\documentclass[10pt,a4paper]{article}

% Packages
\usepackage{fancyhdr}           % For header and footer
\usepackage{multicol}           % Allows multicols in tables
\usepackage{tabularx}           % Intelligent column widths
\usepackage{tabulary}           % Used in header and footer
\usepackage{hhline}             % Border under tables
\usepackage{graphicx}           % For images
\usepackage{xcolor}             % For hex colours
%\usepackage[utf8x]{inputenc}    % For unicode character support
\usepackage[T1]{fontenc}        % Without this we get weird character replacements
\usepackage{colortbl}           % For coloured tables
\usepackage{setspace}           % For line height
\usepackage{lastpage}           % Needed for total page number
\usepackage{seqsplit}           % Splits long words.
%\usepackage{opensans}          % Can't make this work so far. Shame. Would be lovely.
\usepackage[normalem]{ulem}     % For underlining links
% Most of the following are not required for the majority
% of cheat sheets but are needed for some symbol support.
\usepackage{amsmath}            % Symbols
\usepackage{MnSymbol}           % Symbols
\usepackage{wasysym}            % Symbols
%\usepackage[english,german,french,spanish,italian]{babel}              % Languages

% Document Info
\author{Songjm}
\pdfinfo{
  /Title (computer-network.pdf)
  /Creator (Cheatography)
  /Author (Songjm)
  /Subject (Computer Network Cheat Sheet)
}

% Lengths and widths
\addtolength{\textwidth}{6cm}
\addtolength{\textheight}{-1cm}
\addtolength{\hoffset}{-3cm}
\addtolength{\voffset}{-2cm}
\setlength{\tabcolsep}{0.2cm} % Space between columns
\setlength{\headsep}{-12pt} % Reduce space between header and content
\setlength{\headheight}{85pt} % If less, LaTeX automatically increases it
\renewcommand{\footrulewidth}{0pt} % Remove footer line
\renewcommand{\headrulewidth}{0pt} % Remove header line
\renewcommand{\seqinsert}{\ifmmode\allowbreak\else\-\fi} % Hyphens in seqsplit
% This two commands together give roughly
% the right line height in the tables
\renewcommand{\arraystretch}{1.3}
\onehalfspacing

% Commands
\newcommand{\SetRowColor}[1]{\noalign{\gdef\RowColorName{#1}}\rowcolor{\RowColorName}} % Shortcut for row colour
\newcommand{\mymulticolumn}[3]{\multicolumn{#1}{>{\columncolor{\RowColorName}}#2}{#3}} % For coloured multi-cols
\newcolumntype{x}[1]{>{\raggedright}p{#1}} % New column types for ragged-right paragraph columns
\newcommand{\tn}{\tabularnewline} % Required as custom column type in use

% Font and Colours
\definecolor{HeadBackground}{HTML}{333333}
\definecolor{FootBackground}{HTML}{666666}
\definecolor{TextColor}{HTML}{333333}
\definecolor{DarkBackground}{HTML}{0EB7EB}
\definecolor{LightBackground}{HTML}{EFFAFD}
\renewcommand{\familydefault}{\sfdefault}
\color{TextColor}

% Header and Footer
\pagestyle{fancy}
\fancyhead{} % Set header to blank
\fancyfoot{} % Set footer to blank
\fancyhead[L]{
\noindent
\begin{multicols}{3}
\begin{tabulary}{5.8cm}{C}
    \SetRowColor{DarkBackground}
    \vspace{-7pt}
    {\parbox{\dimexpr\textwidth-2\fboxsep\relax}{\noindent
        \hspace*{-6pt}\includegraphics[width=5.8cm]{/web/www.cheatography.com/public/images/cheatography_logo.pdf}}
    }
\end{tabulary}
\columnbreak
\begin{tabulary}{11cm}{L}
    \vspace{-2pt}\large{\bf{\textcolor{DarkBackground}{\textrm{Computer Network Cheat Sheet}}}} \\
    \normalsize{by \textcolor{DarkBackground}{Songjm} via \textcolor{DarkBackground}{\uline{cheatography.com/39339/cs/12234/}}}
\end{tabulary}
\end{multicols}}

