System Configuration

5-22

•

MCS

– The Modulation and Coding Scheme (MCS) is a value that determines the

modulation, coding and number of spatial channels. (Options: value [range] = 0~7

(1 Tx Stream), 8~15 (2 TxStream), 32 and auto (33). Default: auto)

•

Reverse Direction Grant (RDG)

– When enables Reverse Direction Grant, the

wireless AP/Router can reduce the transmitted data packet collision by using the

reverse direction protocol. During TXOP (Transmission Opportunity) period, the

receiver could use remaining transmission time to transmit data to a sender. The

RDG improves transmission performance and scalability in a wireless

environment.

•

Extension Channel

– When 20/40MHz channel bandwidth has been set, the

extension channel option will be enabled. The extension channel will allow you to

get extra bandwidth. (Options: 2417MHz/Channel 2, 2457MHz/Channel 10.

Default: 2457MHz/Channel 10.)

•

Aggregate MSDU (A-MSDU)

– This option enables Mac Service Data Unit

(MSDU) aggregation. (Default: Disable)

•

Auto Block ACK

– Select to block ACK (Acknowledge Number) or not during data

transferring.

•

Decline BA Request

– Select to reject peer BA-Request or not.

Other HT Settings

Figure 5-18.

HT Physical Mode Settings

•

HT TxStream

– HT means High Throughput. The number of HT TxStream means

how many antennas will transmit data simultaneously. (Options: 1 or 2. Default: 2)

•

HT RxStream

– The number of HT RxStream means how many antennas will

receive data simultaneously. (Options: 1 or 2. Default: 2)

Wireless Settings

5-23

Advanced Wireless Settings

The Advanced Setting page allows you to configure the more advanced radio

settings, many of which are enabled by default.

Click “Wireless Settings” followed by “Advanced”.

Figure 5-19.

Advanced Wireless Settings

•

BG Protection

– Enables a backward

compatible protection system for

802.11b clients. There are three modes.

(Default: Auto):

-

Auto

: The wireless AP/Router enables

its protection mechanism for 802.11b

clients when they are detected in the network. When 802.11b clients are not

detected, the protection mechanism is disabled.

-

On

: Forces the unit to always use protection for 802.11b clients, whether they

are detected in the network or not.

-

Off

: Forces the unit to never use protection for 802.11b clients. This prevents

802.11b clients from connecting to the network.

Note:

Enabling “On” b/g Protection can slow throughput for 802.11g/n clients by as

much as 50%.

System Configuration

5-24

•

Beacon Interval

– The rate at which beacon signals are transmitted from the

access point. The beacon signals allow wireless clients to maintain contact with the

access point. They may also carry power-management information. (Range:

20-999 TUs; Default: 100 TUs)

•

Data Beacon Rate (DTIM)

– The rate at which stations in sleep mode must wake

up to receive broadcast/multicast transmissions. Known also as the Delivery Traffic

Indication Map (DTIM) interval, it indicates how often the MAC layer forwards

broadcast/multicast traffic, which is necessary to wake up stations that are using

Power Save mode. The default value of 2 indicates that the access point will save

all broadcast/multicast frames for the Basic Service Set (BSS) and forward them

after every second beacon. Using smaller DTIM intervals delivers broadcast/

multicast frames in a more timely manner, causing stations in Power Save mode

to wake up more often and drain power faster. Using higher DTIM values reduces

the power used by stations in Power Save mode, but delays the transmission of

broadcast/multicast frames. (Range: 1-255 beacons; Default: 1 beacon)

•

Fragment Threshold

– Configures the minimum packet size that can be

fragmented when passing through the access point. Fragmentation of the PDUs

(Package Data Unit) can increase the reliability of transmissions because it

increases the probability of a successful transmission due to smaller frame size. If

there is significant interference present, or collisions due to high network utilization,

try setting the fragment size to send smaller fragments. This will speed up the

retransmission of smaller frames. However, it is more efficient to set the fragment

size larger if very little or no interference is present because it requires overhead

to send multiple frames. (Range: 256-2346 bytes; Default: 2346 bytes)

•

RTS Threshold

– Sets the packet size threshold at which a Request to Send

(RTS) signal must be sent to a receiving station prior to the sending station starting

communications. The access point sends RTS frames to a receiving station to

negotiate the sending of a data frame. After receiving an RTS frame, the station

sends a CTS (clear to send) frame to notify the sending station that it can start

sending data. If the RTS threshold is set to 0, the access point always sends RTS

signals. If set to 2347, the access point never sends RTS signals. If set to any other

value, and the packet size equals or exceeds the RTS threshold, the RTS/CTS

(Request to Send / Clear to Send) mechanism will be enabled. The access points

contending for the medium may not be aware of each other. The RTS/CTS

mechanism can solve this “Hidden Node Problem.” (Range: 0-2347 bytes)

•

TX Power

– Adjusts the power of the radio signals transmitted from the access

point. The higher the transmission power, the farther the transmission range.

