two ADSL connections on one PC

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peter_mcc
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two ADSL connections on one PC

Post by peter_mcc » Tue Jul 12, 2011 11:05 pm

hi
If I hook up 2 ADSL connections to a Windows 7 PC (on 2 different ethernet ports) can I easily get all the VoIP traffic to go out one modem and all the other traffic to go out the other?
The "voip" ADSL modem would only be connected to the Win7 machine - all the other machines on the network (including the Win7 one) would be connected to the other ADSL modem.
Or do I need to buy a dual port router?

Looking around, I think I can do it using the standard Windows 7 firewall public/private firewall profiles. I set up say the "private" network firewall to only let in/out VoIP traffic and the "public" one to block VoIP traffic but let everything else in/out.

thanks
peter

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Re: two ADSL connections on one PC

Post by NetworkAdmin » Wed Jul 13, 2011 10:48 am

First question would be; why use two circuits? VoIP runs very well over a single circuit shared with data.

But if you are going to use to circuits, and two DSL modems than all you really have to plan for is the IP address range you will use.

Say you are using a LAN address range of 192.168.1.0/24:

- Make your 'data' DSL modem 192.168.1.1
- Make your VoIP modem 192.168.1.2
- Make sure only the data modem has DHCP enabled, or, disable DHCP on both modems and assign your PC addresses manually
- On each PC, put in a static route that points the VoIP server address to the VoIP modem, for example, if the voip server is 203.111.112.113:
c:\> route add -p 203.111.112.113 mask 255.255.255.255 192.168.1.2

If there are several VoIP/SIP servers, then you will need a static route for each, or if they are all in the same netblock, a static route to that network.

- make sure your default route points to the data modem, ie 'route print' should return a gateway address of 192.168.1.1

peter_mcc
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Re: two ADSL connections on one PC

Post by peter_mcc » Wed Jul 13, 2011 2:10 pm

NetworkAdmin wrote:First question would be; why use two circuits? VoIP runs very well over a single circuit shared with data.
I've never managed to get it to coexist properly with other traffic, especially if there is more than one call active. I've tried QOS on the router and using a ClarkConnect Linux gateway - in both cases the audio broke up when someone started to upload/download stuff.

I'd be happy to only have one connection but I figure it's cheaper to dedicate an ADSL connection to VoIP where I can run multiple lines over it than to get a single landline!

Is there a specific brand/model of ADSL modem/router that has good QOS support for VoIP so that I can have 2 or 3 concurrent phone calls and not experience breakup when internet traffic starts/stops?

regards
peter

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Re: two ADSL connections on one PC

Post by NetworkAdmin » Wed Jul 13, 2011 2:59 pm

What I use myself at home is a CIsco 827 router on an ADSL1+ circuit (8Mbps/384k). Over the last seven years I have also had ADSL2 ~ 15M/256k, ADSL1 1.5M/256k and ADSL1 512k/512k. All have had essentially the same performance characteristic using both VoIP and data together.

The Cisco IOS has full QoS features, but I don't use any of them. I do have 3 teenage sons, one of whom makes a practice of downloading his uni assignments - RAW video and photo data, from home. So the circuit can at times become very heavily used for data downloads.

In most cases, with moderate to heavy downloads, VoIP works fine. Since most heavy d/l use is in the evening, and I use VoIP mostly during the day. I could put QoS on for the times when there is a conflict, but pulling the plug to the wifi hub that serves the rest of the house (since I am on wired Ethernet) is more expedient for me.

Anyway, the point I am trying to make is that only in cases of extreme saturation will QoS make any difference. VoIP UDP packets will barge through a lot of TCP contention before the call quality drops below an acceptable level - at least for downloads.

What I would suggest is this:

- make sure your VoIP devices are on a wired LAN connected directly to your ADSL modem.
- if you can, make sure your LAN is using 100Mbps full duplex and not 10Mbps etherent
- check to see if anything is uploading data (such as a shared torrent file for example). Uploads have a much greater effect on performance due to the asymmetric nature of DSL. Also, uploads tend not to be controlled by QoS in any event.

If you are satisfied that your LAN environment is as good as it can be, your cables are good, and your neighbors or a virus/botnet isn't stealing you bandwidth, then the thing to check as a the last resort is the performance profile of your DSL circuit. In rare cases line attenuation or some other physical issue might cause the upload half of your circuit to be less than the reported connection speed. In such a case your data d/l speed is relatively unaffected, but you could have, say, only 64k available for upload out of the 256k reported by the modem. And that would cause your VoIP to turn to mush for even moderate downloads.

If you think that is the case - which let me stress - is a very rare occurrence, then open a helpdesk ticket and we will get the carrier to check the circuit.

A final point - while the specs of any ADSL modem are on paper the same, ie they sync to the ADSL service at the same speed, I was happy to spend $1,000 for a Cisco router rather than $100 for a normal ADSL modem. The amortized cost difference over the last seven years amounts to not even a cup of coffee a week.

jokiin
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Re: two ADSL connections on one PC

Post by jokiin » Wed Jul 13, 2011 3:46 pm

peter_mcc wrote:
NetworkAdmin wrote:First question would be; why use two circuits? VoIP runs very well over a single circuit shared with data.
I've never managed to get it to coexist properly with other traffic, especially if there is more than one call active. I've tried QOS on the router and using a ClarkConnect Linux gateway - in both cases the audio broke up when someone started to upload/download stuff.
since you're familiar with Linux anyway I'd suggest changing ClarkConnect for SME Server (formally known as E-Smith) http://wiki.contribs.org/Main_Page the people behind this have a strong VoIP background (Mitel Networks) and you'll find it works extremely well, I've used it for about 11 years (7 years with VoIP) on various connections and have never had to play with any settings relating to QOS regardless of what other people are doing on the network, it just works, definitely worth a look before you go spending any money on hardware

CorporateVoIP

Re: two ADSL connections on one PC

Post by CorporateVoIP » Wed Jul 13, 2011 4:55 pm

You may also like to consider the following:

http://www.draytek.com.au/products.php?type=dv2950

and you will need 2x ADSL modems to make the ADSL connections to the dual WAN ports.

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