower layers. Upper layers are logically closer to the user and deal with more abstract data, relying on lower layer protocols to translate data into forms that can eventually be physically transmitted. The TCP/IP model consists of four layers.
From lowest to highest, these are the Link Layer, the Internet Layer, the Transport Layer, and the Application Layer.
The main differences between the OSI architecture and that of TCP/IP relate to the layers above the transport layer (layer 4) and those at the network layer (layer 3). OSI has both, the session layer and the presentation layer, whereas TCP/IP combines both into an application layer. The requirement for a connectionless protocol also required TCP/IP to combine OSI’s physical layer and data link layer into a network level.

1. Physical Layer

The physical layer may be either ethernet, SDH-DCC, or some timeslot of a PDH signal. Either OSI protocols and TCP/IP protocols build on the same physical layer standards, thus there is no difference between OSI and TCP/IP in this aspect.

2. Data Link Layer

The purpose of the data link layer is to provide error free data transmission even on noisy links. This is achieved by framing of data and retransmission of every frame until it is acknowledged from the far end, using flow control mechanisms. Error detection is done by means of error detection codes. In the internet world there is no real data link layer protocol, but the subnet protocol which has quite many similarities.
The subnet protocol consists of the IMP-IMP protocol which aims to provide a reliable connection between neighboured IMPs. For Ethernet based networks e.g. LANs (Local Area Network), the data link protocol LLC (Logical Link Control) is equally used in OSI and TCP/IP networks.

3. Network Layer

The network layer provides routing capabilities between source and destination system. TCP divides messages in datagrams of up to 64k length. Each datagram consists of a header and a text part. Besides some other information, the header contains the source and the destination address of the datagram. IP routes these datagrams through the network using e.g. the protocol OSPF (Open Shortest Path First) or RIP (Route Information Protocol) for path calculation purposes. The service provided by IP is not reliable. Datagrams may be received in the wrong order or they may even get lost in the network.

4. Transport Layer

The transport layer provides a reliable end-to-end connection between source and destination system on top of the network layer. It builds an integral part of the whole OSI layering principle and of the internet protocol.
The OSI transport layer protocol (TP4) and the internet tranport protocol (TCP) have many similarities but also some remarkable differences. Both protocols are built to provide a reliable connection oriented end-toend transport service on top of an unreliable network service. The network service may loose packets, store them, deliver them in the wrong order or even duplicate packets. Both protocols have to be able to deal with the most severe problems e.g. a subnetwork stores valid packets and sends them at a later date. TP4 and TCP have a connect, transfer and a disconnect phase. The principles of doing this are also quite similar. 

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