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- 2. THE OSI NETWORKING MODEL
- 4. THE OSI NETWORKING MODEL Physical Layer (Layer 1) The physical layer of the OSI model identifies the network’s physical characteristics, including the following specifications: Hardware:The type of media used on the network, such as type of cable, type of connector, and pinout format for cables. Topology:The physical layer identifies the topology to be used in the network. Common topologies include ring, mesh, star, bus, and hybrid. Protocols and technologies such as USB, Ethernet, DSL, ISDN,T-carrier links (T1 and T3), GSM, and SONET operate at the physical layer. In addition to these characteristics, the physical layer defines the voltage used on a given medium and the frequency at which the signals that carry the data operate. These characteristics dictate the speed and bandwidth of a given medium, as well as the maximum distance over which a certain media type can be used.
- 5. THE OSI NETWORKING MODEL Data Link Layer (Layer 2) The data link layer is responsible for getting data to the physical layer so that it can transmit over the network. The data link layer is also responsible for error detection, error correction, and hardware addressing. The term frame describes the logical grouping of data at the data link layer. The data link layer has two distinct sublayers: Media Access Control (MAC) layer:This controls access to network media.The MAC address (physical or hardware address) of NIC is defined at this layer. Logical Link Control (LLC) layer: Responsible for the error and flow-control mechanisms. Protocols and technologies such as High-Level Data Link Control (HDLC), Layer 2 Tunneling Protocol (L2TP), Point-to-Point Protocol (PPP), Point-to-Point Tunneling Protocol (PPTP), Spanning Tree Protocol (STP), and virtual LANs (VLANs) operate at the data link layer.
- 6. THE OSI NETWORKING MODEL Network Layer (Layer 3) The primary responsibility of the network layer is routing—providing mechanisms by which data can be passed from one network system to another. Functionality at the network layer is provided through routing protocols, which are software components. Protocols at the network layer are also responsible for route selection, determining the best path for the data to take throughout the network. Network layer protocols use software configured addresses and special routing protocols to communicate on the network. The term packet describes the logical grouping of data at the network layer. Routes can be configured in two ways: In a static routing environment, routes are manually added to the routing tables. In a dynamic routing environment, routing protocols communicate routing information between networked devices on the network.
- 7. THE OSI NETWORKING MODEL Transport Layer (Layer 4) The basic function of the transport layer is to provide mechanisms to transport data between network devices. Primarily it does this in three ways: Error checking: Protocols at the transport layer ensure that data is correctly sent or received. Service addressing: A number of protocols support many network services. The transport layer ensures that data is passed to the right service at the upper layers of the OSI model. Segmentation:To traverse the network, blocks of data need to be broken into packets of a manageable size for the lower layers to handle. Protocols that operate at the transport layer can either be connectionless, such as User Datagram Protocol (UDP), or connection oriented, such as Transmission Control Protocol (TCP). The transport layer is also responsible for data flow control, which refers to how the receiving device can accept data transmissions.
- 8. THE OSI NETWORKING MODEL Session Layer (Layer 5) The session layer is responsible for managing and controlling the synchronization of data between applications on two devices. It does this by establishing, maintaining, and breaking sessions. Whereas the transport layer is responsible for setting up and maintaining the connection between the two nodes, the session layer performs the same function on behalf of the application. Protocols that operate at the session layer include NetBIOS, Network File System (NFS), and Server Message Block (SMB). Presentation Layer (Layer 6) The presentation layer convert the data intended for or received from the application layer into another format. Some common data formats handled by the presentation layer: Graphics files: JPEG,TIFF, GIF, Text and data: American Standard Code for Information Interchange (ASCII) and Extended Binary Coded Decimal Interchange Code (EBCDIC). Sound/video: MPEG, MP3, and MIDI files Encryption and decryption of data takes place at this layer.
- 9. THE OSI NETWORKING MODEL Application Layer (Layer 7) The function of the application layer is to take requests and data from the users and pass them to the lower layers of the OSI model. Incoming information is passed to the application layer, which then displays the information to the users. Some of the most basic application layer services include file and print capabilities. The application layer defines the processes that enable applications to use network services. If an application needs to open a file from a network drive, the functionality is provided by components that reside at the application layer. Protocols defined at the application layer: Dynamic Host Configuration Protocol (DHCP), Domain Name System (DNS), Server Message Block (SMB), File Transfer Protocol (FTP), Hypertext Transfer Protocol (HTTP)
- 12. THE OSI NETWORKING MODEL Comparing OSI to the Four-Layer TCP/IP Model The network interface layer in the TCP/IP model is sometimes referred to as the network access or link layer, and this is where Ethernet, FDDI, or any other physical technology can run. The Internet layer is where IP runs (along with ICMP and others). The transport layer is where TCP and its counterpart UDP operate. The application layer enables any number of protocols to be plugged in such as HTTP, SMTP, Simple Network Management Protocol (SNMP), DNS, and many others.
- 13. THE OSI NETWORKING MODEL Identifying the OSI Layers atWhichVarious Network Components Operate