CCENT/CCNA ICND1 Chapter 1

Which OSI layer defines the standards for cabling and connectors? a. Layer 1 b. Layer 2 c. Layer 3 d. Layer 4 e. Layer 5 f. Layer 6 g. Layer 7

A

DEFINE: OSI Reference Model Layer 7

Application : Layer 7 provides an interface between the communications software and any applications that need to communicate outside the computer on which the application resides. It also defines processes for user authentication.

TCP/IP Architectural Model and Example Protocols: Application

Application: HTTP, POP3, SMTP

Which of the following terms is used specifically to identify the entity created when encapsulating data inside data link layer headers and trailers? a. Data b. Chunk c. Segment d. Frame e. Packet f. None of these—there is no encapsulation by the data link layer.

D

Which of the following protocols are examples of TCP/IP transport layer protocols? (Choose two answers.) a. Ethernet b. HTTP c. IP d. UDP e. SMTP f. TCP

D and F

OSI Functional Summary Layer 1

Physical : Defines the electrical, optical, cabling, connectors, and procedural details required for transmitting bits, represented as some form of energy passing over a physical medium.

DEFINE: adjacent-layer interaction

adjacent-layer interaction The general topic of how on one computer, two adjacent layers in a networking architectural model work together, with the lower layer providing services to the higher layer.

DEFINE: decapsulation (de-encapsulation)

decapsulation (de-encapsulation) On a computer that receives data over a network, the process in which the device interprets the lower-layer headers and, when finished with each header, removes the header, revealing the next-higher-layer PDU.

DEFINE: frame

frame A term referring to a data-link header and trailer, plus the data encapsulated between the header and trailer.

DEFINE: same-layer interaction

same-layer interaction The communication between two networking devices for the purposes of the functions defined at a particular layer of a networking model, with that communication happening by using a header defined by that layer of the model. The two devices set values in the header, send the header and encapsulated data, with the receiving device(s) interpreting the header to decide what action to take

OSI Functional Summary Layer 7

Application : Interfaces between network and application software. Also includes authentication services.

Which of the following protocols are examples of TCP/IP network access layer protocols? (Choose two answers.) a. Ethernet b. HTTP c. IP d. UDP e. SMTP f. TCP g. PPP

A and G

Which OSI layer defines the functions of logical network-wide addressing and routing? a. Layer 1 b. Layer 2 c. Layer 3 d. Layer 4 e. Layer 5 f. Layer 6 g. Layer 7

C

OSI Functional Summary Layer 2

Data link : Formats data into frames appropriate for transmission onto some physical medium. Defines rules for when the medium can be used. Defines means by which to recognize transmission errors.

DEFINE: OSI Reference Model Layer 2

Data link : The data link layer defines the rules that determine when a device can send data over a particular medium. Data link protocols also define the format of a header and trailer that allows devices attached to the medium to send and receive data successfully.

Which OSI layer defines the standards for data formats and encryption? a. Layer 1 b. Layer 2 c. Layer 3 d. Layer 4 e. Layer 5 f. Layer 6 g. Layer 7

F

TCP/IP Architectural Model and Example Protocols: Internet

Internet: IP

OSI Functional Summary Layer 3

Network : Logical addressing, routing, and path determination.

DEFINE: OSI Reference Model Layer 3

Network : The network layer defines three main features: logical addressing, routing (forwarding), and path determination. Routing defines how devices (typically routers) forward packets to their final destination. Logical addressing defines how each device can have an address that can be used by the routing process. Path determination refers to the work done by routing protocols to learn all possible routes, and choose the best route.

TCP/IP Architectural Model and Example Protocols: Network Access

Network Access: Ethernet, Point-to-Point Protocol (PPP), T/1

DEFINE: OSI Reference Model Layer 1

Physical:This layer typically refers to standards from other organizations. These standards deal with the physical characteristics of the transmission medium, including connectors, pins, use of pins, electrical currents, encoding, light modulation, and the rules for how to activate and deactivate the use of the physical medium.

DEFINE: OSI Reference Model Layer 4

Transport : Layer 4 protocols provide a large number of services, as described in Chapter 6 of this book. Although OSI Layers 5 through 7 focus on issues related to the application, Layer 4 focuses on issues related to data delivery to another computer—for instance, error recovery and flow control.

