diff --git a/plot_transmission_timeline.py b/plot_transmission_timeline.py
index 16430d0..e1a3967 100755
--- a/plot_transmission_timeline.py
+++ b/plot_transmission_timeline.py
@@ -151,7 +151,7 @@ if __name__ == "__main__":
     time_range = pd.date_range(transmission_df.index.min(), transmission_df.index.max(), freq="{}s".format(args.interval))
 
     # create bins by pd.cut, aggregate sum
-    transmission_df = transmission_df.groupby(pd.cut(transmission_df.index, bins=time_range, labels=time_range[:-1]))["goodput"].sum().reset_index()
+    transmission_df["goodput"] = transmission_df.groupby(pd.cut(transmission_df.index, bins=time_range, labels=time_range[:-1]))["payload_size"].sum().reset_index()
     #transmission_df["goodput"] = transmission_df["payload_size"].rolling("{}s".format(args.interval)).sum()
     transmission_df["goodput"] = transmission_df["goodput"].apply(
         lambda x: ((x * 8) / args.interval) / 10**6