\fancyfoot[L]{ \footnotesize
\noindent
\begin{multicols}{3}
\begin{tabulary}{5.8cm}{LL}
  \SetRowColor{FootBackground}
  \mymulticolumn{2}{p{5.377cm}}{\bf\textcolor{white}{Cheatographer}}  \\
  \vspace{-2pt}Songjm \\
  \uline{cheatography.com/songjm} \\
  \end{tabulary}
\vfill
\columnbreak
\begin{tabulary}{5.8cm}{L}
  \SetRowColor{FootBackground}
  \mymulticolumn{1}{p{5.377cm}}{\bf\textcolor{white}{Cheat Sheet}}  \\
   \vspace{-2pt}Not Yet Published.\\
   Updated 6th July, 2017.\\
   Page {\thepage} of \pageref{LastPage}.
\end{tabulary}
\vfill
\columnbreak
\begin{tabulary}{5.8cm}{L}
  \SetRowColor{FootBackground}
  \mymulticolumn{1}{p{5.377cm}}{\bf\textcolor{white}{Sponsor}}  \\
  \SetRowColor{white}
  \vspace{-5pt}
  %\includegraphics[width=48px,height=48px]{dave.jpeg}
  Measure your website readability!\\
  www.readability-score.com
\end{tabulary}
\end{multicols}}




\begin{document}
\raggedright
\raggedcolumns

% Set font size to small. Switch to any value
% from this page to resize cheat sheet text:
% www.emerson.emory.edu/services/latex/latex_169.html
\footnotesize % Small font.

\begin{multicols*}{4}

\begin{tabularx}{3.833cm}{X}
\SetRowColor{DarkBackground}
\mymulticolumn{1}{x{3.833cm}}{\bf\textcolor{white}{Introduction}}  \tn
% Row 0
\SetRowColor{LightBackground}
\mymulticolumn{1}{x{3.833cm}}{{\bf{Internet}}: interconnection of networks - Interrconnected ISPs} \tn 
% Row Count 2 (+ 2)
% Row 1
\SetRowColor{white}
\mymulticolumn{1}{x{3.833cm}}{{\bf{Communication links}}:fiber,copper,radio...} \tn 
% Row Count 3 (+ 1)
% Row 2
\SetRowColor{LightBackground}
\mymulticolumn{1}{x{3.833cm}}{{\bf{Trans rate R}}=bandwidth{[}bits/s{]}=capacity} \tn 
% Row Count 4 (+ 1)
% Row 3
\SetRowColor{white}
\mymulticolumn{1}{x{3.833cm}}{{\bf{Hosts}}=end systems: break app data into packets of length L bits, transmit packet into access network at transmission rate R} \tn 
% Row Count 7 (+ 3)
% Row 4
\SetRowColor{LightBackground}
\mymulticolumn{1}{x{3.833cm}}{{\bf{Packet trans delay}} = time to transmit L-bit packet into link = {\bf{L}}(bits)/{\bf{R}}(bits/s)} \tn 
% Row Count 9 (+ 2)
% Row 5
\SetRowColor{white}
\mymulticolumn{1}{x{3.833cm}}{{\bf{Protocols}}: Rules for data communication includes Syntax, Semantics(meaning of each section of bits), Timing} \tn 
% Row Count 12 (+ 3)
% Row 6
\SetRowColor{LightBackground}
\mymulticolumn{1}{x{3.833cm}}{{\bf{Internet standards}} define protocols: developed by IETF(Internet Engineering Task Force), IETF standards documents are called: RFCs(Request for comments);} \tn 
% Row Count 16 (+ 4)
% Row 7
\SetRowColor{white}
\mymulticolumn{1}{x{3.833cm}}{{\bf{Circuit Switching}}: dedicated circuit for every connection. FDM vs TDM(Freq/time Division Multiplexing)} \tn 
% Row Count 19 (+ 3)
% Row 8
\SetRowColor{LightBackground}
\mymulticolumn{1}{x{3.833cm}}{{\bf{Packet Switching}}: break msgs to smaller chunks/packets. Store-and-forward:entire packet must arrive at router before sending. {\bf{+}} It allows more users,good for bursty data,resource sharing, no call setup, but excessive congestion possible: packet delay\&loss} \tn 
% Row Count 25 (+ 6)
\hhline{>{\arrayrulecolor{DarkBackground}}-}
\end{tabularx}
\par\addvspace{1.3em}

