In this illustration, we see a portion of a link-layer frame as a row divided into segments. The segments are labeled (from left to right): PPP or Ethernet header, MPLS header, IP header, and Remainder of link-layer frame. The MPLS header segment of the frame is expanded below the frame in order to show what it includes, and appears also as a row divided into segments. From left to right, we see a large segment labeled "Label," followed by a smaller segment labeled "Exp," a narrow segment labeled "S," and a small segment labeled "TTL."