\documentclass[12pt,psfig]{report}\begin{document}  \chapter{The General Packet Radio Service - GPRS}This chapter describes the implentation GSM/GPRS in {\it ns}. Only the MobileStation (MS) -BaseStation(BS) interactions are dealt with so far.  The focus is onhandling of the radio resources and on the ntework stack ie the Link Layer(LL),  the Radio Link Control (RLC) and the Medium Access Control (MAC)operating between the MS and the BS.  We allow for operation in a single cell. The BS may be interfaced withwired nodes (using hierarchical routing) to simulate the GPRS scenario.Traffic can be set-up in either direction from MS to BS or vice-versa. Thenumber of frequencies available in a cell can be varied by the user throughthe OTcl script. The maximum number of mobile nodes permissible in the cellcan also be set through the users' script.Mobile nodes can be configured as GSM MS or GPRS MS. The difference here isthat GPRS MS release slots when there is no active packet transfer, whileGSM MS retain their slots till the call ends. Each MS can transmit/receiveonly on one frequency at a time. The BS however, can listen to/transmit onmany frequencies simultaneously.In order to provide these, the LL, RLC  and MAC layers have been implementedwith the following features\begin{itemize}\item {\bf LL}: Fragmentation and reassembly of higher layer PDUs; a stop-and-waitretransmit mechanism.\item {\bf RLC}: Fragmentation and reassembly of LL PDUs; a selective retransmitmechanism.\item {\bf MAC}: Separate uplink and downlink frequencies; TDMA frames with 8 time slotson each; slot allocation by request; symmetrically allocation of  uplink anddownlink channels; slotrelease.\end{itemize}These are further described in later sections. The LL and RLC  ack/fragmentation mechanisms can be used can be used withany other stack implementation (ie apart from GPRS) with minor modificationsas described later.Note that for GSM/GPRS, we require the mobile nodes to be ``non-adhoc" ie theyshould communicate  only with the BaseStation and not amongst themselves.The NOAH (Non-Adhoc ) routing agent  may be used for this purpose and isincluded in this patch. Details can be found athttp://www.icsi.berkeley.edu/~widmer/mnav/ns-extension/\input{configuration.tex}%\section {Link Layer (LL)}\input{mac.tex}\input{algo.tex}\input{rlc.tex}\input{ll.tex}%\section {Radio Link Control (RLC)}%\section {Medium Access Control (MAC)}%\section {Scope}%\input scope.tex%\input traffic.tex not needed!%\section {Commands at a glance}\input{commands.tex}\end{document}