Answer:
Each entry in the label stack contains four fields:
A 20-bit label value. A label with the value of 1 represents the router alert label.
a 3-bit Traffic Class field for QoS (quality of service) priority and ECN (Explicit Congestion Notification). Prior to 2009 this field was called EXP.[8]
a 1-bit bottom of stack flag. If this is set, it signifies that the current label is the last in the stack.
an 8-bit TTL (time to live) field.
