eXpansys VoIP - How to set up Wi-Fi
eXpansys VoIP lets you make free or VoIP-rate calls wherever there is Internet access available via Wi-Fi. We have published the following guidelines to help you get the best from the service. These explain some of the changes you can make to your Wi-Fi setup.
The bad news is that wireless (Wi-Fi, WLAN) and broadband (ADSL) connections, and indeed the Internet as a whole, are designed and optimised for data traffic rather than voice traffic. Data traffic is generally non time critical - i.e. that, within reason, it doesn't matter how long it takes any particular data packet to arrive, what order they arrive in, and whether some of them get lost (as they can always be re-sent). For voice traffic, on the other hand, it is very important that the data packets arrive as fast as possible in the correct sequence with no dropped packets.
The good news is that if you experience problems with call quality or call reliability there is a lot that you can do to optimise your own network for voice traffic.
Search for Wi-Fi Hotspots at myhotspots.co.uk
What phones does it work on?
eXpansys VoIP aims to bring VoIP to mass-market mobile phones, starting with Nokia's N-series and E-series, to be quickly followed by other handsets.
Testing
One of the easiest and most useful tests is at http://www.testyourvoip.com - use the ‘conserve bandwidth’ setting. If you have a laptop with a Wi-Fi connection you can repeat this test using both a wired and a wireless connection. This test is not exactly analogous to using eXpansys VoIP (it uses a different codec, and the antenna on your laptop is mounted behind the screen and is much larger and more efficient than the one in the mobile handset) but it nonetheless gives useful information about latency and packet loss. Packet loss in particular leads to problems in the reliability of call setup and tear-down as well as with voice quality. Note that the quality of ADSL connections varies with time (see more information below) so you may have to repeat this test on more than one occasion.
Equipment Selection
We have observed two sorts of problems with Wi-Fi access points and routers - either they don't work with the eXpansys VoIP service at all, or they crash from time to time and require rebooting.
If an access point does not work at all then the chances are it is because the manufacturer has implemented a Session Initiation Protocol Application Layer Gateway (SIP ALG) but done it in an incomplete or buggy way - this is commonplace as relatively few people are using these features yet. Often these problems can be cured by updating to the latest firmware or turning the ALG off (e.g. see details for BT, Zyxel and Draytek routers below), but sometimes it is necessary to buy an access point or router that does not have this functionality built-in - it is of no benefit to the eXpansys VoIP service and generally only gets in the way.
If an access point or router keeps crashing, there is not very much that can be done about it. The problem seems to be caused by corrupted packets at the extremes of radio range (or caused by other radio interference) confusing the software in the router. We daren't risk lawsuits by providing a league table of manufacturers and how prone to these problems they are, but if you are experiencing frequent lock-ups than you might want to try a Linksys product instead.
Access Point and Router Configuration
One of the easiest things you can do is to set your access point to use 802.11b (10Mbs) instead of 802.11g (100Mbs, the default on all modern equipment). Unless you are doing frequent large local file transfers over the radio network you will not notice the difference in speed as the restriction is the ADSL connection in any case, and the reduced speed of the radio link results in greater reliability of communication.
Turn off the SIP ALG. I'm afraid you are probably going to have to read the manual for this as every manufacturer's commands are different. For example the command line for Zyxel routers is "ip nat service sip active 0" and for Draytek routers is "sys sip_alg 0".
Un-block port 5060: Some routers block list by default (e.g. BT Voyager modems), and this will prevent registration to the eXpansys VoIP service. Again, you will have to check the manual, but for BT Voyager modem the solution is to telnet into the router, unbind the SIP protocol and reboot the modem:
- nat unbind application=SIP port=5060
- config save
- system rebootthis
ADSL Selection
ADSLMax (i.e. most services that claim speeds above 2Mbs) can be a problem for VoIP. The way that the exchange establishes the maximum speed is to continually increase the speed until the error rate becomes large and then back off a bit. Unfortunately, ADSL performance can vary quite a lot over time, especially in more rural areas when it rains! This can result in the ADSL line hunting for a possible speed and inducing lots of transmission errors. If you are experiencing an unstable line speed (after the initial 10 day bedding in period for a new service), you may be better off switching to a service with a fixed line speed that is significantly lower than the best you have achieved but which will be more reliable - e.g. if your best result with ADSLMax was 4Mbs them choose a fixed line speed of 2Mbs.
Other Notes
Turn off any nearby Bluetooth devices when you are not using them - Bluetooth uses the same frequency spectrum as Wi-Fi and causes a loss of radio layer interference.
If you are using multiple access points, space the channels as far apart as possible - e.g. if you are using three access points in the UK you would put them on channels 1, 7, 13. Any gap of less than three channels and the access points will interfere with each other.
Note that unlike cellular coverage there is currently no way to have a seamless call transition between one access point and another if you are walking between coverage zones - it takes the handset some time to establish the new connection.
