EDCA (Enhanced distributed channel access)

Enhanced Distributed Channel Access (EDCA) is a protocol used in wireless networks that uses Quality of Service (QoS) parameters to prioritize traffic in order to optimize network efficiency. EDCA is used in IEEE 802.11e wireless networks, which is an amendment to the IEEE 802.11 wireless networking standard. The purpose of EDCA is to provide differentiated QoS to different types of traffic by giving higher priority to more important traffic.

Wireless networks can experience congestion when there is too much traffic being transmitted at the same time. This can lead to delays, dropped packets, and other issues that can negatively impact network performance. In order to avoid congestion, EDCA divides the available network bandwidth into several priority levels, each of which has a different QoS parameter. The QoS parameter is a set of rules that specifies the minimum requirements for the different types of traffic, such as delay, jitter, and packet loss. EDCA assigns higher priority levels to traffic with more stringent QoS requirements.

EDCA divides the available network bandwidth into four Access Categories (ACs), each of which has a different priority level. These are:

1. Voice (AC_VO) – This category is used for real-time voice traffic, such as VoIP. It requires a high level of QoS with low latency and low jitter.
2. Video (AC_VI) – This category is used for real-time video traffic, such as video conferencing. It requires a high level of QoS with low latency and low jitter.
3. Best Effort (AC_BE) – This category is used for general data traffic, such as web browsing and file transfers. It requires a lower level of QoS than voice and video traffic.
4. Background (AC_BK) – This category is used for low priority traffic, such as email and software updates. It requires the lowest level of QoS.

Each Access Category is assigned a different set of QoS parameters, which are used to determine how traffic is prioritized on the network. The QoS parameters are:

1. Arbitration Inter-Frame Space (AIFS) – This parameter specifies how long a station must wait before attempting to transmit a packet. The smaller the AIFS value, the higher the priority level.
2. Contention Window (CW) – This parameter specifies the range of time intervals a station can randomly choose from to attempt to transmit a packet. The smaller the CW value, the higher the priority level.
3. Transmission Opportunity (TXOP) – This parameter specifies the maximum amount of time a station can transmit data in one session. The higher the TXOP value, the higher the priority level.
4. Minimum Data Rate (MDR) – This parameter specifies the minimum data rate a station can use to transmit data. The higher the MDR value, the higher the priority level.

EDCA works by assigning different priority levels to each Access Category, and then assigning different QoS parameters to each priority level. This allows the network to prioritize traffic based on its QoS requirements, which improves network efficiency and reduces congestion.

When a station wants to transmit data on the network, it first listens for a Clear Channel Assessment (CCA) to determine if the channel is free. If the channel is free, the station waits for a period of time based on its AIFS value, and then randomly selects a time interval based on its CW value to attempt to transmit data. The station will then transmit data for a period of time based on its TXOP value. If the station is interrupted during transmission, it will wait for the next AIFS interval and then start again.

If multiple stations attempt to transmit data at the same time, they will randomly select time intervals based on their CW values. If two stations select the same time interval, a collision will occur, and both stations will wait a random amount of time before attempting to transmit again. The CW value for each station will increase after each collision, which helps to reduce the probability of future collisions.

EDCA allows for dynamic adjustment of the QoS parameters based on network conditions. If the network is experiencing congestion, the QoS parameters for lower priority Access Categories can be adjusted to reduce the amount of traffic they transmit. This allows higher priority traffic to receive more network resources and reduces the likelihood of congestion.

EDCA also supports Admission Control (AC) to prevent network overload. AC is used to control the amount of traffic that is allowed on the network based on the available network resources. If the network is congested, AC can reject new traffic to prevent further congestion.

In summary, EDCA is a protocol used in wireless networks that uses Quality of Service parameters to prioritize traffic based on its QoS requirements. It divides the available network bandwidth into four Access Categories, each of which has a different priority level and set of QoS parameters. EDCA uses a combination of AIFS, CW, TXOP, and MDR parameters to prioritize traffic and prevent congestion. It also supports dynamic adjustment of QoS parameters and Admission Control to optimize network efficiency and prevent network overload.