Polling List Table

where the new frame Rx time means the receiving time for the first QoS frame which was generated by the traffic source from silence state to talk-spurt state (see Fig 3.9).

3.5 Polling List Table

We need a new polling list format and management policy to support our adaptive time-stamp polling scheme. This polling list contains some information that we need, and we can set up this polling list by combining it with the TSPEC table or establishing it in the independent field. No matter what method is used, we will update the information in this polling list, therefore the polling list management will be more complicated than the management in the round-robin polling scheme.

3.5.1 Polling List Format

In order to implement our adaptive time-stamp polling scheme, we construct a new polling list. This polling list contains all information we need such as when and which station the HC should start to poll, and other variables. For this reason, we propose a new polling list format that contains what we need in our adaptive time-stamp polling scheme. Table 3.1 shows the proposed polling list format.

Table 3.1 Proposed polling list format.

TSID MAC Address Polling Time Maximum Service Interval

Number of QoS-Null

Detection State TSID1 MAC Address1 Polling Time1 Maximum Service

Interval 1 0 True

TSID2 MAC Address2 Polling Time2 Maximum Service

Interval 2 3 False

……. ……. ……. ……. ……. …….

TSIDn MAC Addressn Polling Timen Maximum Service

Interval n 2 False

Each element in the proposed polling list encapsulates the following information:

z TSID: This is the traffic stream identifier to distinguish the traffic stream with a particular specification. The TSID is assigned in the layers above the MAC and the same TSID may be used for multiple traffic streams at different QSTAs.

z MAC Address: This is the MAC address of the QSTA that owns this traffic stream.

This element can be convenient to find the corresponding TSPEC .

z Polling Time: This is the expected polling time that is calculated by the HC for the associated traffic stream. The calculation formula is shown in Equations 3.1, 3.2 and 3.3. When the current time exceeds this value, the HC should poll the corresponding QSTA for traffic stream.

z Maximum Service Interval: This is the maximum service interval which is registered in the corresponding TSPEC. This element is used by calculating next polling time at Equations 3.2 and 3.3 in section 3.1.1.

z Number of QoS-Null: This is the number of times that this traffic stream replies the CF-Poll frames with QoS-Null frames consecutively. It is used to determine whether this traffic stream is in talk-spurt or silence periods in the section 3.4.

z Detection State: This is used to decide whether currently the traffic stream needs the

short interval polling function in Section 3.2.2. If this value is true, the HC will execute this option function just after it received the QoS data frames from the corresponding traffic stream. If this value is false, the HC never execute the short interval polling function.

Beside the information in the polling list we proposed, we still need some information that can be recorded in other way. For example, we need to record the value of this short interval which we defined, but it is the same for all traffic streams and is inefficient if we remove it from the polling list. Also some information will vary with the different implementations. For example, the maximum number of times or the end time of executing the short interval polling functions.

3.5.2 Polling List Update

When we try to establish the polling list, we can set up it with an array and then look for the one that has the earliest polling time, or we can build it into a dynamic list which is arranged in order of time when those stations should be polled. No matter what method is used, the HC recorded those initial informations from the TSPEC in the polling list after it accepted this request. The value of Polling Time is the service start time. Then the HC looks for the traffic stream which has the earliest Polling Time and waits until the expected time is up, then polls this stream. If the Polling Time is earlier than the current time, the HC polls as soon as possible. After the HC polls some traffic stream, it must calculate the next polling time and updates this Polling Time in the polling list and repeat the process.

The default value of Detection State element for all traffic streams should be True except those streams whose values of Maximum Service Interval are less than the double of short interval. If the HC receives the QoS data frames from some traffic stream whose Detection State is True, the HC must execute the short interval polling function for this traffic stream. During the period of carrying out this function, the HC would change the Detection State value into False

when it receives the following QoS data frames.

The default value of Number of QoS-Null element is zero, the HC increases this element by one every time the HC found this associate traffic stream replies QoS-Null frames after the polling, and the HC will reset this element to zero when it received the QoS data frames from the corresponding traffic stream. When this element is greater than or equals to three, the HC will consider that the traffic stream is in silence state and polls it at the silence polling interval.

However, the HC does not change the Number of QoS-Null value during this short interval polling duration because it assumes that this element is implemented correctly.