OV Copyright © 2011 Element K Content LLC. All rights reserved. Networking Models  The OSI Model  The TCP/IP Model

OV Copyright © 2011 Element K Content LLC. All rights reserved. The OSI Model Application Presentation Session Transport Network Data Link Physical

OV Copyright © 2011 Element K Content LLC. All rights reserved. Layer 1: The Physical Layer The Physical layer of the OSI model:  Provides the means for transmitting data packets over a physical medium.  Specifies the electrical and mechanical characteristics of the network.  Receives fully formatted data packets from the Data Link layer.  Includes technologies such as: Ethernet, Fast Ethernet, ATM, token ring, and FDDI.

OV Copyright © 2011 Element K Content LLC. All rights reserved. Layer 2: The Data Link Layer The Data Link layer of the OSI model:  Is responsible for the error-free transfer of data packets on a network.  Is responsible for grouping data packets into frames and attaching the address of the receiving node to each frame – thus forming the data packet.  Adds error correction and detection codes to frames.  Includes two sublayers: MAC and LLC. Devices and protocols:  Switches operate at this layer.  PPP and SLIP are the protocols that operate at this layer.

OV Copyright © 2011 Element K Content LLC. All rights reserved. Layer 2: The Data Link Layer (Cont.) Data Link Sub-Layer Description LLC  Identifies the Network-layer protocols and manages frames between the layers.  Controls the the Physical layer device and also performs error control.  Checks the CRC of the frame, and either ACKs or NACKs the data.  Controls data flow to maintain the bandwidth of the network medium.  Tells the Data Link layer how to handle the frame it receives. MAC  Defines how packets are placed on the media.  Is responsible for the carrier sense to detect collision in a contention- based network.  Is responsible for the token in a token passing network.  Controls elements of addressing such as error notification, the frame delivery sequence, and flow control in an Ethernet network which uses contention-based media access.

OV Copyright © 2011 Element K Content LLC. All rights reserved. Layer 3: The Network Layer The Network layer of the OSI model:  Is responsible for addressing and routing the data packets from a source to a destination through a network.  Ensures delivery of packets across a network.  Is responsible for controlling congestion on the network by taking proper routing decisions.  Defines protocols for interconnecting two or similar networks such as IP, ARP, ICMP, DHCP, RIP, OSPF, BGP, and IGMP.

OV Copyright © 2011 Element K Content LLC. All rights reserved. Layer 4: The Transport Layer The Transport layer of the OSI model:  Accepts data from upper layers and breaks it into smaller units known as segments.  Passes the segments to the lower layers and ensures that all segments arrive correctly at the receiving end.  Adds a sequence number to reconstruct original sequence of segments. This is useful in case of out of order sequencing.  Is responsible for error correction and sending acknowledgments at the network level.  Gateways operate at this layer.  TCP, UDP, IPSec, PPTP, RDP and L2TP are the protocols that operate this layer.

OV Copyright © 2011 Element K Content LLC. All rights reserved. Network- and Transport-Layer Protocols Protocol Family Function Reliability protocols Provides a method of ensuring reliable data transfer. For example, a header or trailer might contain a Checksum value or request that you need to acknowledge received data by sending an acknowledgement message back to the sender. Connection protocols Establish and maintain a connectionless or connection-oriented service for the upper layers. In a connection-oriented service, the sending and receiving nodes maintain constant communication to mediate the transfer of data. Sequencing, flow control, and reliability are monitored at both ends. In a connectionless service, the message is packaged, delivered, and sent. The message is transferred only if communication exists between the two nodes. Routing protocols Provides a method of ensuring data transfer to the correct destination. In an unswitched network, routing is virtually unnecessary because the nodes are directly connected. In a switched network, however, the routing protocol determines the path a packet will take to reach its destination. This function is particularly important and complex in a packet-switched network, because there can be many possible paths to a destination and many intermediary devices such as routers along the path. Routing protocols determine the strategies used to transmit data through the network.

OV Copyright © 2011 Element K Content LLC. All rights reserved. Layer 5: The Session Layer The Session layer of the OSI model:  Establishes and connection between network devices and applications, maintains the connection, and then terminates or reestablishes it when required.  Controls how, when, and for how long a device can transmit or receive data.  Specifies procedure for the connection, termination, and reestablishment of sessions.  Specifies the procedures for synchronizing data transfer between two devices with different data transmission rates.  Sockets and session establishment in TCP function at this layer.

OV Copyright © 2011 Element K Content LLC. All rights reserved. Layer 6: The Presentation Layer The Presentation layer of the OSI model:  Is responsible for encoding data into a standard network-compatible format, which enable devices with different representation techniques to communicate with each other.  Adds services such as data compression and encryption.  MME, SSL, TLS, GIF, JPEG, and TIFF are the protocols and technologies that operate at this layer.

