# Passing through custom streams
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You can passthrough any stream from a source TS to the output MPTS. You can pass through any number of streams. 

This section describes the procedure for passing through a stream whose PID isn't reserved for an SI/PSI table. For example, you might want to pass through a stream that isn't part of any program because your downstream system can use the data. 

If you want to pass through an SI/PSI table rather than a custom stream, see the next section.

**Setting up**

You include the stream by setting it up in the MPTS as a *passthrough stream*. The source of the stream can be any well-formed transport stream.

To include a passthrough stream, design the workflow in the regular way. When you create the MPTS, add the passthrough stream. You must specify the following information for the stream:
+ The location where the upstream system is sending the source transport stream. Elemental Statmux listens for the stream at that location.
+ The PID to assign to this stream in the output MPTS. 

For detailed instructions about passing through a stream, see [Including passthrough streams in an MPTS](crud-mpts-pasthrough-streams.md).

**Handling by Elemental Statmux**

When the MPTS starts, Elemental Statmux connects to the location where the upstream system is publishing the transport stream, and extracts the packets for the specified PID. 
+ Elemental Statmux ignores and discards any SI/PSI tables that are in the transport stream. It extracts only the specified stream.
+ Elemental Statmux includes the stream in the MPTS. 
+ Elemental Statmux doesn't include the stream PID in any of the SI/PSI tables for the MPTS.