User's Manual

Configuration MP.11 4954-R Installation and Management

Network Parameters

Edit the route information and click OK. The IP address and subnet mask combination is validated for a proper

combination.

Enable or Disable Roaming

Roaming Overview

Roaming is a feature by which an SU terminates the session with the current BSU and starts the registration procedure

with another BSU when it finds the quality of the other BSU to be better. Roaming provides MAC level connectivity to the

SU that roams from one BSU to another. Roaming takes place across the range of frequencies and channel bandwidths

(5, 10, or 20 MHz) that are available per configuration. The current release offers handoff times of up to a maximum of

80 ms. This is fast enough to allow the SU to seamlessly roam from one BSU to the other therefore supporting session

persistence for delay-sensitive applications. The feature also functions as BSU backup in case the current BSU fails or

becomes unavailable.

The Roaming feature lets the SU monitor local SNR and data rate for all frames received from the current BSU. As long

as the average local SNR for the current BSU is greater than the slow scanning threshold, and the number of

retransmitted frames is greater than the slow scanning threshold given in percentage, the SU does not scan other

channels for a better BSU.

•The normal scanning procedure starts when the average local SNR for the current BSU is less than or equal to the

slow scanning threshold and the number of retransmitted frames is greater than the slow scanning threshold given in

percentage. During the normal scanning procedure the SU scans the whole list of active channels while maintaining

the current session uninterrupted.

• Fast scanning is the scanning procedure performed when the average local SNR for the current BSU is very low

(below the fast scanning threshold) and the number of retransmitted frames is greater than the fast scanning

retransmission threshold given in%, so that the current session should terminate as soon as possible. During this

procedure, the SU scans other active channels as fast as possible.

Roaming can only occur if the normal scanning or fast scanning procedure is started under the following conditions:

1. If the roaming is started from the normal scanning procedure (after the SU scans all the active channels), the SU

selects the BSU with the best SNR value on all available channels. The SU roams to the best BSU only if the SNR

value for the current BSU is still below the slow scanning SNR threshold, and best BSU offers a better SNR value for

at least roaming threshold than the current BSU. The SU starts a new registration procedure with the best BSU

without ending the current session.

2. If the roaming is started from the fast scanning procedure, the SU selects the first BSU that offers better SNR than the

current BSU, and starts a new registration procedure with the better BSU without ending the current session.

Roaming with Dynamic Data Rate Selection (DDRS) Enabled

When an SU roams from BSU-1 to BSU-2 and DDRS is enabled, the data rate at which the SU connects to BSU-2 is the

default DDRS data rate. If this remains at the factory default of 6 Mbps, there can be issues with the application if it

requires more then 6 Mbps (for example multiple video streams).

Applications requiring a higher data rate could experience a slight data loss during the roaming process while DDRS

selects a higher rate (based upon link conditions).

When the applications re-transmit at a possibly slower rate, the WORP protocol initially services the data at 6 Mbps and

increases the data rate up to the "Maximum DDRS Data Rate" (ddrsmaxdatarate) one step at a time. Because the

applications are not being serviced at the best possible rate, they further slow down the rate of data send.

The DDRS algorithm requires data traffic (a minimum of 128 frames) to raise the rate to a higher value. Although roaming

occurs successfully, the previous scenario causes applications to drop their sessions; hence session persistence is not

maintained.

For a discussion on how to configure DDRS, see Dynamic Data Rate Selection (DDRS).