Last Call Review of draft-ietf-ippm-6man-pdm-option-05
review-ietf-ippm-6man-pdm-option-05-genart-lc-korhonen-2016-09-23-00

I am the assigned Gen-ART reviewer for this draft. The General Area

Review Team (Gen-ART) reviews all IETF documents being processed

by the IESG for the IETF Chair. Please wait for direction from your

document shepherd or AD before posting a new version of the draft.

For more information, please see the FAQ at

<

http://wiki.tools.ietf.org/ar

ea/gen/trac/wiki/GenArtfaq>.

Document: draft-ietf-ippm-6man-pdm-option-05

Reviewer: Jouni Korhonen

Review Date: 9/23/2016

IETF LC End Date: 2016-09-28

IESG Telechat date: (if known)

Summary: The draft needs some work.

Major issues:

I have two technical issues here:

1) There is no mention of what is the time reference plane for internal time
stamping. All other timing and synchronization related documents I am aware of
(at least outside IETF) describe it very clearly where in the processing/packet
handling the time stamp is to be taken. Now the document gives me no idea as an
implementer where that should take place. At least it makes it hard to
calculate the *network* RTT precisely.

2) The PDM option relation to actual "server" time is somewhat confusing and
the 5-tuple does not allow me to detect the real relationship between the
server/application action that caused the generation of the packet and the PDM
within the packet. This is specifically an issue with transport/application
protocols that multiplex/interleave multiple application streams into one
transport. I have no idea of the actual individual application time since the
packets get generated independent of the processing of a single thread. I would
welcome some discussion around here. Section 1.4 last paragraph is going to
this direction but is not sufficient IMHO.

Minor issues:

1) This is a larger editorial issue. The document is far too long with a lot of
repetition considering it describes only one IPv6 destination option. It is a
writing style issue and I am fully aware of that. I have proposals how to cut
text in the editorial comments section.

2) Section 1.2 3rd paragraph talks about IoT and that speed matters there. I
find this too generalized statement. There are many other things that matter in
this application domain and speed might not be that important as being able to
send/receive that one to two bytes of data in a given time window. I suggest
removing this paragraph.

Nits/editorial comments:

1) Section 1.4 numbered list: add missing full stops.

2) Section 3.2: remove

  "The 5-tuple consists of

   the source and destination IP addresses, the source and destination

   ports, and the upper layer protocol (ex. TCP, ICMP, etc)."

since this is unnecessary repetition.

3) Section 3.2: remove

  "Operating systems MUST NOT implement a single

   counter for all connections."

Seems again like unnecessary repetition to previous sentence.

4) Section 3.2 again unnecessary repetition of IPv6 basics that can be read
from RFC2460. Suggest strongly to remove:

  "This indicates the

   following processing requirements:

   00 - skip over this option and continue processing the header.

   RFC2460 [RFC2460] defines other values for the Option Type field.

   These MUST NOT be used in the PDM."

and

  "The

   possible values are as follows:

   0 - Option Data does not change en-route

   1 - Option Data may change en-route

   The three high-order bits described above are to be treated as part

   of the Option Type, not independent of the Option Type.  That is, a

   particular option is identified by a full 8-bit Option Type, not just

   the low-order 5 bits of an Option Type."

5) Section 3.3 same as in comment 4). Suggest strongly removing:

  "This follows the order defined in RFC2460 [RFC2460]

                 IPv6 header

                 Hop-by-Hop Options header

                 Destination Options header  <--------

                 Routing header

                 Fragment header

                 Authentication header

                 Encapsulating Security Payload header

                 Destination Options header <------------

                 upper-layer header"

6) Suggest removing entire Section 3.4 and moving the following text to Section
3.3:

  "PDM MUST be placed before the ESP header in

   order to work.  If placed before the ESP header, the PDM header will

   flow in the clear over the network thus allowing gathering of

   performance and diagnostic data without sacrificing security."

7) Section 3.6 suggest removing the following text. I see no value it would add
to what has already been said:

  "As with all other destination options extension headers, the PDM is

   for destination nodes only. As specified above, intermediate devices

   MUST neither set nor modify this field."

8) Section 3.6 suggest removing the following 5-tuple text as it has already
been described earlier in Section 2:

  "The 5-tuple is:

   SADDR : IP address of the sender SPORT : Port for sender DADDR : IP

   address of the destination DPORT : Port for destination PROTC :

   Protocol for upper layer (ex. TCP, UDP, ICMP)"

9) Sections 4.2 and 4.3 suggest removing them entirely. I see what value these
sections add. I acknowledge they are good to know information of timer hardware
implementation difference but do not really add value on the on-wire encoding
of the PDM option.

10) Section 4.4 suggest removing the entire section. Time Base was already
described in detail enough in Section 3.2.

11) Section 4.5 time base for picoseconds is 11 not 00.

12) Section 4.5 suggest removing the following text, since it does not add any
more clarity to what has already been said in my opinion. This is because all
the examples follow nice nybble increment in scaling:

  "Sample binary values (high order 16 bits taken)

   1 psec            1                                              0001

   1 nsec          3E8                                    0011 1110 1000

   1 usec        F4240                          1111 0100 0010 0100 0000

   1 msec     3B9ACA00           0011 1011 1001 1010 1100 1010 0000 0000

   1 sec    E8D4A51000 1110 1000 1101 0100 1010 0101 0001 0000 0000 0000"

12) Section 4.6 I do not understand why this section is here. I strongly
suggest removing it. Sections 4.5 and 3.2 already describe how I would encode
the delta time using scaling as a separate fields not embedded (option fields
ScaleDTLR and ScaleDTLS). Did I misunderstand something here?

13) Section 5 suggest removing the following text because of it repeating what
has already been said earlier:

  "Each packet, in addition to the PDM contains information on the

   sender and receiver. As discussed before, a 5-tuple consists of:

      SADDR : IP address of the sender

      SPORT : Port for sender

      DADDR : IP address of the destination

      DPORT : Port for destination

      PROTC : Protocol for upper layer (ex. TCP, UDP, ICMP)

   It should be understood that the packet identification information is

   in each packet. We will not repeat that in each of the following

   steps."

14) Section 5.3 suggest merging the following text into one example and do
necessary rewording. There is no need to do the same calculation twice on
almost adjacent lines:

  "Sending time : packet 2 - receive time : packet 1

   We will call the result of this calculation: Delta Time Last Received

   (DELTATLR)

   That is:

   Delta Time Last Received = (Sending time: packet 2 - receive time:

   packet 1)"

15) Expand RTT and PSN on their first use.

Phew.. after all this I found the document good reading and most likely a
useful tool to be used.

Regards,

   Jouni