Subject: [ANCP] Small ANCP issues -- definition of sub-TLV

From: Tom Taylor <[email-masked]>
Date: Tue, 09 Feb 2010 14:23:10 -0500

I'm doing a revision of the multicast extensions draft and have a couple of 
trivial issues, the sort of thing that is important to an editor.

Can we provide a consistent definition of a sub-TLV? My problem is that 
currently the text in the base document says that the Status-Info TLV, for 
instance, can contain sub-TLVs. However, these sub-TLVs are actually TLVs which 
happen to be encapsulated in the Status-Info. On the other hand, both the base 
protocol draft and the multicast extensions draft have IANA registries for 
sub-TLV numbers.

I make the following proposal:

a) A sub-TLV is defined as a tag-length-value field that is always a subordinate 
part of a specific TLV type. That is, sub-TLVs are not reusable between TLVs. I 
doubt this introduces much if any specification redundancy. This definition 
should be given as part of the terminology section of the base protocol document.

b) If we want the set of sub-TLVs for a given TLV type to be extensible, we 
define an IANA registry for "Sub-TLVs of TLV Type xxxxx".

c) It is also possible for TLVs to be encapsulated in other TLVs. We would use 
the term "encapsulated TLV" instead of "sub-TLV" for this case.