Survey of Real-Time Communication in CSMA-Based Networks

Abstract

The purpose of this paper is to survey the state-of-the-art on real-time (RT) communication in CSMA-based networks and to identify the most suitable approaches to deal with the requirements imposed by next generation communication environments. The paper focuses in the two of the most relevant solutions that operate in shared broadcast environments, according to the CSMA medium access protocol (IEEE 802.3/802.11). RT communication solutions are classified according to two classification axes. The first axis is related to how collisions are dealt with. A second classification axis is related to the compatibility degree achieved by each of the proposed approaches. Finally, a RT communication framework that is adequate to support RT communication in shared environments is briefly discussed.

Wi-Bio: management policy aimed at the establishment of networks for patient monitoring using IEEE 802.11

“…Such an approach, however, cannot be adopted in IEEE 802.11 because radio shutdown could result in the loss of information transmitted over the network, whereas the stations can receive frames at any instant of time; • Non-deterministic data delivery: in DCF, stations send data independently, which may result in collisions between frames transmitted by the wireless network (Moraes et al, 2010). At this point, to avoid further collisions, the exponential recoil mechanism (backoff) used in CSMA/CA introduces random waiting times at stations so that they can carry out new attempts to send frames that collided (Institute..., 2007).…”

“…However, achieving this goal is not trivial because user applications may have higher rates of data generation (such as audio/video streams) that require large bandwidth (Moraes et al, 2010). Therefore, the Wi-Bio was set to operate on the IEEE 802.11 standard (Institute..., 2007) because, in addition to ensuring sufficiently large bandwidth, this standard is very widespread in the market and has low implementation cost (Moraes et al, 2010 According to Ko et al (2010b), the presence of a network infrastructure decreases the loss of data transmitted over wireless links. Therefore, the WiBio works using resources defined in infrastructured operation mode described in IEEE 802.11 standard.…”

“…At this point, to avoid further collisions, the exponential recoil mechanism (backoff) used in CSMA/CA introduces random waiting times at stations so that they can carry out new attempts to send frames that collided (Institute..., 2007). The adoption of this strategy, however, incorporates non-determinism in the delivery of data, a feature that is not interesting for applications having real-time restrictions (Moraes et al, 2010;Ni et al, 2004) (Institute..., 2005). In EDCA, the stations send data independently, but before being sent, the data are mapped into predefined categories of access (voice, video, best effort and background traffic) that have different priorities for medium access (Institute..., 2005).…”

“…For example, similar to IEEE 802.11, IEEE 802.11e has issues regarding the consumption of energy at stations. Moreover, as occurs in the DCF and PCF, the EDCA has been shown to be inefficient in the delivery of data that have real-time constraints (Moraes et al, 2006), and HCCA presents scalability problems (Moraes et al 2010).…”

“…Some of these requirements are as follows (Chipara et al, 2009;Ko et al, 2010a;Moraes et al, 2010;Shin and Ramanathan, 1994;Varshney, 2006):…”