OSI Functional Summary Layer 4

Transport : establishment and termination, flow control, error recovery, and segmentation of large data blocks into smaller parts for transmission.

TCP/IP Architectural Model and Example Protocols: Transport

Transport: TCP, UDP

DEFINE: segment

segment In TCP, a term used to describe a TCP header and its encapsulated data (also called an L4PDU). Also in TCP, the process of accepting a large chunk of data from the application layer and breaking it into smaller pieces that fit into TCP segments. In Ethernet, a segment is either a single Ethernet cable or a single collision domain (no matter how many cables are used).

The process of HTTP asking TCP to send some data and making sure that it is received correctly is an example of what? a. Same-layer interaction b. Adjacent-layer interaction c. OSI model d. All of these answers are correct.

B. Adjacent-layer interaction occurs on one computer, with two adjacent layers in the model. The higher layer requests services from the next lower layer, and the lower layer provides the services to the next higher layer.

The process of TCP on one computer marking a TCP segment as segment 1, and the receiving computer then acknowledging the receipt of TCP segment 1 is an example of what? a. Data encapsulation b. Same-layer interaction c. Adjacent-layer interaction d. OSI model e. All of these answers are correct.

B. Same-layer interaction occurs on multiple computers. The functions defined by that layer typically need to be accomplished by multiple computers—for example, the sender setting a sequence number for a segment, and the receiver acknowledging receipt of that segment. A single layer defines that process, but the implementation of that layer on multiple devices is required to accomplish the function.

Which of the following terms are not valid terms for the names of the seven OSI layers? (Choose two answers.) a. Application b. Data link c. Transmission d. Presentation e. Internet f. Session

C and E. OSI includes the transport layer (not transmission layer) and the network layer (not Internet layer).

OSI Functional Summary Layer 6

Presentation : Defines the format and organization of data. Includes encryption.

DEFINE: OSI Reference Model Layer 6

Presentation : This layer's main purpose is to define and negotiate data formats, such as ASCII text, EBCDIC text, binary, BCD, and JPEG. Encryption also is defined by OSI as a presentation layer service.

OSI Functional Summary Layer 5

Session : Establishes and maintains end-to-end bidirectional flows between endpoints. Includes managing transaction flows.

DEFINE: OSI Reference Model Layer 5

Session : The session layer defines how to start, control, and end conversations (called sessions). This includes the control and management of multiple bidirectional messages so that the application can be notified if only some of a series of messages are completed. This allows the presentation layer to have a seamless view of an incoming stream of data.

The process of a web server adding a TCP header to the contents of a web page, followed by adding an IP header, and then adding a data link header and trailer is an example of what? a. Data encapsulation b. Same-layer interaction c. OSI model d. All of these answers are correct.

A. Encapsulation is defined as the process of adding a header in front of data supplied by a higher layer (and possibly adding a trailer as well).

DEFINE: encapsulation

encapsulation The placement of data from a higher-layer protocol behind the header (and in some cases, between a header and trailer) of the next-lower-layer protocol. For example, an IP packet could be encapsulated in an Ethernet header and trailer before being sent over an Ethernet.

DEFINE: networking model

networking model A generic term referring to any set of protocols and standards collected into a comprehensive grouping that, when followed by the devices in a network, allows all the devices to communicate. Examples include TCP/IP and OSI.

DEFINE: packet

packet A logical grouping of information that includes the network layer header and encapsulated data, but specifically does not include any headers and trailers below the network layer.

DEFINE: protocol data unit (PDU)

protocol data unit (PDU) A generic term referring to the header defined by some layer of a networking model, and the data encapsulated by the header (and possibly trailer) of that layer, but specifically not including any lower-layer headers and trailers.

summarize the benefits of layered protocol specifications:

■ Less complex: Compared to not using a layered model, network models break the concepts into smaller parts. ■ Standard interfaces: The standard interface definitions between each layer allow for multiple vendors to create products that fill a particular role, with all the benefits of open competition. ■ Easier to learn: Humans can more easily discuss and learn about the many details of a protocol specification. ■ Easier to develop: Reduced complexity allows easier program changes and faster product development. ■ Multivendor interoperability: Creating products to meet the same networking standards means that computers and networking gear from multiple vendors can work in the same network. ■ Modular engineering: One vendor can write software that implements higher layers—for example, a web browser—and another vendor can write software that implements the lower layers—for example, Microsoft's built-in TCP/IP software in its OSs.