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Unread 09-16-2007, 04:27 PM   #20
DracoFelis
 
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For those of you having problems, how do you have your home router setup for your VoIP?

I'm not sure if it's the problem here. However, it's been my experience that 1-way (and 0-way) audio problems are OFTEN the fault of your home router, that is incorrectly treating the audio stream as an "attack" from the internet, vs properly forwarding it to your VoIP equipment. i.e. in many cases the audio is actually getting to you, but your router (or the router of the person on the other end) is preventing the audio from making it the whole trip between the two VoIP end points.

Now, if the above is what is going on, than there are many settings that could be done to the various VoIP equipment, and probably even a few changes that could be done to VoXaLot, to help convince the routers to "behave". However, such changes are not certain to work, and would really only be "work arounds" away. IMHO the proper "fix" for this (because it's the only "fix" that addresses this issue 100% of the time, because it works directly on problem routers themselves), is to have people configure their routers to always allow this VoIP traffic (and always send it on to their VoIP adapters). And that is usually done with "port forwarding" on your home/NAT router.

Specifically, VoIP is naturally more reliable if/when SIP and RTP ports of the VoIP adapters are exposed to the internet (although you generally do NOT want the web interface of VoIP adapters to be exposed, just the VoIP ports, which is why I usually avoid using the router's DMZ and instead "port forward" the SIP and RTP ports)! The way port forwarding is done varies with your router, and which ports to use varies with which VoIP adapters you have, and how you have them setup. So I can only give general advice on this. However, in general, it should be possible to modify this technique for other adapters and routers, the details will just vary slightly.

1) In general you need to first assign a fixed IP address on your LAN to your VoIP adapter. This is often necessary, so you have a consistent place to tell your router to forward VoIP ports to. Because if you let the router auto-configure based upon DHCP, it might get a different IP address (on your LAN) when you reboot the router, and therefore mess up your attempts to "port forward" (because the adapter has "moved" on your LAN, as it were). This is usually done on your VoIP adapter's "advanced" settings, and you should try to pick a LAN IP address that is part of your LAN (which with a lot of routers means that the 1st three numbers are the same as other devices on your LAN), but which isn't used for any other device on your LAN, and also is not part of the range that your DHCP server (that is often part of your router) auto-assigns to devices (because you will get real network headaches if/when two devices get the same IP address on your LAN).

2) Once you have the VoIP adapter at a fixed LAN address, you can proceed to "forward" the SIP and RTP ports for your adapter, to the IP address (on your LAN) you now have the adapter on. If you already know the UDP ports used (by your VoIP adapter) for SIP and RTP, than you should be good to go. If not, you will have to do some investigation in your VoIP adapter, to find the info.

2a) The SIP port is the port used to setup a call (i.e. ring your phone, and similar issues). It is often UDP 5060, but many adapters will let you set this to other numbers. And even with the "default" settings, many adapters use a different port number for the 2nd/3rd/etc line, than they do for the 1st VoIP line. So it's usually easiest (and most accurate) to get this number (or these port numbers, if your VoIP adapter supports more than one line), by just checking the SIP port settings in your adapter (with many adapters, this info can be seen in the advanced settings of the adapter's web interface).

2b) The RTP port RANGE is the range of UDP ports that can be used for VOICE TRAFFIC. With most adapters, this range is (by default) MUCH bigger than it needs to be. For example, some LinkSys adapters is 16384-16486 (over 100 different ports) by default, and some devices even use 10000-20000 (about 10,000 different ports) by default. IMHO even having 5 times as many ports as you have "lines" in your equipment is over-kill, so you really do NOT need anywhere near as many port options as VoIP adapters like to use "by default". Instead, you can often considerably lower this range (if desired), to give you less ports to "forward" to your adapter. And you can also edit the range, to allow multiple VoIP adapters to exist on your LAN, but with different RTP ports (so you can have your router forward the proper voice traffic to each adapter). I actually did the latter, as I have two VoIP adapters on my LAN (which I have setup with different, non-overlapping RTP port ranges, each properly "port forwarded" to the proper VoIP adapter on my LAN).

NOTE: On many LinkSys adapters, the RTP port range is defined/set on the "SIP tab" (of the web interface of the adapter), as being between the values "RTP port min" and "RTP port max". On other adapters, you will have to consult the adapter's manual to find the RTP port range.

Again, most of the above is often "not necessary", as many routers will often open the required ports dynamically as needed (based upon the actions of the VoIP adapters). However, it is the approach that seems to give the most consistent VoIP results, and therefore the approach I take on my LAN. Because without the above "port forwarding", you are counting on things like the "keep alive" packets from your adapter to keep the call channels open. And that can be "hit or miss" as to if it will work with any given router. But when you explicitly allow all VoIP call traffic to your LAN to be sent to your VoIP adapter (setup technique above), than issues such as "missed calls" (your router blocked the SIP port was blocked when it tried to "ring your phone"), or "1-way audio" (your router blocked the inbound voice from the other end) often go away.

NOTE: And as long as you only open the SIP and RTP ports (and then only to your VoIP adapter), you really aren't lowering your internet security much. But such an approach will give inbound VoIP traffic (which includes receiving the voice from the other end of the "call") a more open (unrestricted) path to your VoIP adapter.

Of course, this isn't a "cure all", and sometimes even this won't be enough to get fully working voice. But in many cases, the router on your LAN is the culprit that is causing the problems (by blocking the inbound VoIP packets needed for the call). And often the better the router's "firewall", the more likely the router is to cause problems in this respect (so higher end routers can actually be WORSE in this regard). But if you explicitly "port forward" the VoIP traffic (to your VoIP adapter), the problem often goes away. Because you have then told the router to always accept that traffic (and always send it to your VoIP adapter), even if/when the router thinks it came in "unsolicited" from the internet.
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