TELECOM Digest OnLine - Sorted: Re: Two VOIP Boxes on the Same Port

Re: Two VOIP Boxes on the Same Port

Robert Bonomi (
Sat, 20 Aug 2005 21:47:56 -0000

In article <>, Fred Atkinson
<> wrote:

> As I've previously mentioned, I've just moved from Columbia, SC to
> Sylva, NC. I took my Vonage phone (Columbia number) with me and got a
> new VOIP phone from Voicepulse (Sylva, NC number). I've got both of
> them connected to my Cisco 831 router via Ethernet cables.

> I've been having some problems getting fast busies when dialing. I
> hang up and dial it a second time and it goes through. Voicepulse was
> not able to sort it out so I contacted Sipura, who was the
> manufacturer of the VOIP adapter (Sipura 3000).

> Sipura said that having two VOIP devices on a single router can be a
> problem. To fix it, they said that you have to change the SIP port on
> one of them. Typically, I believe they said that it was on port 5061
> and 5062. They suggested changing one of them to 5063 or above.

> I called Voicepulse and asked them to make the change. They said that
> wasn't possible. I spoke with the supervisor there. He said that
> their system wouldn't accomodate me using a different SIP port from
> the one I have now.

> Can the VOIP experts on here sort this out? To expand upon my system,
> I have a Cisco 831 home/office router connected to Mediacom
> cablemodem. Each VOIP device is plugged directly into an Ethernet
> port on the router.

> Is Sipura's story plausible? How likely is it that Voicepulse is
> telling the truth about not being able to change the SIP port to
> communicate with their system?

They are right. And you are right.

To use their system, you have to contact their system at the IP
address and port number(s) they specify.

YOUR system, on the other hand, can be at any IP address you can use,
and can _originate_ from any available port number on that address.

Two devices trying to use the same originating address _and_ the same
port number *will* confuse anything you try to talk to.

Details of 'fixing' the situation depend on the gory details of your
set-up. Do you have multiple IP addresses available to you? Or only
a single address? Are you using DHCP? Are you using NAT/PAT?
Depending on those answers, you _may_ be able to do the necessary
things entirely in the Cisco 831. Or, you may have to access the
configuration stuff for the VoIP devices.

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