7.3 Different types of Queue objects

A queue object is a general class of object capable of holding and possibly marking or discarding packets as they travel through the simulated topology. Configuration Parameters used for queue objects are:
limit_
The queue size in packets.

blocked_
Set to false by default, this is true if the queue is blocked (unable to send a packet to its downstream neighbor).

unblock_on_resume_
Set to true by default, indicates a queue should unblock itself at the time the last packet packet sent has been transmitted (but not necessarily received).

Other queue objects derived from the base class Queue are drop-tail, FQ, SFQ, DRR, RED and CBQ queue objects. Each are described as follows:

CBQCLASS OBJECTS
CBQClass objects implement the traffic classes associated with CBQ objects.

$cbqclass setparams parent okborrow allot maxidle prio level
Sets several of the configuration parameters for the CBQ traffic class (see below).

$cbqclass parent cbqcl|none
specify the parent of this class in the link-sharing tree. The parent may be specified as ``none'' to indicate this class is a root.

$cbqclass newallot a
Change the link allocation of this class to the specified amount (in range 0.0 to 1.0). Note that only the specified class is affected.

$cbqclass install-queue q
Install a Queue object into the compound CBQ or CBQ/WRR link structure. When a CBQ object is initially created, it includes no internal queue (only a packet classifier and scheduler).

Configuration Parameters are:

okborrow_
is a boolean indicating the class is permitted to borrow bandwidth from its parent.

allot_
is the maximum fraction of link bandwidth allocated to the class expressed as a real number between 0.0 and 1.0.

maxidle_
is the maximum amount of time a class may be required to have its packets queued before they are permitted to be forwarded

priority_
is the class' priority level with respect to other classes. This value may range from 0 to 10, and more than one class may exist at the same priority. Priority 0 is the highest priority.

level_
is the level of this class in the link-sharing tree. Leaf nodes in the tree are considered to be at level 1; their parents are at level 2, etc.

extradelay_
increase the delay experienced by a delayed class by the specified time

QUEUE-MONITOR OBJECTS
QueueMonitor Objects are used to monitor a set of packet and byte arrival, departure and drop counters. It also includes support for aggregate statistics such as average queue size, etc.

$queuemonitor
reset all the cumulative counters described below (arrivals, departures, and drops) to zero. Also, reset the integrators and delay sampler, if defined.

$queuemonitor set-delay-samples delaySamp_
Set up the Samples object delaySamp_ to record statistics about queue delays. delaySamp_ is a handle to a Samples object i.e the Samples object should have already been created.

$queuemonitor get-bytes-integrator
Returns an Integrator object that can be used to find the integral of the queue size in bytes.

$queuemonitor get-pkts-integrator
Returns an Integrator object that can be used to find the integral of the queue size in packets.

$queuemonitor get-delay-samples
Returns a Samples object delaySamp_ to record statistics about queue delays.
There are no configuration parameters specific to this object.
State Variables are:

size_
Instantaneous queue size in bytes.

pkts_
Instantaneous queue size in packets.

parrivals_
Running total of packets that have arrived.

barrivals_
Running total of bytes contained in packets that have arrived.

pdepartures_
Running total of packets that have departed (not dropped).

bdepartures_
Running total of bytes contained in packets that have departed (not dropped).

pdrops_
Total number of packets dropped.

bdrops_
Total number of bytes dropped.

bytesInt_
Integrator object that computes the integral of the queue size in bytes. The sum_ variable of this object has the running sum (integral) of the queue size in bytes.

pktsInt_
Integrator object that computes the integral of the queue size in packets. The sum_ variable of this object has the running sum (integral) of the queue size in packets.

QUEUEMONITOR/ED OBJECTS
This derived object is capable of differentiating regular packet drops from early drops. Some queues distinguish regular drops (e.g. drops due to buffer exhaustion) from other drops (e.g. random drops in RED queues). Under some circumstances, it is useful to distinguish these two types of drops.
State Variables are:

epdrops_
The number of packets that have been dropped ``early''.

ebdrops_
The number of bytes comprising packets that have been dropped ``early''.

Note: because this class is a subclass of QueueMonitor, objects of this type also have fields such as pdrops_ and bdrops_. These fields describe the total number of dropped packets and bytes, including both early and non-early drops.

QUEUEMONITOR/ED/FLOWMON OBJECTS
These objects may be used in the place of a conventional QueueMonitor object when wishing to collect per-flow counts and statistics in addition to the aggregate counts and statistics provided by the basic QueueMonitor.

$fmon classifier cl
This inserts (read) the specified classifier into (from) the flow monitor object. This is used to map incoming packets to which flows they are associated with.

$fmon dump
Dump the current per-flow counters and statistics to the I/O channel specified in a previous attach operation.

$fmon flows
Return a character string containing the names of all flow objects known by this flow monitor. Each of these objects are of type QueueMonitor/ED/Flow.

$fmon attach chan
Attach a tcl I/O channel to the flow monitor. Flow statistics are written to the channel when the dump operation is executed.

Configuration Parameters are:

enable_in_
Set to true by default, indicates that per-flow arrival state should be kept by the flow monitor. If set to false, only the aggregate arrival information is kept.

enable_out_
Set to true by default, indicates that per-flow departure state should be kept by the flow monitor. If set to false, only the aggregate departure information is kept.

enable_drop_
Set to true by default, indicates that per-flow drop state should be kept by the flow monitor. If set to false, only the aggregate drop information is kept.

enable_edrop_
Set to true by default, indicates that per-flow early drop state should be kept by the flow monitor. If set to false, only the aggregate early drop information is kept.

QUEUEMONITOR/ED/FLOW OBJECTS
These objects contain per-flow counts and statistics managed by a QueueMonitor/ED/Flowmon object. They are generally created in an OTcl callback procedure when a flow monitor is given a packet it cannot map on to a known flow. Note that the flow monitor's classifier is responsible for mapping packets to flows in some arbitrary way. Thus, depending on the type of classifier used, not all of the state variables may be relevant (e.g. one may classify packets based only on flow id, in which case the source and destination addresses may not be significant). State Variables are:

src_
The source address of packets belonging to this flow.

dst_
The destination address of packets belonging to this flow.

flowid_
The flow id of packets belonging to this flow.

Tom Henderson 2011-11-05