[EFM-P2MP] EPON and PAUSE operation
I'm having a little trouble seeing how MPCP is compatible with flow control,
so before I submit a comment, I'd like some feedback from this forum.
Subclause 64.3.3.1 states that "Even though MPCP is compatible with flow
control, optional use of flow control may not be efficient in the case of
large propagation delay." Figures 64-11 and 64-12 seem to show that any MAC
Control frame can be transmitted from an OLT or ONU provided it has a
supported opcode. Figures 64-9 and 64-10 seem to show that any MAC Control
frame with a supported opcode will be received and acted upon in the
appropriate manner.
When a device does support and receives a validly formed PAUSE frame, it
will then inhibit transmissions from the MAC Client for the specified amount
of time. For a 1Gb/s ethernet system, this can be up to approximately 33ms.
I'm confused about what would happen if a PAUSE frame is received by an OLT
from ONU[j], assuming for now that both the OLT and ONU[j] support flow
control. I would think that only client[j], associated with MAC[j] would be
stopped from transmitting. Will this prevent all data frames from being
transmitted to ONU[j]? What about frames sent by the single copy broadcast
MAC or other frames that may be sent in the shared LAN Emulation? If any
data frame is sent to ONU[j], then it would seem that the PAUSE protocol has
been compromised. Another problem would be if a single ONU was able to
prevent other ONUs from receiving frames.
Does anyone have any comments on this? Would it be wise to put a sentence
or two in 64.3.3.1 warning people that flow control may not only be
inefficient, but could also have undesireable effects?
-Eric