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rtPS (Real-Time Polling Service)

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Real-Time Polling Service (rtPS) is a type of Quality of Service (QoS) mechanism used in packet-switched networks, particularly in the context of Internet Protocol (IP) networks. It is defined in the Institute of Electrical and Electronics Engineers (IEEE) 802.16 standard, also known as WiMAX (Worldwide Interoperability for Microwave Access).

rtPS is designed to provide guaranteed bandwidth and low latency for time-sensitive traffic, such as real-time streaming media, voice over IP (VoIP), and interactive gaming. It ensures that these applications receive the necessary network resources and are given priority over other types of traffic.

Here's how rtPS works:

  1. Service Flow: rtPS operates on a per-subscriber basis. A service flow is established for each subscriber requiring rtPS. A service flow is a logical connection between the subscriber's device (such as a WiMAX modem) and the base station. It defines the characteristics and requirements of the traffic associated with that subscriber.
  2. Traffic Parameters: Each rtPS service flow is associated with specific traffic parameters that determine the QoS requirements. These parameters include the maximum sustained traffic rate (specified in bits per second), the maximum burst size, and the minimum reserved bandwidth.
  3. Transmission Opportunities: The base station periodically allocates transmission opportunities to different service flows, including rtPS. A transmission opportunity represents a time slot during which a subscriber can transmit data to the base station.
  4. Polling Mechanism: Unlike other QoS mechanisms like Unsolicited Grant Service (UGS) or Extended Real-Time Polling Service (ertPS), which have fixed allocations, rtPS uses a polling mechanism. The base station periodically sends a poll to the subscriber to check if it has any data to transmit.
  5. Request/Grant Mechanism: When a subscriber receives a poll from the base station, it can request a specific amount of bandwidth for transmitting its data. The base station evaluates the request and grants the necessary resources based on the available bandwidth and the QoS parameters of the rtPS service flow.
  6. Priority and Scheduling: rtPS traffic is given a higher priority compared to other types of traffic in the network. This ensures that rtPS packets are scheduled and transmitted with minimal delay. The base station's scheduler takes into account the QoS requirements of the rtPS service flows when allocating transmission opportunities.
  7. Policing: The base station monitors the traffic sent by each rtPS service flow to ensure that it adheres to the defined traffic parameters. If a subscriber exceeds its allocated resources or violates the specified QoS parameters, the base station may take corrective actions, such as dropping packets or reducing the allocated bandwidth.

By providing guaranteed bandwidth and low latency for time-sensitive traffic, rtPS ensures that real-time applications can operate smoothly and efficiently over IP-based networks. It allows for the efficient transmission of voice, video, and other time-critical data, contributing to a better user experience.