Fix Design/P4/BMV2

doc/Design.tex

@@ -259,25 +259,7 @@ session table inside the python controller. While the Jool and Tayga
 both support cleaning up old session entries,
 our P4 based solution does not support this feature at the moment.
 % ----------------------------------------------------------------------
-\section{\label{Design:BMV2}BMV2}
-Development of the thesis took place on a software emulated switch
-that is implemented using Open vSwitch~\cite{openvswitch}
-and the behavioral model~\cite{_implem_your_switc_target_with_bmv2}.
-The development followed
-closely the general design shown in section
-\ref{design:nat64}. Within the software emulation checksums can be
-computed with two different methods:
-\begin{itemize}
-\item Recalculating the checksum by inspecting headers and payload
-\item Calculating the difference between the translated headers
-\end{itemize}
-The BMV2 model is rather sophisticated and provides many standard
-features including checksumming over payload. This allows the BMV2
-model to operate as a full featured host, including advanced features
-like responding to ICMP6 Neighbor discovery requests~\cite{rfc4861}
-that include payload checksums.
-A typical code to create the checksum can be found in figure
-\ref{fig:checksum}.
+\section{\label{design:bmv2}P4/BMV2}
 \begin{figure}[h]
 \begin{verbatim}
 /* checksumming for icmp6_na_ns_option */
@@ -306,12 +288,39 @@ update_checksum_with_payload(meta.chk_icmp6_na_ns == 1,
 );
 \end{verbatim}
   \centering
-  \caption{IPv4 Pseudo Header}
-  \label{fig:checksum}
+  \caption{P4/BMV2 checksumming}
+  \label{fig:bmv2checksum}
 \end{figure}
-
+The software emulated switch that is implemented using
+Open vSwitch~\cite{openvswitch} and the
+behavioral model~\cite{_implem_your_switc_target_with_bmv2}
+offers the fastest and easiest way of P4 development. All NAT64
+features are tested first on P4/BMV2 and in a second step ported to
+P4/NetFPGA and modified, where necessary.
+The development follows closely the general design shown in section
+\ref{design:nat64}.
+As outlined in section \ref{background:checksums}, checksums inside
+higher level protocols need to be adjusted after translation.
+Within the software emulation checksums can be
+computed with two different methods:
+\begin{itemize}
+\item Recalculating the checksum by inspecting headers and payload
+\item Calculating the difference between the translated headers
+\end{itemize}
+The BMV2 model is sophisticated and provides direct support
+for calculating the checksum over the payload. This allows the BMV2
+model to operate as a full featured host, including advanced features
+like responding to ICMP6 Neighbor discovery requests~\cite{rfc4861}
+that include payload checksums. Sample code that calculates the
+required checksum for answering NDP queries is shown in figure
+\ref{fig:bmv2checksum}. The code shows how the field
+\texttt{hdr.icmp6.checksum} is updated with the \texttt{csum16} method
+depending on the IPv6 and ICMP6 headers as well as the payload. The
+second option of using the differences is described in section
+\ref{design:netpfga}.
+% ok
 % ----------------------------------------------------------------------
-\section{\label{Design:NetPFGA}NetFPGA - FIXME: relate things}
+\section{\label{design:netpfga}NetFPGA - FIXME: relate things}
 While the P4-NetFPGA project ~\cite{netfpga:_p4_netpf_public_github}
 allows compiling P4 to the NetPFGA, the design slightly varies.
 In particular, the NetFPGA P4 compiler does not support reading