Real-Time Communication Support in IEEE 802.11-Based Wireless Mesh Networks

Real-Time Communication Support in IEEE 802.11-Based Wireless Mesh Networks

Carlos M. D. Viegas (University of Porto, Portugal), Francisco Vasques (University of Porto, Portugal) and Paulo Portugal (University of Porto, Portugal)
Copyright: © 2015 |Pages: 13
DOI: 10.4018/978-1-4666-5888-2.ch713
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Background

The IEEE 802.11 standard defines four MAC sub-layer functions to control medium access (IEEE Standard 802.11-2012, 2012):

  • 1.

    Distributed Coordination Function (DCF) is the basic medium access mechanism based on Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA);

  • 2.

    Point Coordination Function (PCF) is a polling scheme where stations are interrogated in order to determine which have the right to transmit;

  • 3.

    Hybrid Coordination Function (HCF) introduces the concept of QoS and Transmission Opportunities by means of Enhanced Distributed Channel Access (EDCA) and HCF Controlled Access (HCCA) mechanisms;

  • 4.

    Mesh Coordination Function (MCF) defines an optional medium control mechanism for IEEE 802.11s mesh networks called MCF Controlled Channel Access (MCCA).

However, regarding real-time communication support, these functions present some limitations. DCF only provides best effort services, where packets are simply discarded when queue is full. This leads to an undesirable behavior when considering real-time communication, since important messages may be discarded. In addition, there is no traffic differentiation mechanism to separate traffic according to its priorities (Ni, 2005).

PCF is not able to handle multiple QoS requirements of different traffic types, because it defines only a round-robin scheduling algorithm. In addition, the access point contends for the medium with the same priority of other stations in order to transmit the beacon frame, causing delays and decreasing network performance (Ni, 2005; Mangold, Choi, Hiertz, Klein, & Walke, 2003).

Key Terms in this Chapter

Resource Reservation: Ensures enough resources allocation for priority traffic transmission.

Rate Adaptation: Uses multi-rate network capacity in order to adapt transmission data rate according to channel conditions.

Admission Control: Manages traffic admission according to specific requirements.

Quality of Service (QoS): A set of service requirements that need to be met by the network while transmitting data.

Channel Assignment: Assigns multiple channels to different traffic transmissions.

Wireless Mesh Network (WMN): A set of wireless stations that work together to convey data packets between end users, relaying in a multi-hop infrastructure.

IEEE 802.11: A family of standards that implements a wireless local area network by a set of medium access control and physical layer specifications.

Medium Access Control (MAC): A sub-layer of data link layer that controls channel access, allowing the communication of several devices over a shared medium.

Congestion Control: Controls the network traffic in order to avoid congestion.

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