\begin{tabularx}{3.833cm}{X}
\SetRowColor{DarkBackground}
\mymulticolumn{1}{x{3.833cm}}{\bf\textcolor{white}{Delay, Loss and Throughput}}  \tn
% Row 0
\SetRowColor{LightBackground}
\mymulticolumn{1}{x{3.833cm}}{{\bf{Delay}} when arrival rate \textgreater{} output link capacity; {\bf{Loss}} when no free buffers} \tn 
% Row Count 2 (+ 2)
% Row 1
\SetRowColor{white}
\mymulticolumn{1}{x{3.833cm}}{\seqsplit{d(nodal)=d(proc)+d(queue)+d(trans)+d(prop)}} \tn 
% Row Count 3 (+ 1)
% Row 2
\SetRowColor{LightBackground}
\mymulticolumn{1}{x{3.833cm}}{{\bf{d(proc)}}=nodal processing:check bit errors\&determine output link, typically \textless{} msec} \tn 
% Row Count 5 (+ 2)
% Row 3
\SetRowColor{white}
\mymulticolumn{1}{x{3.833cm}}{{\bf{d(queue)}}:time waiting to be transmitted . a:average packet arrival rate. Queuing delay larger when traffic intensity La/R goes to 1} \tn 
% Row Count 8 (+ 3)
% Row 4
\SetRowColor{LightBackground}
\mymulticolumn{1}{x{3.833cm}}{{\bf{d(trans)}} = L/R; d(propagation) = length of physical link/prop speed(2 x 10\textasciicircum{}8)} \tn 
% Row Count 10 (+ 2)
% Row 5
\SetRowColor{white}
\mymulticolumn{1}{x{3.833cm}}{{\bf{End-to-End Delay}} (PSw) = Time to deliver all for hop + 1 packet for each hop...} \tn 
% Row Count 12 (+ 2)
% Row 6
\SetRowColor{LightBackground}
\mymulticolumn{1}{x{3.833cm}}{{\bf{End-to-End Delay}} (CSw) = Call setup time + Trans time + Prop time} \tn 
% Row Count 14 (+ 2)
% Row 7
\SetRowColor{white}
\mymulticolumn{1}{x{3.833cm}}{{\bf{Throughput}}: rate at which bits transferred btw sender and receiver (bottleneck)} \tn 
% Row Count 16 (+ 2)
\hhline{>{\arrayrulecolor{DarkBackground}}-}
\end{tabularx}
\par\addvspace{1.3em}

\begin{tabularx}{3.833cm}{p{0.66726 cm} x{1.42551 cm} x{0.94023 cm} }
\SetRowColor{DarkBackground}
\mymulticolumn{3}{x{3.833cm}}{\bf\textcolor{white}{Internet protocol stack}}  \tn
% Row 0
\SetRowColor{LightBackground}
\seqsplit{application} & no of bytes & FTP,SMTP,HTTP \tn 
% Row Count 2 (+ 2)
% Row 1
\SetRowColor{white}
\seqsplit{transport} & identify apps & TCP, UDP \tn 
% Row Count 4 (+ 2)
% Row 2
\SetRowColor{LightBackground}
network & identify end host & IP, Routing \tn 
% Row Count 5 (+ 1)
% Row 3
\SetRowColor{white}
data link & identify next hop router & Ethernet, 802.11 \tn 
% Row Count 7 (+ 2)
% Row 4
\SetRowColor{LightBackground}
\seqsplit{physical} & identify group of bits & Wire \tn 
% Row Count 9 (+ 2)
\hhline{>{\arrayrulecolor{DarkBackground}}---}
\end{tabularx}
\par\addvspace{1.3em}


% That's all folks
\end{multicols*}

\end{document}