Last Call Review of draft-ietf-ippm-6man-pdm-option-05
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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.
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.
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.
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."
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]
Hop-by-Hop Options header
Destination Options header <--------
Encapsulating Security Payload header
Destination Options 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
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
Delta Time Last Received = (Sending time: packet 2 - receive time:
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.