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CYBER240 > 2.2 OSI Networking Model > Flashcards

2.2 OSI Networking Model Flashcards

The OSI model classifies and organizes the tasks that hosts perform to prepare data for transport across the network. You should be familiar with the OSI model because it is the most widely used method for understanding and talking about network communications. However, remember that it is only a theoretical model that defines standards for programmers and network administrators. It is not a model of actual physical layers.

1
Q

Secure Sockets Layer (SSL)

A

SSL is a data encrypting technology

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2
Q

Simple Mail Transport Protocol (SMTP)

A

SMTP is an email relay protocol

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3
Q

Post Office Protocol Version 3 (POP3)

A

POP3 is an email relay protocol

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4
Q

File Transfer Protocol (FTP)

A

FTP is a file transferring protocol that uses TCP

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5
Q

Trivial File Transfer Protocol (TFTP)

A

TFTP is a file transferring protocol that uses UDP

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6
Q

Secure Shell (SSH)

A

SSH is a remote device connectivity protocol

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7
Q

Telnet

A

Telnet is a remote device connectivity protocol

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8
Q

Simple Network Management Protocol (SNMP)

A

SNMP is a management and troubleshooting protocol

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9
Q

Domain Name System (DNS)

A

DNS is a translating protocol

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10
Q

Dynamic Host Configuration Protocol (DHCP)

A

DHCP is an IP configuration delivery protocol

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11
Q

What are the seven layers of the OSI model?

A

7) Application
6) Presentation
5) Session
4) Transport
3) Network
2) Data Link
1) Physical

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12
Q

Application (Layer 7)

A

The Application layer 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. These services include:

Interface–provides an interface for a service to operate.

Communication–enables communication partner identification.

File services–transferring, storing, and updating shared data.

Print services–enabling network printers to be shared by multiple users.

Message services–transferring data in many formats (text, audio, video) from one location to another or from one user to another.

Application services–sharing application processing throughout the network and enabling specialized network servers to perform processing tasks.

Database services–storing, retrieving, and coordinating database information throughout the network.

**Most Application layer protocols operate at multiple layers, down to the Session layers and even Transport layers. They are classified as Application layer protocols because they start at the Application layer (the Application layer is the highest layer where they operate).

  • HTTP
  • Telnet
  • FTP
  • TFTP
  • SNMP
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13
Q

Presentation (Layer 6)

A

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.

Compatibility with the host.

Encapsulation of data into message envelopes through encryption and compression.

Restoration of data through decryption and decompression.

  • JPEG, BMP, TIFF, PICT
  • MPEG, WMV, AVI
  • ASCII, EBCDIC
  • MIDI, WAV
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14
Q

Session (Layer 5)

A

The Session layer’s primary function is managing the sessions in which data is transferred. Functions at this layer may include:

Keeps data streams separate (session identification).

Sets up, maintains, and tears down communication sessions.

Establishment and maintenance of communication sessions between the network hosts, ensuring that data is transported.

Management of multiple sessions (each client connection is called a session ). A server can maintain thousands of sessions simultaneously.

Assignment of the session ID number to each session, which is then used by the Transport layer to properly route the messages.

Dialog control that specifies how the network devices coordinate with each other (simplex, half-duplex, and full-duplex).

Termination of communication sessions between network hosts after completion of the data transfer.

Coordination of requests and responses between different hosts using the same application.

  • Network File System (NFS)
  • Apple Session Protocol (APS)
  • Structured Query Language (SQL)
  • Remote procedure call (RPC)
  • X Window
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15
Q

Transport (Layer 4)

A

The Transport layer:

Enables end-to-end flow control.

Provides a transition between the upper and lower layers of the OSI model, making the upper and lower layers transparent from each other.
*Upper layers format and process data
without regard for delivery.
*Lower layers prepare the data for
delivery by fragmenting and attaching
transport required information.

Uses port (or socket) numbers to identify distinct applications running on the same system. This allows each host to provide multiple services.

