Net+ Chapter 2 OSI Layers

encapsulation

the process of encoding data as it goes down the OSI model layers

Open Systems Interconnection reference model

OSI, the 7 layers

OSI Model

the primary architecture model for networks

reference model

a conceptual blueprint of how communications should take place

layer

a logical grouping in a model, particularly in OSI

binding

communication processes that are related to each other are bound, or grouped together, at a particular layer

physical layer

1, physical topology

data link layer

2, framing

network layer

3, routing

transport layer

4, end-to-end connection

session layer

5, dialog control

presentation layer

6, data encryption, compression, translation services

application layer

7, file, print, msg, db, and application services (interface)

application layer

7, provides a user interface

presentation layer

6, presents data, handles processing such as encryption

session layer

5, keeps different applications' data separate

transport layer

4, provides reliable or unreliable delivery

network layer

3, provides logical addressing, which router uses for path determination

data link layer

2, combines packets into bytes and bytes into frames

data link layer

2, provides access to media using MAC address

data link layer

2, performs error detection, not correction

physical layer

1, moves bits between devices, specifies voltage, wire speed, and pin-out of cables

application layer

chooses and determines the availability of communicating partners along with the resources necessary to make their required connections

application layer

coordinates partnering applications and forms a consensus on procedures for controlling data integrity and error recovery

application layer

layer comes into play only when it's apparent that access to the network will be needed soon

application layer

acts as an interface between the application program

presentation layer

presents data to the Application layer and is responsible for data translation and code formatting

presentation layer

data compression, decompression, encryption, and decryption are all associated with this layer

session layer

responsible for setting up, managing, and then tearing down sessions between Presentation layer entities

session layer

coordinates communication between systems and organizes their communication by offering three different modes

session layer

allows multiple web browser sessions on your desktop at the same time

simplex

one direction

half-duplex

both directions, but only one direction at a time

full-duplex

bidirectional

transport layer

segments and reassembles data into a data stream

transport layer

handles data from upper-layer applications and unites it into the same data stream

transport layer

provides end-to-end data transport services and can establish a logical connection between the sending host and destination host on the internetwork

transport layer

provides the mechanisms for multiplexing upper-layer applications, establishing virtual connections, and tearing down virtual circuits

transport layer

hides the many and sundry details of any network-dependent information from the higher layers, facilitating data transfer

transport layer

can be connection-oriented or connectionless

virtual circuit

the result of the following steps > a transmitting host starts to send segments down the OSI layered model, the sender's TCP process contacts the destination's TCP process to establish a connection

connection oriented

a connection based on a virtual circuit

handshake

where processes agree beforehand how much data will be sent in either direction before it is sent

TCP 3 way handshake

request for sync, acknowledge sync request and establish rules, acceptance of rules and establish sync

overhead

the steps taken to fully establish data transfer

flow control

provides a means for the receiver to govern the amount of data sent by the sender, prevents overwhelming of the buffers of the receiving host

flow control

delivered segments are ack, non-ack segments are retransmitted, segments are resequenced at destination, manageable data flow is maintained

buffer

where excess datagrams are stored, can be overflowed, transport can issue signals to indicate status

connection oriented characteristics

A virtual circuit is set up (such as a three-way handshake). It uses sequencing. It uses acknowledgments. It uses flow control.

window

quantity of data segments (measured in bytes) that the transmitting machine is allowed to send without receiving an acknowledgment

window size

how many data segments can be sent before an acknowledgment is needed, delimits the number of bytes that can be sent at a time

positive acknowledgment with retransmission

a technique that requires a receiving machine to communicate with the transmitting source by sending an acknowledgment message back to the sender when it receives data. Source will retransmit if no ack is received for a segment, receiver also acknowledges a loss in transit

network layer

manages logical device addressing, tracks the location of devices on the network, and determines the best way to move data

network layer

must transport traffic between devices that aren't locally attached

data packets

used to transport user data through the internetwork

routed protocols

Protocols used to support data traffic, IP, IPv6

route-update packets

used to update neighboring routers about the networks connected to all routers within the internetwork

routing protocols

Routing Information Protocol (RIP), RIPv2, Enhanced Interior Gateway Routing Protocol (EIGRP), and Open Shortest Path First (OSPF)

routing table

stores network address, interface, and metric

Network Addresses

protocol-specific network addresses

Interface

exit a packet will take when destined for a specific network

Metric

value equals the distance to the remote network, RIP uses hop count

hop count

number of routers a packet must pass through to reach destination

Routers

by default, won't forward any broadcast or multicast packets

Routers

use the logical address in a Network layer header to determine the next-hop router to forward the packet to

Routers

can use access lists, created by an administrator, to control security on the types of packets that are allowed to enter or exit an interface

Routers

can provide layer 2 bridging functions if needed and can simultaneously route through the same interface

Routers

a layer 3 device, provide connections between virtual LANs (VLANs)

Routers

can provide quality of service (QoS) for specific types of network traffic

Routers

Layer 3 switch

data link layer

provides the physical transmission of the data and handles error notification, network topology, and flow control

data link layer

ensures that messages are delivered to the proper device on an LAN using hardware (MAC) addresses and translates messages from the Network layer into bits for the Physical layer to transmit

data frame

data link layer formats into pieces, and adds a customized header containing the destination and source hardware addresses

data link layer

the only layer with sublayers

logical link control

data link sublayer, responsible for identifying Network layer protocols and then encapsulating them, header tells the Data Link layer what to do with a packet once a frame is received

media access control

data link sublayer, defines how packets are placed on the media. Physical addressing is defined here, as are logical topologies

media access control

line discipline, error notification (not correction), ordered delivery of frames, and optional flow control can also be used at this sublayer

physical layer

it sends bits and receives bits, uses state transitions, defines topology

physical layer

specifies the electrical, mechanical, procedural, and functional requirements for activating, maintaining, and deactivating a physical link between end systems

data communication equipment

DCE, located at the customer, a modem

encapsulation

data is wrapped with protocol information at each layer, each layer only communicates with its peer layer at destination

protocol data units

hold control information attached to the data at each layer of the model, can be header or trailer

data encapsulation steps

Application data → [TCP segment | UDP datagram] → IP packet (IP datagram) → Frame → Bits

802.1

LAN/MAN Management and MAC Bridges

802.3

CSMA/CD (Ethernet)

802.11

Wireless LAN

802.15

Wireless PAN