Call Mode; Scanning Algorithm; Dfs Channel Probing - ASCOM Myco 3 Troubleshooting Manual

The Handset as a WLAN Wireless Client
The algorithm then decides where and when a handset disconnects from one AP and connects to a
different AP.
An additional factor that must be included in any roaming algorithm is to provision for sudden, large and
often unpredictable reductions in received signal strength due to some dynamic event that is introduced
into the physical environment, such as the closing of a heavily clad steel door or the handset user enters an
elevator. These events can occur between the scans performed at the fixed time intervals and cause
additional scans to be performed.
For example, consider a doorway between an associated AP and a handset, with a metal door in the open
position. If the door was momentarily closed and then opened, there might be a sudden 16bB reduction in
received signal strength and a rapid loss in communication. However, this would be largely restored once
the door was opened again and make an extra scan unnecessary and a waste of network resources.
However, if the door was left closed, the loss in received signal strength would be sustained and probably
worsen as the user moved away from the AP. An extra scan would therefore be justified.
4.5.1

Call Mode

In call mode, received signal strength is very important for ensuring voice quality, particularly if the user is
moving around the site. To improve roaming while in a call, the handset will periodically scan for better AP
candidates if it detects traffic in voice or video queue above a threshold level. The threshold level is set to
10 packets with a 5- second interval, which is then defined as a scan interval.
4.5.2

Scanning Algorithm

Ascom Myco 3 scans for new APs according to a RSSI-based roaming-scan trigger:
Case
During the call
Not in call
Additional Scans
The handset may perform additional scans and roam decisions when a drop is detected in RSSI both in call
and non-call modes.
4.6

DFS Channel Probing

The 5 GHz band supports a minimum of 21 non-overlapping channels and potentially a few more depending
on different regulatory domains. The following table, for example, shows the channels supported in the ETSI
regulatory domain:
Band
UNII-1
UNII-2
UNII-2e
UNII-3
1. Channel 144 is slightly outside the specified band (5.710–5.730 GHz).
12
Scans
Periodic scan with aprox. 5sec. interval.
RSSI low periodic scan with aprox. 10sec. interval.
Channel
36, 40, 44, 48
52, 56, 60, 64
100, 104, 108, 112, 116, 120,124, 128, 132, 136, 140,
144
1
149, 153, 157, 161, 165
TD 93297EN / 19 December 2019 / Ver. B
TROUBLESHOOTING GUIDE
Ascom Myco 3