According to a priority based service disciplines, the transmission of ready packets are scheduled in priority driven manner. Waited fair queuing (WFQ) and Waited round robin scheduling are common approach for scheduling the packets in real time communication network.

1. Waited Fair Queuing (WFQ) Discipline

It is a rate allocating service discipline and provides each flow with at least its proportional fair share link capacity and isolates the timing between flows such that it is also called as packet by packet generalized processor sharing algorithms. It is define as a packet switch has several inputs, feeding to an output link shared by n established flows where each flows i is allocated to ui of the link such that total bandwidth allocated to all connections is:

In WFQ, the output buffer comprise of two queues as FIFO and shortest finish number (SFN) for scheduling of packets. FIFO is used to scheduled n flows whereas priority ordered SFN is used to schedule the job obtained from the head FIFO queue on the basis of finish number. The finish number specifies the number of ready packets for transmission. The structure of queue is shown below.

  • A packet becomes ready on FIFO queue, a finish number is calculated and SFN queue The newly arrived packet is placed on the head of SFN queue without preempting the current transmission. When packet completes its transmission then it is removed from head of SFN and FIFO queue.
  • A packet becomes ready on FIFO queue, a finish number is calculated and SFN queue The newly arrived packet is placed on the head of SFN queue without preempting the current transmission. When packet completes its transmission then it is removed from head of SFN and FIFO queue.

2. Waited Round Robin Scheduling

In this approach jobs are placed in FIFO queue. The job at the head of queue executes for one time slice. If it doesnot complete with in the time slice, it is preempted and put back into the queue. There are n jobs in the queue, each job gets one slice every n time slots in a round. The weighted round robin schedule extends this to give each job with weight Wi such that ith job gets Wi lenth time slice for execution. In this method each packets obtained from set of n flows are arranged in FIFO order and gets the connection for Wi time after connection and preempted and backlogged to the end of the queue if it is not completely transmitted otherwise removed from the queue. This service disciplines is shown below.

When in each round, if more than Wi packets are backlogged on queue i then Wi packets are transmitted such that

  • Each flow is guranted Wi slots in each round
  • Rate allocating may send more , if nothing to transmit

Then such WRR scheduling scheme is called Greedy WRR scheduling only when there must be a design parameter (RL) satisfies the following conditions.