Overview

A queue is a collection of data packets collectively waiting to be transmitted by a network device using a pre-defined structure methodology. Queuing works almost on the same methodology used at banks or supermarkets, where the customer is treated according to its arrival.

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• /queue simple menu - designed to ease configuration of simple, every day queuing tasks (such as single client upload/download limitation, p2p traffic limitation, etc.).
• /queue tree menu - for implementing advanced queuing tasks (such as global prioritization policy, user group limitations). Requires marked packet flows from /ip firewall mangle facility.

RouterOS provides a possibility to configure queue in 8 levels -  the first level is an interface queue from "/queue interface" menu and the other 7 are lower-level queues that can be created in Queue Simple and/or Queue Tree.

Rate limitation principles

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Next figure explains the difference between rate limiting and rate equalizing:

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As you can see in the first case all traffic exceeds a specific rate and is dropped. In another case, traffic exceeds a specific rate and is delayed in the queue and transmitted later when it is possible, but note that the packet can be delayed only until the queue is not full. If there is no more space in the queue buffer, packets are dropped.

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A simple queue is a plain way how to limit traffic fora for a particular target. Also, you can use simple use simple queues to build advanced QoS applications. They have useful integrated features:

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In the following example, we have one SOHO device with two connected units PC and Server.

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We have a 15 Mbps connection available from ISP in this case. We want to be sure the server receives enough traffic, so we will configure a simple queue with a limit-at parameter to guarantee a server to receive 5Mbps:

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The queue tree creates only a one-directional queue in one of the HTBs. It is also the only way how to add a queue on the a separate interface. This way it is possible to ease mangle configuration - you don't need separate marks for download and upload - only the upload will get to the Public interface and only the download will get to a Private interface. The main difference from Simple Queues is that the Queue tree is not ordered - all traffic passes it together.

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MQ-PFIFO is pfifo with support for multiple transmit queues. This queue is beneficial on SMP systems with ethernet interfaces that have support for multiple transmit queues and have a Linux driver support for multiple transmit queues (mostly on x86 platforms). This kind uses the mq-pfifo-limit parameter.

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Random Early Drop is a queuing mechanism that tries to avoid network congestion by controlling the average queue size. The average queue size is compared to two thresholds: a minimum (min_th) and maximum (max_th) threshold. If the average queue size (avg_q) is less than the minimum threshold, no packets are dropped. When the average queue size is greater than the maximum threshold, all incoming packets are dropped. But if the average queue size is between the minimum and maximum thresholds packets are randomly dropped with probability P_d where probability is exact a function of the average queue size: P_d = P_max(avg_q – min_th)/ (max_th - min_th). If the average queue grows, the probability of dropping incoming packets grows too. P_max - ratio, which can adjust the packet discarding probability abruptness, (the simplest case P_max can be equal to one. The 8.2 diagram shows the packet drop probability in the RED algorithm.

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SFQ

Stochastic Fairness Queuing (SFQ) is ensured by hashing and round-robin algorithms. SFQ is called "Stochastic" because it does not really allocate a queue for each flow, it has an algorithm that divides traffic over a limited number of queues (1024) using a hashing algorithm.

Traffic flow may be uniquely identified by 4 options (src-address, dst-address, src-port, and dst-port), so these parameters are used by the SFQ hashing algorithm to classify packets into one of 1024 possible sub-streams. Then round-robin algorithm will start to distribute available bandwidth to all sub-streams, on each round giving sfq-allot bytes of traffic. The whole SFQ queue can contain 128 packets and there are 1024 sub-streams available. The 8.3 diagram shows the SFQ operation:

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PCQ

PCQ algorithm is very simple - at first, it uses selected classifiers to distinguish one sub-stream from another, then applies individual FIFO queue size and limitation on every sub-stream, then groups all sub-streams together and applies global queue size and limitation.

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 It is possible to assign a speed limitation to sub-streams with the pcq-rate option. If "pcq-rate=0" sub-streams will divide available traffic equally.

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For example, instead of having 100 queues with 1000kbps limitation for download, we can have one PCQ queue with 100 sub-streams

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CoDel (Controlled-Delay Active Queue Management) algorithm uses the local minimum queue as a measure of the persistent queue, similarly, it uses a minimum delay parameter as a measure of the standing queue delay. Queue size is calculated using packet residence time in the queue.

Properties

FQ-Codel

CoDel - Fair Queuing (FQ) with Controlled Delay (CoDel) uses a randomly determined model to classify incoming packets into different flows and is used to provide a fair share of the bandwidth to all the flows using the queue. Each flow is managed using CoDel queuing discipline which internally uses a FIFO algorithm.

Properties

CAKE

CAKE - Common Applications Kept Enhanced (CAKE) implemented as a queue discipline (qdisc) for the Linux kernel uses COBALT (AQM algorithm combining Codel and BLUE) and a variant of DRR++ for flow isolation. In other words, Cake’s fundamental design goal is user-friendliness. All settings are optional; the default settings are chosen to be practical in most common deployments. In most cases, the configuration requires only a bandwidth parameter to get useful results,

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Properties

Interface Queue

/queue interface

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[admin@MikroTik] > queue interface print
Columns: INTERFACE, QUEUE, ACTIVE-QUEUE
# INTERFACE QUEUE ACTIVE-QUEUE
0 ether1 only-hardware-queue only-hardware-queue
1 ether2 only-hardware-queue only-hardware-queue
2 ether3 only-hardware-queue only-hardware-queue
3 ether4 only-hardware-queue only-hardware-queue
4 ether5 only-hardware-queue only-hardware-queue
5 ether6 only-hardware-queue only-hardware-queue
6 ether7 only-hardware-queue only-hardware-queue
7 ether8 only-hardware-queue only-hardware-queue
8 ether9 only-hardware-queue only-hardware-queue
9 ether10 only-hardware-queue only-hardware-queue
10 sfp-sfpplus1 only-hardware-queue only-hardware-queue
11 wlan1 wireless-default wireless-default
12 wlan2 wireless-default wireless-default 

Queue load visualization in GUI

In Winbox and Webfig, a green, yellow, or red icon visualizes each Simple and Tree queue usage based on max-limit.