gprs.tex

用C++编写的GPRS协议栈源代码

\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 on
handling 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 with
wired nodes (using hierarchical routing) to simulate the GPRS scenario.
Traffic can be set-up in either direction from MS to BS or vice-versa. The
number of frequencies available in a cell can be varied by the user through
the OTcl script. The maximum number of mobile nodes permissible in the cell
can also be set through the users' script.

Mobile nodes can be configured as GSM MS or GPRS MS. The difference here is
that GPRS MS release slots when there is no active packet transfer, while
GSM MS retain their slots till the call ends. Each MS can transmit/receive
only on one frequency at a time. The BS however, can listen to/transmit on
many frequencies simultaneously.

In order to provide these, the LL, RLC  and MAC layers have been implemented
with the following features
\begin{itemize}
\item {\bf LL}: Fragmentation and reassembly of higher layer PDUs; a stop-and-wait
retransmit mechanism.

\item {\bf RLC}: Fragmentation and reassembly of LL PDUs; a selective retransmit
mechanism.

\item {\bf MAC}: Separate uplink and downlink frequencies; TDMA frames with 8 time slots
on each; slot allocation by request; symmetrically allocation of  uplink and
downlink channels; slot
release.
\end{itemize}
These are further described in later sections.

 The LL and RLC  ack/fragmentation mechanisms can be used can be used with
any other stack implementation (ie apart from GPRS) with minor modifications
as described later.

Note that for GSM/GPRS, we require the mobile nodes to be ``non-adhoc" ie they
should communicate  only with the BaseStation and not amongst themselves.
The NOAH (Non-Adhoc ) routing agent  may be used for this purpose and is
included in this patch. Details can be found at
http://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}