Receives large packets of information from higher layers and breaks them into smaller packets called segments. Segmentation is necessary to enable the data to meet network size and format restrictions.

The receiving Transport layer uses packet sequence numbers to reassemble segments into the original message.

Connection-oriented protocols perform error detection and correction and identify lost packets for retransmission. A connection-oriented protocol is a good choice when:
*Reliable, error-free communications
are more important than speed.
*Larger chunks of data are being sent.

Connectionless services assume an existing link between devices and allow transmission without extensive session establishment. Connectionless communications use no error checking, session establishment, or acknowledgments. Connectionless protocols allow quick, efficient communication at the risk of data errors and packet loss. Connectionless protocols are a good choice when:
* Speed is important.
* Smaller chunks of data are being sent.

> TCP (connection-oriented)
UDP (connectionless)

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16
Q

Network (Layer 3)

A

The Network layer:

Defines logical addresses (host and network).

Uses path determination (identification and selection).

Routes packets.

Describes how data is routed across networks and to the destination.

Maintains addresses of neighboring routers.

Maintains a list of known networks.

Determines the next network point to which data should be sent. Routers use a routing protocol to take 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.

Packets forwarded from the Transport layer to the Network layer become datagrams, and network-specific (routing) information is added. Network layer protocols then ensure that the data arrives at the intended destinations.

  • IP
  • AppleTalk
17
Q

Data Link (Layer 2)

A

Data Link {part 1}

  • Converts bits into bytes and bytes into
    frames.
  • Uses MAC address (also called the
    burned in address or hardware
    address).
  • Defines the logical network topology.
  • Specifies media access methods.
  • Implements host-to-host flow control.
  • Uses parity and CRC.

Logical Link Control (LLC) {Part 2}

The Logical Link Control (LLC) layer provides an interface between the MAC layer and upper-layer protocols. LLC protocols are defined by the IEEE 802.2 committee. The LLC sub-layer is responsible for:

  • Maintaining orderly delivery of frames
    through sequencing.
  • Controlling the flow or rate of
    transmissions using:
    * Acknowledgements
    * Buffering
    * Windowing
  • Ensuring error-free reception of
    messages by retransmitting.
  • Converting data into an acceptable form
    for the upper layers.
  • Removing framing information from the
    packet and forwarding the message to
    the Network layer.
  • Providing a way for upper layers of the
    OSI model to use any MAC layer
    protocol.
  • Defining Service Access Points (SAPs) by
    tracking and managing different
    protocols.

Media Access Control (MAC) {Part 3}

The Media Access Control (MAC) layer defines specifications for controlling access to the media. The MAC sub-layer is responsible for:

  • Adding frame start and stop information
    to the packet.
  • Adding Cyclical Redundancy Check (CRC)
    for error checking.
  • Converting frames into bits to be sent
    across the network.
  • Identifying network devices and network
    topologies in preparation for media
    transmission.
  • Defining an address (such as the MAC
    address) for each physical device on the
    network.
  • Controlling access to the transmission
    medium.

LAN Protocols:
- 802.2 (LLC), 802.3 (Ethernet)
- 802.11 (Wireless)

18
Q

Physical (Layer 1)

A

The Physical layer:

  • Moves bits across the media.
  • Defines cables, connectors, and pin
    positions.
  • Specifies electrical signals (voltage, bit
    synchronization).
  • Defines the physical topology (network
    layout).
  • Sets standards for sending and receiving
    electrical signals between devices. It
    describes how digital data (bits) are
    converted to electric pulses, radio
    waves, or pulses of lights. Devices that
    operate at the physical layer send and
    receive a stream of bits.
  • EIA/TIA 232 (serial signaling)
  • V.35 (modem signaling)
  • CAT6
  • RJ45
19
Q

File Transfer Protocol (FTP)

A

FTP provides a generic method of transferring files. It can include file security through user names and passwords. It allows file transfer between dissimilar computer systems.

