OSI Questions

The open system interconnection model is a conceptual model that characterizes and standardizes the communication functions of a telecommunication or computing system without regard to their underlying internal structure and technology.

Answer: * Controlling how messages are propagated through the network. * Identifying physical network devices. Explanation: The Data Link layer controls identifying devices on a network as well as how messages travel through the network (the logical topology). The other functions listed here are performed by the Physical layer.

Answer: * Routes messages between network Explanation: The network layer is responsible for routing messages between networks.

Answer: * Encrypt and compress data *Specify data format (such as file formats) Explanation: The presentation layer encrypts data, changes and converts character sets, and compresses data. File formats (such as .jpg, .wmv , and .wav) are part of the presentation layer. The application layer provides network services. The Session Layer maintains separate client connections through sessions IDs, and maintains those sessions. Flow control and error detection the provided at both the Transport layer and the Data Link layer. Transmitting frames happens at the Physical layer.

Answer: *Integration of network functionality into the host operation system *Enabling communication between network clients and services Explanation: The Application layer enables network services, and integrates network functionality into the host operating system. Applications actually run above the OSI Application layer. Conversation identification is accomplished at the Session layer through connection or transaction ID numbers. Data translation is performed at the Presentation layer.

Answer: *Movement of data across network cables Explanation: The Physical layer is concerned with how to transmit data and how to connect network hosts.

Answer: *MAC *LLC Explanation:The Data link layer is split into the following sublayers: *Logical Link control (LLC) Sublayer- Provides the operating system link to the device driver. *Media Access Control (MAC) Sublayer- Translates generic network request into device specific terms.

Answer: *Defining a unique hardware address for each device on the network. Explanation: The MAC Sublayer defines a unique MAC or data-link address for each device on the network. This address is usually assigned by the manufacturer. The MAC sublayer also provides devices with access to the network media.

Answer: * Transport Explanation: The transport layer is responsible for connection services that provide reliable message delivery through error detection and correction mechanisms. Specifically, the TCP protocol provides these services. Explanation:The Application layer integrates network functionality into the host operating system, and enables network services. The session layer's primary function is managing the sessions in which data is transferred. The Data link layer defines the rules and procedures for hosts as they access the physical layer.

Answer: Presentation --> Application Data Link --> Network interface Application --> application Session--> Application Network --> Internet Transport --> Transport Explanation:The TCP/IP networking model maps to the OSI networking model as follows: TCP/IP Model Layer --> OSI Model Layer Application ---------------> Application Presentation Session Transport --------------------> Transport Internet-----------------------> Network Network Interface --------> Data Link (Hardware)-------------------> Physical

Answer: Application ----------------------> HTTP Presentation-------------------->ASCII Session--------------------------->Session ID number Transport----------------------->Port numbers Network------------------------->Router Data Link------------------------>Switch Physical------------------------->Wireless access point Explanation:The following function at the following layers of the OSI model: Device or function -------> OSI Model Layer HTTP-------------------------->Application Session ID number------>Session Port numbers------------->Transport Router----------------------->Network Switch----------------------->Data Link Wireless access point-->Physical

Answer: *Network Explanation: A router uses the logical network address specified at the Network layer to forward messages to the appropriate LAN segment. A bridge, on the other hand, uses the MAC address and works at the Data Link layer.

Answer: *Data Link Explanation: The bridge is operating at the Data Link layer.

Answer: *Physical Explanation: Hubs operate at layer 1, or the physical layer of the OSI model.

Answer: *Switch *Network interface card Explanation: A network interface card and a switch operate at layer 2 (Data Link) of the OSI model. Layer 2 includes protocol that define the MAC address. The MAC address is burned into the network interface card, and switch uses the MAC address to make forwarding decisions. A hub or a repeater operate at layer 1; they regenerate a signal without looking at layer 2 or layer 3 information. A router operates at layer 3 or higher, using packet or data contents for making filtering decisions.

Answer: *Bridges *Network interface cards (NICs) *Switches Explanation: Network interface cards (NICs), bridges, and switches all operate at the OSI Data Link layer. They use the physical device address (MAC address) to identify packets. Hubs and repeaters operate at the physical layer they simply repeat packets without regard to addresses. Routers function at the Network layer they examine the logical device and network address to perform routing tasks.