When this pseudowire CoS profile's frame CoS policy is set to fixed, this is the constant Traffic Class value (0-7) stamped onto the MPLS header for every packet carried by any pseudowire using this profile, overriding the original frame's marking entirely. Because this is set at the profile level, changing it affects every pseudowire sharing the profile simultaneously, making it a high-leverage, and higher-risk, setting compared to changing a single tunnel's fixed TC value. A profile with FixedTC set to 0 (best-effort) accidentally applied to a profile intended for premium voice pseudowires would silently downgrade the priority of every customer assigned to that profile.