Toshiba CTX28 用户手册

Installing and Operating the SoftIPT

The Toshiba SoftIPT™ works on wireless 802.11 networks. However, current access point 
technology does not provide for the management of quality of service over the wireless network, 
which can result in a few observable degradations in voice quality.

Our objective here is to describe these issues for the network engineer, and offer some 
recommendations. As the technology evolves, and the knowledge base grows, other problems and 
solutions will emerge, hence the network engineer is encouraged to search out other sources of 
information, from the specific access point manufacturers or from experts in the 802.11 wireless 
industry.

Possible problems and their implications are:

1. Dropped packets may occur due to RF signal strength, especially as you get further away from 

the access point. When small amounts of packet loss occur, you will notice a popping or 
clipping sound. With larger amounts of packet loss, gaps in the conversation will occur.   This 
is very similar to the behavior of digital cell phones in the same situations. The best way to deal 
with this is to design the wireless network for good coverage where it is needed.

2. Dropped packets may also occur due to excessive traffic on the wireless network. With multiple 

devices accessing data through the same wireless network, current access points do not have a 
method for prioritizing voice packets over data packets so when data applications create more 
traffic than the wireless bandwidth can sustain, voice packets may get dropped. In addition, 
access points do not have a mechanism for limiting the number of simultaneous sessions. In our 
lab we find that up to seven calls can take place simultaneously on a single access point. This 
number will vary depending on the access point, the RF environment, and any other activity in 
the wireless environment.

3. When one terminal is in a poor signal area for the access point that it is associated with, the 

access point may automatically reduce its data rate in order to achieve better communications 
with that terminal. This new data rate affects communications with all terminals, which will 
reduce the number of simultaneous calls the access point can support. Network engineers 
should consider whether they want to disable the Auto TX Data Rate Feature.

4. Disconnected calls will result if you move too far away from the access point, or generally are 

in a poor signal strength area. With current 802.11 wireless technology, when a terminal can’t 
communicate with an access point, it will disassociate with it. This appears to the phone 
application as a loss of the network, and the phone application disconnects. Even if you quickly 
move back into range of an access point, it will take several seconds for the 802.11 terminal to 
detect and re-associate with the access point.

5. Wireless networks can only get so large, before you have to break them up into multiple 

subnets. Somewhere between 256 and 1000 nodes is where networks begin to need to be 
broken up into multiple subnets. When multiple subnets are employed, the call will get dropped 
as the terminal gets out of range of its subnet. But the terminal can reestablish its call after 
associating with the new subnet. 

FYI: At Toshiba we are working on technology to address problems 2~4 for the SoftIPT. Check 
back with us.