This chapter describes the implentation GSM/GPRS in 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
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/