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Introduction: Internet
involves the interconnection of workstations, terminals and other networked
devices. In most cases a network allows computers of different types to
intercommunicate using a
network protocol. The protocol that the computers use is the most
important to communication, than their actual make. Thus, in order for them
to intercommunicate, computers on a
network must have a common protocol.
Many of the first computers were standalone devices, and thus
worked independently from other computers. This caused many problems,
including:
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The difficulty to intercommunicate between
computers. |
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The difficulty in managing the
configuration of the computers. |
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The requirement for duplication of
resources, as each computer required its own resource, such as a dedicated
printer, a dedicated modem, and so on. |
This problems were solved with local area
networks (LANs), which connected
computers and other devices within a single building. One of the great
advantage of LANs was that they allowed the sharing of files and printers.
They are also efficient in transferring files within a organization, but it
was still difficult to transmit data over a large geographical area. This
led to the the development of WANs
(Wide Area Networks), and MANs
(Metropolitan Area Networks).
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Normally a communication request originates
at the highest layer (Application Layer). The request is passed
down through the lower layers in the form of a packet called a
protocol data unit (PDU). Layers in the protocol stack
communicate with their adjacent layers via one or more
Service Access Points (SAP). Each succeeding layer in the
stack adds its own information to the PDU that will be read by its
counterpart (peer) layer on the receiving system. Once the data
arrives at the lower layers, the PDU is encoded into data frames
and placed onto the cable for transmission. The data frames make
their way to the receiving system and the entire process is
reversed as the PDU makes its way up the protocol stack. As it
moves up the stack, each layer "unwraps" the PDU and receives the
information from its peer layer on the sending system. |
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Repeater regenerates and
retransmits a signal and functions at the Physical (1st) Layer |
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Bridge links separate LANs and
functions at the Data Link (2nd) Layer |
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Router routes data between LANs
and functions at the Network (3rd) Layer |
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Gateway links and translates
between LANs with different protocols and can function across all
layers but are commonly reported as functioning at the Application
(7th) Layer |
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Communities & Forums
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