From SNIP Release 3_04_50 onward a revised process is now used to count up the available slots which any copy of SNIP is allowed to use for Push-Out connections. This is described further below. The net upshot is that SNIP now allows twice as many Push-Out connections to occur without the need for purchasing additional Add-on stream slot licenses.
Background
In the SNIP licensing model, each connection with a base station is called a “stream” or a “slot” and SNIP provides several different stream types to support a variety of connections. Larger deployments pay an additional one-time fee for adding more slots to their networks. [By design, SNIP does not measure the number of NTRIP Client connections, so you can have thousands of users (User Accounts) on any model of SNIP, even the free Lite model. ] The cost of additional slots can be found here, and most deployments add more slots (and Plug-In features) over time as their network and needs grow.
Some SNIP deployments want to run redundant NTRIP Casters (two copies of SNIP) and there are several popular configurations used to do this. In some deployments both copies are individually connected to the network of GNSS Base stations. A combination of Remote-Relay and Push-In stream types is often used for this. In other deployments, one SNIP Caster will Push-Out a stream to the other Caster. In still others, one SNIP Caster will connect to to the other Caster as an NTRIP Client using the Remote-Relay tab. When connecting a data stream from one SNIP Caster to another, the primary difference between using Push_in and Push-Out when compared to Remote-Relay is which side initiates the connection (or initiates the re-connection when needed).
Considerations of enterprise protection and security are also part of determining how to best set up redundant NTRIP Casters. Consider a redundant NTRIP Caster deployment where one device is within a secure environment (accessible only by other trusted devices) and the other is outside (accessible over the public internet).
From a strict security point of view it is generally preferable to reduce the number or types of incoming connections which can be an attack surface. It is preferred that such connections be initiated from the more secure side and “reach out” to the other endpoint. This then requires a Push-Out connection from the Caster within the secure environment to contact the outside Caster.
Redundant NTRIP Casters
If redundant NTRIP Casters connect to each other using Remote-Relay, then one slot is needed on the Caster that initiated the connection (in the Remote-Relay tab) per Base Station. Note that no additional slots are needed on the Caster that receives the connection, as that connection is simply considered yet another NTRIP client. This method has somewhat increased security issues as the secure NTRIP Caster must accept inbound connections from the outside Caster.
If redundant NTRIP Casters connect to each other using Push-Out, then one slot is needed on the Caster that initiated the connection (in the Remote-Relay tab) per Base Station. And an additional slot is needed (per Base Station) on the Caster that receives the connection, as that connection is received as a Push-In connection. This method has somewhat reduced security issues as the secure NTRIP Caster does not accept connections from the outside Caster and initiates the connections with that Caster.
So a Caster with many bases which are to be sent (pushed) to another Caster will require (in the old system) two slots per base. The new systems mitigates this, counting each Push_Out usage as “one half” a slot.
New Counting method
In the revised (new) system the following rule is applied when checking for unused slots. Whenever there are 75 slots or more present, then every use of a Push_Out slot (any entries in the Push_Out tab) shall be counted as ½ a slot.
This is applied to all uses of the Push_Out stream (the data stream need not be routed to another SNIP Caster). This is applied to all models SNIP with additional slots present (Basic, Pro, and Enterprise) .