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. (39 cards)
Secure Sockets Layer (SSL)
SSL is a data encrypting technology
Simple Mail Transport Protocol (SMTP)
SMTP is an email relay protocol
Post Office Protocol Version 3 (POP3)
POP3 is an email relay protocol
File Transfer Protocol (FTP)
FTP is a file transferring protocol that uses TCP
Trivial File Transfer Protocol (TFTP)
TFTP is a file transferring protocol that uses UDP
Secure Shell (SSH)
SSH is a remote device connectivity protocol
Telnet
Telnet is a remote device connectivity protocol
Simple Network Management Protocol (SNMP)
SNMP is a management and troubleshooting protocol
Domain Name System (DNS)
DNS is a translating protocol
Dynamic Host Configuration Protocol (DHCP)
DHCP is an IP configuration delivery protocol
What are the seven layers of the OSI model?
7) Application
6) Presentation
5) Session
4) Transport
3) Network
2) Data Link
1) Physical
Application (Layer 7)
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
Presentation (Layer 6)
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
Session (Layer 5)
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
Transport (Layer 4)
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)
Network (Layer 3)
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
Data Link (Layer 2)
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)
Physical (Layer 1)
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
File Transfer Protocol (FTP)
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
Trivial File Transfer Protocol (TFTP)
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
Hypertext Transfer Protocol (HTTP)
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
Simple Mail Transfer Protocol (SMTP)
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
Simple Network Management Protocol (SNMP)
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
Remote Terminal Emulation (Telnet)
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
