[RPRWG] Frame reorder in 802.17b
Assume the following ring: S1-S2-S3-.....-S64
S1 is transmitting a frame with user DA=A, and the user with MAC=A is
connected to S64. S1 does not have an entry in the SAS DB for A, so it
floods it (assume unidirectional flood) through ringlet0 (S2, S3, ....
S64).
Eventually S64 receives the frame and it reaches user A. User A
responds, and S64 forwards the frame to S1.
- If we optimize the path by using minimum hops as the direct path: S64
sends the frame to S1 directly through ringlet0, and the next frame from
S1 to A will use ringlet1 with a direct frame since it has already
learned that A is represented by S64. Reorder will result since old
frames from S1 to A may be in flight in the long ringlet0 flooded path.
- A trivial solution would be for S1 to continue using ringlet0 with
direct frames. This is suboptimal since S1 uses the longest path.
- Using bidirectional flooding, with the right cleave point solves the
problem, but in wrapping rings unidirectional flood is used, and even
for steering rings unidirectional flooding is simpler (no duplication).
Comments please.
Leon