[sfc] Shepherd review of draft-ietf-sfc-nsh-tlv

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Dear Authors,
I've reviewed the document and would like to share my notes. 
The document is well-written and is easy to read, thank you. I have several questions that, I believe, would be easy to resolve:
In the Introduction, SFC NSH is characterized as an "encapsulation required to support the SFC architecture". It seems that "required" is a statement a bit too bold since there are other solutions, e.g., RFC 8595, that support SFC architecture as defined in RFC 7665. Perhaps a slight re-wording as below be acceptable:
OLD TEXT:
   The Network Service Header (NSH) [RFC8300] is the Service Function
   Chaining (SFC) encapsulation required to support the SFC architecture
   [RFC7665].
NEW TEXT:
   The Network Service Header (NSH) [RFC8300] is the Service Function
   Chaining (SFC) encapsulation that supports the SFC architecture
   [RFC7665].
Section 3 opens with the following:
   An NSH is composed of a 4-octet Base Header, a 4-octet Service Path
   Header and Context Headers.
Since the use of a context header in the SFC NSH is optional (as noted further in the text), it might be appropriate to reflect that in the sentence:
   An NSH is composed of a 4-octet Base Header, a 4-octet Service Path
   Header and optional Context Headers.
The interpretation of the Context Type field in Section 4.1 refers to the Tenant ID field:
      Context Type (CT) is four bits-long field that defines the length
      and the interpretation of the Tenant ID field.
I think that instead of the Tenant ID it is meant to refer to the Forwarding Context ID field.
I've noticed that in all figures that display the format of TLVs in the document, with the exception of Figure 7, the value of the Length field is shown. Perhaps, for consistency, in Figure 7 can update s/Length/Length = var/.
I think that the length of the Flow ID field (Section 4.5) is four octets. Unless there are plans to use other formats, the Flow ID TLV may be defined as the fixed-length and the value of the Length field defined as 4. (Also, in the figure that displays the format s/~/|/ two times.)

Regards,
Greg Mirsky
Sr. Standardization Expert
预研标准部/有线研究院/有线产品经营部  Standard Preresearch Dept./Wireline Product R&D Institute/Wireline Product Operation Division
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