Telos Z/IP ONE - Managing Connections

Updated 2 weeks ago by John (JP) Powell

The Z/IP ONE, with it’s Agile Connection Technology™ offers the best experience with point to point codec calls over the Internet.  It all started with the ISDN Zephyr, allowing users to send and receive stereo, high fidelity, digital audio from one place to another using the Public Switched Telephone Network (PSTN).  As the world of Internet Protocol (IP) replaces the traditional PSTN, we’ve developed the Z/IP ONE as a viable replacement for this newer protocol. Once of the benefits to using the public Internet versus the PSTN is the amount of control you, the user, have over the connection to the rest of the world.  With the PSTN, a connection to another device is handled by the phone company and this device connects directly to that device until the phone company disconnects the route. With IP technology, every device is connected to every other device all the time and the data is filtered based on IP address and a few other things that we won’t get into here.  The main player in this role for the is the router.

The Router

A router (or firewall) is a separate device that may have a modem and an Ethernet switch built in.  It’s job is to interface a private network with the public Internet and route data from the public Internet to the appropriate locations on the private network.  This is where you have the control that the PSTN simply does not offer. With a router, you can house one or more Z/IP ONEs on a private network and manage their connections to the Public internet on a single IP address with port forwards sometimes without the help of the provider. 

The ZIP Directory Server

In most installations, absolutely no adjustments to the router are necessary.  the Z/IP ONE along with the ZIP directory server works with the router to make connections without your help.  Here’s how it works:

Every 10 seconds or so, the Z/IP will send a ping to the directory server.  If the listen port is set to 0 (We'll explain in a minute) this ping will go out on a random port.  This ping will carry your router's outward facing IP address and the port the Z/IP is using to ping.  When the ZIP Server sees the ping, it will respond and ZIP indicator on the front panel status window will light up.

In the most simple of terms, a server assisted call works just like a ‘411’ directory assistance call:

"Information, how can I direct your call?"
"Hi Operator, I want to call WXYZ_ZIP@public."
"Thank you, that's at this address  Would you like me to connect you?"
"Thank you"

The operator (directory server) hands the connection off and the Z/IPs will be directly connected.  The server steps completely out of the picture and moves on to it’s next task.

Server Relay Calls

In situations when the connection hand-off is unsuccessful, the server will allow a route for the audio through it’s already established connection with the Z/IP ONEs.  When this happens, a message to this effect will display on the front panel of the Z/IP ONE. Connection status in the web UI will also reflect this condition by indicating that it’s connected to the other side “thru server.” 

This is a failsafe and it has its own problems like bandwidth limiting and latency. This problem is usually the result of a firewall or router getting in the way and rejecting the connection hand-off. This is when an adjustment or some configuration at the router is needed.  First, you will want to find out which firewall (local or remote) is the one with the issue. You can try to call other Z/IPs including ZephyrIP10@public (the telos Z/IP Test line) and if you only get the message when you call certain Z/IPs, the fire-walling is at the far end. If you get it each and every time, the fire-walling is local.  The Z/IP ONE has a configurable UDP port that can be used to manage this with the help of a port forward.

Listen Port

Each Z/IP ONE behind the router can have a unique listen port assigned to it.  We recommend a port in the 21000 or so range to keep the Z/IP away from other network traffic.  This port is specified in the STREAMING page of the Z/IP's GUI or in the front panel SETUP / ZIP SERVER menu.

In this example, we are using 21011 for this Z/IP ONE.  If we had another Z/IP ONE on this network, we would give it a different port, like 21012, etc.

Once the Listen port is configured and the changes have been saved, a UDP port forward for 21011 will need to be set up at the router.  In this example, we are using a basic Linksys router made by Cisco and the Z/IP ONE we just configured has it’s streaming interface set to a private static IP address of

When the listen port is specified and forwarded in this manner, the Z/IP Server will be able to hand the connection off without negotiation and it will be much more reliable.

An added bonus to this is the ability to connect to this Z/IP ONE without the help of the directory server.  The server’s main task is to keep track of which Z/IP is using which IP address on which port. If the public IP is dynamic and changes, the server will be aware and will make adjustments to it’s records.  If we already know this information and if the public IP address is static, the server doesn’t really need to be involved at all! You can enter this information directly into the call setup and dial the unit directly.

Dialing a Z/IP ONE directly

Once the public IP address for the router is made static by the ISP and once the Z/IP ONE’s listen port is specified and forwarded at the router, this Z/IP ONE can now be dialed directly using the router's outward facing IP address and this port.  Since a rule is established as a port forward, the router will know what to do with the request coming in with this port specified.

To dial this Z/IP ONE, use the MANUAL tab on the web GUI connection page and select “TSCP Direct” for PROTOCOL and enter the information.

You can also use the front panel and strip the GROUP NAME and enter the IP and port in this manner:

Obviously, this will be a challenge if the unit you are calling is on an Internet connection with a dynamic IP.  This is why the name-based directory server is handy.

With no port forward and a listen port of 0 (default) the Z/IP relies on the open communication that it has with the server instead of the router for completing the call.  So the server is critical in these cases.

Other management is possible with firewalls and routers like VPN (Virtual Private Network) which creates a “tunnel” over the public IP address to another router.  This has benefits like restriction of public traffic from the interface, but is slightly beyond the scope of this discussion. More information about setting up a VPN will be provided with the setup information that comes with your particular router or firewall.

The Z/IP you are trying to reach is not answering:

This is a message you may see from time to time and it has a double meaning.  The first one is the most obvious: the Z/IP ONE at the far end is not set up to auto answer and it is literally not answering the call.  This message can also indicate a problem with the router at the far end. It means the request to call the unit got rejected by the router at the other side and the messaging never made it to the Z/IP ONE.  The Z/IP ONE trying to make the call doesn’t know the difference between these two states. With confidence however, we can say that it’s either number one or number two. Number two indicates the need to create a port forward for the TSCP listen port.  In this case, re-read this document.

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