Compare the layers of the OSI and TCP/IP models OSI model: The Open Systems Interconnection (OSI) Reference Model is amodular framework for developing standards that are based on adivision of network operations into seven, sets of networkservices. At one time, most vendors agreed to support OSI in one form oranother, but the OSI was too loosely deﬁned and proprietarystandards were too entrenched. Except for the OSI-compliantX.400 and X.500 e-mail and directory standards, which are stillwidely used, what was once thought to become the universalcommunications standard now serves as the teaching model for allother protocols. Most of the functionality in the OSI model exists in allcommunications systems, although two or three OSI layers may beincorporated into one. A look at each of the OSI layers , and the role it plays. APPLICATION layer 7 Gives user applications access to network. This layer represents the services, that directly support the user applications such as software for ﬁle transfers,database access, and E-mail PRESENTATION layer 6 The presentation layer, usually part of an operating system, converts incoming and outgoing data from onepresentation format to another. Presentation layer services include data encryption and text compression. SESSION Opens manages, and closes conversations between two computers. It performs name recognition and the
layer 5 functions such as security, needed to allow two applications to communicate over the network, also provides error handling. TRANSPORT layer 4 This layer provides transparent transfer of data between end systems, or hosts, and is responsible for end-to-end error recovery and ﬂow control. It ensures complete data transfer. Sequences data packets, and requests retransmission ofmissing packets. It also repackages messages for more eﬃcient transmission over the network. NETWORK layer 3 Establishes, maintains and terminates network connections. Routes data packets across networksegments. Translates logical addresses and names into physical addresses. DATA LINK layer 2 Transmits frames of data from computer to computer on the same network segment. Ensures the reliability ofthe physical link established at layer 1. Standards deﬁne how data frames are recognized and provide thenecessary ﬂow control and error handling at the frameset. The data link layer is divided into two sublayers: The Media Access Control (MAC) layer and the Logical Link Control (LLC) layer. The MAC sublayer controls how acomputer on the network gains access to the data andpermission to transmit it. The LLC layer controls frame synchronization, ﬂow control and error checking. PHYSICAL layer 1 The Physical layer deﬁnes all the electrical and physicalspeciﬁcations for devices. This includes the layout ofpins, voltages, and cable speciﬁcations. Hubs, repeaters and network adapters are physical-layer devices. Deﬁnes cabling and connections. Transmits data overthe physical media. Example of how the OSI Layers work using an e-mail sent from the computer on the left. Data travels from the sending computer down through all thelayers to the physical layer where the data is put onto the networkcabling, and then sent to the physical layer of the receiving
computer where the process reverses and the data travels upthrough the layers to the application layer of the receivingcomputer. E-mail sent from John: Meet me at Carl's 1:30 John E-mail received fromJohn: Meet me at Carl's 1:30 John Identify sender and intended receiver;is there an e-mail application available? APPLICATION layer 7 Identiﬁed sender and intended receiver;found e-mail application. Encode data with X coding key; use ASCII characters. PRESENTATION layer 6 Decoded data with X decoding key; used ASCII characters Initiate and terminate the session according to X protocol SESSION layer 5 Initiated and terminated the session according to X protocol. Make sure all data is sent intact. TRANSPORT layer 4 Make sure all data has arrived intact. Keep track of how many hops; open shortest path First; Go to IP address 255.65.0.123 NETWORK layer 3 Keep track of how many hops; opened the shortest path First; Went to IP address 255.65.0.123
Is the initial connection set up? Put data into frames according to Xstandard DATA LINK layer 2 The initial connection set up. Decoded data in frame according to Xstandard. Send as electrical signal over the network cableat X voltage, and X Mbps. PHYSICAL layer 1 Receive electrical signal over the network cableat X voltage, and X Mbps. TCP/IP model: The TCP/IP model is not same as OSI model. OSI is a seven-layeredstandard, but TCP/IP is a four layered standard. OSI Layers TCP/IP Layers APPLICATION layer 7 PRESENTATION layer 6 APPLICATION LAYER(Layer 4) SESSION layer 5 TRANSPORT layer 4 TRANSPORT LAYER(Layer 3) NETWORK layer 3 INTERNET LAYER (Layer 2) DATA LINK layer 2
PHYSICAL layer 1 NETWORK INTERFACE LAYER(Layer 1) Network Interface Layer The network interface layer speciﬁes the form in which data mustbe routed by the type of network is used. Internet Layer The internet layer is between Network Access Layer and TransportLayer.The internet layer has the responsibility of sending packetsacross potentially multiple networks. Internetworking requiressending data from the source network to the destination network.This process is called routing. Transport Layer The transport layer can be thought of as a transport mechanism,e.g., a vehicle with the responsibility to make sure that its contents(passengers/goods) reach their destination safely and soundly,unless another protocol layer is responsible for safe delivery. Thelayer simply establishes a basic data channel that an applicationuses in its task-speciﬁc data exchange. Application Layer (Also described as: Link Layer, Internet Layer,Transport Layer, Application Layer) The three top layers in the OSI model the application layer, thepresentation layer and the session layer are not distinguishedseparately in the TCP/IP model where it is just the applicationlayer. The application layer deﬁnes TCP/IP application protocolsand how host programs interface with transport layer services touse the network.