An Encoding Method to Signal 3 States with a Single PCN Bit

Pre-congestion notification (PCN) is currently being developed by the IETF to provide admission control in DiffServ networks for non-elastic flows. Various marking schemes are being proposed as part of this effort. We evaluate a new marking behaviour that could be used to signal three different states by means of a single bit. This scheme is of interest to networks operating with MPLS as the label QoS coding space is limited to three EXP bits. Similar to the ECN standard for MPLS, this research assumes that just two codepoints will be available to indicate different congestion states. Of these two codepoints, one would be used to differentiate between PCN and non-PCN traffic and the other would be used for PCN marking. This paper outlines the approach and presents the advantages and limitations of the proposal using the evaluations performed. A comparison of the method with a two bit PCN marking approach is also studied.