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IP links: Ready for STL?

Posted by Ted Alexander on Jul 26, 2012 11:35:00 AM

Your STL is your lifeline. Everything you are travels over that STL. Ideally, the STL should be a “nailed up” connection, whether via microwave, or leased lines. It should be always there, always on.

But, because of the rising costs of leased lines and other “nailed up” lines such as a T-1, or switched lines such as ISDN BRI, some stations are looking for an alternate path for their STL. If the station is willing to accept the slight risk of audio (and sometimes control) interruption in STL usage, a connection from ISP to Internet, and back to ISP can be considered.

So, is IP via the public Internet a worthy solution for STL? The answer right now is “maybe.”

Let’s examine this scenario. Using the Telos Z/IP ONE, you can establish a direct connection using the TCSP protocol for connections between 2 units with static IP addresses and some guaranteed bandwidth (QoS) if you can get it. The connection between the ISP and the studio, and the ISP and the transmitter should be provisioned for the best possible reliability.

To set up an STL that uses the TSCP protocol, you will need two Z/IP ONEs, one at the studio and one at the transmitter, to utilize the advantages of Telos ACT error correction and concealment of anomalies in an Internet data connection. You also can connect by using the Z/IP Server (a free service Telos provides to Z/IP owners, allowing them to register their devices and get around NATS and firewalls) to establish the connection.

So, how do you connect 2 Z/IP ONEs together directly, without going through the Z/IP Server? You use a direct “TSCP” call which maintains all of the ACT advantages. This can also be useful for backup or temporary STL service, but if you want to set up a permanent STL, you should seriously consider asking your ISP to provide QoS service for this, which guarantees bandwidth. You will need your ISP to provide outside IP addresses for each of the two units in any case.

Configure each of the Z/IP ONEs’ WAN port network parameters with a normal internal IP address and the proper gateway address (usually the address of the Router). To call the other unit, press the CONN button and set the Device Name to the IP address of the other unit. Delete any “Group Name” that is present so that it indicates “(For TSCP Calls)” and set the “Call Type” to TSCP. You should now be able to connect to the far-end unit. Be sure to set the Codec parameters as appropriate for the available bandwidth. For STL use, “regular” AAC is suggested at 256kbps or higher (bandwidth permitting). It would also probably be a good idea to set General Settings / “Autoredial Broken Connections” to “Forever”. 

You will need to make available ports 24 and 308 (used for updating), port 11926 (used for listening), and ports 5060 and 5061 (used for SIP negotiation). Also, the default port for TCP is 5060, and 9150 for UDP.

Using the setup outlined here, it’s possible to achieve an STL link via IP over public Internet connections. However, remember that, without QoS, the IP link provided by your Internet supplier is reliable only so long as their network remains intact and uncongested!

While we don’t believe that the reliability of the public Internet is solid enough to support full-time STL connections yet, the steady increase of bandwidth everywhere indicates that the time will come when this is possible, if not inevitable. Right now, however, an STL connection via IP should be considered as extremely viable for use as a backup path to your transmitter.

Topics: Telos Z/IP ONE

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