\section{Configuration - How to use the LL/RLC/MAC} Configuration for the LL/RLC/MAC is described below. Each can be usedseperately/independantly for any other stack implementation. A GPRS/GSM configuration would require to use all together.Configuration is similar to any wired-cum-wireless example (note - presenceof the BS makes it a wired-cum-wireless scenario).\begin{itemize}\item {\bf Setting the LL}:  Set the LL layer type while configuring the nodes\begin{verbatim}        set opt(ll)     LL            ;# Link layer type           :           :        # configure for base-station/mobile nodes           :        $ns_ node-config -llType $opt(ll) \\end{verbatim}\item {\bf Setting the RLC}: Introduce an RLC while configuring the nodes.\begin{verbatim}         set opt(ll)    RLC          ;# Radio Link Control type           :           :        #configure for base-station node/mobile nodes           :        $ns_ node-config -rlcType $opt(rlc)  \\end{verbatim}\item{\bf Setting the Mac}: Set the MAC to GPRS.  The Mac requires a non-adhocrouting agent. Set the adhoc routing agent to NOAH.\begin{verbatim}         set opt(mac)     Mac/Gprs        set opt(adhoc)  NOAH           :           :        # configure for base-station node/mobile nodes        $ns_ node-config -macType $opt(mac)  \        $ns_ node-config -adhocRouting $opt(adhoc)\\end{verbatim}\item {\bf Configuring the Base Station (BS)}: The BS should be configured first ,ie before any other wireless node.  Therefore it will have a herarchicaladdress of the form 0.0.0 or 1.0.0 etc. This is requred by the Macimplementation.\item {\bf Configuring the Mobile Stations (MS)}: The MS are normal  ns-mobile nodeand can be configured to act as  GPRS mobiles or GSM mobiles. The onlydifference being that GPRS mobiles release resources ( ie release the slotreserved for them)  if their IFQ is empty and there is no packet transferfor a while.  The slot can then be alloted to another GPRS mobile ifrequred.  The GPRS mobile can ask for resources again whenever it haspackets to send. GSM mobiles on the other hand, keep resources "forever".This severly limits the number of GSM mobiles a system can support. Toconfigure the moble node as GPRS or GSM,  for each mobile node set\begin{verbatim}         Mac/Gprs set gprs_   1 ; # for GPRS; default value=1                   or        Mac/Gprs set gprs_   0 ; # for GSM\end{verbatim}\end{itemize}