OV Copyright © 2011 Element K Content LLC. All rights reserved. Layer 7: The Application Layer  Offers services and utilities that enable application access to the network and its resources.  HTTP, DNS, FTP, Gopher, NFS, NTP, SMTP, SNMP, and Telnet are the technologies, protocols, and services that function at this layer.

OV Copyright © 2011 Element K Content LLC. All rights reserved. Application-, Presentation-, and Session-Layer Protocols Protocol FamilyFunctions Terminal- emulation protocols  Allow the user access to a text terminal and all its applications.  Enable computers to act as standard terminals so that they can access hosts. File access and file transfer protocols File access protocols:  Enable nodes to access files on the network.  Provide a common means to access network files. File transfer protocols: Enable copying of files between network storage and other storage, such as a computer's local disk drive. protocols  Provide for delivery and handling of messages. Remote-action and multiple- session protocols Remote-action protocols:  Determine whether processes should be performed remotely on a client node or directly by a server.  Required for setting up a client-server relationship. Multiple-session protocols:  Enable multiple network links to be established.

OV Copyright © 2011 Element K Content LLC. All rights reserved. Application-, Presentation-, and Session-Layer Protocols (Cont.) Protocol FamilyFunctions Network management protocols Provide tools for setting up and maintaining the network. Task-to-task protocols Enable software processes to communicate over the network. Codeset and data structure protocols  Define the representation of data.  Translate data for nodes that use different coding schemes.

OV Copyright © 2011 Element K Content LLC. All rights reserved. The OSI Data Communication Process Application Presentation Session Transport Network Data link Physical SenderReceiver Data added to Application layer 2.Data forwarded to lower layers from sender 3.Data added to Physical layer 4.Data is forwarded to the Application layer

OV Copyright © 2011 Element K Content LLC. All rights reserved. The TCP/IP Protocols TCP/IP Enables computers to communicate over all types of networks

OV Copyright © 2011 Element K Content LLC. All rights reserved. The TCP/IP Network Model Transport Network Interface Application Internet

OV Copyright © 2011 Element K Content LLC. All rights reserved. Layers in the TCP/IP Network Model TCP/IP LayerFunctions Application  Provides definition of protocols for file, mail, and hypertext transfer.  Handles the encoding of data and controlling of the sessions.  Defines socket services and other utilities over TCP/IP. Transport  Provides connection establishment and communication services.  Defines protocols for end-to-end transfer of data, along with error and flow controls. Internet  Provides addressing and routing services.  Controls congestion on the network.  Involves transferring data from a source to destination network when multiple networks are connected together. Network Interface  Provides services to send and receive data packets on the network.  Defines protocols for moving data frames between adjacent nodes, and for accessing the medium by the devices.  Defines the protocols for encoding and transmitting data over the network media.

OV Copyright © 2011 Element K Content LLC. All rights reserved. Comparison of the OSI and TCP/IP Models Application Presentation Session Transport Network Data Link Physical Transport Network Interface Application Internet TCP/IP model OSI model

OV Copyright © 2011 Element K Content LLC. All rights reserved. Comparison of the OSI and TCP/IP Models CategoryDescription Similarities  Both the models have a similar architecture.  Both the models have an Application, Transport, and Network layer.  Both the models have their lowest layer connected to the actual physical network. Dissimilarities  OSI was developed to standardize networking. TCP/IP was specifically developed to execute Internet-related tasks  The OSI reference model consists of seven architectural layers whereas the TCP/IP only has four layers.  The TCP/IP model does not have a Session or a Presentation layer.  The Application layer in TCP/IP handles the responsibilities of layers 5, 6, and 7 in the OSI reference model.  The TCP/IP model combines the OSI Data Link and Physical layers into the Network Interface layer.  The OSI reference model was invented before protocols, therefore the functionality allotted in each layer is not very optimized. But the TCP/IP protocols are the standards around which the Internet was developed and therefore, the functionality allotted at each layer is perfectly optimized.

OV Copyright © 2011 Element K Content LLC. All rights reserved. Data Encapsulation  Process of adding delivery information to the actual data transmitted on each layer.  Takes place in the transmission end as data is passed down the layers.  At the receiving end, the reverse process of removing the added information is done as data passes to the next higher layer in a process called de- encapsulation.  The added information is called a header if it is before the data, or a trailer if it is added after the data.

OV Copyright © 2011 Element K Content LLC. All rights reserved. Protocol Bindings Network interface Protocols bound to the network interface

OV Copyright © 2011 Element K Content LLC. All rights reserved. Reflective Questions 1. What are the Physical layer devices that you have come across in your network? 2. What are the similarities and differences between the OSI model and the TCP/IP model?