TIME COMMUNICATIONS

Time Communications

Time Communications

Introduction

The users in today's world demand multimedia traffic transmission with a satisfactory QoS (Quality of Service) level along with reliable data traffic transmission. The realtime applications are strictly time-constraint and need a good throughput level, while slightly unreliable connections are allowed. On the other hand data traffic does not need particularly reduced delay, but reliability is crucial. These criteria arises the need for a network where all types of traffics can be served with their specific QoS requirements.

Wireless LAN was first presented with WiFi, and then gradually arrived the WiMAX, 3G and even 4G networks like LTE, which are well renowned for high-speed and broad area coverage. But this paper proposes some enhancement of the earliest expertise WiFi, because still today, WiFi is the unbeatable and only solution for reduced cost deployment over a smaller coverage area.

The most prevalent standard used for wireless networking is the IEEE 802.11 [IEEE, 1997] which was released by the Institute of Electrical and Electronics Engineers (IEEE) in 1997. Different versions have since been created to continue and advance the IEEE 802.11 standard in many aspects, which varies from the support of quality of service (QoS) features to higher data rates. The importance of the IEEE 802.11 comes from its capability of two operational modes: the infrastructure mode and the ad hoc mode. The infrastructure mode is similar to a cellular infrastructure-based network, where a node acts as the access issue (AP) for other nodes. This is the most widespread operational mode used to construct Wi-Fi hotspots. Nevertheless, it is the ad hoc mode of operation that has attracted the largest attention inside the research community employed in the area of wireless ad hoc networks.

Figure 1.: Network layers for wireless networks

The IEEE 802.11 standard is a platform that gives specifications for two of the fundamental layers in the protocol stack of any wireless ad hoc network: the physical (PHY) layer and the medium access control (MAC) layer. Figure 1.2 shows the locations of the PHY and the MAC layers on the protocol stack characterised by the International Standard Organization's Open System Interconnect (ISO/OSI) model. Wireless network architecture is similar to that of a connected network as it normally consists of three or more layers.

The lowest layer in the form is the physical layer. This layer defines the characteristics of transmitting and obtaining packets through the medium that interconnects the nodes of the network. It generally defines a number of parameters and procedures such as the bandwidth and channels allocation, signal modulation schemes, transmit power levels, mistake correcting/detecting codes, etc. The PHY layer is also responsible for mapping the information bits obtained from the top network layers into a framing format suitable for transmission over the physical medium and also for the de-mapping operation of the information obtained over the medium.

The second layer, the data connection layer, consists of two sub-layers: the medium access control (MAC) layer and the connection ...