A2.2. Determining the Higher-Order Bits (Seqh) of the Sequence Number

A2.2. Determining the Higher-Order Bits (Seqh) of the Sequence Number

Because only 'Seql' will be transmitted with the packet, the receiver must deduce and track the sequence number subspace into which each packet falls, i.e., determine the value of Seqh. The following equations define how to select Seqh under "normal" conditions; see Section A3 for a discussion of how to recover from extreme packet loss.

• Under Case A (Figure 1):

  • If Seql >= Bl (where Bl = Tl - W + 1), then Seqh = Th
  • If Seql < Bl (where Bl = Tl - W + 1), then Seqh = Th + 1

• Under Case B (Figure 2):

  • If Seql >= Bl (where Bl = Tl - W + 1), then Seqh = Th - 1
  • If Seql < Bl (where Bl = Tl - W + 1), then Seqh = Th