mirror of https://github.com/tLDP/LDP
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@ -8,7 +8,7 @@
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been made to ensure that the instructions and information herein are
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accurate and reliable. Send comments, corrections, suggestions and questions
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to the author Binh Nguyen, linuxfilesystem(at)yahoo(dot)com(dot)au with the
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subject heading of Linux Networking. There is however, no guarantee of response.
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subject heading of 'Linux Networking'. There is however, no guarantee of response.
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</para>
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<para>
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@ -92,6 +92,8 @@ There are eight main network technology issues that must be addressed at each la
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in the architecture though. These are outlined below:
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</para>
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<para>
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<screen>
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1. Mechanism of identifying senders and receivers: addressing.
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2. Rules for data transfer: simplex, half-duplex, or full-duplex.
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3. Logical channels: sharing a link among a number of connections.
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@ -100,6 +102,8 @@ in the architecture though. These are outlined below:
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6. Incompatible speed between fast sender and slow receiver.
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7. Message fragmentation and assembly.
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8. Strategies for choosing routes.
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</screen>
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</para>
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<para>
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To study the above issues in detail please consult, Tannenbaum 4th edition.
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@ -121,35 +125,41 @@ and their respective functions and services.
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</para>
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<para><variablelist>
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<para>
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<screen>
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entity:
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in software, it is sometimes called a process;
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in hardware in hardware it could mean in pratice an I/O chip
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<varlistentry><term>entity:</term>
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<listitem><para>in software, it is sometimes called a process; in hardware in hardware it could mean in pratice an I/O chip</para></listitem></varlistentry>
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peer enties:
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entities at the same layer in different machines/devices
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<varlistentry><term>peer enties:</term>
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<listitem><para>entities at the same layer in different machines/devices</para></listitem></varlistentry>
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<varlistentry><term>service provider:</term>
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<listitem><para>eg. layer n, a layer that provides a service</para></listitem></varlistentry>
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service provider:
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eg. layer n, a layer that provides a service
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<varlistentry><term>service receiver:</term>
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<listitem><para>eg. layer n + 1, a layer that receives a service</para></listitem></varlistentry>
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service receiver:
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eg. layer n + 1, a layer that receives a service
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<varlistentry><term>service access point (SAP):</term>
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<listitem><para>a point where service is accessed, for example a function call in software, or the telephone for a telephone company</para></listitem></varlistentry>
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service access point (SAP):
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a point where service is accessed, for example a function call
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in software, or the telephone for a telephone company
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<varlistentry><term>protocol data unit (PDU):</term>
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<listitem><para>a data unit that is communicated between peer entities</para></listitem></varlistentry>
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protocol data unit (PDU):
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a data unit that is communicated between peer entities
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<varlistentry><term>service data unit (SDU):</term>
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<listitem><para>the PDU from the serice receiver</para></listitem></varlistentry>
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service data unit (SDU):
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the PDU from the serice receiver
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<varlistentry><term>protocol control information (PCI):</term>
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<listitem><para>is appended by a service receiver to an SDU in order to indicated the type of service required and forms the IDU</para></listitem></varlistentry>
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protocol control information (PCI):
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is appended by a service receiver to an SDU in order to
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indicated the type of service required and forms the IDU
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<varlistentry><term>interface data unit (IDU):</term>
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<listitem><para>the data unit that is given from a service receiver to a service provider.</para></listitem></varlistentry>
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interface data unit (IDU):
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the data unit that is given from a service receiver to a
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service provider.
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</variablelist></para>
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</screen>
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</para>
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<para>
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The term "service" can be deemed to mean a number of things. These are outlined
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@ -184,24 +194,24 @@ the service interface. The primitives differ for different services. As a simple
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example, a service may provide the following primitives:
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</para>
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<para><orderedlist>
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<para>
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<screen>
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LISTEN:
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listen for an incoming communication request
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<varlistentry><term>LISTEN:</term>
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<listitem><para>listen for an incoming communication request</para></listitem></varlistentry>
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CONNECT:
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make a communication request
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<varlistentry><term>CONNECT:</term>
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<listitem><para>make a communication request</para></listitem></varlistentry>
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RECEIVE:
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receive data of a communication
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<varlistentry><term>RECEIVE:</term>
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<listitem><para>receive data of a communication</para></listitem></varlistentry>
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SEND:
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send data of a communication
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<varlistentry><term>SEND:</term>
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<listitem><para>send data of a communication</para></listitem></varlistentry>
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<varlistentry><term>DISCONNECT:</term>
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<listitem><para>disconnect or discontinue a communication</para></listitem></varlistentry>
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</orderedlist></para>
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DISCONNECT:
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disconnect or discontinue a communication
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</screen>
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</para>
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<para>
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As discussed before, each layer has specfic functions and offers certain services
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