Reservation MAC Protocols for Ad-Hoc Networks: Analysis of the Approaches

Reservation MAC Protocols for Ad-Hoc Networks: Analysis of the Approaches

Ghalem Boudour (IRIT - Paul Sabatier University, France), Cédric Teyssié (IRIT - Paul Sabatier University, France) and Mammeri Zoubir (IRIT - Paul Sabatier University, France)
DOI: 10.4018/978-1-60960-589-6.ch007
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Multimedia and real-time applications require bandwidth guarantees, which may be achieved by resource reservation. Several researches were done to propose efficient reservation MAC protocols for ad-hoc networks. In these schemes, channel is segmented into super-frames composed of fixed number of slots. They allocate slots to each traffic source, and make sure that neighbor nodes record the reservation in order to ensure consistency of reservations between neighbor nodes. However, resource reservation in ad-hoc networks remain a very challenging task due to the instability of radio channels, node mobility and lack of coordination between mobile nodes. Proposed reservation MAC protocols like CATA, FPRP, R-CSMA and SRMA/PA have limitations and are suitable only for particular situations. In this paper, we propose a comparative analysis of the most representative reservation MAC protocols. We identify the major issues unresolved by reservation MAC protocols. A performance evaluation and comparative analysis with the IEEE 802.11e are achieved through the NS-2 simulator.
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Channel access protocols in MANETs can be classified into two categories: contention-based and reservation-based protocols. Contention-based protocols are non-deterministic and nodes compete to get access to the wireless channel. The IEEE 802.11 is the most known example of contention-based protocols.

The IEEE 802.11 (IEEE Std. 802.11, 1999) standard is considered as the de-facto MAC protocol for wireless networks. The DCF mode is based on the Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA). It uses two mechanisms to avoid collision: the physical carrier sensing and the virtual carrier sensing. The physical carrier sensing is used to detect the presence of signal on the common physical channel. The virtual carrier sensing uses the duration field of the MAC frame header to indicate the duration during which a node will reserve the channel.

DATA transmission in DCF is accomplished following the RTS / CTS / DATA / ACK handshake. A station which has a DATA packet to send waits the channel to be idle for the duration of DIFS (DCF Inter Frame Space). If the channel lasts idle for DIFS, the station transmits an RTS packet. Otherwise, the station enters in a backoff period, by choosing a backoff timer uniformly distributed in [0, CW], where CW is the Contention Window (CW) size. The backoff timer is decremented for each idle time-slot. The station transmits its RTS packet when the backoff timer expires. When the receiver receives successfully the RTS packet, it waits for SIFS (Short InterFrame Space) before replaying with a CTS packet. Both the RTS and CTS packets contain the Duration field which is used in order to prevent neighbours from accessing the channel during the RTS / CTS / DATA / ACK handshake.

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