Net+ 1.3 The OSI Model

What OSI layer does a router operate to forward network messages?

A router uses logical network address specified at the Network layer to forward messages to the appropriate LAN segment.

What is a Mnemonic device to remember the OSI model?

All People Seem To Need Data Processing. OR Please Do Not Throw Sausage Pizza Away. (Application, Presentation, Session, Transport, Network, Data Link, Physical)

Correspond the layer of the TCP/IP model with it's OSI model layer.

Application: Application Presentation Session Transport: Transport Internet: Network Network Interface: Data Link (Hardware): Physical

Correspond a device/function with each layer of the OSI model.

Application: HTTP Presentation: ASCII Session: Session ID number Transport: Port Numbers Network: Router Switch: Data Link

Describe the Internet layer of the TCP/IP model

Comparable to the Network layer of the OSI model. It is responsible for moving packets through a network. This involves addressing hosts and making routine decisions to identify how the packet traverses the network. Protocols associated with the internet layer include ARP, ICMP and IGMP.

Describe the Host-to-Host layer of the TCP/IP model

Comparable to the Transport layer of the OSI model. It is responsible for error checking and reliable packet delivery. Here, the data stream is broken into segments that must be assigned sequence numbers so they can be reassembled correctly on the remote side after they are transported. Protocols associated with the Host-to-Host layer include TCP and UDP.

Describe the Application layer of the TCP/IP model

Corresponds to the Session, Presentation and Application of the OSI model. Protocols associated with the Application layer include FTP, HTTP, Telnet, SMTP, DNS, and SNMP.

What is the layer 2 of the OSI model?

Data Link

Describe the Network layer.

Describes how data is routed across networks and on the destination. Network layer functions include: Identifying hosts and networks by using logical addresses. Maintaining a list of known network and neighboring routers. Determining the next network point to which data should be sent. Routers use a routing protocol that takes into account various factors, such as the number of hops in the path, link speed, and link reliability, to select the optimal path for data. Data at the Network layer is referred to as packets.

Name (5) services that happen on the Application Layer

HTTP (Hypertext Transfer Protocol) Telnet FTP (File Transfer Protocol ) TFTP (Trivial File Transfer Protocol) SNMP (Simple Network Management Protocol)

At which layer of the OSI model do hubs operate?

Hubs operate at layer 1, the Physical layer.

Name two specifications of the Data Link layer.

Identifying physical network devices. Controlling how messages are propagated through the network.

What is the layer 1 of the OSI model?

Physical

In the OSI model, what is the primary function of the Network layer?

Routes messages between networks.

What is the layer 5 of the OSI model?

Session

Describe the Data Link layer.

The Data link layer defines the rules and procedures for hosts as they access the Physical layer. These rules and procedures specify or define: How hosts on the network are identified (physical or MAC address). How and when devices can transmit on the network medium (media access control and logical topology). How to verify that the data received from the Physical layer are error free (parity and CRC) How devices control the rate of data transmission between hosts (flow control) Data at the Data Link layer is referred to as frames.

What is the layer 4 of the OSI model?

Transport

Name (2) devices that operate at the OSI model layer 2.

A NIC and a Switch operate at layer 2 of the OSI model. Layer 2 includes protocols that define the MAC addresses. The MAC address is burned into the network interface card, and a switch uses the MAC address to make following decisions.

What is the layer 7 of the OSI model?

Application

Name the (4) layers of the TCP/IP model.

Application Host-to-Host Internet Network Access

Name the (7) layers of the OSI model.

Application Presentation Session Transport Network Data Link Physical

Describe the Network Access layer of the TCP/IP model

Corresponds to the Physical and Data Link layers of the OSI model. It is responsible for describing the physical layout of the network and how messages are formatted on the transmission medium.

Describe the (5) conversion steps of data encapsulation

Data (Application, Presentation, Session) Segments (Transport) Packets (Network) Frames (Data Link) Bits (Physical)

Name (2) functions that are preformed at the Application layer.

Enabling communication between network clients and services. Integration of network functionality into the host operating system.

Describe the Presentation layer.

Formats or "presents"data into a compatible form for receipt by the Application layer or the destination system. Specifically, the Presentation layer ensures: Formatting and translation of data between systems. Negotiation of data transfer syntax between systems by converting character sets to the correct format. Encapsulation of data into message envelopes by encryption and compression. Restoration of data by decryption and decompression.

Describe the Application layer.

It integrates network functionality into the host operating system and enables network services. The Application layer does not include specific applications that provide services, but rather provides the capability for services to operate on the network. Most application layer protocols operate at multiple layers down to the Session and even Transport layers. However, they are classified as Application layer protocols because they start at the Application layer (the Application layer is the highest layer where they operate).

Name the (2) sublayers of the Data Link layer.

LLC (Logical Link Control MAC (Media Access Control

Name (2) functions of the MAC sublayer.

Letting devices on the network have access to the LAN. Defining a unique hardware address for each device on the network. 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.

The Data Link layer of the OSI model is comprised of two sublayers. What are they?

MAC-Translates generic network requests into device-specific terms LLC-Provides the operating system link to the device driver.

Name a function that is preformed at the Physical layer of the OSI model.

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

Name (3) devices that operate at the Data Link layer of the OSI model.

NICs, Bridges, and Switches all operate at the OSI Data Link layer. They use the physical device address (MAC), to identify packets.

What is the layer 3 of the OSI model?

Network

What are some of the limitations of the OSI model?

OSI layers are theoretical and do not actually perform real functions. Industry implementations rarely have a layer-to-layer correspondence with the OSI layers. Different protocols within the stack perform different functions that help send or receive the overall message. A particular protocol implementation may not represent every OSI layer (or may spread across multiple layers).

What is the layer 6 of the OSI model?

Presentation

What are some of the advantages of using the OSI model to discuss networking concepts?

Provides a common language and reference point for network professionals. Divides networking tasks into logical layers for easier comprehension. Allows specialization of features at different levels. Aids in troubleshooting. Promotes standards of interoperability between networks and devices. Provides modularity in networking features (developers can change features without changing the entire approach)

Describe the Transport layer.

Provides transmission between the upper and lower layers of the OSI model, making the upper and lower layers transparent from each other. Transport layer functions include: End-to-end flow control. Port and socket numbers. Segmentation, sequencing, and combination. Connection services, either reliable (connection-oriented) or unreliable (connectionless) delivery of data. Data at the Transport layer is referred to as segments.

Describe the Physical layer.

Sets standards for sending and receiving electrical signals between devices. Protocols at the Physical layer identify: How digital data (bits) are converted to electric pulses, radio waves, or pulses of light. Specifications for cables and connectors. The physical topology. Data at the Physical layer are referred to as bits.

Name (2) functions that are performed at the Presentation layer.

Specify data format (such as file formats) Encrypt and compress data.

What is the OSI model?

The Open Systems Interconnection (OSI) model is a theoretical way of classifying and talking about the complex process of sending data on a network.

What OSI model layer is responsible for guaranteeing reliable message delivery?

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.

Your company purchases a new bridge, which filters packets based on MAC address of the destination computer. On which layer of the OSI model is this device functioning?

The bridge is operating at the Data Link layer.

Describe the Session layer.

The session layer manages the sessions in which data are transferred. Session layer functions include: Management of multiple sessions (each client connection is called a session). A server can concurrently maintain thousands of sessions. Assignment of a session ID number to each session to keep data streams separate. The setting up, maintenance, and tearing down of communication sessions.