Multiple BFD sessions over one path

[Mach Chen <mach at huawei.com>]

Hi,

After reading the two drafts (draft-ietf-bfd-generic-05 and 
draft-ietf-bfd-v4v6-1hop-09), I have some confusion about the session 
limitation over a specific network-layer path.

Section 2 of draft-ietf-bfd-v4v6-1hop-09 says:
"Each BFD session between a pair of systems MUST traverse a separate 
network-layer path in both directions..."

But section 6 of draft-ietf-bfd-generic-05 says:
"...if multiple differentiated services [DIFFSERV] are being operated over 
IPv4, an independent BFD session may be run for each service level...", this 
implicates that there may be mulitiple BFD sessions over one 
network-layer(ipv4) path, but it seems that this is not allowed in 
draft-ietf-bfd-v4v6-1hop-09. How to understand this conflict?  or do I miss 
something?

Best regards,
Mach Chen