Power selection is not just a trade off between coverage area and maximum

supported clients. You also have to ensure that high-power signals do not interfere

with the operation of other radio devices in the service area.

•

Short Preamble

– Enables the length of the signal preamble that is used at the

start of a data transmission. (Default: Disable)

Wireless Settings

5-25

•

Short Slot

– Sets the basic unit of time the wireless AP/Router’s uses for

calculating waiting times before data is transmitted. Enabling a short slot time can

increase data throughput on the wireless AP/Router, but requires that all clients

can support a short slot time (that is, 802.11g-compliant clients must support a

short slot time). (Default: Enable)

•

Tx Burst

– Enables data transmission bursting to boost throughput for high data

transmissions. (Default: Enable)

•

Pkt_aggregation

– Enables grouping together of some packets and sending them

together to boost bandwidth. (Default: Enable)

Configuring Wi-Fi Multimedia

Wireless networks offer an equal opportunity for all devices to transmit data from

any type of application. Although this is acceptable for most applications, multimedia

applications (with audio and video) are particularly sensitive to the delay and

throughput variations that result from this equal opportunity wireless access method.

For multimedia applications to run well over a wireless network, a Quality of Service

(QoS) mechanism is required to prioritize traffic types and provide an enhanced

opportunity wireless access method. The access point implements QoS using the

Wi-Fi Multimedia (WMM) standard. Using WMM, the access point is able to prioritize

traffic and optimize performance when multiple applications compete for wireless

network bandwidth at the same time. WMM employs techniques that are a subset of

the developing IEEE 802.11e QoS standard and it enables the access point to inter

operate with both WMM enabled clients and other devices that may lack any WMM

functionality.

Figure 5-20.

Wi-Fi Multimedia Settings

•

WMM Capable

– Wi-Fi Multimedia (WMM), also known as Wireless Multimedia

Extensions (WME), is a Wi-Fi Alliance interoperability certification. It provides basic

Quality of Service (QoS) features for IEEE 802.11 wireless network. Enabling

WMM support provides prioritization of Wi-Fi data packets on four categories

voice, video, best effort, and background. (Default: Enabled)

System Configuration

5-26

•

APSD Capable

– Auto Power Save Delivery is used for saving power

consumption. APSD allows a longer beacon interval until the traffic arrives.

(Default: Disable.

, See “Beacon Interval” on page 5-24

)

•

DLS Capable

– The Direct Link Setup (DLS) allows all clients transfer data more

effectively. When enables DLS, the wireless AP/Router will all clients on this unit to

establish directly connection and speed up the data transmission, especially for

multimedia data files. (Default: Disable)

•

WMM Parameters

– Display the WMM Parameters.

Access Categories –

WMM defines four access categories (ACs): voice, video,

best effort, and background. These categories correspond to traffic priority levels

and are mapped to IEEE 802.1D priority tags (see Table 5-1). The direct mapping of

the four ACs to 802.1D priorities is specifically intended to facilitate inter operability

with other wired network QoS policies. While the four ACs are specified for specific

types of traffic, WMM allows the priority levels to be configured to match any

network-wide QoS policy. WMM also specifies a protocol that access points can use

to communicate the configured traffic priority levels to QoS-enabled wireless clients.

WMM Operation

— WMM uses traffic priority based on the four ACs; Voice, Video,

Best Effort, and Background. The higher the AC priority, the higher the probability

that data is transmitted. When the access point forwards traffic, WMM adds data

packets to four independent transmit queues, one for each AC, depending on the

802.1D priority tag of the packet. Data packets without a priority tag are always

added to the Best Effort AC queue. From the four queues, an internal “virtual”

collision resolution mechanism first selects data with the highest priority to be

granted a transmit opportunity. Then the same collision resolution mechanism is

used externally to determine which device has access to the wireless medium.

Table 5-2. WMM Access Categories

Access Category

WMM Designation

Description

802.1D Tags

AC_VO (AC3)

Voice

Highest priority, minimum delay. Time-sensitive

data such as VoIP (Voice over IP) calls.

7, 6

AC_VI (AC2)

Video

High priority, minimum delay. Time-sensitive data

such as streaming video.

5, 4

AC_BE (AC0)

Best Effort

Normal priority, medium delay and throughput.

Data only affected by long delays. Data from

applications or devices that lack QoS capabilities.

0, 3

AC_BK (AC1)

Background

Lowest priority. Data with no delay or throughput

requirements, such as bulk data transfers.

2, 1