\section{Network Architecture}

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\begin{slide}{}

   \subsection{Layering}

   \begin{sitem}
      \item Use abstractions to hide complexity
      \item Abstraction naturally leads to layering

      \pichere{layers1.eps,height=2in}

      \item Can have alternative abstractions at each layer

      \pichere{layers2.eps,height=2in}

   \end{sitem}
\end{slide}

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\begin{slide}{}

   \subsection{\bf Protocols}

   \begin{sitem}
      \item Building blocks of a network architecture
      \item Each protocol object has two different interfaces
      \begin{sitem}
         \item {\it service interface}: defines operations on this protocol
         \item {\it peer-to-peer interface}: defines messages exchanged with 
          peer
      \end{sitem}

      \pichere{interfaces.eps,height=3in}

      \item Term ``protocol'' is overloaded
      \begin{sitem}
         \item specification of peer-to-peer interface
         \item module that implements this interface
      \end{sitem}
   \end{sitem}
\end{slide}

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\begin{slide}{}

   \begin{sitem}
      \item Protocol Graph
      \begin{sitem}
         \item collection of protocols and their dependencies
         \item most peer-to-peer communication is indirect
         \item peer-to-peer is direct only at hardware level
      \end{sitem}

      \pichere{protgraph.eps,height=2.5in}

      \item Multiplexing and Demultiplexing (demux key)

      \item Encapsulation (header/body)

      \pichere{encapsulation.eps,height=2in}

   \end{sitem}
\end{slide}

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\begin{slide}{}

   \subsection{Standard Architectures}

   Open Systems Interconnect (OSI) Architecture 
   \begin{sitem}
      \item International Standards Organization (ISO)
      \item International Telecommunications Union (ITU); formerly CCITT
      \item ``X dot'' series: X.25, X.400, X.500
      \item Reference Model
   \end{sitem}

   \pichere{osi.eps,height=5in}

\end{slide}

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\begin{slide}{}

   Internet Architecture
   \begin{sitem}
      \item Internet Engineering Task Force (IETF)

      \pichere{internet.eps,height=2.5in}

      \pichere{internet_alt.eps,height=2in}

      \item Application vs Application Protocol (FTP, HTTP)
      \item Features
      \begin{sitem}
         \item does not imply strict layering
         \item hourglass shape
         \item design and implementation go hand-in-hand
      \end{sitem}
   \end{sitem}
\end{slide}