[trill] cc in "draft-ietf-trill-oam-framework-00"

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Hi, all trill-oam-framework authors

I have some troubles on understanding cc function described in section 
4.1.1 in draft-ietf-trill-oam-framework-00, wish you can help me for more 
clear understanding.

1. 4.1.1 Fault Detection (Continuity Check)
".....
The proactive fault detection function must detect the following
   types of defects:

   - Loss of continuity (LoC) to one or more remote MEPs
   - Unexpected connectivity between isolated VLANs (mismerge)
   - Unexpected connectivity to one or more remote MEPs
   - Period mis-configuration"

In my mind, maybe the sencond and third types of  defects should be 
defects detected by CV ?

2. 4.1.2.1 Forward Defect Indication

"......
a simple network comprising of four RBridges connected in tandem: RB1, 
RB2, RB3 and RB4. Both RB1 and RB4 are hosting TRILL OAM MEPs, whereas RB2 
and RB3 have MIPs. If the link between RB2 and RB3 fails, then RB2 can 
send a forward defect indication towards RB1 while RB3 sends a forward 
defect indication towards RB4......"

my question is how to detect the link faliure between RB2 and RB3 , 
through TRILL oam? such as one hop TRILL BFD?

3.Does CC should be supported on sections? if it is, how the ingress and 
egress nickname be set? the same as CV on sections( see the last paragraph 
in section 4.2.1.1 in trill-oam-framework)?


please correct me if I have some misunderstanding :)


Best Regards,
xuehui