OSI Communications Model

apprehensiveheehawΔίκτυα και Επικοινωνίες

26 Οκτ 2013 (πριν από 3 χρόνια και 9 μήνες)

86 εμφανίσεις

OSI Communications Model

OSI Communications model


Open System Interconnection
Reference Model


Organizes services into layers


A layer is a set of services that
provide services to layers above and
receive services from layers below.


Allows for protocols to be coded at
one layer without having to worry
about handling lower layers.

OSI Model Breakdown

OSI Model

Data Unit

Layer

Function

Host

layers

Data

7. Application

Network process to
application

6. Presentation

Data representation and
encryption

5. Session

Interhost communication

Segment

4. Transport

End
-
to
-
end connections
and reliability

Media

layers

Packet

3. Network

Path determination and
logical addressing

Frame

2. Data Link

Physical addressing

Bit

1. Physical

Media, signal and binary
transmission

Source: http://en.wikipedia.org/wiki/OSI_model

Layer 1: Physical Layer


Defines the layout of pins, voltages,
cable specifications, hubs, repeaters,
network adapters, Host Bus Adapters,
etc.


The physical layer deals with the
communication of one device to the
medium.

Layer 1: Physical Layer


Major functions:


Establishing and terminating a connection to
the medium.


Flow control


Modulation, the conversion between the
digital data and the signals sent over the
medium. This can be done over physical
cables (copper, fiber) or over radio.

Layer 2: Data Link Layer


Transfers data between adjacent nodes
on a WAN (Wide Area Network) or
between nodes on the same local LAN
(Local Area Network)


Outside of those boundaries the data is
handed off to a higher layer for transfer.

Layer 2: Data Link Layer


Layer 2 services:


Error control


Flow control


Layer 2 error and flow control are not used
in LAN protocols like Ethernet
, but are
used
in modems, and wireless networks


Physical addressing (MAC)


Packet switching



Layer 3: Network Layer


Provides a means to transfer variable
length data from a source to a
destination via one or more networks.


Routing is preformed on this layer.


Best known Layer 3 protocol is IP
(Internet Protocol)


Layer 4: Transport Layer


Controls flow control,
segmentation/
desegmentation
, and error
control.


Best known protocols are TCP
(Transmission Control Protocol) and
UDP (User Datagram Protocol)


Layer 5: Session Layer


Manages the connections between
computers.


Establishes, manages and terminates
connections.


Allows for full
-
duplex, half
-
duplex, or
simplex operation.

Layer 6: Presentation Layer


Deals with the delivery and formatting of
information given to the application
layer.


Examples: ASCII, UTF8, SSL, MIME

Layer 7: Application Layer


Provide ways for applications to
communicate with the lower layers.


Examples: HTTP (Hyper Text Transfer
Protocol), FTP (File Transfer Protocol)