VoIP and WAN Bandwidth

The real question is how much traffic you expect is going to go across your WAN.

With an Asterisk System and softphones we budgeted about 64kbit/s per "conversation". We only really expect 2 or 3 people to be using them across the WAN at a time though so our 2Mbit/s SDSL circuit copes without any issues, even without QoS defined.

Were using SIP and G711 Codec by the way.
 
64kbit/s does seem like a fairly sensible ammount, i'll do some digging regarding the number of outgoing calls.

Just looking to hear peoples experience with this really.

Surely you would want QoS configured though because what if someones downloading a file at 200kb/s leaving you with too little bandwidth and poor VoIP
 
we're running a simple enough system here atm and have a couple of softphones and a couple of hard phones too but we find that even with QOS when someone uploads anything the VoIP quality dies thats with a 350k/s upload speed (speedtest.net)
two concurrent calls work ok but again uploads/downloads make things evil.
 
Wardie said:
64kbit/s does seem like a fairly sensible ammount, i'll do some digging regarding the number of outgoing calls.

Just looking to hear peoples experience with this really.

Surely you would want QoS configured though because what if someones downloading a file at 200kb/s leaving you with too little bandwidth and poor VoIP
Click to expand...

If it becomes an issue then I'll configure it. So far everyone has commented on how good the quality is. I think this is due to the amount of upload bandwidth we have which is not really affected much if someone is downloading a big file. Upload bandwidth is what is needed for VPN and WAN VoIP connection capacity planning imo.
 
Is that 64kbit/s both up and down, or 32k up, and 32k down?

Have you limited the outgoing calls so any more over a certain amount can not be made and they must wait for an available 'line'?

I guess not though since you've not had any problems...
 
http://www.newport-networks.com/whitepapers/voip-bandwidth3.html

Thats a good place to start regarding what you might need to budget for.

Regarding your question on limiting calls there is no need as we have only 3 members of staff at a time that might be using the VPN simultaneously. Most of our staff with VPN access are required by the general manager to be office based unless at a customer or supplier site. He actively DOESNT want routine home working unless necessary (bit of a ludite really!)

Thats the benefit of being in a small business with only 50 staff ;)
 
That's saying upwards of 90kbit/s, not 64? Or were you refering to the quality when you said 64kbit?

I've got a pretty limited understandinf of VoIP, at what point does a VoIP to normal landline call switch to the PSTN network and stop using your WAN link, or does it never reach the WAN link and is converted to PSTN before it leaves your network?

If that makes any sense at all ha-ha
 
I was referring to the codec quality before IP encapsulation overheads. Different codecs use different amounts of bandwidth. G729a is good but I think it involves an additional licensing cost so we didn't bother with it.

RE: VoIP breakout to PSTN it depends on how your system and provider are set-up.

Some people sign up with an ISP who does a VoIP service. Most of the time the call across the WAN to the ISP will be IP, but when it leaves the providers network it will do so either by IP or by ISDN/PSTN. They handle the switching and call setup/connection between your system and the endpoint.

Another way of doing it (which is what we did) is lease our own ISDN circuit using a least cost routing provider (in our case ED Communications). We have an ISDN30 circuit with 8 active channels (allows for 8 simultaneous external calls). This interfaces directly with our Asterisk system and so all calls routed out from or into our organisation break out to PSTN (or IP if its 21cn i think!). All internal calls are IP based. Using softphones and the VPN roaming users connect to the Asterisk system via IP but again any calls to outside the organisation are routed by Asterisk through the ISDN circuit.

We deliberately wanted to use ISDN breakout when the call left our system rather than chance it on the Internet as the call quality can suffer dramatically over a broadband connection (you have no guarantee of call quality over a braodband connection as you don't know whether QoS is employed from end to end or what routing takes place). Additionally we couldn't get an SLA from any broadband provider on uptime. All fixes are on a best efforts basis. With ISDN the fix times in our experience are exceptionally quick and its very very reliable (except when your ISDN box is fried in a lightning storm)

All these things are worth considering before you choose whats best for your transport mechanism.
 
VeNT said:
we're running a simple enough system here atm and have a couple of softphones and a couple of hard phones too but we find that even with QOS when someone uploads anything the VoIP quality dies thats with a 350k/s upload speed (speedtest.net)
two concurrent calls work ok but again uploads/downloads make things evil.
Click to expand...

You need far more upload capacity then! ;)

Are you using a standard ADSL circuit? Any significant uplod requirement and you are looking at SDSL I'm afraid.
 
By not using your WAN link for calls outside of your LAN, aren't you missing out on the majority of potential cost savings?

If you had say remote branch offices, you could perhaps use VoIP out to them over a WAN link, but all totally external calls over PTSN?
 
difficult to say
depends what you're trying to acheave (sp?)
if you're looking for a internal calling system with voicemail etc then its all good but if you're looking to cut down your outgoing call charges then its less so.
 
like over a VPN? that would work but you're still gonna be screwed by the up/down bandwidth unless you've a nice big fat pipe
you'll need QOS on both ends to make it even playable.
why not try it out? astrix is free and you can use x-lite and a headset
 
Remote branch offices will work with VoIP over a WAN link, but as VeNT rightly says upload bandwidth is the issue.

Whats your budget? Our SDSL circuit from Zen is £299 a month for 2Mbit/s. Asterisk is free but you may want to budget for consultancy if you are unsure about how to get the best out of it (Credativ are an excellent consultancy for all open source stuff). In terms of server hardware, you can comfortably run 100 users on a low end server with a gig of RAM and 40Gb HDD. Handsets are the biggest expense. We use Cisco 7941g handsets and they are fully featured and robust. Much cheaper handsets available though. The 7941g is about £200 each!
 
Wardie said:
By not using your WAN link for calls outside of your LAN, aren't you missing out on the majority of potential cost savings?
Click to expand...


Yes potentially, but for us we came from a managed service to bringing it in house and we saved over £700 a month doing this. A lot of the cost saving is choosing a decent least cost routing provider and bringing down the line rental costs. For us though UPTIME is the key. We can't afford to have a service that can fail, so we have server hardware redundancy, ISDN failover etc.

We also save a fair bit on travel telephony costs. Mobile user gets on a WiFi link, gets into VPN, logs onto Xlite, and their PC becomes an Internal phone with free calls to other internal phones.
 
Yeah :)

Well, if remote branches will work then there's no difference between using the WAN for the rest of calls made to entirely external destinations.

If you have a leased line to the ISP, then they handle the switching to the PSTN network from there on, surely it would effectively be the same as calling a remote branch over VPN?
 
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