[Ndn-interest] FinalBlockId in non-final segment

Junxiao Shi shijunxiao at email.arizona.edu
Wed Jun 27 10:45:34 PDT 2018

Dear folks

I have a question regarding the use of FinalBlockId element in a Data
packet that is not the final segment itself.
Note that "segment" in this message could be replaced with "timestamp",
"sequence number", etc, because FinalBlockId is not required to be a
segment number.

NDN Packet Spec defines
FinalBlockId as follows:

The optional FinalBlockId identifies the final block in a sequence of
fragments. It should be present in the final block itself, and may also be
present in other fragments to provide advanced warning of the end to
consumers. The value here should be equal to the last explicit name
component of the final block.

CCNx has the same definition

As I remember (but couldn't find records):
In the final segment, FinalBlockId must equal the last explicit name
In earlier segments, producer may include FinalBlockId as an "advanced
warning" that a stream is ending. In that case, the segment number in
FinalBlockId represents an estimation, and is not required to be exact.
A use case is that, a video stream is going to end within 5 seconds but the
producer does not know the exact segment number of the last segment, so it
provides an estimate so that consumers can stop sending Interests much more
beyond that segment number.

Change 4651 patchset 26 treats a different FinalBlockId in a stream as an
Although the later merged code has reverted to my view above, I think the
NDN protocol should clarify whether FinalBlockId in non-final segment must
be exact, or may be an estimation and therefore could change in later

Yours, Junxiao
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