# Does the message port propagate tags?

**URL:** <https://www.ruby-forum.com/t/does-the-message-port-propagate-tags/242096>\
**Category:** GNU Radio\
**Created:** [May 26, 2015, 8:24pm UTC](https://www.ruby-forum.com/t/does-the-message-port-propagate-tags/242096 "2015-05-26T20:24:04Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![Detlef\_R](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/58f4c7/32.png) [@Detlef\_R](https://www.ruby-forum.com/u/Detlef_R)\
**Post date:** [May 26, 2015, 8:24pm UTC](https://www.ruby-forum.com/t/does-the-message-port-propagate-tags/242096/1 "2015-05-26T20:24:04Z")

</div>

Hi all,

I’ve been wondering if a message port propagate the tag that come from a  
previous input ports. I’ve been reading about propagation and  
propagation  
politics and I was just playing around putting a Tag debug in front of  
several blocks connected to a USRP source that is generating a rx\_time  
tag.

However, staying with the default “all to all” politic, at some point I  
was  
just wondering about the message port, as it doesn’t really count as an  
in/output port at the signatures, and also the “Tag debug” port has no  
“message” option for the input (maybe for obvious reasons that answer my  
question) However I would just like to have it clear.

Thank you all in advance.

Regards

luikn

---

<div class="post-metadata">

**Author:** ![Lucas\_RodSSs](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/2acd7d/32.png) [@Lucas\_RodSSs](https://www.ruby-forum.com/u/Lucas_RodSSs)\
**Post date:** [May 26, 2015, 10:18pm UTC](https://www.ruby-forum.com/t/does-the-message-port-propagate-tags/242096/2 "2015-05-26T22:18:38Z")

</div>

Hi Luikn,

Message ports and stream tags are orthogonal concepts: messages don’t  
come in streams, and hence don’t carry stream tags.  
A tag is always specific to a numbered item, and since message ports are  
not item-based but meant to transport messages that will cause a handler  
to be called in the receiving block’s thread, there’s nothing to  
“attach” a stream tag to.

Best regards,  
Marcus