Input Queue - Networking

Networking

In networking, packets are the key foundation for scheduling. There are many different types of packet travelling around network core every day, and they are treated totally different. For example, voice and video packets have higher priority than normal packets. In order to manage and distribute packet effectively, network devices also use input queue to determine which packet will be transmitted first.
First in, first out queue (FIFO)

In this mode, packets are taken out from the queue in the order that they are coming from the queue. Every packet is treated the same priority. If a large packet A comes before a small packet B, B still has to wait until A is completely served. If a system treats every packet the same, users can experience the delay in transmitting such as: voice packets.
Weighted fair queue (WFQ)

Weighted fair queue uses the min-max-fair-share algorithm to distribute packets. The min fair-share means the network OS will distribute equally minimum resource for each type of packet. The max fair-share means the network OS will provide more resource for packets that need to transfer large amount of date at that moment, but it will take the resource back after transferring. “Weighted” means the scheduler will assign weight for each type of packet. Base on the weight, it will determine how to put packet into the queue and serve them. Usually, each packet will be weighted based on IP Precedence field from IP header of each packet.

Fair allocation = (resource capacity – resource already allocated) / number of packets

Priority queue (PQ)

Priority queue is divided into 4 sub queues with different priorities. Data in each queue are only served when the higher priority queues are empty. If data come into the empty higher priority queue while the network OS is transferring data of lower priority queue, network OS will hold data of the lower priority queue and process data in higher priority queue first. The network OS does not care how long lower priority queues have to wait for their turn because it always finishes each queue from highest to lowest priority first before moving to the next queue. Within each queue, packets are forwarded based on First-In-First-Out basis.
Custom queue (CQ)

Custom queue is divided into 17 different sub queues. The first queue, queue 0, is reserved for the network OS to transmit system packet, the other 16 queues are for user-defined packets. User can define various important packets and assign them into each queue. Each queue has limited size and it will drop all coming packets if it reaches that limit. Each queue is serviced based on how much packets are served in each queue. If that limit is met, the network OS will hold packets of current queue and services the next queue until that queue is empty or it reaches its packet limit. If one queue is empty, the network OS will skip that queue and service the next queue.