1. Fast and scalable priority queue architecture for high-speed network switches Ranjita Bhagwan, Bill Lin Center for wireless communications university of California, San Diego Infocom 2000

2. Introduction Future packet-switched integrated- service network should provide wide variety of real- time application diverse Qos requirement 1. Average throughput 2. End to end delay 3. Cell loss rate must be satisfied at extremely high speeds without compromising on network utilization

3. Priority queue architecture requirement Highest priority first Maintain real-time sorting Fast hardware priority queue implementation scalable

4. Hardware-based sorted priority queue architectures Calendar queues Binary-tree-of-comparators-based priority queues Shift-register-based priority queues Systolic-array-based priority queues

5. Pipelined-heap Similar to a conventional binary heap enqueue and dequeue with hardware complexity low and execute in essentially constant time Scalable over 4 billion priority using 32 bit The number of comparator datapath needed in the architecture is logarithmic to queue size The storage required for the queue elements can be efficiently organized into on chip- SDRAM modules

7. Binary heap Parent(i)=i/2 Left(i)=2*i Right(i)=2*i+1

8. Binary array B[i]:active : this is a boolean field which is set to true if the node B[i] is filled with a valid priority value (the node is active ). It is set to false if the node is empty, or inactive. B[i]:value : if the node is active, this field holds the actual priority value. B[i]:capacity : this field contains the number of inactive nodes in the sub-tree rooted at B[i].

9. P-heap Property P-heap Property : Let B[i] be a node in B and B[j] be an immediate (left or right) child of B[i]. Then, 1.B[i]:active ^ B[j]:active =>B[i]:value >=B[j]:value 2. B[j]:active => B[i]:active

10. Token array (T) T[i]:operation: this field holds an instruction, depending on the operation to be executed at level Li of the P-heap. It is useful in the pipelined implementation of P-heaps. T[i]:value: This field may hold a priority value that needs to be inserted into B. T[i]:position: this field can hold the index of a node at level Li of B.

24. Conclusions Fast and scalable pipelined priority queue with constant time enqueue and dequeue Efficiently in a high speed packet switch providing fine-grained quality of service guarantees