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Summary about The OSI Model , Peer-to-Peer Process, Interfaces between Layers, Internet Layers (TCP/IP), Interfaces between Layers.
Typology: Study notes
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An ISO (International standard Organization) that covers
all aspects of network communications is the Open
System Interconnection (OSI) model.
An open system is a model that allows any two different
systems to communicate regardless of their underlying
architecture (hardware or software).
The OSI model is not a protocol; it is model for
understanding and designing a network architecture that is
flexible, robust and interoperable.
The OSI model is a layered framework for the design of
network systems that allows for communication across
all types of computer systems.
The OSI model is built of seven ordered layers:
Within a single machine, each layer calls upon services of
the layer just below it.
Layer 3, for example, uses the services provided by layer 2
and provides services for layer 4.
Between machines, layer x on one machine communicates
with layer x on another machine, by using a protocol ( this
is Peer-to-Peer Process ).
Communication between machines is therefore a peer-to-
peer process using protocols appropriate to a given layer.
Internet Layers (TCP/IP)
the functions required to
transmit a bit stream over a
physical medium. It also
defines the procedures and
functions that physical devices
and interfaces have to perform
for transmission occur.
The physical layer is responsible for transmitting individual bits from one
node to the next.
The physical layer is concerned with the following:
Physical characteristics of interfaces and media: The
physical layer defines the characteristics of the interface
between devices and the transmission media, including
its type.
Representation of the bits: the physical layer data consist
of a stream of bits without any interpretation. To be
transmitted, bits must be encoded into signals –electrical
or optical-. The physical layer defines the type of
encoding.
Data rate: The physical layer defines the transmission
rate, the number of bits sent each second.
the physical layer, a raw
transmission facility, to a
reliable link and is responsible
for node-to-node delivery. It
makes the physical layer appear
error free to the upper layer
(network layer).
The data link layer is responsible for transmitting frames
from one node to the next.
Node-to-node delivery
Flow Control. If the rate at which the data are absorbed by
the receiver is less than the rate produced in the sender,
the data link layer imposes a flow control mechanism to
prevent overwhelming the receiver.
Error control. The data link layer adds reliability to the
physical layer by adding mechanisms to detect and
retransmit damaged or lost frames. Error control is
normally achieved through a trailer to the end of the frame.
Access Control. When two or more devices are connected
to the same link, data link layer protocols are necessary to
determine which device has control over the link at any
time.
Functions:
Logical addressing.
Routing
The network layer is responsible for the delivery of packets from the original
source to the final destination.
Source-to-destination delivery
The transport layer is responsible for process-to-process
delivery of the entire message.
The network layer oversees host-to-destination delivery of
individual packets, it does not recognize any relationship
between those packets.
The transport layer ensures that the whole message arrives
intact and in order, overseeing both error control and flow
control at the process-to-process level.
