diff --git a/School/Analyse/Layers/1. Physical Layer.md b/School/Analyse/Layers/1. Physical Layer.md
index cfbdb89..1d4cb20 100644
--- a/School/Analyse/Layers/1. Physical Layer.md	
+++ b/School/Analyse/Layers/1. Physical Layer.md	
@@ -116,3 +116,7 @@ This will reduce the impact noise has on the signal.
 
 This is also called signal to noise ratio (SNR)
 
+## Transmission Media
+These signals are send through a transmission medium.  A transmission medium is a physical object that can carry the information from source to destination.
+
+Transmission mediums are often space (air), metallic cable or fibv
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