OSI Model Layer(s):
- Application
- Presentation
- Session

TCP/IP Model Layer(s):
- Application/Process

20
Q

Trivial File Transfer Protocol (TFTP)

A

TFTP is similar to FTP. It lets you transfer files between a host and an FTP server. However, it provides no user authentication and uses UDP instead of TCP as the transport protocol.

OSI Model Layer(s):
- Application
- Presentation
- Session

TCP/IP Model Layer(s):
- Application/Process

21
Q

Hypertext Transfer Protocol (HTTP)

A

HTTP is used by web browsers and web servers to exchange files, such as web pages, through the World Wide Web and intranets. HTTP can be described as an information requesting and responding protocol. It is typically used to request and send web documents but is also used as the protocol for communication between agents using different TCP/IP protocols.

OSI Model Layer(s):
- Application
- Presentation
- Session

TCP/IP Model Layer(s):
- Application/Process

22
Q

Simple Mail Transfer Protocol (SMTP)

A

SMTP is used to route electronic mail through the internetwork. E-mail applications provide the interface to communicate with SMTP or mail servers.

OSI Model Layer(s):
- Application
- Presentation
- Session

TCP/IP Model Layer(s):
- Application/Process

23
Q

Simple Network Management Protocol (SNMP)

A

SNMP is a protocol designed for managing complex networks. SNMP lets network hosts exchange configuration and status information. This information can be gathered by management software and used to monitor and manage the network.

OSI Model Layer(s):
- Application
- Presentation
- Session

TCP/IP Model Layer(s):
- Application/Process

24
Q

Remote Terminal Emulation (Telnet)

A

Telnet allows an attached computer to act as a dumb terminal, with data processing taking place on the TCP/IP host computer. It is still widely used to provide connectivity between dissimilar systems.

OSI Model Layer(s):
- Application
- Presentation
- Session

TCP/IP Model Layer(s):
- Application/Process

25
Q

Network File System (NFS)

A

NFS was initially developed by Sun Microsystems. It consists of several protocols that enable users on various platforms to seamlessly access files from remote file systems.

OSI Model Layer(s):
- Application
- Presentation
- Session

TCP/IP Model Layer(s):
- Application/Process

26
Q

Voice over Internet Protocol (VoIP)

A

VoIP is a protocol optimized for the transmission of voice through the internet or other packet switched networks. Voice over IP protocols carry telephony signals as digital audio encapsulated in a data packet stream over IP.

OSI Model Layer(s):
- Application
- Presentation
- Session

TCP/IP Model Layer(s):
- Application/Process

27
Q

Domain Name System (DNS)

A

DNS is a system that is distributed throughout the internetwork to provide address/name resolution. For example, the name www.testout.com would be identified with a specific IP address.

OSI Model Layer(s):
- Application
- Presentation
- Session

TCP/IP Model Layer(s):
- Application/Process

28
Q

Transmission Control Protocol (TCP)

A

TCP provides connection-oriented services and performs segment sequencing and service addressing. It also performs important error-checking functions.

OSI Model Layer(s):
- Transport

TCP/IP Model Layer(s):
- Host-to-Host (Transport)

29
Q

User Datagram Protocol (UDP)

A

UDP is considered a host-to-host protocol like TCP but is not connection-oriented. Because of less overhead, UDP transfers data faster but is not as reliable.

OSI Model Layer(s):
- Transport

TCP/IP Model Layer(s):
- Host-to-Host (Transport)

30
Q

Internet Protocol (IP)

A

IP is the main TCP/IP protocol. It is a connectionless protocol that makes routing path decisions based on the information it receives from ARP. It also handles logical addressing issues through the use of IP addresses.

OSI Model Layer(s):
- Network

TCP/IP Model Layer(s):
- Internet

31
Q

Internet Control Message Protocol (ICMP)

A

ICMP works closely with IP in providing error and control information that helps move data packets through the internetwork.

OSI Model Layer(s):
- Network

TCP/IP Model Layer(s):
- Internet

32
Q

Internet Group Membership Protocol (IGMP)

A

IGMP is a protocol for defining host groups. All group members can receive broadcast messages intended for the group (called multicasts). Multicast groups can be composed of devices within the same network or across networks (connected with a router).

