D-Link DWL-2210AP Router Manual PDF (Setup & Configuration Guide)

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Specify the number of client stations you want as a “stations threshold”

for disassociation. If the number of client stations associated with the

AP at any one time is equal to or less than the number you specify

here, no stations will be disassociated regardless of the “Utilization for

Disassociation” value.

Theoretically, the maximum number of client stations allowed is 2007.

Stations Threshold

for Disassociation

We recommend setting the maximum to between 30

and 50 client stations. This allows for a workable load

on the access point, given that bandwidth is shared

among the AP clients.

Updating Settings

To apply your changes, click

Update Settings

.

Utilization rate limits relate to wireless

bandwidth utilization.

Provide a bandwidth utilization rate percentage

limit for this access point to indicate when to

disassociate current clients.

When the utilization rate exceeds the speciﬁed

limit, a client currently associated with this

access point will be disconnected.

If you specify 0 in this ﬁeld, current clients will

never be disconnected regardless of the

utilization rate.

Utilization for

Disassociation

Field

Description

Conﬁguring Queues for Quality of Service

(QoS)

Quality of Service (

QoS

) provides you with the ability to specify parameters on multiple

queues for increased throughput and better performance of differentiated wireless trafﬁc

like

Voice-over-IP

(VoIP), video, and streaming media as well as traditional IP data over

the D-Link DWL-2210AP.

Load Balancing

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The following sections describe how to conﬁgure Quality of Service queues on the

D-Link DWL-2210AP:

• Understanding QoS

• QoS and Load Balancing

• 802.11e and WME Standards Support

• QoS Queues and Parameters to Coordinate Trafﬁc Flow

• Navigating to QoS Settings

• Conﬁguring QoS Queues

• Updating Settings

Understanding QoS

A primary factor that affects QoS is network congestion due to an increased number

of clients attempting to access the air waves and higher trafﬁc volume competing for

bandwidth during a busy time of day. The most noticeable degradation in service on a

busy, overloaded network will be evident in time-sensitive applications like

Voice-over-

IP

(VoIP) and streaming media.

Unlike typical data ﬁles which are less affected by variability in QoS, VoIP and streaming

media must be sent in a speciﬁc order, at a consistent rate, and with minimum delay

between

Packet

transmission. If the quality of service is compromised, the audio or

video will be distorted.

QoS and Load Balancing

By using a combination of load balancing (see “Load Balancing” on page 95) and QoS

techniques, you can provide a high quality of service for time-sensitive applications

even on a busy network. Load balancing is a way of better distributing the trafﬁc volume

across access points. QoS is a means of allocating bandwidth and network access

based on transmission priorities for different types of wireless trafﬁc within a single

access point.

802.11e and WME Standards Support

QoS

describes a range of technologies for controlling data streams on shared network

connections. The

IEEE 802.11e

task group is in the process of deﬁning a QoS standard

for transmission quality and availability of service on wireless networks. QoS is designed

to provide better network service by minimizing network congestion; limiting

Jitter

,

Latency

, and

Packet Loss

; supporting dedicated bandwidth for time-sensitive or mission

critical applications, and prioritizing wireless trafﬁc for channel access.

Conﬁguring Queues for Qualty of Service (QoS)

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As with all IEEE

802.11

working group standards, the goal is to provide a standard

way of implementing QoS features so that components from different companies are

interoperable. The D-Link DWL-2210AP provides QoS based on the

Wireless Multimedia

Enhancement

(

WME

) speciﬁcation, which is an implementation of a subset of

802.11e

features.

QoS Queues and Parameters to Coordinate Trafﬁc Flow

Conﬁguring QoS options on the D-Link DWL-2210AP consists of setting parameters

on existing queues for different types of wireless trafﬁc. You can conﬁgure different

minimum and maximum wait times for the transmission of packets in each queue based

on the requirements of the media being sent. Queues automatically provide minimum

transmission delay for VoIP, multimedia, and mission critical applications, and rely on

best-effort parameters for traditional IP data.

For example, time-sensitive multimedia and VoIP are given effectively higher priority

for transmission (lower wait times for channel access), while other applications and

traditional IP data which are less time-sensitive but often more data-intensive are

expected to tolerate longer wait times.

The D-Link DWL-2210AP implements QoS with a custom extension to the trafﬁc control

mechanism in the Linux kernel. Our Linux-based queuing class is used to tag packets

and establish multiple queues. The queues provided offer built-in prioritization and

routing based on the type of data being transmitted.

The Administration UI provides a way for you to conﬁgure parameters on the queues.

QoS Queues and Type of Service (ToS) on Packets

QoS on the D-Link DWL-2210AP leverages existing information in the IP packet header

related to Type of Service (

ToS

). Every IP packet sent over the network includes a ToS

ﬁeld in the header that indicates how the data should be prioritized and transmitted

over the network. The ToS ﬁeld consists of a 3 to 7 bit value with each bit representing

a different aspect or degree of priority for this data as well as other meta-information

(low delay, high throughput, high reliability, low cost, and so on).

