Optional in/out for tch/f demapper
diff --git a/grc/demapping/gsm_tch_f_chans_demapper.xml b/grc/demapping/gsm_tch_f_chans_demapper.xml
index deb2187..23d77ee 100644
--- a/grc/demapping/gsm_tch_f_chans_demapper.xml
+++ b/grc/demapping/gsm_tch_f_chans_demapper.xml
@@ -16,13 +16,16 @@
<sink>
<name>bursts</name>
<type>message</type>
+ <optional>1</optional>
</sink>
<source>
<name>tch_bursts</name>
<type>message</type>
+ <optional>1</optional>
</source>
<source>
<name>acch_bursts</name>
<type>message</type>
+ <optional>1</optional>
</source>
</block>