OSI Model Layer(s):
- Network

TCP/IP Model Layer(s):
- Internet

33
Q

Address Resolution Protocol (ARP)

A

ARP is used to get the MAC address of a host from a known IP address. ARP is used within a subnet to get the MAC address of a device on the same subnet as the requesting device.

OSI Model Layer(s):
- Network

TCP/IP Model Layer(s):
- Internet

34
Q

Reverse Address Resolution Protocol (RARP) and Bootstrap Protocol (BOOTP)

A

Both BOOTP and RARP are used to discover the IP address of a device with a known MAC address. BOOTP is an enhancement to RARP and is more commonly implemented than RARP. As its name implies, BOOTP is used by computers as they boot to receive an IP address from a BOOTP server. The BOOTP address request packet sent by the host is answered by the server.

OSI Model Layer(s):
- Network

TCP/IP Model Layer(s):
- Internet

35
Q

Dynamic Host Configuration Protocol (DHCP)

A

DHCP simplifies address administration. DHCP servers maintain a list of available and assigned addresses and communicate configuration information to requesting hosts. DHCP has the following two components:

  • A protocol for delivering IP configuration
    parameters from a DHCP server to a
    host.
  • A protocol specifying how IP addresses
    are assigned.

OSI Model Layer(s):
- Network

TCP/IP Model Layer(s):
- Internet

36
Q

Open Shortest Path First (OSPF)

A

OSPF is a route discovery protocol that uses the link-state method. It is more efficient than RIP in updating routing tables, especially on large networks.

OSI Model Layer(s):
- Network

TCP/IP Model Layer(s):
- Internet

37
Q

Routing Information Protocol (RIP)

A

RIP is a route discovery protocol that uses the distance-vector method. If the network is large and complex, OSPF should be used instead of RIP.

38
Q

CRC (Cyclic Redundancy Check)

A

The purpose of CRC (Cyclic Redundancy Check) in network communications is to detect errors in transmitted data. It’s a type of error-detecting code used in digital networks and storage devices to ensure the integrity of data transmission. Here’s how it works:

  1. Error Detection: When data is transmitted over a network, it may get corrupted due to noise, interference, or other factors. CRC generates a fixed-size checksum (a sequence of bits) based on the data being transmitted. This checksum is appended to the data before transmission.
  2. Checksum Calculation: The CRC algorithm calculates the checksum by dividing the data by a predetermined divisor (a fixed binary number) using binary polynomial division. The remainder obtained from this division becomes the checksum.
  3. Checksum Verification: Upon receiving the data, the recipient performs the same CRC calculation using the received data and the same divisor. If the remainder obtained matches the checksum appended to the data, it indicates that the data has not been corrupted during transmission. If there’s a mismatch, it signals that errors have occurred.
  4. Error Correction: While CRC detects errors reliably, it doesn’t correct them. Instead, it prompts re-transmission of the data, allowing the sender to resend the corrupted data.

In summary, the purpose of CRC in network communications is to provide a mechanism for detecting errors in transmitted data. By appending a checksum to the data, CRC enables recipients to verify data integrity and request retransmission if errors are detected, ensuring reliable and accurate data transmission over networks.

39
Q

Which of the following are functions of the MAC sublayer in the OSI model? (Select two.)

1) Defining a unique hardware address for each device on the network.

2) Mapping hardware addresses to link-layer addresses.

3) Creating routing tables based on MAC addresses.

4) Maintaining orderly delivery of frames through sequencing.

5) Letting devices on the network have access to the LAN.

A

1 and 5

Explanation:

The MAC sublayer in the OSI model 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.

Mapping hardware addresses to link-layer addresses and creating routing tables based on MAC addresses are not functions of the MAC sublayer.

Maintaining orderly delivery of frames through sequencing occurs at the Logical Link Control layer.

CYBER240 (12 decks)

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