For example, the ToS for FTP data packets is likely to be set for maximum throughput

since the critical consideration for FTP is the ability to transmit relatively large amounts

of data in one go. Interactive feedback is a nice-to-have in this situation but certainly

less critical. VoIP data packets are set for minimum delay because that is a critical factor

in quality and performance for that type of data.

The access point examines the ToS ﬁeld in the headers of all packets that pass through

the AP. Based on the value in a packet’s ToS ﬁeld, the AP prioritizes the packet for

transmission by assigning it to one of the queues. This process occurs automatically,

regardless of whether you deliberately conﬁgure QoS or not.

Conﬁguring Queues for Qualty of Service (QoS)

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Packets in a higher priority queue will be transmitted before packets in a lower priority

queue. Interactive data in the queue labeled “Data 2” is always sent ﬁrst, best effort data

in “Data 1” is sent next, and bulk data in “Data 0” is sent last. Each lower priority queue

(class of trafﬁc) gets bandwidth that is left over after the higher classes of trafﬁc have

been sent. At an extreme end if you have enough interactive data to keep the access

point busy all the time, low priority trafﬁc would never get sent.

Using the QoS settings on the Administration UI, you can conﬁgure parameters that

determine how each queue is treated when it is sent by the access point.

DCF Control of Data Frames and Interframe Spaces

Data is transmitted over 802.11 wireless networks in

frames

. A

Frame

consists of a

discrete portion of data along with some descriptive meta-information packaged for

transmission on a wireless network.

A different type of data is associated with each queue. The queue and associated

priorities and parameters for transmission are as follows:

•

Data 0 (bulk). Lowest priority queue, high throughput. Bulk data that requires

maximum throughput and is not time-sensitive is sent to this queue (FTP data,

for example).

Data 1 (best effort). Medium priority queue, medium throughput and delay. Most

traditional IP data is sent to this queue.

Data 2 (interactive). Highest priority queue, minimum delay. Time-sensitive data

such as VoIP and streaming media are automatically sent to this queue.

Data 3 (not used)

•

Wireless trafﬁc travels:

• Downstream from the access point to the client station

• Upstream from client station to access point

• Upstream from access point to network

• Downstream from network to access point

QoS settings on the D-Link DWL-2210AP affect only the ﬁrst of these;

downstream

trafﬁc ﬂowing

from the access point to client station. The other phases of the trafﬁc ﬂow are not under control

of the QoS settings on the AP.

A Frame is similar in concept to a

Packet

, the difference being that a packet operates on the

Network layer (layer 3 in the OSI model) whereas a frame operates on the Data-Link layer

(layer 2 in the

OSI

model).

Conﬁguring Queues for Qualty of Service (QoS)

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Each frame includes a source and destination MAC address, a control ﬁeld with protocol

version, frame type, frame sequence number, frame body (with the actual information

to be transmitted) and frame check sequence for error detection.

The 802.11 standard deﬁnes various

frame

types for management and control of

the wireless infrastructure, and for data transmission. 802.11 frame types are (1)

management frames

, (2)

control frames

, and (3)

data frames

. Management and

control frames (which manage and control the availability of the wireless infrastructure)

automatically have higher priority for transmission.

802.11e uses

interframe spaces

to regulate which frames get access to available

channels and to coordinate wait times for transmission of different types of data.

Management and control frames wait a minimum amount of time for transmission;

they wait a

short interframe space

(SIF). These wait times are built-in to 802.11 as

infrastructure support and are not conﬁgurable.

The D-Link DWL-2210AP supports the

Distribution Coordination Function

(

DCF

) as

deﬁned by the

802.11e

standard. DCF, which is based on

CSMA/CA

protocol, deﬁnes

the interframe space (IFS) between

data frames

. Data frames wait for an amount of

time deﬁned as the

DCF interframe space

(DIF) before transmitting.

This parameter is conﬁgurable.

(Note that sending data frames in DIFs allows higher priority management and control

frames to be sent in SIFs ﬁrst.)

The DCF ensures that multiple access points do not try sending data at the same time

but instead wait until a channel is free.

Random Backoff and Minimum / Maximum Contention Windows

If an access point detects that the medium is in use (busy), it uses the DCF

random

backoff

timer to determine the amount of time to wait before attempting to access a given

channel again. Each access point waits some random period of time between retries. The

wait time (initially a random value within a range speciﬁed as the

Minimum Contention

Window

) increases exponentially up to a speciﬁed limit (

Maximum Contention Window

).

The random delay avoids most of the collisions that would occur if multiple APs got

access to the medium at the same time and tried to transmit data simultaneously. The

more active users you have on a network, the more signiﬁcant the performance gains

of the backoff timer will be in reducing the number of collisions and retransmissions.

Conﬁguring Queues for Qualty of Service (QoS)

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