Advance Computer Networks (Lecture # 01)
1.1 Definition and Structure of Computer Networks
Definition:
"A computer network connects independent computers for the purpose of data exchange".
Node : point of
connection into the network such as computer, router, switch etc
Standard Organizations
Standardization is absolutely necessary for networks of computers from different manufacturers.
Examples of standardization organizations include
◦International
Organization for Standardization (ISO)
◦International
Telecommunications Union (ITU)
◦CEN/CENELEC/ETSI
(European)
◦National
Institute of Standards and Technology (NIST)
and many more.
The Structure of Networks
Structuring the problem
Protocol Architecture in Layers
We structure the complex communication system into layers:
◦The
lowest layer (layer 1) provides the physical connection.
◦Each
higher layer adds more functionality, hiding details from the next higher
layer.
◦“Horizontal”
interfaces between layers are a local matter (there is no need for
standardization). They are called “service interfaces”.
◦The
rules of communication between two entities at the same layer are called
“communication protocol”.
1.2 The ISO/OSI Reference Model for OSI
◦OSI
= OPEN SYSTEMS INTERCONNECTION
◦In
short: ISO/OSI Reference Model
◦ISO
International Standard 7498
◦Introduces
the layered architecture and basic terminology
◦Proposes
seven layers and their functionality
Seven Layers and Their Functionality
Clink the link below:
Seven Layers of the ISO-Reference Model (1)
◦The
physical
layer provides the transmission of a
digital data stream over a transmission line.
◦The
data
link layer provides error and flow
control for the physical bit stream. In LANs it also implements medium access
control.
◦The
network
layer provides routing
algorithms to compute end-to-end paths through the network. It also implements packet queueing
and forwarding in the “routers”.
◦The
transport
layer provides reliable
end-to-end data connections from a process at the source node to a process at
the destination node.
◦The
session
layer coordinates the
cooperation (dialog) between applications.
Click the link bellow:
Seven Layers of the ISO-Reference Model (2)
◦The
presentation
layer provides a common
transfer syntax for all systems, and conversion rules from the local to the
common data representation.
◦The
application
layer implements the
application-specific protocols.
Headers and Trailers in the Layered Model
Headers and Trailers in the Layered Model
Conclusions:
Network architectures consist of layers.
A protocol is defined between two entities of the same layer.
The ISO Reference Model for Open System Interconnection
distinguishes seven layers.
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