<div>
Problem might be some sort of high port blocking.<br />
<br />
Each VOIP system tends to work in a slightly unique way, so likely you can see problem quickly running a packet sniffer like tshark, looking to whatever port block is causing the problem.
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skullnobrains

<div>
Tip: One technique you can use to potentially narrow the problem area is disable all firewalls every where in your VOIP packet flow.<br />
<br />
Then enable each device's firewall, one by one, till calls stop working.<br />
<br />
This approach generally gives clues which might speed up fixing the problem... as working with packet sniffers tends to be tedious...
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IT Manager

Ian Price

<div>
Voip is using several protocols to get to work.<br />
1) SIP - Signaling, it makes the phones ring (on INVITE message) or announce their availability (on REGISTER messages).<br />
2) RTP - Real Time protocol for the &quot;Media&quot; channels. (The Voice, one channel for each direction).<br />
(and possibly a few more, these are most commonly used)...<br />
All are UDP based (SIP can be TCP, but is mostly UDP).<br />
<br />
SIP is used to negotiate a conversation, including portnumbers on the endpoints. And there is the problem... VOIP has one enemy NAT.<br />
NAT transforms IP address &amp;&nbsp;Ports.. &nbsp;In your case the outgoing voice is handled OK, the voice from ext -&gt; int is blocked by the NAT Router (firewall)<br />
<br />
Some routers come equipped with ALG Application Layer Gateways. For VOIP they have been mostly implemented those WRONG... so they cause more trouble than they solve. <br />
In General: DISABLE SIP ALG. &nbsp;(modern PBX can cope with Far end NAT quite well).<br />
<br />
You may need to enable the firewall rules to allow UDP in the range of the phones for receiving them. In the case of NAT you may actualy need to port forward them.<br />
(An On prem. PBX can help as well so you can forward all traffic to the on Prem. PBX and use that as proxy in between all conversations).<br />
<br />
For Toying around:<br />
3CX has a &quot;home use&quot; PBX that you can use free for a few phones.<br />
FusionPBX can be an option. <br />
Both need a VM &nbsp;or dedicated hardware to run.<br />
<br />
For seeing what is negotiated <b>sngrep</b> &nbsp;is an excelent easy to use tool that can be used to monitor traffic onany system where PBX traffic passes (PBX or Firewall based on linux).<br />
If you can take recordings in the form of pcap files then wireshark can help decoding the traffic and if you also have the RTP to listen to the sound channels.
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<div>
Arnold, I think this make sense to be honest.<br />
<br />
The office phones are on VLAN 216 which is setup and controlled via Cisco Switch\Router that I do not have access to. I presumes the either the switch or router issue DHCP address. <br />
<br />
However some on the phones are not on a VLAN at all as they have the same ip numbers as our computer picked up via our Windows server DHCP and they seem to work fine. I am guessing this is an oversight and should be like that.<br />
<br />
So I wonder is I try putting two phones on the same VLAN if that will solve the problem.<br />
<br />
I'll try after the holidays<br />
<br />
Thank you all for commenting
</div>


<div>
<div class="content wysiwyg-content">
Hi Experts<br />
<br />
I am on a personal mission to under a little bit more about VoIP.<br />
<br />
So we run a Gamma \ Horizon system at work. All configured and working via Cisco.<br />
<br />
Our Wifi is controlled via Unfi USG, Switches etc. I've plugged in (With Consent) one of our spare Voip phones into a spare port on one of the Unifi switches and configure on it own Vlan etc.<br />
<br />
The phone can call external numbers no problem, but if I try to ring an internal ext the internal phone rings but once connected I can not hear the person on the other end.<br />
<br />
I get that something is blocking it or its not configure I just do know where to start trouble shooting,<br />
<br />
Maybe someone could point me in the right direction?<br />
<br />
Ian
</div>
</div>


Hi Experts

I am on a personal mission to under a little bit more about VoIP.

So we run a Gamma \ Horizon system at work. All configured and working via Cisco.

Our Wifi is controlled via Unfi USG, Switches etc. I've plugged in (With Consent) one of our spare Voip phones into a spare port on one of the Unifi switches and configure on it own Vlan etc.

The phone can call external numbers no problem, but if I try to ring an internal ext the internal phone rings but once connected I can not hear the person on the other end.

I get that something is blocking it or its not configure I just do know where to start trouble shooting,

Maybe someone could point me in the right direction?

Ian

Can anyone help me a VoIP Question

Wireless networking is anything related to the transfer of data between two (or more) devices without the use of a physical connection, ranging from getting advice on a new Bluetooth headset to configuring sophisticated enterprise level networks.

Wireless Networking

Cisco PIX is a dedicated hardware firewall appliance; the Cisco Adaptive Security Appliance (ASA) is a firewall and anti-malware security appliance that provides unified threat management and protection the PIX does not. Other Cisco devices and systems include routers, switches, storage networking, wireless and the software and hardware for PIX Firewall Manager (PFM), PIX Device Manager (PDM) and Adaptive Security Device Manager (ASDM).

Cisco

Voice over IP (VoIP) is a methodology and group of technologies for the delivery of voice communications and multimedia sessions over Internet Protocol (IP) networks, such as the Internet. Other terms commonly associated with VoIP are IP telephony, Internet telephony, broadband telephony, and broadband phone service. The term specifically refers to the provisioning of communications services (voice, fax, SMS, voice-messaging) over the public Internet, rather than via the public switched telephone network (PSTN).  Examples of the VoIP protocols are H.323, Media Gateway Control Protocol (MGCP), Session Initiation Protocol (SIP), H.248 (also known as Media Gateway Control (Megaco)), Real-time Transport Protocol (RTP), Real-time Transport Control Protocol (RTCP), Secure Real-time Transport Protocol (SRTP), Session Description Protocol (SDP), and Inter-Asterisk eXchange (IAX).